Very astute, grasshopper.

Usually, it's a fix of a "quote failure". The HTML tags get deleted and the quote does not post properly.

Sometimes I'll fix spelling and/or composition errors when the mood strikes me.............;)

Just finished the transmission swap, which of course meant new flex discs. Its a good thing too, they were about done.

Here are some pictures.

http://pgmfi.org/~firepyroandy/flex%20disk%201.jpg
http://pgmfi.org/~firepyroandy/flex%20disk%202.jpg

Yikes,

Yeah those needed to be changed out alright. But then again I've seen some many a disc like that so they must last awhile like that.

I would like to have a digital camera right about now.

I inspected my flex disks, and both of them look pretty much the same. There are some visible surface cracks all over the rubber, and some deeper cracks where the enlarged rubber bosses meet the thinner section. On each side of the M-B star and the printing on Sady's disks above. There is no sign of any deformation or separation of the metal inserts from the rubber. No cracks in the direction of rotation, as I see in a lot of the pictures in this thread. There are lots of pictures of disks that clearly need to be changed, but none of disks which aren't new, but are still serviceable. We have the "no-go" part only, of the "go, no-go" test.

I was going to change them, but now I think I'm just going to see how they look after another 10K.

What's a flex disk?

Flexdisk has the same job as a u-joint on the drive shaft.

Similar job, but it won't deal with very much of an angle. The Benz has a body-mounted final drive unit, so the driveshaft doesn't move around when the suspension moves.

U-joints fail on RWD live-axle cars also, with similar very bad results. Drag racers are required to have driveshaft hoops to contain the shaft in the case of a joint failure.

That is good info. Those hoops would be good on production cars as well.

Ahh, I see. But on my truck, when the U-joint starts to go out, it vibrates like hell around 50 mph.

Any similar symptom on the flexdisk?

I have not experienced a bad flex disk yet, but from what I have read, yes, the syptoms can be the same, or sudden and catastophic. Flex disks need to be checked just like u-joints. After reading stories about people being killed by a u-joint failure at highway speed, if I notice any type of drive line issues, the vehicle is parked until I can get it repaired.

I wish I had a picture...

But from my experience, If you can feel it... you'd better pull over and have a gander.

I just replaced my rear disc, which was cracked. It seemed to clear up a vibration at lower RPMS.

It does not look like the rear disk can catastrophically fail. The drive shaft has a hole that engages a pin on the rear differential. If the disk were to fail the shaft would spin, but not flail about causing damage. The front disc is a different matter though...

Just during the past few days, I have been noticing mild shudder on my 84 D during startup at lower speeds (0-25mph) and disappears as I speed up. The vibration seems to be coming from the shaft/propeller area.

Is this an indication that the discs are going bad? I have not crawled under the car yet to check. Would a loose disc/shaft be obvious?

I plan to check it tomorrow since its a bit late to tinker right now. Am also not driving the car until I am sure what it is.

That depends on how obvious it is.

It gets obviouser as it gets obviouser.

It can be hard to see depending on the position of the wear relitave to the shaft position, and how well lit your checkup is... If you can get the rear wheels off the ground and rotate the shaft, like up on a lift it would be easier to see.

As a general rule I would say the more drive shaft vibration you are having the less agressivly you would be advised to drive until you can get it checked out..

flex disk / center bearing
 

I've had a bit of a vibration at higher speeds, -could be rear tire balancing issue, but when I was pulling out the diff and drive shaft (to change diffs) I found the center bearing rubber support was worn loose. It was not supporting the shaft properly. The bearing seems o.k., and the flex disks seem fine, but I am replacing both disks, bearing support, and bearing anyway. Heck I have it all off so it is the price of the parts only, not a lot more labour. And when the replacement diff goes in it will be with all new seals, and new boots on the axles. I kinda like working on the old girl but no where near enough that I want to do stuff like this twice cause I cheaped out the first time.
Not that I'm throwing any rocks at those who need to take the cheap route. been there done that, had to. But this car is fairly low miles (140k) and I'd be happier if I don't need to get under there again for a while, and (at least till the next recession) I can afford the parts.
Maybe I'll save the old disks in case I ever am running a much older 240 and use them on that...