Broken rear differential mounts/transmission leakin...fix/replace...broken hearted
 

Hi all,

Got my 87 300d back from the mechanic with some disheartening news...

Rear differential mounts are busted, Indy wants $1088 to replace it. I did some research and this definitely looks out of my league. I've read that this needs attention pretty quickly, but please tell me if I am wrong.

Also I have had a very slow leak in the transmission for 2 years now...takes about a year to use a qt. I check the transmission fluid often, so unles the dipstick is lying to me, then it doesn't appear to be leaking a ton. However, this has been an issue for two years, so I am worried that the tranny will go at any time, which means a rebuild...at least $2000

This past year I just replaced the entire front suspension, fan clutch and fan...which cost $1600.

So, if I do these repairs then the maintenance will be $4000 for the year, more than the old girl is worth.

The engine is in great shape, very little blowby (the Indy was impressed by how little blowby there was) and I have replaced quite a few things over the years.

I love this car, but spending $4000 in a year on repairs (a ton diy, so could have been way more) is leaving me with a sick feeling in my stomach. The thought having to spend another $4000 next year, the year after...:(

Any thoughts? Advice? This forum has helped me maintain the old girl well over the past few years...I guess I am frustrated, disheartened, and just reaching out to the community. Looking for some encouragement, to steady the course, or, a smack in the face of some common sense

Thanks

Replacing diff mounts is no fun but $1000 is steep. Your transmission could quit before you retire your car but not from leaking a quart a year. The question is whether you should throw $2000 into rebuilding the rear suspension. What good is a tight front suspension is the rear is loose and creaky? You can replace diff bushings without dropping the rear subframe and it'll take an afternoon. The book calls for dropping the subframe. If that's the route your shop is taking, a few hundred more in parts should net you a fresh rear suspension.

Sixto
83 300SD

Thank you sixto, gave me some hope to at least try the rear differential mounts myself. I am pretty handy, but after looking at the FSM it was overwhelming.

I read that it is possible to remove the mounts w/o completely removing the rear differential, but could not find the procedure to do it. I know there are bolts that hold the rear differential in place (the bolts that go through the mounts), but it has to be held on by other bolts, right? I also know that i will have to place a jack under the rear differential and lower it just enough to get access to the mounts. I guess before attempting this, i need to know exactly what I need to do. (could not find that info)

Can you tell me the procedure to lower the rear differential enough to get access? I could not find this info anywhere, but i definitely wont stop trying.

Also, these are the tools, correct?

http://www.pelicanparts.com/cgi-bin/ksearch/pel_search_2014.cgi?SUPERCAT_FLAG=Y&make=&Context_make=&please_wait=N&LastVisited_input=&Previous_Se ction=&forumid=&threadid=&command=DWsearch&description=BM-966-0043&SearchButtonGo.x=0&SearchButtonGo.y=0

Lastly, I read in one of your old posts sixto that (besides getting the correct orientation of the mounts) that you must look at the old bushings to see how far to insert the new ones, correct? " Not MB's finest engineering hour" as you said. Any advice on this besides a 'good eye"?

About the transmission...the mechanic said, in his write up, that "now, almost every seal on the transmission is leaking". It is messy down there, but I don't understand how he came to that conclusion, considering I use so little atf. My guess is that the leaking atf is being blown around by the torque converter, or some other moving part...it has been leaking for 2 years after all...

I replaced the rear subframe on my 190DT this spring (it has a similar architecture). dropping the subframe isn't an awful job, but it does take some tools, muscle, and perseverance. It's easy on paper: remove the muffler, slack off the emergency brake and undo the inner ends of the cables, unbolt the rear diff flange, and hang the calipers. Then slide a jack under the diff, undo the four bolts and slide it out. Rust and age are the complications.

Once the subframe is out, you can replace anything you want without too much trouble. In my case, the problem was the frame itself, so I unbolted everything and moved it to the new frame. Two days and done.

If your transmission is leaking but otherwise functioning well I agree with the others: leave it alone and keep fluid topped up.

If the leaks bother you then you can try some Trans-X or other solvent-based stop-leak to soften and swell the seals, but understand that it will always need this additional fluid from that day forth. Also, if it's not having any cold-shift problems or park-to-reverse / park-to-drive hesitation it would seem like the internal seals are still healthy, in which case I would avoid any additives if you can live with the external leaks.

Rear Differential Bushings - Completed - Mercedes-Benz Forum

Found this write up, and another poster mentions not needing to drop the differential. Can anyone comment on the instructions written here? Any help is appreciated! Thanks babymog with the transmission advice!

Looks like that's the way to go. When I did mine, I had to replace the axle stub seals so the diff had to come all the way off. I'd be tempted to unfasten the axles anyway to avoid stressing the old CV joint boots. And, yup, I set bushing depth by feel. Those bushings can't be manufactured to any precision tolerance at that price. Find some pipe or a socket that's just smaller than the bushing bore so you press it out as a unit rather than pressing out the core then cutting the bushing frame.

Sixto
83 300SD

Be warned... If you take the flex disc bolts out, throw them away and get new ones... Or just change the flex discs.

With the right tools, it is an easy job... It is super easy with the subframe sitting beside the car!

I havn't tried swapping them with everything still connected.

Does one just go to a local nut and bolt shop and try to match those bolts or is there a supplier who sells replacement sets?

Don't the bolts come with the flex disk? I have used extras in my junk box and don't remember buying them specifically. I would definitely change the disks when the opportunity arrives if they haven't been changed.

Note: use Lemforder parts and mark the driveshaft halves so you can put them back in the same position relative to each other.

I think the question is where do you get bolts for when you're not eplacing the flex disc. They must be some sort of toque-to-yield bolt if the FSM says to not reuse them.

Sixto
83 300SD

Thanks for the insight! In the instructions I posted, one of the posters said that, with the special puller, you can just unbolt the three mounts and lower the rear differential just enough to get acces to the mounts...I am very tempted to try this route.

My flex disk is in great shape, so there is no need for me to replace it now, so I don't want to remove it and the drive shaft, since I'll have to get another flex disk with new bolts.

I think my plan will be to unbolt the three mounts, then lower the differential, pay close attention that I am not stressing the cv joint boots, then replace the mounts.

Does this sound reasonable, or am I just inviting a disaster to happen??

I think doing an R&R on the flex disk will stress it less than lowering the diff.

I think you have a good plan except for reusing the flex disk. If it has cracks I'd replace it. That takes care of reusing the bolts which is forbidden by the FSM and many of the senior members here on this forum. I strongly recommend you heed that advise and consider replacing the other disk in the near future.

If anyone sources replacement bolts for reusing good flex disk please let us know.

Thanks clemson!! As of now, I am not planning on removing the flex disk, I'll leave it intact. Does that sound reasonable or is there something I am overlooking?