Main.TrailIndexPage | Suspension | Rear End

Rear End

This component is part of Suspension.

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Maintenance

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Rear Subframe Mount Replacement

The rear axle is attached to the car at the center above the differential. The rubber and steel mount is like a really big engine mount. The carrier arm comes up from the differential through the floor and is suspended on the mount. If the rubber has collapsed, it can result in too much negative camber of the rear wheels. To get to it in the roadster, it is under a plastic cover located in the trunk under the soft top compartment. The photos in this article are in a ďCaliforniaĒ Coupe so access is easy as it is under the carpet behind the rear seat.

Inspection.

The plastic cover removes with two Philips head screws. There should be about 10 Ė 12 mm of rubber showing between the top plate washer and the base.

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The differential actually hangs on this mount. The rear springs push down on the axle so if you unbolt it without supporting the differential, the springs will drive the rear end down onto the floor. Thatís not good. So, begin by supporting the differential with a floor jack. Then remove the center bolt.

Remove & Replace:

There is every chance that the rubber has bonded to the metal, so soaking it with penetrating oil overnight might save a lot of tugging and cursing.

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This is where you can use the springs to your advantage. Gently and carefully let some of the pressure off of the floor jack and the carrier arm should let go. You donít want it to drop more than a few millimeters.

Next remove the four bolts holding the mount to the floorboard and remove the mount. Because you now have nothing keeping the rear end in place, it is likely to move a bit. The centering of the rear axle is determined by this mount so there is no adjustment. This can make installing the new mount somewhat difficult. (PITA) It is the reason that you use a floor jack with wheels. It is helpful to have someone who can wiggle the floor jack a bit and lift or lower it to center the arm so that the person in the car can align the four mounting bolts. This is also why the job can take 20 minutes or 2 hours.

Once you get the four mounting bolts installed, replace the plate washer and center bolt, and the plastic cap and youíre done.

Tip:

If you have camber issues after this job, the adjustments are made with the thickness of the spring rubbers. If you still have negative camber, you can add shims. McMaster-Carr sells a flat flange washer that is 1/8 inch thick with an outside diameter of 5-3/8 inches. They are Hi-temp silicone with a medium-hard rating of M60 and are less than $5. Part number 8521T928. Itís much cheaper than replacing the pair of Mercedes spring rubber to get a thicker one. Iíve had them on my car for 7 years now.

If you have positive camber, you need to replace the spring rubbers and probably the rubber on the compensating spring.

Old Yahoo content

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The rear wheels are pointing inward slightly at the bottom. The car was aligned professionally and all Mercedes parts were used. Will this resolve itself once some compression occurs or is an adjustment needed?

Will says: I think you are on the right track about waiting for the new rubber to settle and allow the rear wheels to sit more straight. Although I do not think it is a great problem. Do they straighten out when the car is driven? Have someone drive the car and you drive behind and look. But, the spring on top of the rear axle could be out of place (hard to believe). More likely the rubber on either side of it is still in place. The rubber usually slips out a little and this will allow the spring to exert less pressure on the rear axle and let the axle straighten out.

I recently replaced the rear springs and shocks on my '66 230 SL because the rear end seemed to be "squatting". Now It looks like it is too high. The rear wheels have an excessive negative camber. It looks very funny to me. BUT - there is no adjustment, only the tension of the compensator spring. Do I need to cut a coil off the compensator spring, or put sand bags in the trunk?

I believe that I have heard from this group that there are different thickness of rubber available for the pieces that the compensator spring sets in. Am I wrong? I may be thinking of the rubber that the suspension springs set into. That could help you as well. Anyway, you may also need to examine the rest of the rear end for worn or broken parts. Replacing one part could expose other parts that are out of spec (worn or broken). Then again, you may just need to wait for it to "settle" or something. I need to do shocks and suspension rubber sometime, but I have no personal experience with this yet. I'm just regurgitating what I've read.

The rear suspension replacement was pretty easy. There are few parts, and they are not too expensive. The hardest part and most expensive were the new coil springs. I don't recall the availability of different thickness rubber for the compensator spring. If there are, that is most likely my problem.

I doubt that you have negative camber if you just changed the springs. That would be positive camber, if any. The camber is set individually by a combo of the bottom spring plate turning and different thickness top rubber seats. Changing the compensator spring rubber thickness changes both sides at once.

I spent all day today working on my rear suspension. Armed with acquired knowledge from this group, and my shop manual, I put my '66 230 SL on jack stands. I compressed the rear springs, unbolted the shocks from the top, and slowly lowered the jack holding up the rear axle. I studied the drawings and tables from the manual and confirmed what some of the list members told me. There are three positions the lower spring "cup" can pivot in. They are marked 1,2,3 --3 being the lowest position. This will only affect the camber slightly. The rubber spacer on the top, however, according to the manual, should be 8mm thick. Mine is 20mm. That WILL affect the height considerably and increase the camber noticeably. I looked in Star Quality catalog, and only one part number is listed - the one I have (20mm). Hopefully I can find the correct spacer elsewhere. While everything was apart, I gave the surrounding areas a coat of POR-15 (rust-preventative-paint-like-stuff). Now to find the spacers...

I think that if you had 20 mm spacers in there and the car was fine to begin with, then the problem is your new springs. Did you compare them carefully to the old ones? i.e # of coils, overall length and especially wire thickness. I know there were different springs available in different strengths for different road conditions. MB should be able to tell you what part no. spring goes with what rubber and it seems to me you just ended up with the wrong one.

The rear camber should be with 2 passengers and 40kg weight in the trunk negative 1.75 degrees according to one manual I have. This is for vehicles without a hydropneumatic compensator. It must have a spring in the middle of the rear axle. Vehicle must be driven after every lifting of rear to allow wheels to settle to proper position. This is important because the wheels do look inwards when the rear is let down from a jack. Rotating the disc adjusts 0 deg10' per notch. Using the next thinner or thicker rubber adjusts 0 deg 30'. For the 230 SL there are 2 rear springs:

  1. Standard no. 113 324 040 4
  2. For poor road conditions no. 113 324 02 04. These numbers may of course have changed over the years. If your springs have one only single blue stripe (no of stripes is important!) then that means that you must adjust to the following:
    1. Rubber dim a=8mm part no. 110 325 04 85 (also old no.)
    2. Disc position 3 O n the rear rubbers the dimension a is not at the thickest point. However, it is not at the thinnest point either. It is measured 90 degrees away from the thinnest point to thickest point edge. i.e. where the last coil ends, go 90 degrees backwards and measure there.

The spring itself is as follows:

 Length with no weight = 289.5mm
 Length with car weight ~ 214 +/-9mm
 Coils of wire = 5 1/2 
 Wire diameter 15.8mm
 Spring diameter at centre of wire = 120mm

All this is for the standard spring.

I see references by some of you to dropping the rear suspension and removing the compensator spring. This seems somewhat, shall we say, *dangerous*! Can I do this without killing myself? If so, please let me know since the "lost child" 250 SL needs the transmission(4-spd) removed and rebuilt and I thought that since I'm under there I might drop the whole rear and replace stuff.

I am still trying to get the camber correct on the rear. I have the smallest possible pads and I am looking at the center differential mount as well as the plates upon which the springs rest. Regarding the plates that turn at the bottom of the springs...I understand there are three positions. Can someone describe how I position the number to reduce the height of the spring? For example, which number on the adjustable plate shows at what position to get the lowest spring height?
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