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1985 300D Gone 1985 230CE Perfect, 1984 300TD Driver, 1981 300TD Bad engine
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Discussion Starter #1
I am seriously considering converting my 300D to rack and Pinion. I am having trouble getting past the first step: Finding a suitable doner rack. What I am doing is measuring racks in wrecking yards looking two basic elements: tie rod length and overall width. My search has been limited to vehicles of the near the same weight and of course ones that are mounted behind the axle. Mounting the rack to the car would be time consuming but a doable task.

The only reference that I have found about this conversion is one where the guy put an American engine in his car. His rack was mounted in front of the axle. This would not work on our cars because the oil sump would not allow enough clearance.

One thing that I like about the 300D it the tight turning radius. I'd want to make sure that this I'd not affected.

I'd like to get a discussion going about this conversion.
 

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5 Speed "85" Euro TD , 5 speed "85" Euro 240D, "79" 5 spd 240D, 5 spd "94" Dodge/Cummins PU
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I find the steering in the W123 better than in any car Ive ever had, that illustrates one of the advantage of always having old cars:)
 

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1983 300D
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There is a lot of purest here on these w123 sites, so you might ruffle some feathers.:D You might want to post the question in superturbodiesel.com. You might get some good responses there.

With that said, there should be some racks that will possibly work in a "Rear Steer" (behind the cross member) location with new welded on mounting points. Take a look at 1978-87 Dodge Omni and Plymouth Horizons, and Late '80s to Mid-'90s GM cars like Chevrolet Luminas, Pontiac Grand Prix, etc. These racks have been used in custom Classic car applicatoins with success. So I'm thinking it may work also. There probably other racks that may work from other brand cars.


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1985 300D Gone 1985 230CE Perfect, 1984 300TD Driver, 1981 300TD Bad engine
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1,418 Posts
Discussion Starter #4
I find the steering in the W123 better than in any car Ive ever had, that illustrates one of the advantage of always having old cars:)
That is not the case with my car. There is enough play in the box that the adjuster won't take up that I am always having to correct when going in a straight line. I've demonstrated this to my self by tightening the adjuster very tight so that the pitman arm does not move and there is still slack in the steering box. I've tested several boxes in yards and they seem the same.
 

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1981 W123 300D non turbo, 1992 190E 1.8 <=> 2.0
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6,561 Posts
That is not the case with my car. There is enough play in the box that the adjuster won't take up that I am always having to correct when going in a straight line. I've demonstrated this to my self by tightening the adjuster very tight so that the pitman arm does not move and there is still slack in the steering box. I've tested several boxes in yards and they seem the same.
My experience is that you need to adjust the box with it off of the car

What a feeling it will be! A properly adjusted W123 / W116 / W126 power steering box - PeachParts Mercedes ShopForum

But anyway if you wanted rack and pinion - how about looking at modern Mercedes solutions such as sprinters?
 

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1984 300D
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5,070 Posts
Need to start searching the internet; as said it has been done before. Someone has done this before.

The real question is if the gain is worth the work. I think it is more one of those I just want to have something different projects.

That being said my Volvo Diesel Steers more easily than the Mercedes and it has R&P Steering.
 

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1985 300D Gone 1985 230CE Perfect, 1984 300TD Driver, 1981 300TD Bad engine
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Discussion Starter #7
My experience is that you need to adjust the box with it off of the car
I read your post some time ago. If I remember correctly, you hadn't driven since your adjustments. Is that still the case?

From working on a spare box I am pretty sure that the looseness is in the ball screw or nut.

But anyway if you wanted rack and pinion - how about looking at modern Mercedes solutions such as sprinters?
I looked at one Mercedes. The tie rod was close to the same length but the overall width was several inches wider. I am sure that a Sprinter would be wider yet. Getting the two basic dimensions mentioned before is what is giving me trouble.
 

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1985 300D Gone 1985 230CE Perfect, 1984 300TD Driver, 1981 300TD Bad engine
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1,418 Posts
Discussion Starter #8
There is a lot of purest here on these w123 sites, so you might ruffle some feathers.:D You might want to post the question in superturbodiesel.com. You might get some good responses there.

With that said, there should be some racks that will possibly work in a "Rear Steer" (behind the cross member) location with new welded on mounting points. Take a look at 1978-87 Dodge Omni and Plymouth Horizons, and Late '80s to Mid-'90s GM cars like Chevrolet Luminas, Pontiac Grand Prix, etc. These racks have been used in custom Classic car applicatoins with success. So I'm thinking it may work also. There probably other racks that may work from other brand cars.


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The smaller car might give me the right dimensions but they are quite a bit lighter than the 300D. I am worried that it would not be strong enough. I've checked the GM racks and the overall width is too much.
 

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1983 300D
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The smaller car might give me the right dimensions but they are quite a bit lighter than the 300D. I am worried that it would not be strong enough. I've checked the GM racks and the overall width is too much.
That might not be the case because these racks are used in custom applications on heavy 1950's lead sleds and '50-60's pickup trucks.


Here are some custom places that deal with these conversions.
Power Rack & Pinion - Billet-Power? Mustang II Style Front Steer Power Rack & Pinion - Billet-Power? Universal Rear Steer Power Rack & Pinion - Billet-Power? Universal Front Steer Power Rack & Pinion

Dodge or Plymouth Omni power rack and pinion custom build 1970s and 1980s

omni+rack+and+pinion - JEGS High Performance


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'86 W123 200, OM617 non-turbo, bastard 5-speed; '95 W202 C250 Diesel, OM605 non-turbo, 5-spd man
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4,275 Posts
I am seriously considering converting my 300D to rack and Pinion. I am having trouble getting past the first step: Finding a suitable doner rack. What I am doing is measuring racks in wrecking yards looking two basic elements: tie rod length and overall width. My search has been limited to vehicles of the near the same weight and of course ones that are mounted behind the axle. Mounting the rack to the car would be time consuming but a doable task.

I'd like to get a discussion going about this conversion.
Join the club.

I am slightly torn between being a purist and pro-progress. I have found racks that will fit exactly the length of the central drag link, but they either lack the travel or have too many turns lock-to-lock.

My reasoning is that I can improve steering feel and save some weight (aluminium rack, minus steel steering box and minus central drag link) while eliminating steering wear. I just don't want to lose the high steering rate of the W123 as that makes parking a breeze.

I think mounting should be quite easy, actually.

P.S.

Don't be too concerned about cars of similar weight. Most of the racks I have looked at come off recent front-wheel-drive cars, which have not only similar kerb masses to Donkey, but a much heavier mass over the front wheels - a far greater consideration IMHO.
 

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1981 W123 300D non turbo, 1992 190E 1.8 <=> 2.0
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6,561 Posts
I read your post some time ago. If I remember correctly, you hadn't driven since your adjustments. Is that still the case?

From working on a spare box I am pretty sure that the looseness is in the ball screw or nut.

...
You are correct - I still haven't driven since the box was stripped down and adjusted. May be one day. I'm hopefull that it will be the best it can be as I've followed the FSM instructions. I've done what a servicing shop should do albeit with my own (cheaper) versions of the special tools.

I think I was lucky in that the internals of the steering box showed minimal wear - I have great expectations!


I think I should have tried a bit harder in my first post - the point I would like to make is that if you don't measure the torque needed to turn the shaft then you have no way of knowing if your adjustment is correct.

You can't measure the torque with the steering box fitted to the car. There is a check that you can make by measuring the torque at the steering wheel but I think it is prudent to note that whilst that check exists in the FSM it is not part of a procedure of adjustment.

I found the process of adjusting the steering box to be pretty tricky. If you go too far on the adjusting screw and just back it off a bit to compensate for your error you will find that you loose your place. It isn't a linear relationship - it is very non-linear - I found that you need to slacken the adjusting nut right off and start anew.
 

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1983 300D
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...
I think mounting should be quite easy, actually.
..
Here is an example of mounting a GM rack, Chevy Cavalier, to a '68 Mustang.


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1984 300D, 1983 300TD, 1995 E300
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That is not the case with my car. There is enough play in the box that the adjuster won't take up that I am always having to correct when going in a straight line. I've demonstrated this to my self by tightening the adjuster very tight so that the pitman arm does not move and there is still slack in the steering box. I've tested several boxes in yards and they seem the same.
Then buy a new box. The rotating ball system is vastly superior to anything rack and pinion.

A refurb box is going to cost you ~$400 from a supplier. I reseal/adjust boxes for $135+ $45 core charge (I've done about 30 of them). Or you could go over to [email protected]@rts and find the writeup to reseal/adjust one yourself.

Yes, there will almost always be a smidgen of play in the boxes. But do yourself a favor and check your steering linkage, ball joints, suspension and steering coupler first. The box gets blamed far more often than it needs to be.
 

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1984 300D, 1983 300TD, 1995 E300
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You are correct - I still haven't driven since the box was stripped down and adjusted. May be one day. I'm hopefull that it will be the best it can be as I've followed the FSM instructions. I've done what a servicing shop should do albeit with my own (cheaper) versions of the special tools.

I think I was lucky in that the internals of the steering box showed minimal wear - I have great expectations!


I think I should have tried a bit harder in my first post - the point I would like to make is that if you don't measure the torque needed to turn the shaft then you have no way of knowing if your adjustment is correct.

You can't measure the torque with the steering box fitted to the car. There is a check that you can make by measuring the torque at the steering wheel but I think it is prudent to note that whilst that check exists in the FSM it is not part of a procedure of adjustment.

I found the process of adjusting the steering box to be pretty tricky. If you go too far on the adjusting screw and just back it off a bit to compensate for your error you will find that you loose your place. It isn't a linear relationship - it is very non-linear - I found that you need to slacken the adjusting nut right off and start anew.
Army, IT'S AWESOME. I've driven on 3 different resealed boxes (I keep swapping them out of my DD) and the steering is so much lighter! And way more precise.:thumbsup:
 

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1981 W123 300D non turbo, 1992 190E 1.8 <=> 2.0
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Army, IT'S AWESOME. I've driven on 3 different resealed boxes (I keep swapping them out of my DD) and the steering is so much lighter! And way more precise.:thumbsup:
Great stuff - I'm glad to hear it (from someone who manages to tackle one problem with his car at a time!)
 

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1984 300D, 1983 300TD, 1995 E300
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Great stuff - I'm glad to hear it (from someone who manages to tackle one problem with his car at a time!)
I haven't yet sold a box at a gtg, but it seems that after getting that tool made people want to see the tool and the big wrench more than they do my car!

As a side note: I bought the big 65mm combination wrench (Chinese) for around $35 and hated it every time I used it because it was too dang heavy. I was browsing on ebay.de and found a 65mm Gedore wrench for ~$7 (USD) and got it shipped to me for ~$10 (USD)! So now I have a German wrench of the same era as the boxes I'm fixing. And it's super comfortable:thumbsup:

For the life of me I've broken two pin wrenches, I can't seem to find one that fits well and holds up to the torque I put on it. (or it could be that I keep buying cheap wrenches) What brand did you end up buying?
 

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1981 W123 300D non turbo, 1992 190E 1.8 <=> 2.0
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For the life of me I've broken two pin wrenches, I can't seem to find one that fits well and holds up to the torque I put on it. (or it could be that I keep buying cheap wrenches) What brand did you end up buying?
Gedore!
 

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'86 W123 200, OM617 non-turbo, bastard 5-speed; '95 W202 C250 Diesel, OM605 non-turbo, 5-spd man
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Then buy a new box. The rotating ball system is vastly superior to anything rack and pinion.
Excuse me, what!?!

Sorry, but I beg to differ. A recirculating ball system has far more components to wear out and pick up damage, it reduces (if not completely eliminates) steering feedback, the worm and nut/peg are designed to wear out - fundamental operating principle - and it is heavy.

Rack-and-pinion systems are lighter, simpler, more robust, lower maintenance and cheaper. Not to mention "tunable". Variable rate rack-and-pinion systems are percise and responsive at centre position and effort-reducing at the extremes without eliminating feedback, allowing for the best possible driver awareness and control.
 

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1985 300D Gone 1985 230CE Perfect, 1984 300TD Driver, 1981 300TD Bad engine
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Discussion Starter #20
Then buy a new box. The rotating ball system is vastly superior to anything rack and pinion.

A refurb box is going to cost you ~$400 from a supplier. I reseal/adjust boxes for $135+ $45 core charge (I've done about 30 of them). Or you could go over to [email protected]@rts and find the writeup to reseal/adjust one yourself.

Yes, there will almost always be a smidgen of play in the boxes. But do yourself a favor and check your steering linkage, ball joints, suspension and steering coupler first. The box gets blamed far more often than it needs to be.
I've considered "Rebuilt" boxes. I asked an eBay vendor about his rebuilt boxes trying to find out what was done to get rid of the slack or if it was just resealed. He did not reply to my question.

All the steering components are new. I am confident that my test of binding the gears with the adjusting screw show that the slack is inside the box. With my work on the extra box, I believe that it is in the recirculating ball portion.
 
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