I sourced the 39lb. 300D manual flywheel on Ebay. It wasn’t cheap at $1000.00 but it’s one of the keys to having a smooth running car with the manual. I’d read posts where the where the 240D flywheel was used and they generally talked about vibration.

Not in my experience. I have used a 240 flywheel for 13 years and my friend has used one for 20 years. ZERO issues with using the 240 flywheel. Its plenty heavy for smooth idle.
The important thing is BALANCE. These are externally balanced engines, the flywheel MUST be balanced to the auto flywheel.

I read that a 240 automatic crossmember would fit but it was way off.

Nope. Its what I use and it is a perfect fit for both the iron and aluminum transmissions.
The bolt receivers must be moved to the correct tab holes in the chassis.

I used the speedometer cable from the donor car as the ends on the cable for the automatic don’t fit the manual transmission. It is slightly longer but not a material difference.

They are actually the same. The only difference besides length is a flat driver end on the older transmissions.

The crank modification might be a little beyond the weekend mechanic

As a note, that only applies to 84+ engines. 81-late83 fit a normal pilot.

 

Thanks for comments. I agree on the speedometer cable. Laying on the work bench the older part looked longer by a couple inches but they may well have been the same. I couldn't agree more on the balance issue. Key is to have same for same go back into the engine. I can state that both my automatic flywheel or flex plate mount was very near neutral (within a couple grams), same for the heavy flywheel. I had the balance shop note the heavy side anyway and put the new part in the same orientation. I'm glad people have success with the lighter 4 cylinder flywheel. I wasn't willing to take the risk. I'd like to see pictures of your crossmember. I actually ordered the 240D automatic part by MB part number. When it arrived the bolt spacing and span was identical to the 300D automatic part with the transmission mount in a slightly forward location but nowhere near enough. May have got the wrong part.

Thanks again.

John

 

I couldn't agree more on the balance issue. Key is to have same for same go back into the engine. I can state that both my automatic flywheel or flex plate mount was very near neutral (within a couple grams), same for the heavy flywheel.

Right, but even a few grams at 4800rpm is a lot of force for the main bearings to absorb.

I actually ordered the 240D automatic part by MB part number. When it arrived the bolt spacing and span was identical to the 300D automatic part with the transmission mount in a slightly forward location but nowhere near enough. May have got the wrong part.

The one I have is 1232420701. It was pure luck there was an auto 240D in a pick-n-pull on the way to getting my 240D parts car.

Which transmission did you use? I like the Getrag the best so far. The slope-back was a bit more durable and my current flat-back grinds into every gear too easily if I want to shift quickly.

 

Thanks for the pictures and part number. I'm using a cast iron case 716.210 transmission, not for any strength or technical reason. It was the simply the transmission in my donor car.

 

716.210 is the cast aluminium single-piece 'box. The 2-piece "Slope 2" aluminium 'box was 716.00x. I don't know the cast iron unit's number, but I think it was 711.xxx

 

cast iron gear box with bolt on bell housing: 716.005

 

Wow, well done

 

Since the 300D manual conversion uses the 240D auto crossmember would it also use the 240D auto driveshaft?

 

The 300D 5-speed doesn't originally use the 240D auto's cross member. But that's also what I did to make my 5-speed conversion work.

The car's own prop shaft will have to be shortened or lengthened to fit. From my experience, there are almost as many variations of prop shaft as there are W123s.

 

No, a 240D auto driveshaft will not fit anything but a 240D auto.
If you start with a 240D manual driveshaft, remove 4".

In addition, different models had different driveshaft center support mounting locations. That is a welded part of the chassis that can't be relocated.
For example, the entire driveshaft for a 280E 5-speed and 300D 5-speed is the correct length, but the center mount is in a different location, so one is useless for the other.

300D auto US A1234105801
240D auto US A1234108101
300D 4-speed manual A1234104701
300D 5-speed manual A1234108501
280E 4-speed manual A1234105301
280E 5-speed manual A1234107701

 

Neat to see those side-by-side.

 

Nice write up!

 

There are a number of threads that talk about this conversion but I haven’t seen one that covers the swap from start to finish. I just completed the job and think some and decided to post the particulars.
The car converted is my 300D Turbo automatic. It’s a fairly low mile car in very good condition that I use as a daily driver. The automatic worked as designed but I enjoy a manual transmission and decided to undertake the project.
I sourced the 39lb. 300D manual flywheel on Ebay. It wasn’t cheap at $1000.00 but it’s one of the keys to having a smooth running car with the manual. I’d read posts where the where the 240D flywheel was used and they generally talked about vibration. Mercedes used this heavy flywheel for a reason.
The rest of the parts came from a salvage 1978 240D manual at a cost of $600. I chose to buy a whole car as sourcing the parts ala carte is for sure more time consuming and probably costlier in the long run.
Below lists the broad steps.
• I removed the automatic trans.
• I marked the cast flex plate location to the crank before removal. I had a local balancing shop compare the flex plate to my flywheel after resurfacing. They were both neutrally balanced and quite accurate. I did have the flywheel matched and marked so whatever slight imbalances were present were in the same orientation as the flex plate casting that was removed.
• I had a set of used flywheel bolts from an old project and re-used them. This is discussed a lot on the forum. Mercedes has a minimum diameter for the neck on these stretch bolts and mine were well over the minimum for re-use. I did torque using the torque angle method.
• The pilot bearing posed a problem. There was over 0.003” interference between the bore of the crank and the bearing OD. I assume this is because Mercedes skipped the grinding operation for the bore on cranks for Turbo engines. I considered making a bronze pilot bushing but chose to open the crank bore instead. With a lot of patience, a flap wheel, a modified brake hone and a bore gauge I opened the bore 0.0025”. It took some time but the result was excellent and the pilot bearing fit with the right amount of interference. If I wasn’t a machinist in a well-equipped shop this would have been a big problem.
• I installed all new clutch components.
• I installed a new slave cylinder with the manual transmission on the bench along with a new flex disc and measured the overall length compared to the automatic for the required drive shaft modifications, then installed the transmission.
• The transmission crossmember was the next obstacle. I ended up using a 240D manual crossmember. I read that a 240 automatic crossmember would fit but it was way off. The modification was simple on the 240D manual part I pulled from the donor car. I cut ¾ inch from both sides, welded it back together and slotted its mount holes to the chassis and the mount slightly. Finally, I lowered the flange on the crossmember to provide a little clearance against the bottom of the transmission. The fit was perfect. It does require the smaller 240D transmission mount but the result was perfect, no vibration at all.
• I had the 300D drive shaft lengthened and balanced at a local shop for about $300 and installed it with a new center bearing and rear flex disc.
• Installing the pedal cluster is frankly difficult. There is very little room to move under the car but it will fit with patience. I installed a new clutch master cylinder on the bench before installing the pedal cluster.
• I was able to locate a new clutch hydraulic hose assembly from Pelican Parts. The required holes are in the chassis. Again the fit was perfect.
• The shifter assembly from the donor car was in poor condition so I changed all the bushings before installation.
• I had intended to shorten the shift rods from the donor car but located a set of correct 300D manual rods on eBay and used them instead.
• The wiring harness connecting the reverse light switch on the shifter assembly plugged into the main chassis harness without modification. I have reverse lights but obviously no NSS.
• I used the speedometer cable from the donor car as the ends on the cable for the automatic don’t fit the manual transmission. It is slightly longer but not a material difference.
• The last obstacle was the cruise control amplifier. The manual pedal cluster occupied space it used under the dash. As I considered options, I noticed molded-in screw holes on the under dash panel the exact spacing as the amplifier bracket. The wiring harness didn't leave me enough room to mount the amplifier and plug into the harness. I ended up making a spacer to rotate the amplifier slightly so the wiring connection could be made. The result was good.

The swap is not terribly difficult but I didn’t cut corners and it wasn’t cheap. The crank modification might be a little beyond the weekend mechanic and the crossmember modification would be a challenge. Other than that, it’s really a bolt together process. I couldn’t be happier with the results. It’s much quicker and comfortable to drive with none of the disconnectedness of ‘80’s automatic transmissions.

The clutch pedal has an electrical swith that needs to interact with cruise control, it switches cruise control off each time you depress the clutch. Its an odd seeming way to do it, it interrupts the ground (if I remember right) by way of a circuit to one of the lights at the rear. Needs to be spliced into a wire in a harness under the drivers foot well area. I stared at that wiring diagram for a long time, and spent time with my head in the driver foot well.

 

I hadn’t noticed that but it makes sense. The system prevents CC with the clutch depressed which protects against an engine runaway in the unlikely event a driver would shift with CC in.

I didn’t even notice it and actually use CC quite a bit. I never shift with it on though.

 

Hi. Doing a 5 speed conversion on an 85 300rd and noticed above Forced Induction saying that the pilot is different for 84 and 85 models. Does anyone know a part number or how and where to get the correct sized pilot bearing? Thanks

 

There are not two different size pilot bearings. I'm assuming you're working on a turbo engine. The turbo engine was never sold with a manual transmission therefore the factory didn't need to grind the pilot bearing bearing diameter for turbo engine crankshafts. I assume the factory simply skipped the unnecessary finish grinding operation. Some say it's only later engines but it's not been my experience. Logically all turbo cranks would be undersized and all non-turbo cranks would be the correct size and this has been my experience.

When you measure the bore in the turbo crankshaft you will find it's about 0.003 less than the pilot bearing od, way too much press. There is no special bearing for this. You can either use a flap wheel and carefully open up the crank bore until you have a reasonable press fit, about 0.0005" interference. Be very careful about taper and roundness. I don't think this can be done without a precision bore gauge and some machining experience to use the tool well while holding taper, roundness and size. Another solution is to have a machine shop make a pilot pushing from oil impregnated bronze fit to the crank and the transmission input shaft.

There is only one pilot bearing bearing used on om615, 616, 617 and probably many other engines. I hope this answers your question.

 

careful, I do not think it is. its a press fit, can seem snug

 

Uh oh.

I’m working on bolting a 717.400 to a 1982 617A. Seems I could run into this. I haven’t bought the pilot bearing yet.

But is sure seems like guys add manual transmissions to their 300Ds, including turbo models, pretty frequently. Usually it’s 4 speeds from a 240D. I actually had a shop do it for me before I was a DIYer. I’ve never heard of problems with this.

FB

 

I’m working on bolting a 717.400 to a 1982 617A. Seems I could run into this. I haven’t bought the pilot bearing yet.

You will use a standard pilot bearing for a 240D.

 

• The last obstacle was the cruise control amplifier. The manual pedal cluster occupied space it used under the dash. As I considered options, I noticed molded-in screw holes on the under dash panel the exact spacing as the amplifier bracket. The wiring harness didn't leave me enough room to mount the amplifier and plug into the harness. I ended up making a spacer to rotate the amplifier slightly so the wiring connection could be made. The result was good.

This is gold. It's from a 2 and half year old post, but it's a big deal (for me). I never knew this, and have spent a considerable amount of time looking for this solution. On past cars I have just tucked the amp in the looms of wires and applied wire ties liberally. This is much more elegant. Thank you, Jroth.

I know, I'm missing the insulation in the picture, but it's to demo to location.

For the web search engines: this is where to mount a cruise control amp in a W123 with a manual transmission.

FB