Best practices for W123 sedan rear suspension rebuild - PeachParts Mercedes-Benz Forum

tgantos · #1 08-13-2005, 02:35 AM

I have spent several hours reading through all the suspension-related posts and have learned a lot from them, thanks. I think we could really use a good thread on the best procedure for a complete W123 rear suspension rebuild (without lowering ride height). Richard Easly documented a procedure for the W126, but there are no photos and the procedure is just for the subframe bushings. I just got done changing all the calipers to the newer ATE ones. I got tired of having issues with the Bendix junk. Also got new Balo rotors and Pagid pads, changed the brake fluid, and replaced all the brake hoses.

I am planning on doing the following maintenance work and documenting everything with photos and notes as I go for everyone needing these things done.....

1. Replace subframe bushings, possibly bolts too depending on condition.

2. Replace trailing arm bushings, bolts if necessary. Which one should I use, there's a repair size and a regular size. Also which vendor has the best rubber?

3. Straighten the spider plates (one was bent), removing rust - treating with POR-15 and chip guard.

4. I have a broken left (generic it turns out) rear shock from a bogus mechanic's work when I was living in Chicago. (That jerk also broke my injection pump rack damper mount by turning the bolt too far, put in a non-MB washer pump screwed to my inner fender, and hung my exhaust in the wrong place. I sent the guy packing! He was so incompetent he should be glad I didn't sue him...BTW - Import and Domestic in Evanston, IL ---avoid these guys...) Manfred (the Man!!) Pfeiffer at H&M ******** in Westchester, IL (German born and MB-factory trained expert, now retired, his company, H&M was passed on to Manfred's top mechanic...my Diesel misses you Manfred!) put everything back right again, except for the shocks which we did not know then were generic. I am now replacing both rear shocks with new Bilstein HD's.

5. Removing rear springs, rustproofing, repainting, replacing (the old vaporized) rubber coil top shim pads with the 19mm ones. That oughta stop the knock knock jokes this car keeps repeating...

6. Rust removal and treatment of all suspension subframe and trailing arm components. Por-15 paint, then Transtar Tex coat Chip Guard.

7a. Replace differential mount.

7b. Check differential seals and replace leaking ones. Am I crazy to try this? Anybody done it?

8. Replace driveshaft flex discs and mount/bearings. Again is this a *****? No procedure found other than in service manual.

9. Rustproof exhaust system. and re-hang with new rubber.

10. Change trans shifter bushings (I hear it's easy and I'll be under there anyway)

11. Change the fuel tank strainer. Yucky black stuff...ewwww..thank God for gloves.

12. Replace rear sway bar connecting rod ends and bushings. What's the best vendor for these?

13. Replace big rubber snubber stops near sway bar ends. Again who's the best vendor?

14. Lots of rust removal, welding and reinforcing if necessary. Followed by rustproofing with POR-15, and acid-etch primer. Then coat everything with Transtar Tex Coat Chip guard...

I am looking for other suggestions on things I should do while I'm under there....and especially photos or procedures of how others have done this if they exist...believe me I've looked.

Brian Carlton · #2 08-13-2005, 09:06 AM

You certainly have done your homework.

It appears, from the list, that you may be removing the differential from the subframe to reseal it. In any case, you have removed the drive shafts to get the trailing arms out.

So, the only thing I would add is to consider replacing the rubber boots on the drive shafts before they fail.

There are shops that can do this for about $100.00 each, or you can consider lifetime replacements from AutoZone and the like. However, the success rate with these "rebuilt" axles has been spotty.

Some members have replaced these boots themselves, but, it's a real PITA without the proper press.

tgantos · #3 08-13-2005, 10:48 AM

My boots are actually in very good shape, no cuts at all. I might treat the rubber while I'm under there.

Manfred (the man!) at H&M replaced one axle for me about 4 years ago when it failed due to a bad boot. Do I need to remove the axles from the hubs to change the seal at the driveshaft or can I just lower the differential with the axles attached and do it.

The manual is pretty sketchy/few photos.

Should I think about changing the rear transmission mount or is that a real PITA?

I've never messed with the driveshaft either before. Is the flexdisc and bearing stuff worth the hassle? My flexdiscs actually look and feel pretty solid for being 20 years old but maybe they've petrified...

:

Brian Carlton · #4 08-13-2005, 01:00 PM

You had mentioned that you are going to do trailing arm bushings.

I presume that you will remove the trailing arm from the vehicle to get them out, or can you do it underneath? I recently abandoned the idea of doing trailing arm bushings on the SDL due to the difficulty of trying to get them out while working on your back. I was not about to remove the arm from the vehicle.

If you remove the trailing arm, the axles must come out first.

tgantos · #5 08-14-2005, 11:00 AM

Most of the notes I have read refer to using a press and/or liberal amounts of PB-Blaster, all-thread rod, washers, and nuts to press the bushings out. One guy spoke about removing them, but I am not in favor of disturbing the axles, bearings, and hubs. If one speck of dirt gets in the hub bearings or differential gears you can have major problems.

My mechanic pointed out when I changed the brake calipers that the diff looked like it was leaking a little, but also told me that I should leave the diff alone unless I am going to do a complete rebuild, and that changing the seals is a *****. I did not get any feedback on changing diff seals to the contrary, and can find no posts of anyone DIYing it. He said the leak looks minor and slow, and to just check the fluid every couple of months and refill it. If I do win the lottery and decide to rebuild the diff after all, I will remove it and take it to him to do a complete rebuild for me on a proper bench with dial indicators, micrometers, etc, as called for in the Mercedes shop manual. I have none of those. I don't think it would cost more than 3-4 hours of labor to do it, which would be under $500.

So I am going to try and locate the proper Mercedes tool for pressing out/in the bushings if I cannot do it with the all-thread rod or a more generic press. That means leaving the axles in the hubs, just disconnecting it from the subframe, lowering it, and pressing in/out new ones.

At least that is the plan unless I get some more/better feedback from those who have gone before...

Brian Carlton · #6 08-14-2005, 11:09 AM

Quote:

Originally Posted by tgantos

So I am going to try and locate the proper Mercedes tool for pressing out/in the bushings if I cannot do it with the all-thread rod or a more generic press.

Definitely repost on how you make out with those bushings. I haven't changed these and might consider it, provided I don't need to remove the arm from the vehicle.

tgantos · #7 08-14-2005, 11:14 AM

I will keep everyone up to speed and of course plan to document the whole procedure and subprocedures with photos. That way future DIYers will be able to pick up where I left off.

stayalert · #8 10-21-2005, 03:54 PM

Hi Theo,

I'm started to look into a subframe removal and renewal of rubber bits. One of the incentives for me to pursue this was to replace leaking/corroding fuel lines and possible the brake line. Have you made progress on your car?

samiam4 · #9 10-21-2005, 04:30 PM

2 Things,

Your mechanic DOES NOT have the correct tools to rebuild a MB diff. I think there are reportable- (2) 1.3 liter diff tools in the country. To my knowledge, there are no 1.0 liter tools which is what is required. Much cheaper to get one from a junkyard.

You can replace the input seal or the axle seals. Front seal, you basically mark the nut and return it to exactly the same place with locktite.

Good axles- wouldn't mess with them. Maybe clean them gently and give them a coat of silicone.

I don't think the mb vendors or MBUSA list the rear swaybar bushings. I've replaced them and they are the W115 bushings. MBclassics can lookup the p/n for your local dealership.

Flex disc replacement is standard benz maintence. I'd do the diff front seal at the same time as the fexdiscs. Then you can mess with side-seals if you replace wheel brgs or axles in the future.

Spider- might be cheaper/easier just to buy a new one for $10.

Man, all that work and you are making me happy I don't have that W123 any more!
Michael

tgantos · #10 10-22-2005, 04:07 PM

I have not yet started the project, as I don't want to get in the middle of it and have to curse myself. Rusty Cullen had the swaybar bushings and the coil top bushings. I am considering replacing the front diff seal if it's easy. Will probably leave the axles in place. I would replace flexdiscs too if they are easy since they are original from 1985. I am getting setup to do the whole job and plan to take photos and document.

samiam4 · #11 10-22-2005, 06:04 PM

I'm sure there are writeups on "front pinion seal" replacement here....

Basically, after you take the drive shaft loose. Use an impact wrench to break the nut loose. You could count turns, mark the nut/pinion relationship with paint or a scribe. Those things are setup very exact, so you want to put it back exactly with the nut in the same spot. Pull yoke and replace seal. Then tighten the nut back in the same spot. MB bends the nut over to be a locking featur- I believe. Anyway, you can add a little locktite for good measure or use the new nut and make sure you've turned it exxactly the same number of revolutions and degrees.

Michael

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