Flex disc replacement

[tecqboy]

1991 300 SL R129 at 98,000 miles Visual inspection shows some minor cracks in the front flex disc coupling between the output of the transmission and the drive shaft. The rear coupling "looks" perfect. My indy Mercedes mechanic says it's good practice to change both at the same time, but doing the rear requires dropping the exhaust system which adds considerably to the labor charge. I'm looking at $150 for parts, plus 4 hours labor at $75 per. It'd be less than half that if I only have the front done. Anybody here have any recommendations? Is it really necessary to drop the exhaust to change the rear?

[BobK]

This gets into how much do you know about the car? If the rear one has never been replaced or was replaced with the front one some time ago, then they are both the same age and subject to nearly the same stresses. When I replaced the front one on my SEL (it was shredding) I did the rear on general principle. It looked a lot worse when I had it out in my hand than it did when it was up in the car. I was glad I replaced it. On the SEL it was easier to just unhook the rubber exhaust hangers and lower the exhaust about 8 inches. PITA job and I sure would not want to have to do (or pay for) it twice. Oh, and BTW, if they completely fail, it can get REAL expensive.

[tecqboy]

Well, "drop" the exhaust is the term my mechanic used, but I suspect he meant that it would just be lowered enough (as Bob described) to get to the rear disc. The flex discs on the car are originals. I'll have them both changed and consider it preventive maintenance. It just seemed to me (from looking at the discs) that it would take less than 3 to 4 hours. Surely universal joints would be easier.

[bwheitman]

I replaced both of my flex discs and I didn't have to drop the exhaust, it would have been a lot easier if I did, but I was able to replace the rear one without doing it. I used 2 wrenches and put the car in neutral, with the rear on jack stands. This enables you to rotate the drive shaft as you remove each bolt. The disk just drops out and you put the new one in it's place. The new kit comes with new bolts so use those. It is really easy to do, and don't drive your car until they are replaced. Good luck!
Brian

[lymlyt]

what are the symptoms you experienced as a result of "bad"
flex disc?

[tecqboy]

I my case there were no symptons. I was under the car looking for an exhaust rattle and noticed that the front disc had a lot of small hairline fractures. The rear disc looked perfect. So, it was a precautionary repair. My car is 1991 300SL 98K miles. From what I've gleened from this forum, discs usually last much longer (mileage wise). Symptoms of bad discs are vibration that is more dependant on engine and transmission RPM rather than actual road speed. That is to say, as the engines revs up, it is most noticable just before each up-shift. Tod

[BobK]

In my case the symptoms were a gosh awfull vibration. When I got under there, the front disc was close to gone. Back looked ok till I removed it, then you could see lotsa big cracks. Seems another MB owner on one of the boards had the front disc go out and it took part of the transmission with it. Big $$$$$

[Kebowers]

should not be more than 2 hours to do both. 4 hours is way excessive. This is not a big damn deal job.