what are flex discs?
 

Could someone help me understand the role of flex discs? I have a 1982 300sd and have two issues I am trying to work out. One is the clunk, clunk, clunk in park with engine running. I figure from other posts is may be flex discs, center driveshaft support bearing, transmission mount or broken exhaust hanger.

The second is the clunk, clunk clunk durning downshift which is most likely a vacuum problem with the T fitting going to the modulator.

I would like to be educated on the flex discs and their role in all of this and where I can inspect them myself and what to look for.

Thanks.

They are at each end of the driveshaft. They have through bolts that fasten to the driveshaft and either the transmission or rear end. Inspect visually for deterioration of the elastomer.

Quote:

..what are flex discs?

They're what I used to have in my back before I raced Mcycles. And crashed a lot.

They are used to transmit rotation forces through two shafts that are not in exact alignment and what alignment is there is somewhat variable. There are various other means of achieving this.

They are basicly a dark colored rubber and fiber-impregnated device used as a semi-flexible coupling between the tranny/driveline and driveline/rear diff. They are also used as driveline vibration absorbers.

What to look for is cracks on any point of them, bolt shanks that look like they are coming out of the rubber, and any soft spots.

Here is a pic of one that is worn out.

Jim, that one still has a few miles left in it........











......riding in the back of the trash truck on the way to the dump. ;)

just got my front flex disc and driveshaft carrier support unit in the mail. buddy said if the front is dead, it would be best to replace both flex discs while its down. but the rear looks OK? I know in a perfect world yes that would be good but do you guys normally replace them both at the same time?

how much of a PITA is changing the front flex and carrier? how long should i plan for?

also where to get a good used driveshaft incase my universal joint is worn out?


Thanks,

sorry im rambling, im not awake yet.
its a 240D manual
Joel

you'll need to remove the driveshaft cover (9 M8 bolts and 2 nuts) first. You do not need to move the exhaust, it will clear even with 4 wheels on the ground. Then, you need to loosen a large nut on the driveshaft. This can be problematic because there is not much clearance and the nut is good size. (This gets tightened at end of job after new flex disc is installed.) Then you remove 6 M10 bolts with nuts and washers from flex disc. Disc may stick a bit, you may need to pry it off with a screwdriver.

The rear ones seem to last longer, because they are not exposed to as much heat. But on my car I would just do both and be done with it.