Pinon seal and rear flex disc on a W116, DIYer?
 

I had my car jacked up, changing the parking brake shoes and noticed that my flex disc is cracked. Then I noticed that my pinon seal, at the front of the diff., is leaking. Is this something a DIYer can do. I have already priced the disc and seal at Fastlane, now I just need to figure our how to do it.

Hardest part of the job will be to get out the old seal. You will probably need a sharp tool like a screwdriver and hammer to cut thru the old seal so you can pry it out. Put some grease on the new seal lips and outside perimeter before you tap it in place.
P E H

Warning!!!!!!
 

The torque applied in the course of reassembly after installing the new seal is critical. A plumber posing as a Mercedes technician in an independent shop once replaced the seal in my differential and 400 miles later the differential was toast.

It is my opinion that unless you have the proper special tools and the MB shop manual spelling out each step, it would not be a good idea to DIY. Differentials are expensive- -I know.

Good luck.

Rick,

I recently had both flex discs, center support bearing and front yoke replaced (I'm at 140k miles).

I had it done by the dealer. After reading the manual regarding:
- displacing the exhaust
- loosening the drive shaft collar nut
- tightening procedures for the collar nut
- etc

I determined that it would best be left to the pros. It was worth the couple of hours of labor. He found trouble that I would have not been able to correct as efficiently as he did. The front yoke off of the transmission had a wallowed out mounting hole. It seems that one of the bolts at the factory was not tightened properly and its looseness allowed some slop. New yoke and ZERO REGRETS. Best two point five hours I've bought in a while.

Good luck with making a decision. If I didn't have bad luck, I'd have no luck at all, but every once in a while I make a good choice. So I revel in it when I can. CHEERS!!!

I do have the factory manuals and a Haynes manual (for W123 series, same running gear) I have read the Haynes manual and it does look quite involved. They keep mentioning to mark positions of various pieces and not to turn certain other pieces. I may just ask my ind. garage to do the work. JRBrown, you mentioned having to replace your rear diff., I'll be doing that here in near future probably. My rear diff. makes a whinning noise when I let off the accelerator, but the sound goes away as soon as you accelerate just a little a bit.

Rick,
Keep in mind that a rear differential will go many, many miles making that noise. It would be interesting to hear from someone that has ever seen a properly maintained rear differentail wear out (excluding problems like Ted eludes to). I would think that the milage would have to be WAY up there. The hardcopy W123 service manual - Chassis and Body does go through the rebuild procedure for the rear differential - looks like it would be best done in a machine shop type of setting.

Rick,

Your rear end is already toast. Don't waste any time or money with it.

The reason you are getting the noise is the same reason you are getting the leak. The pinion bearings are loose, probably due to wear.

The results that Ted got are quite common and I would say that even the best techs are in a real quandry with your condition. The seal is leaking due to the movement of the pinion (maybe a little age helps out). To resecure the pinion would require a rebuild. The pinion is originally tightened by crushing a spacer located between the two bearings, untill the pinion shaft requires a certain degree of force to rotate (usually around 15in-lbs). With the carrier installed (ring) this measurement can not be made. Besides the manufacturers say to never recrush crush sleeves. The bearings that at one time filled the area till they were tight are now loose. That came due to wear and they need to be replaced and reset up.

On cars with no noise the situation is still a real problem. If no noise and no verticle play, I will install a new pinion seal after first marking the nut to the shaft. After replacing the seal tighten the nut to its exact point as original.

Rick,

Ted2222 was the gent that R&R his diff.

After Steve's sobering post, I wonder how long mine will last and how much parts and labor are for an new one. Mine is quiet and no fluid loss. Have to wait and see.

Also having been down this path and with your considering an independent garage, my unsolicited opinion is to make sure that the garage has seen many of this disc replacements and are very familiar with it.

Otherwise, its worth the extra couple of bucks to take it to an independent MB or to the dealer.

Yeah, the ind. garage I was talking about, services primarily Mercedes, Porsche, and BMWs. Most of his customers are MB owners though. They even restored a mid '60's Bentley for a customer who lived in Germany.
So Steve, you think my rear diff. has had it? What will happen, by doing nothing about it and just keep on driving it as is? Also, why is it I only hear the noise when coasting. I would think the noise would be there all the time.

I can't say exactly why the noise occurs on decel, but it is a common way for noises to occur due to worn pinion bearings. It also can happen due to worn center driveshaft bearings and due to loose slip couplings on the driveshaft itself, so don't let me scare you too bad.

My comments were to keep you from wasting time on a seal repair that either might not hold or may hasten the demise of the slowly sinking differential.

BTW, doing nothing is a good alternative. Keep gear oil in it and when it goes get a used unit and slap it in. This is a very efficient repair due to the good overall long term life these units have. A used unit is fairly low risk and definitely cheaper than a complete overhaul with ring and pinion.

After reading what was involved with replacing this seal, I was thinking, as you suggested, to let her go as is. Thinking, what would be the point of spending time and money on a seal when I'll probably be replacing the whole diff. anyways.
What signs would I look for that would indicate that the diff. is getting worse? Would it be a louder whinning sound or will something let go and I'll start hearing grinding sounds. Basicly I am asking, is this something that would lock up on me and leave me stranded. Also thank you for the advice, you have been a great source of info. for other problems I have had.

To JRBrown
 

From what I have been able to learn, you probably shouldn't waste any time or lose any sleep over how long your differential is going to last. It seems, that for the most part, if they are properly maintained they will likely last as long as the rest of the car.

My original was replaced at about 50,000 miles when the seal began to allow a very slow drip. Because I used the car on the highway a great deal, I feared that the seal might give way completely, dump all of the grease on the highway and leave me stranded. Hindsight tells me I should have run the risk. I wouldn't have been any worse off than what actually happened.

Prior to the failure, there was absolutely no noise in the differential. I only wish that there had been a Steve around to take care of it for me. The nut was torqued so tight that it took a long breaker arm to loosen it. The man who did the job obviously didn't know what he was doing.

Good luck with yours!