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Repair or Replacement of 1975 350SL Seats

8K views 30 replies 9 participants last post by  GoldDragon 
#1 ·
As a winter project, I removed the seats in my 1975 350SL Euro and examined how best to address the need for repair or replacement. The leather covers are badly cracked and rotted. See photo below.

The framing is in good shape, but the horse hair seat backs are deteriorated. The driver’s side crumbled when I removed the cover. So, I started looking for replacement parts. EPC is always an excellent source for information on parts, to understand the construction and how I could plan the best course of action.

The first major lesson I learned about seat repair is how expensive it is to rebuild them. Depending on the amount of repair needed, $500 to $1200 is a normal expense just for parts. If I couldn’t do the work myself, the cost would be much higher. I began a journey to find a suitable replacement for the stock seats. Sorting out what would fit and meet my need proved extremely time consuming, frustrating and disappointing.

I searched out and read all the past discussions posted on the forum. There’s a lot of good information. As with many, the use of 1980’s and early 1990’s SAAB seats appeared to me a good solution. New seat covers are available. The challenge is finding rebuildable seats to put them on. Every lead that was in reach within the Midwest was a dead end. The seats were either gone, had parts missing or the owner wanted to sell the whole car complete. I broadened my search to other brands. Toyota has many models that might work if adapted properly and the German cars appeared to be possible options, too.

One of the most serious and difficult challenges to fitting seats into a 107 is how the seats are mounted. Anyone who has removed their seats becomes aware that the anchors which hold them in place are bolted to the transmission tunnel and the outer framing, not the floor of the car. The floor of the 107 does not have the thickness of metal nor the strength to anchor seats during a collision. The seats would tear loose and crush the rider between the seat and seat belt. Without the construction of heavy and complicated adapters, that eliminates a large number of the floor mounted seats.

Another major consideration is the physical size of the seat. The space within the 107 is limited to 22” wide and about that distance long. That proved to be too narrow for most of the seats I looked at. For longer seats, the fronts must clear the three inch high box frame on the floor where the front of the seat sits. I’m still uncertain what the purpose of that frame. It must provide support for the floor. It elevates the front of the seat and is not of strong enough steel to anchor the seat to.

In my search for possible high end replacement seats with good adjustability and lumbar support, I happened upon a pair of Recaro seats in very good condition that fit a late nineties Audi. What got my attention beside the seats being Recaros is that the back seat mounts are side mounts and that they move within a track similar to the original MB seats. Since these seats are electric, only the rear mounts need to move within a track. The front mounts are stationary and bolt down onto an appropriate unmoving anchor. The simple control switches move the seat up, down, tilt, forward, back and tilt the backrest forward and backward. The lumbar support is manual with a side knob giving a wide range of adjustment and the front section of the bottom cushion slides out to enlarge the area. The powered forward and backward adjustment eliminates the need for a lever protruding forward. In addition to the controls, the driver’s side has an attached six position armrest with storage compartment and the seats have heaters. They are comfortable and well made with soft black leather. These seem like ideal seats to adapt.

I’ve spent a great deal of time measuring the available space and on the seats to work out the best way to mount them. The first concern is the width of the rear side mount brackets. They are too wide by approximately one inch. I considered cutting off the mounts, trimming them and welding them back on, but since trimming and realigning the shafts would be tricky, I plan on cutting the weld off the rear mount brackets raising them about an inch to gain head room and moving them inward a half inch. That would align them with the heavy original MB tracks giving the needed firm anchor to the mounts. They would have the full length of the MB seat track for power positioning the seats. This arrangement seems simple and effective compared to building or buying Recaro seat adapters.

I’m still measuring and planning the best solutions to mounting these seats. Other than where and how to mount the seats, I’m concerned about maintaining comfortable head room. The Recaro seats are firmer and about an inch taller from floor to the top of the seat cushion. I’m hoping that raising the rear mounts an inch will help. The other consideration is leg room under the steering wheel. I have the original large steering wheel and my leg room has always been limited. Needing to have both legs free because of the left leg movement for the clutch makes sufficient leg room important. Because the rear mounts are wider than the space inside the car, I can’t simply set the seat in and see how it fits. I’d have to cut off the Audi mounts to make it fit.

These are my current adaption concerns. I’ve attached photos showing the design and mounts. It’s an interesting and challenging project. All comments and suggestions by those who have adapted non-MB seats are certainly welcome. If I can’t work out adapting them, I’ll likely resell them. I very much want to seats to work out.

GD
 

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#3 ·
I am in the same place with my seats. I have the MB TEX Vinyl although the covers are in good shape the bases have given way and of course the headrests have become mush.

I have been reading around this for a few weeks and I have read that the Hyundai Tiburon is a viable option. Could I ask if you considered that and if you ruled them out, why? Was it the quality or a fitting issue? I have seen some seat sets going for a reasonable price and considered buying a spare set of 107 tracks and using the original mounts. As you can tell I have not done nearly as much research as you, heck I can't even get the big screws undone yet (arthritis).

If you don't mind me asking. Whats the general price range for the seats you have?
 
#4 ·
I have been reading around this for a few weeks and I have read that the Hyundai Tiburon is a viable option. Could I ask if you considered that and if you ruled them out, why? Was it the quality or a fitting issue?

If you don't mind me asking. Whats the general price range for the seats you have?
I happened upon a set of manual Tiburon seats about a month ago. They were a black and course weave fabric with reddish piping. They were in good shape as far as I could tell. I was plodding through a small local junk yard after a heavy snow and I couldn’t see well because of the windows being covered. The padding seemed very firm. Perhaps too firm for what I want. They are floor mounted, so some sort of heavy bracket (at least 1/8” steel; see thread on SAAB seats for an example) needs to be constructed for them. The yard wanted $75 each You Pull, which I thought was a good price. They were the best possible seats in the yard that day.

One major issue I consider when looking at used seats is how the seat belt will work with them. The MB seats have a very low backrest compared to most modern seats. If the backrest is very high and wide, there may be a problem. Some seats have plastic or metal rings on the sides of the backrests for seat belts to thread through. That would help. What I want to avoid is a seat belt conflict that would make me feel like I was being strangled. Safety is also a concern. Consider what would happen in a collision.

Another feature I look for is how the seat adjustment lever works and protrudes. That 3” high box on the floor at the front of the seats may interfere with the adjustment lever and require the front of the seat to be raised the 3” to clear it. That may decrease leg room between the steering wheel and seat to the point that it’s unusable. I have to have both legs free to work my clutch and brake. Yes, a smaller wheel would be nice, but I don’t have one. So, if you have to mount the whole seat three inches higher, you may run out of head room. If you pitch the front up at an angle, the seat better have a way to adjust for it otherwise you’ll feel like you’re preparing for take off or sitting in a rocker.

Some sedan seats are very nice, but the backrest won’t tip forward. That can cause problems if you need to access behind them. You have to slide the seat forward to get around them. If they don’t clear the 3” box, the may not be movable.

So, there are very many considerations when working on shoe horning non-107 seats in the limited space. Seats from a different MB model may have another set of considerations and not be any better choice.

I had given up on buying leather Recaro seats and just happened upon these Audi models. I found that even worn out Recaro seats that need to be recovered sell for well over $500. Recovered ones are anywhere between $1500 and $2200. I’ve had to make a few repairs, but there were no rips or tears and all the electric motors work great. The leather is soft and the pads good. Having a six position arm rest with a storage compartment is a plus too. The rear side seat mounts are going to take some cutting and welding, but not a great amount. I should be able to avoid having the extra expense of a $600 Recaro adapter using the MB tracks. The measurement and fitting to get it right is going to be tough. There’s very little extra space to work with; especially head room.

I hope this answers your questions. This is an ongoing puzzle. I work a bit on it every day.

GD
 
#5 ·
I'm very interested in your project and have been looking for
a decent set of seats to work with. Fortunately I have a
parts car that I think I'll use as a test jig.

Do keep on posting on your progress.
 
#7 ·
I did a test fitting of the Recaro seat to see if my measurements were proving correct. It's difficult to estimate the headroom available. What I determined is that the motor switches will clear the frame side and that the motorized section of the seat is positioned were the floor is lowest. Both of these are critical.

The rear seat side mounts which would move in the MB track are too wide for the space, so I was not able to set the seat down to measure headroom. That is my major concern. I will have to cut away some of the box on the floor. With as light weight as the metal is, I can't see it providing much support for the floor. If I remove it, I'd weld in some angle iron as replacement.

There appears to be sufficient room for my legs between the front of the seat and the steering wheel. So far, fitting is going well.
 

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#8 ·
That box on the floor is a structural member. It's a box section, the same kind of structure aircraft wing spars are constructed using. I'd be really concerned if it were me...but maybe that's just me. A piece of angle iron would be better than nothing, but nowhere the same in strength.
 
#9 ·
Yes, that is my concern too. But upon close inspection, I was surprised at the thinness of the sheet metal. I understand why the seat tracks are mounted at the angle which runs above the box. Since there is no ability to raise the seat independent of the rest of it, as the seat is slid forward, the seat raises in height giving the shorter person who is adjusting for pedal position extra visibility. That created the empty space that needed to be filled so there wasn't a large gap under the front of the seat. The box would certainly add to floor rigidity, but does not appear to be the sole support. What I do know is that it is a major obstacle when trying to fit any kind of different seat. It causes the seat to be pitched up at a steep angle. Perhaps a tubular replacement might be workable.
 
#10 · (Edited)
My recent journey into seat repair or replacement started with noticing grainy brown stiff coming out of the driver’s side backrest of my 1975 350SL Euro. At first I thought there may have been a mouse nest inside and the remains were sifting out. The leather seat covers are dried out and badly cracked exposing the framing in many places. To prevent the frame from continuing to tear holes in my cloths, I taped over the major cracks and temporarily hid the tape with cheap seat covers. I thought I’d take the seats apart, make any minor repairs and install new seat covers. The project proved to be not that simple.

I have repaired seats in the past, but all of them had been more modern seats with foam padding. What I did not expect to find was a crumbling mess. The only time I had seen horsehair padding was when some old furniture of my grandmother’s was disposed of. The seat pad may be called horsehair, but it looks like some bonded organic fibrous material other than actual hair. I was told by a friend that it provides good and comfortable cushioning. Whatever it is, its useful life span has ended and from driving the car, comfort was not a feature. Removing it from the seat framing was easy. It crumbled in my hands. Finding a replacement was not.

Good advice from a friend led me to a few companies who sold replacement pads. I was surprise by the pricing. Even non-horsehair foam replacements were $180 each. A search on eBay showed one slightly damaged back pad for $70+. Further research showed that all the SL seats from 1972 through 1985 were the same. SLC seats are different in some why. Perhaps the SLC seats are designed to provide more space in the back.

I was able to buy the cushion sections from a pair of seats from a 1984 500SL. The backrest horsehair pads are in usable condition, so that problem is solved. Comparing the bottom seat cushion to the one from my seat opened an new can of worms. When I dismantled my seat, I was surprised how good the bottom cushion was in comparison to the backrest. It was solid and a healthy green color as compared to the crumbling brown mess of the backrest. I assumed that someone had worked on my seats in the past and perhaps had replace the bottom pad, but not the backrest.

I didn’t give the bottom pad much thought until I placed it beside the pad from the ’84. Mine has an additional layer of dense 1” foam on top of the horsehair. That seemed like a good extra benefit. After doing some more research on the SL seats, it became apparent that I have some sort of “orthopedic” or “comfort” seats. That is suggested by the addition of the lumbar pad in the backrest shown in the photo of the crumbling mess. The lumbar support is held in place and is slightly adjustable with the belts that thread through the back of the seat.

I have no history on my car, so I don’t know if I have the original seats that came with my gray market Euro or whether some previous owner had put them in. What I do know if that the addition of the foam to the top of the horsehair will complicate finding proper fitting seat covers. I’ve attached photos showing the measurements of the still intact passenger seat and the front and side of the driver’s seat cover. I am trying to determine whether my seat covers are much taller to accommodate the extra foam padding. If so, unless I can find a seat cover manufacturer who sells “orthopedic” seat covers for my 1975 350SL Euro, I’ll have to find a local company who will use my original seat cover and make new ones. Standard mail order seat covers costing between $450 and $1100 simply won’t fit. If someone would measure their standard MB SL seats for comparison, I’ll have a better idea what might fit. I measured from the bottom of the seat frame where the material turns, then up and across the widest part to the other side.

As the costs kept adding up on repairing my old original MB seats, I kept wondering if complete replacement with more modern seats that provided more support and comfort was a better choice. After many hours of research and searching for possible replacements, and trial and error with some of them, I still don’t have a final solution. The only logical course seems to be to pursue both paths simultaneously to find the best answer. If anyone has any information on “orthopedic” seats installed in a 107, please pass it on. I’ve searched the forum and found some references for other MB models, but nothing specific to a 108 SL or SLC of any year. At one point, I wondered if some previous owner had installed used 560SL seats, but I don’t think so. The seat cover pattern isn’t right for that model of seats. Any help is appreciated.

GD
 

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#11 ·
The "horsehair" we can get now is actually coconut coir. It is impregnated with a rot resistant solution and holds up really well. I replaced pads in my SL, but kept the leather cover. An upholstery shop (auto, not home) will do the job for a reasonable cost.

Saggy seats with good pads, can be updated with a pool noodle wrapped around the side and front. Foam egg crate material sort of can compensate for not using the coconut pads, but not that great. The back pads are harder to fake up than the seat. I have yet to find a viable solution beyond the real pad.

If you can source a pair of seats at a PnP yard, you may be miles ahead. I got lucky and was able to scrounge a set of SLC seats for $60 each for a buddy to put in his 72 SL. He got an armrest, a bit more padding than he had, and the leather was not torn apart the way his seats were.

The seats in a W114/115 are sort of close, but not really. I picked up a W115 that a guy had swapped W126 seats in. Sort of a booger job.
 
#12 ·
The "horsehair" we can get now is actually coconut coir. It is impregnated with a rot resistant solution and holds up really well. I replaced pads in my SL, but kept the leather cover. An upholstery shop (auto, not home) will do the job for a reasonable cost.
Redghost, Thanks for your input on this project. At first, when I looked at the seat pads, the fiber was too course for actual hair. I thought it might be some sort of synthetic material, but by how my backrest pad had rotted and crumbled, I assumed it was organic from some source. I'm glad you clarified what it is.

I've determined that the Recaro seats will mount too high for me. The MB seats barely accomindated my 6'3" hight. These seats may be ideal for someone just 3" shorter. I very much wanted them to work out. The comfort and back support provided was wonderful. The side mount would have secured them as well as the MB seats, too. I'll likely put list them on Craigslist soon and move on to other possibilities. They will still fit and plug right into an Audi.

I haunted another junk yard today looking for possible temporary seat replacements. Every other brand of vehicle I've looked at besides MB and Audi uses floor instead of side mounts. I've trying to find seats that the track can be cut off and replaced with the track frame of the MB 107 seats. They would then mount in the existing MB side tracks. Some Saturn seats I looked at today might work. I'm still measuring and comparing.

I'm moving on with repairing my MB seats, but it will take some time. There seems to be a wide difference of how Brazilian Brown fabric is defined. I've had to ask for swatches to see how their color works with my interior. I've yet to determine if there is any difference in the size of the seat cover due to the addition of the inch of foam. I've had one response to my request for seat measurements. If anyone would measure the width and length of their bottom seat at the widest point to where the cover wraps around the frame, I'd greatly appreciate it. I've found the quickest and easiest way is to use a bit of string to gauge the distance, then measure it on a tape measure. Please check earlier in this threat for the photo showing the measuring. Thanks in advance for any help.

GD
 
#14 ·
Dugald, Thanks a bunch for your input. Your thread was recommended to me. I did a search, but failed to find it. I just read through all seven pages and was very impressed by your approach and results. Why did you abandon the Tiburon seats? They seemed to be a good solution. Of course you final result was far more elegant and did fit the design of the car better. Have you been happy with them?

One of the junk yards I returned to today had a Tiburon. I took the following photo and did some measurements. The low mounting and tracks attracted my attention. These seats must be the standard cloth seats. Certainly not the deluxe version you found. I think I'll try these seats as a temporary fix.

I can't find any way to make the Recaro seats work for me. I'm just too tall. Thanks again for your help.

GD
 

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#15 ·
GD, I never did find any Tiburon seats, else I would have happily used them. Then again, I was looking for leather covered ones which seem rare
Having the Recaros on hand, you are best able to assess their suitability, but have you considered doing without some of their powered features? Bird in the hand and all that ....
 
#17 ·
Having the Recaros on hand, you are best able to assess their suitability, but have you considered doing without some of their powered features? Bird in the hand and all that ....
Dugald, Thanks for the suggestion.

The motors which operate the tilt of the Recaro bottom seat, forward movement and the backrest tilt are all integrated together. I thought about cutting off the bottom mount and the motor for the forward to back movement, then mounting a MB seat base, but there would be no gain over mounting the existing framework close to the floor. The three inch tall box still causes too much lift of the front of the seat for my headroom space.

GD
 
#18 ·
Ian, Those are beautiful seats! The must be very comfortable.

The measurements I'm asking for are for the existing MB seats. I'm trying to figure out if these early Euro seats have a different size cover than the US version. I have an extra inch of foam on top of the pad. Mine also has the addition of a lumbar pad.

Thanks for the offer to measure.

GD
 
#19 ·
I just learned that Coir has anti microbial aspects. That is good to know. Coconut fibers are less likely to rot out the way the horsehair did. Now the Vegans can renovate their seats with less guilt.
 
#20 ·
I measured my seats for you, from frame to frame. When I got my 450 the seats were broke down, but the leather was good, I stopped at a carpet store and got some dense carpet pad scraps. Spray glued them in layers and used it for seat padding. Maybe not the best stuff to use and I'm no upholsterer but they are firm and comfortable!
 

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#21 ·
I measured my seats for you, from frame to frame.
Steve, Thanks a bunch for the measurements. They will help me determine if there is a variation in the seat covers.

You use of the carpeting was innovative. I would have never thought of that. Like packing pool noodles in the springs, when it's covered, who's to know?

I'm still searching for replacement seats, but also planning how to best use my MB 107 seats. As seen in my photos, the backrest pads were disintegrating. Since I've acquired usable used pads, I may reassemble the MB seats with some foam reinforcement, apply more tape on the rips in the leather and apply a good quality seat cover until I can work out a better solution.

Thanks again. I hope to get a few more seat measurements from other members. Hope springs eternal. ;-]

GD
 
#22 ·
Dugald, I found the following photo of side mount brackets for the Corbeau seats. Would you estimate that they would allow the Corbeau seats to be installed with the sliders? I fully understand why you had to fore go the forward and backward movement. The floor reinforcement channel is difficult to work around. Yes, I'm certain that I could install the Recaro seats if I eliminated the forward adjustment ability. Unfortunately, I'd still have very limited headroom. I've noticed that photos of different seat installations rarely show with the hardtop in place. It's hard to gauge the headroom. How much headroom do you have with the Corbeau seats with your hardtop on? Thanks, GD
 

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#23 ·
Tiburon Seat Replacements

After a lot of searching for acceptable MB replacement seats, I decided to try to adapt cloth seats from a 2001 Hyundai Tiburon. In this three month journey for replacement seats, I’ve looked at and measured seats from Toyota, Mitsubishi, Saturn, Audi, Mercedes, VW, Ford, Lincoln, Volvo, various GM, Hyundai, Kia, Honda, SAAB, Corbeau and others. Due to the 3” high floor support member, the side mounts and the limitations of the depth of the seat well with its 22” width, there is a very small group of possible replacements. I very much wanted to make the Recaro seats work, but my height eliminated that idea. The Recaro/Audi seats were the only ones with existing side mounts. Another major limitation is that the seats must not come from a four door sedan. The seats need to tilt forward for access to the back area. I tried to pursue the SAAB seat adaption, but I could never find a pair worth buying or that would fit. The later SAAB models are all built on a GM vehicle base and are too wide.

I spent a lot of time evaluating how I could best make the Tiburon seats work before pulling them out of the car at a local junk yard. I’ve tried to keep the expense and trouble to a minimum. There were a couple of Tiburons with the leather version, but all were in bad shape. The leather versions showed wear though on the outer edges due to rubbing while getting in and out of the car. Being exposed to the elements in the junk yards and poor care while operated destroyed the leather.

The major difference between them is the stiffness of the leather and that the seat bottom of the cloth seat doesn’t have a height adjustment. The leather seats look sexier than the cloth, but leather is colder in the winter and hotter in the summer. Both seats have lumbar support and the cloth version seemed to sit a bit lower allowing more headroom. Headroom is a critical feature for me when evaluating any replacement seat. That is the only reason I had to abandon fitting the Recaro/Audi seats. After building the brackets to adapt the Tiburon seats, I found that I had only lost a half inch of headroom from the original MB seats. The brackets are the lowest that I could construct. Considering what I had to work with, I’m very pleased with the results.

I approached the design of the mounting brackets with change in mind. Since I’m going to continue to try to rebuild my original MB seats, I wanted to do the least amount of damage to the existing hardware, while providing the safest and most effective adaption. The MB seat frames I bought for the backrest pads were badly rusted, so I used the bottom seat frame as a jig to make mounts that would perfectly fit the MB side mount tracks. I cut and had welded to the track sliders 3/8” scrap steel plate. 3/8” plate gave me the strength for the brackets to withstand a collision and prevent the passenger from getting crushed between the dislodged moving seat and seatbelt. Those who bolt floor mounted seats to the thin MB flooring are creating a death trap. The 3/8” plate also gave me ample thickness to drill and tap mounting holes and eliminate the need for nuts on the bolts. Because of that, I’m using the hardened mounting bolts I removed with the seats. Metric hardened bolts are not always easy to find new. One other item of note about these seat mounts is that they are reversible. Flipping them over adds an inch of height. That works against my current needs. If they would have worked that way for me, it would have eliminated the spacers I had to add due to the Tiburon bracket fitting at the weld between the steel plate and the MB slider bracket.

In the research on this forum, I’ve seen many good ideas for adapting non-MB seats. Because I want to keep my option to reinstall my MB seats, I couldn’t weld the mounting bars to the track. That is a very effective approach, but working within my limitations, and that I was very unsure of how best to position the seats, I decided to make the mounts adjustable. If I found seats that would better suit my purposes, the bars could easily be re-positioned, redrilled and tapped to accommodate the change. Another consideration affecting the final positioning is the range of the forward/backward movement of the Tiburon tracks. Since I have a clutch and it requires a much larger range of movement than an automatic’s pedal, I need for the driver’s seat to be fully adjustable. Permanently mounting the seat into position also won’t work because I need for my wife to be able to drive the car in case of an emergency. An unmovable seat would limit salability later, too. Once I decide on the final position, I will install removable hardened bolts through the side tracks to hold the mounting bars in place. The Tiburon seats will have full movement, and due to the upward angle of the tracks, function similar to the MB design raising the height of the seat as it is adjusted forward.

I’m currently at the stage of painting the parts and cleaning and repairing the seats. Next, I must address changes to the seatbelts. My MB seatbelts are in poor condition. The Hyundai belts I removed with the seats are the same color, length and size. Even though the Tiburon retractors have very similar mounts, they are too wide to shoehorn them in place of the MBs. I plan to take the MB retractor apart and thread the Tiburon ones in. That will give me the necessary tongue for the Tiburon latch and safer seatbelts. As you can see in the photos, the backrest of the Tiburon seats are about in inch and a half higher than the MB seats. I’ll need to find a solution for a guide to cut down on wear from friction across the seat. The current thread addressing this need has many good ideas.

Anyone who has adapted seats in these cars can tell you what a pain it is. I lost count how many times I’ve put seats in the car to test fit and adjust. This forum has helped me sort out what would work for me. I know that my explanation is detailed and long. My hope is that it will save someone else some of the challenges and unnecessary expense that I have faced. I wouldn't have done this if my MB seats hadn't been rotten. You can always identify the pioneers by how many arrows are in their butts!

The final two photos will be in the following post.

GD
 

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#25 ·
Seatbelt Anchors

I made significant progress with my seat adaption project. I finally decided where to mount the seatbelt anchors and finished their construction. There were several considerations to make everything fit and operate properly. A kind and generous forum member helped me acquire another set of seat tracks. I want to save as much of my original ’75 seat parts intact as possible. These ’77 SLC tracks have an extra ridge that mine do not. I guess it would make them stronger. It gave a bit more metal to weld to. The bolt pattern is the same.

I drilled out the slots for the tabs and then squared off the holes with my Dremel. It reminded me why I buy so many of the little cutting disks. ;-] Someone on the forum suggested using the middle track bolt tab as a seatbelt anchor. I liked the idea and thought I could just flip both driver's side tracks over and use one on the passenger side's seatbelt. I’d use the passenger tracks on the tunnel side. Well, MB, in their infinite wisdom didn't make the driver's and passenger's tracks the same size. The holes don't line up at all, so I made my own anchor tabs and used the tracks as is. The middle bolt was also too far forward and small for my purposes.

The seatbelt anchor is a heavy hardened 12mm (bolt, not head) size with a collar to allow the seatbelt end to rotate freely when the seat was adjusted. I made the seatbelt tab big so it would have plenty of metal to hold on to the track and support the end of the bolt. The 3/8” plate gave me a good thread depth. I don’t want this seatbelt setup to be uncomfortable while driving. Also, it’s better too much strength than not enough when in a collision. These anchor tabs will allow the driver’s seat height adjusters to continue to work and act as a stop my adapter from sliding backward in the track.

I learned something notable about Metric bolt and thread sizes while making the threaded holes for the seatbelt anchors. The Hyundai seats attach with 10mm 1.25. The seatbelt uses 12mm 1.25. My Metric tap and die set only has 12mm 1.50 and 1.75. While studying my chart on tap and drill sizes, I noticed that 12mm 1.25 was noted as "optional." Not knowing what that meant and thinking that some Metric and SAE Inch sizes match up, so I measured the seatbelt thread rate and found that it was a perfect 20 threads per inch and the anchor bolt easily screwed into a 7/16” 20 die. So, a 12mm 1.25 = 7/16” 20 thread rate tap. That saved me a trip to the hardware store and the trouble of trying to find an odd ball tap to get the project done.

The seats have cleanup and dried nicely. What I thought was charcoal gray fabric turned out to be black. After washing them at a car wash, I sucked as much water out of the cloth and foam as possible. I was surprised how dirty the water was in my shop vac afterwards. Fifteen years of use adds up and who ever cleans their seats? A few more repairs and paint were necessary, but I’m ready to reassemble the seats.

One of the worst things about fabricating stuff is that it looks like it takes five minutes and costs next to nothing to do. I’m sure there are faster and better ways to do a project like this, but with my limited resources and tools, I’m getting it done. Cutting 3/8” plate with a hand grinder goes slow. The good thing is that I'm one step closer to the end and driving the car.

GD
 

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#26 ·
GD, I had been following this thread with great interest but somehow I missed your post 22 asking me a couple of questions.
The seat bracket pictures look nothing like the brackets Corbeaux sold to me. It's not apparent to me how, or if, they work
I am no help regarding headroom either for I haven't mounted the hard top in nearly ten years.

You seem to be doing fine forging your own way. Good work!
 
#27 ·
Tiburon Seats Cleaned And Repaired

Dugald, Thanks for your reply. Many of the steps I've taken to adapt these Tiburon seats were built upon other's ideas and solutions.

I ordered a pair of stainless shoe horns off of eBay. They are about 16+" and should be plenty long to go across the top of these Tiburon seats. They were a little less than $5 each with free shipping. There's even longer ones, but I don't need them that long.

I've had enough seats apart to have a pretty good idea how the headrest grommets are secured in these seats. The best solution for me seems to be to take them out, drill big enough holes to fit around them and to hold the shoe horn down. I'll know more once the shoe horns get here. They are coming from China.

Below is a photo of the cleaned and reassembled cloth Tiburon seats. Black is hard to photograph. It takes a bit of work to dismantle seats, but I've learned it's worthwhile if only to speed the drying process. Milldew can set in quickly onto soggy cushions and covers.

It's also good to check under the covers on used seats. I bought an old Toyota truck once that had transplanted Opal seats installed. I took them apart to clean them and found large blood stains all over the foam pads. I found some better replacements. As aptly mentioned before by another member, seats from wrecked cars can be badly bent, so seeing the car and taking them out oneself is a bonus. You know better where they've been. Good seats are not easy to find.

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#28 ·
Tiburon Seat Installation And Seatbelt Adaption #1

My custom seat mounts were slid into the modified side tracks and hardened bolts locked them into place. I used the original mounting hardware and they fit perfectly. Some forum members were very successful with welding mounts to the side mount tracks, but I needed to fit my seats with the hard top in place so I could check for sufficient headroom. That necessitated very many test fittings. I felt like I was working inside a bottle. I was not sure until close to the end of this process whether the Tiburon seats would work for me. So, I chose to make mounts that could be easily modified for seats other than the 1998-2001 Tiburons.

I have found there to be a wide variation of how seat brackets bolt down. Few of the ones I’ve seen will bolt to a flat surface or have the mounting holes equal distances apart. My mounting bars were just wide enough to allow for the Tiburon mounting holes. Mounting holes for future seats having different requirements can be drilled and tapped. Since the front and back bars are not welded in, they can be relocated. I tried to keep the whole seat mounting process as simple as possible with the absolute minimum of alteration to the car’s body. Original seats can be reinstalled at any time. See first photo.

Resolving issues with the seatbelts was the next challenge. I suspect that many who installed non-107 seats simply attached their original seatbelt latch onto the new seats and left the MB seatbelt assembly unaltered. That would be the easiest approach. That wouldn’t work for me. As you can see in the second photo, the belt was badly chewed up from being pinched in the backrest’s latch bolt. Instead of insuring that the belt was retracted, the PO just let it lay in the backrest hinge and slowly cut through the belt. It’s hard to say how safe it was with half gone, but my wife wouldn’t ride in the car as is. See second photo.

I did my best to find reasonably priced used MB belts in good condition, but couldn’t. I have to wonder how strong and safe forty year old synthetic material which has been exposed to weather and sun light really are? Only a bad accident would answer that question and then it may be too late. The belts listed on eBay were nearly as old, were not cheap and showed similar damage to mine. When I purchased the Tiburon seats at the junk yard, I also pulled out the front and rear belts. The front belts looked like new and seemed to be a good length. I tried to find a way to install the Tiburon retractor, too, but it was a bit too big to fit behind the molding cover.

I removed the Tiburon belt, threaded the Tiburon tongue on and adapted it to the rebuilt MB retractors. It was only about six inches longer than the MB belt, but it was a thicker weave. I cut the belt to the correct length, sealed the end with a soldering iron and restitched the end so it would lock properly into the MB retractor. It was a tight fit, but works perfectly fully retracting. Cleaning and lubricating the MB retractors brought new life to them. The Tiburon seatbelt assemblies were $5 each from the junk yard. From the inquiries I made, just putting new belt material on MB seatbelts is very expensive. If I decide to put my 107 seats back in, all I just need to swap is the latch tongue. See photos three through six.

See Part Two

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#29 ·
Tiburon Seat Installation And Seatbelt Adaption #2

As I showed earlier, I decided to attach the belt end to the car instead of the seat. It seems safer in case the seat breaks loose in an accident. Floor mounted seats depend on a solid floor to add to the rigidity of the seat frame. That’s one of the reasons I built my adapters so heavily. Twisting during an accident might allow the seat to tear loose and crush the rider. With a bit of adjustment, the seats have full forward to backward movement sliding past the seatbelt anchor. See photo one in this part #2 .

Photos two through six show the fit of the Tiburon seats and the hybrid seatbelts. One of the reasons I chose these 2001 Tiburon seats was because they have a shorter backrest closer in size of the MB seats than many I looked at. I tried to allow the seatbelt to go across the top of the seat rather than the side. Since most coupe seats have the belt guide mounted high near the roof, it doesn’t matter how high the backrest is. The last two photos show how the belt comfortably lays across the rider’s shoulder.

I acquired a pair of 16+ inch stainless shoehorns to attach to the top of the backrest. Having a hanger there would make the reach for the belt more convenient and may help reduce wear on the seat’s fabric. I’m undecided whether they are necessary or beneficial. I’m planning on finding some attractive seat covers. How the shoehorn guards would work with them is unknown. Allowing the belts to fully retract and hang behind the seats may be the best solution.

With everything considered, adapting the Tiburon seats was my best solution. The seats I have now are clean, comfortable, fully functional and safe. I did not want to replace the MB seats, but the “horsehair” pads were so rotten that they were sifting out the back and the framing was protruding through the cracked leather covers. The MB seats had little support or comfort. As anyone who looks into rebuilding the MB seats, it’s an expensive and, for DIYs, a difficult process. I thought long and hard about spending $1000 plus for seats listed on eBay, but from what I’ve seen of the insides of my own seats, I wouldn’t trust that the fiber pads were in any better or longer lasting shape than mine. I do plan on rebuilding my MB seats as time and money permit.

I hope this account of my seat work has been helpful. I’ve benefited greatly from the information, advice and help provided here on the forum. I documented this as best in return for that support. Let me know if you have any questions.

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#31 ·
Thanks Dugald! I'm glad you like the job.

I used your shoehorn idea for a seatbelt hanger/guide and I'm pleased with the results. I figured that since I had these sent halfway around the world from China, I'd give it a try.

My headrests are small and I like to have them high, so I couldn't hide the horns under the headrest. Also, because there's so much headrest post showing, if I didn't find some way to hold the horns down, they'd be rattling when the seatbelt wasn't on top of them. I hunted around and found that these slip joint washers. They made a good friction fit on the headrest posts and held the shoehorn securely in place. I have since bent them down so they conform more to the shape of the seat.

These stainless shoehorns are certainly a challenge to drill. I had to trim the holes to remove the burr.

I mounted them as shown so that I wouldn't sit on top of the belt and they would keep the seatbelt within reach. They also should help reduce the abrasion on the top of the seat. I have less than $14 in this solution.

Thanks for the great idea!

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