Need Help-rear allignment problem 85 300D

[300Dguy]

I think I've researched every thread possible on this and related subjects but I need help from anyone out there that may have encounterd this problem.

PROBLEM:
MY 85 300D (136,000 miles) has a rear allignment issue that appears to be isolated to the right rear (Passenger) wheel. The car is dog legging with the left front of the car out to the left of the right rear. The inside of the right rear tire is wearing significantly ahead of the rest of the tire and left rear tire is also wearing on the inside but not as bad. This RR wheel also sits back approx 1/2 inch further to the rear of car. I had the allignment checked and all wheels were well in specs except this right rear, which is cocked slightly out away from the car, causing the problem. For you allignment experts, Toe specs for this RR wheel has Specified Range of -0.01 0.66 degrees, and it came in at -0.91 degrees. I next had the car frame checked out at a reputable body shop which measured the unibody every way possible and was advised the frame is straight. Neither the allignment shop nor the body shop could find and tell tail signs of accident damage. The body shop thinks the RR trailing arm could be bent and just not noticable. He suggested changing the trailing arm next.

I just took a tape measure again to car got exact same distance from jack hole to jack hole on each side, but I did find an additional 1/2 cm or approx 1/4 inch longer distance on the right side of the car from the front jack hole to the center of the large bolt into the rubber bushing at the front of the wishbone that screws vertically into the underside of the chassis, and forward of the rear jacking hole.

So, here are my questions and perhaps one of you folks that frequent this site have had this same issue and can steer me straight. I'm trying to avoid any larger task than necessary.

1. Has anyone had this issue and what was the cause?

2. Althought the trailing arm busings appear to be OK from a visual check, and I really can't see much of the bushing at front of the wishbone that is held in place with a large bolt and additional bracket, could worn bushings on that side cause this much of an issue, just from age etc. Should I start with replacing these three bushings? Or perhaps just the one at the front of the wishbone?

3. Has anyone encounterd a damaged/bent trailing arm that appears to look perfect?

4. If I attempt to change all three bushings on that side, should I attempt this repair without pulling out the entire rear axle/suspension assembly.

5. Havn't yet checked the host of this site for bushings, but if they don't have them, any suggestions where they can be obtained other than from the dealer?

Looking forward to any responses, or if you want, private messages.

Thanks much,
Thoroughly confused.

[boneheaddoctor]

I believe the first place to start would be replacing the bushings in the rear end including the differential mount..20 years they have likely degraded...since there is no adjustment they must be in proper condition to establish if you have other issues...

[300Dguy]

Haven't given much thought to the differential mount bushing, but it makes sense. If the problem was in all of the bushings/mounts, I would think I might have an issue with the left rear wheel as well??

[t walgamuth]

of bushings causing this problem. i suspect a bent or rusty rear a arm. i have had one of each. my lovely daughter #2 slid one of my 240s on ice into a curb. it put the wheel at a very interesting angle. a lighter hit might make it hard to see. .25 inches is not a lot but if it is indicative of a bent a arm it would result in the type of wear you are seeing, i think.

of course look at the bushings as bones suggested but if there is nothing to see there, i would look at the a arm.

tom w

[boneheaddoctor]

Originally Posted by t walgamuth

of bushings causing this problem. i suspect a bent or rusty rear a arm. i have had one of each. my lovely daughter #2 slid one of my 240s on ice into a curb. it put the wheel at a very interesting angle. a lighter hit might make it hard to see. .25 inches is not a lot but if it is indicative of a bent a arm it would result in the type of wear you are seeing, i think.

of course look at the bushings as bones suggested but if there is nothing to see there, i would look at the a arm.

tom w

I know my LCA bushings on my W116 no longer had the holes in the center but were offcenter from age ...I would suspect much the same with rear tire wear issues....however its possible to have a tweeked trailing arm...but with less than perfec bushings how can that be determined...I know its a catch-22 situation.

[300Dguy]

I had originally thought of this scenerio by a prior owner as the possible cause. So, are you saying the arm is suspectable of getting bent in such a case, most likely at or near where the axle shaft sits with out bending the wheel or showing visible signs to the trailing arm etc.

[dmorrison]

As posted replace all the wear items.
Trailing arm bushings, springs, shocks, Differential mount and subframe bushings. Mercedes and fastlane does make a ecentric bushing for the trailing arms. Expensive but made.

http://catalog.eautopartscatalog.com/mercedesshop/sophio/quote.jsp?clientid=catalog.mercedesshop&cookieid=1NB19DAR81NB19DNH4&baseurl=http://catalog.peachparts.com/&partner=mercedesshop&year=1985&product=L2006-16072&application=000013708

But while your removing everything I woudl check all components for damage or rust. The trailing arem are known to rust and present problems.

Dave

[300Dguy]

This car has zero rust inside and out, and the metal on the suspension looks as new as was off the line in 85. Thanks for the tip on the parts. If the subframe bushing is ecentric, does that afford some degree of adjustment?

From what I'm getting in responses, sounds like worn shocks could even play a role, but I don't see how since they are more of vertical component??
Thanks

[Hatterasguy]

Replace subframe bushings, diff mount, and shocks if they are original. If the rear still doesn't come up new springs will be needed.

This is a common problem with age afaik their are no rear allignment adjustments on these cars, you just replace bushings.