Mercedes W124 Rear Suspension Guide - PeachParts Mercedes-Benz Forum

Jeremy5848 · #1 06-13-2011, 03:28 PM

Whenever I work on the rear suspension of my '87 300D, I have to re-learn what all of the names mean. I wrote this guide to remind myself how the suspension works and what all of the parts are. Maybe it will help you too.

The 5-link suspension system was introduced on the 1984 190E (W201). It was designed to allow the rear wheels to move up and down in response to road irregularities while affecting the car's handling as little as possible, or so they say. The best explanation and pictures are in the Model Year 1984 (USA) "Introduction into service" manual for the W201. Since Mercedes assumes you have all previous manuals, they don't repeat themselves in later manuals. For the model 124, which has an almost identical system, Mercedes says only "The rear axle is similar to model 201" and then proceeds to list the (few) differences.

The links that comprise the rear suspension are metal forgings (or pressings, or stampings) with rubber bushings at each end. The usual failure is that one or more of the bushings wears out from repeated use and aging of the rubber. Given that everything in a W124 car is 25 years old or getting close, you should really replace every bushing in the entire system. However, most of us don't want to spend (or simply don't have) the money it would take to do that, so we replace one part at a time as they fail. If it is at all financially possible, replace both the right and the left links in each pair, even though only one may have a bad bushing.

It is possible to replace just the bad bushing; the metal strut itself doesn't go bad unless it's in an accident. However, it takes specialized pullers to remove and install new bushings and the bushings themselves are not always available. Sometimes Mercedes makes a "parts kit" available but it costs more to have someone install the new bushing that it would to buy the complete link.

The various links that make up the system are known by different names, depending on the source. Manuals do not always use the same term; your indy mechanic may use one term, the dealer's parts people another, and an aftermarket supplier a third. Additionally, Mercedes has changed and updated these parts many times and there are a range of part numbers that will fit. (See EPC for the complete list.) Dealers typically have only the latest version while aftermarket suppliers may have earlier revisions. This makes it difficult to know if you are even buying the right part, especially if you aren't able to hold the old and new parts in your hand before forking over a lot of money. The following guide may be of some help.

The pictures, from the Model Year 1984 (USA) "Introduction into service" manual are used as a base for the guide. All parts are the same for the left and right sides except for the note under "6. Spring link." All of these parts are listed in EPC under section 35.075 "Rear Axle Suspension."

1. Rear axle carrier. This is the entire subframe that bolts to the chassis and "carries" the differential and all of the various suspension links, springs, and shock absorbers. The carrier is attached to the frame at four points with rubber bushings. Replacing these bushings is probably classified a "difficult" DIY job. [FSM, chassis, section 35-040.]

2 Camber link. Also known as "control arm" or "camber strut." The Haynes manual for the 124 calls it the "upper camber control arm." This part has a definite curvature and therefore is more easily identifiable in the hand. The latest part number in EPC is 210 350 34 06 and there are ten (!!!) earlier versions. If you have an earlier version with M10 hardware, you will need some extra parts to update your suspension to the new M12 hardware.

3. Pulling link. Also known as "control arm" or "strut." FSM calls it the "torque strut." Haynes calls it the "upper torque control arm." The latest version of this part is 210 350 33 06. If you have an earlier version with M10 hardware, you will need some extra parts to update your suspension to the new M12 hardware.

4. Tie link. Also known as "tie rod." Haynes calls it the "lower track control arm." EPC shows the latest version of this link as a "parts kit," 210 350 21 53. I don't know if this really means you have to assemble it but the previous version, 210 350 09 53, is still available in the aftermarket.

5. Pushing link. Also known as "thrust arm." Haynes calls it the "lower thrust control arm." The latest version of this part is 210 350 38 06. If you have an earlier version with M10 hardware, you will need some extra parts to update your suspension to the new M12 hardware. This link also has a plastic cover, 210 352 09 88, to protect the link from road debris and to improve aerodynamics.

6. Spring link. Also known as "spring control arm." Haynes calls it the "rear suspension lower arm." This is the big piece at the bottom. It holds the bottom of the spring and shock absorber. The latest version shown in EPC is 202 350 02 06 and there are five earlier versions. The spring link has a plastic cover, 203 352 00 88, to protect the link from road debris and to improve aerodynamics. (EPC also lists three earlier versions of this cover.) Note that the 1986 "Introduction into service" manual for Model 124 says (page 195) that the spring links are different for left and right but EPC lists only one part number for both so Mercedes must have made a change.

7. Wheel carrier. This is the part that holds the rear wheel. Haynes calls it the "rear hub carrier." The wheel carrier is attached to the rear axle carrier by the five links.

Alignment of the rear end (camber and toe-in) is done by adjusting eccentric bolts. This requires specialized measuring equipment. If you change one or more links in your rear suspension, you should get (at least) the rear end realigned by a shop that specializes in this kind of work.

Jeremy

Stretch · #2 06-13-2011, 03:31 PM

Nice guide - but quick edit the W210 in the second paragraph to W201 if that is what you meant

http://en.wikipedia.org/wiki/Mercedes-Benz_W210

http://en.wikipedia.org/wiki/Mercedes-Benz_W201

Quick before some smart ass points it out!

Jeremy5848 · #3 06-13-2011, 04:31 PM

Thanks. Slip of the fingers and, since I have a 210 also, when I proofread, "210" looks correct.

Stretch · #4 06-14-2011, 03:39 AM

Quote:

Originally Posted by Jeremy5848

Thanks. Slip of the fingers and, since I have a 210 also, when I proofread, "210" looks correct.

I noticed that.

This later suspension looks really nice and adjustable compared with the W123 and first generation W126. Do you happen to know if the second generation W126 uses a similar set up?

And then here comes the ultimate question - do you think you could fit this later suspension to a W123? (Well I know anything is possible - but an indication of aggravation would be nice)

Oldwolf · #5 06-14-2011, 10:00 AM

Very nice thread. I'll read it when I have time to "absorb" the information it contains.

Jeremy5848 · #6 06-14-2011, 10:42 AM

Quote:

Originally Posted by Army

I noticed that.

This later suspension looks really nice and adjustable compared with the W123 and first generation W126. Do you happen to know if the second generation W126 uses a similar set up?

And then here comes the ultimate question - do you think you could fit this later suspension to a W123? (Well I know anything is possible - but an indication of aggravation would be nice)

I cannot comment on the 126 as I am mostly unfamiliar with them. The 123 does not have an adjustable rear suspension, as you are aware but the chassis is almost the same size as the 124. I'm sure that with a lot of work you could build some adapters and bolt and weld a 124 rear subframe to a 123 chassis but I have serious concerns that you could actually get it to work (track straight, etc.). But that is just my opinion and I'm not a suspension expert.

I read somewhere that Mercedes engineers tried 70 different modifications before they finally settled on the version that went into the 1984 W201 and a year later, the first W124s.

Jeremy

winmutt · #7 06-14-2011, 11:33 AM

You need triple squares to do the rear end!

Stretch · #8 06-14-2011, 11:34 AM

Quote:

Originally Posted by winmutt

You need triple squares to do the rear end!

Explain please - me no understand.

Stretch · #9 06-14-2011, 11:35 AM

Quote:

Originally Posted by Jeremy5848

I cannot comment on the 126 as I am mostly unfamiliar with them. The 123 does not have an adjustable rear suspension, as you are aware but the chassis is almost the same size as the 124. I'm sure that with a lot of work you could build some adapters and bolt and weld a 124 rear subframe to a 123 chassis but I have serious concerns that you could actually get it to work (track straight, etc.). But that is just my opinion and I'm not a suspension expert.

I read somewhere that Mercedes engineers tried 70 different modifications before they finally settled on the version that went into the 1984 W201 and a year later, the first W124s.

Jeremy

Thanks - are the differentials off set to one side of the car on the W124?

winmutt · #10 06-14-2011, 11:37 AM

Quote:

Originally Posted by Army

Explain please - me no understand.

? The tripe square tool, same as used for the head bolts.

Stretch · #11 06-14-2011, 11:39 AM

Quote:

Originally Posted by winmutt

? The tripe square tool, same as used for the head bolts.

Oh right - I thought you meant set squares... OK I'm back up to speed folks - thanks!

sixto · #12 06-14-2011, 02:38 PM

Quote:

Originally Posted by Army

This later suspension looks really nice and adjustable compared with the W123 and first generation W126. Do you happen to know if the second generation W126 uses a similar set up?

There are a lot of parts but I don't see any adjustability. All the struts are a fixed length except for that tie rod looking thing.

The late 126 suspension is no different from the early 126 suspension. Some components might provide clearance for bigger brakes. The 140 has a similar rear suspension.

Sixto
87 300D

Stretch · #13 06-14-2011, 02:58 PM

Quote:

Originally Posted by sixto

There are a lot of parts but I don't see any adjustability. All the struts are a fixed length except for that tie rod looking thing.

The late 126 suspension is no different from the early 126 suspension. Some components might provide clearance for bigger brakes. The 140 has a similar rear suspension.

Sixto
87 300D

Really - then I must be getting confused with something else. I'll try and find the post and pictures I'm thinking of... (I might be some time)

sixto · #14 06-14-2011, 04:11 PM

This is the spare tire well's view of the subframe without diff and axles courtesy of gsxr -

5 links per side, all fixed length. I'm not aware of any eccentrics.

Sixto
87 300D

Jeremy5848 · #15 06-14-2011, 05:46 PM

Sixto, there are two eccentric bolts, one in the tie link to adjust toe-in and one in the pulling link to adjust toe angle. This is according to the 1984 "Introduction into service" manual for the W201 (190E, etc.), where this 5-link suspension was first used. The W124 has an almost identical rear suspension. When I had my '87 aligned, I had to take it to a place that could do a 4-wheel alignment.

Army, the differential is smack in the center, near as I can tell without a measuring tape.

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