Shredded Flex Disk

[George Des]

I know from looking at some previous posts that others have experienced this same problem-a vibration in the drive line and then a shredded driveline flex disk. In my case, I had put in a new flex disk during my 230Sl restoration. Other than requiring some wrestling around on the garage floor in some fairly awkward positions, I thought the job was straightforward enough. I believe where I really caused myself a problem was that I had the car up on jackstands put everything back together and did not do as the manual suggests in keeping all the driveshaft and support bearing clamp nuts/bolts loose and then settling the suspension to let the driveshaft correctly "size" itself and align itself in the support bearing. As a result, I believe the flex disk was either distorted or under stress to the point where it wore out prematurely--like in less than 2000 miles. Now, I am looking forward to doing this job all over again   . I know the job now entails jacking the car up in stages to get it to the point I can comfortably get under it to remove the exhaust system, the heat shield and transmission bottom plate just so I can get at the darn thing. This time I'll take the suggestion, though, to settle the suspension before tightening everything up so I don't have to go through this again in another 2000 miles! Anyone else going through this repair or having gone through it recently?

George Des

[ja17]

Hello George,
Make sure the tabs on the flex disk are oriented correctly or the flex disc will not last. Page 26-1/8 of the late BBB. The three tabs align on the transmission output shaft's three flanges.

Joe Alexander
Blacklick, Ohio

[JimVillers]

Joe .... A picture helps.  The tabs go towards the transmission.

Jim Villers
190SL, 230SL 5-Speed, 190E 2.3-16 Kompressor

[George Davis]

I've done the flex disk two or three times now, and each time I did loosen the d/s clamp nut, drop the car, roll it back and forth and bounce it to settle the d/s, jack it back up and tighten the clamp nut.

When I did the flex disk last time I also replaced the seal ring that goes on the nose of the driveshaft.  After dropping, rolling, bouncing and re-raising, I noticed the new seal ring pushed the d/s back enough to distort the flex disk a bit.  This didn't seem right to me, so I actually pried the d/s forward to straighten out the disk before clamping.  Can't say with any certainty that I did the right thing, but after a 2000 mile trip it still lives.

I've also found that I don't have to drop the exhaust.  If you can get a wrench or flex socket on the plate bolts that are partially blocked by the exhaust, then maybe you can avoid this, too.  It's worth a try.

Good luck and have fun under there!

George Davis
'69 280 SL Euro manual

[George Des]

Thanks all for the cooments on this. One question, though. I just can't seem to recall if the d/s clamp nut is accessible once the transmission plate goes back on. If it is not how do you go about settling the suspension then lifing the car back up to tighten the nut? I do recall my flex disk did look somewhat distorted whn I tightened the d/s nut. I'm certain now that that was the casue of the premature failure. The original flex disk went over 200k miles w/o any signs of trouble and the only reason I replaced it was because everything in the drive train had been disassembled as part of the restoration work. Hopefully, this time the flex disk will go in properly.

George Des

[George Davis]

George,

yes, the d/s clamp nut and the center bearing mount are both accessible through a separate hole a few inches further aft of the plate.

George Davis
'69 280 SL Euro manual

[George Davis]

I should add that you are clearly not spending enough time under the car !

George Davis
'69 280 SL Euro manual

[ja17]

Yes jim,
 It is not mearly a matter of having the flex disc pointing the right direction. You must have the tabs positioned on the three flanges of the transmission. did you watch out for this George? This is more critical than driveshaft length.

Thanks for the nice diagram Jim, I am sure the owners out there without the BBB appreciate this a bunch. Tell me how you post this on your reply so it is open with your post?

Joe Alexander
Blacklick, Ohio

[Bob G ✝︎]

To all of the brave DIY who manage to wear there skin kunkles with pride  I salute you.

Bob Geco

[A Dalton]

G
 Whenever doing a flex , it is important to check the torque on the trans output shaft pin nut.  Specially on standard trans, which require the higher torque spec. They are infamous for loosening, even to the point of losing the clampimg force to drive the speedo gear.
 When this is lose , the flange may not run true, causing both vibrations and flex wear.

[George Des]

Joe, A, George,

I did the flex disk over a year ago, so at this point, I'm not certain of much. The ZF had been rebuilt by ZF while I was in Germany back in 1983 and when I had the box out the trans flange was still securely "locked" in place.  I do recall looking at the BBB and noting all the cautions about the direction of the disk and which bolts go to the trans and which bolts go to the d/s so w/o looking at it I assume I followed this correctly--I'll certainly know when I go back in to pull it! I've got to believe it is more related to the suspension settling because I do know I did not do that part of it for sure. I also know this will not be fun to do again-especially the "crawling around on the floor" part!       [!]

[A Dalton]

<< If you can get a wrench or flex socket on the plate bolts that are partially blocked by the exhaust, then maybe you can avoid this, too. It's >>

 I often thought of slotting those few , but i didn't want to sacrifice the strength  of a bolt hole over a slot....

[ted280sl]

I have done a signficant number of projects on my own. My flex disk was replaced by a "professional". Several months after it was replaced I heard a loud noise from the transmission tunnel. I pulled over immediately and found that a rather large bolt had been ejected from my car. I went back to the "professional" and he immediately recognized the bolt. It was a bolt from the flex disk. He immediately checked and announced that his mechanic had assembled the flex disk without the proper washers. His mechanic was able to quickly install the washers and replace the bolt which had fallen out. I was quite satisfied with the service provided but, the lesson for all of us is to make sure we install the proper washers.
Regards,
Ted 1969 280SL and if the rain will stop in New York I will be able to drive it again!

[RBurg]

George:

One of the main causes for the flex disc to go out is loose sub frame mount (I have replace 3 flex disc in a matter of couple of months.)  When I replace the tran. put new flex disc  - about 500 miles latter I torn up another flex disc. We check and found that the sub frame mounts were shot. One side was  falling apart. Replace sub frame mounts and have add about 7,000 miles and it has been trouble free ever since.  Good Luck!

Ron
71 280SL Tobacco "O GIGI"
97 E420 Silver Mist

[George Des]

Ron--No problem with the sub frame mounts--these were replaced during the restoration. I've go the new disk w/hardware on order. I'll probably get to tackle this job next weekend. Im releuctant to start jacking up the car and placing the jackstands until I've got all the parts and am ready to go. Right now at least I can move the car slowly in an out of the garage so I can get to my other project--completion of the hardtop that is completeley stripped and in primer sitting upright on a moveable dolly. I still need to get a couple of coats of two-pack primer-surfacer on it before I hit it with PPG Concept in DB050(white) then I can get back to reassembling it--more fun, I'm sure--at least I've got gernold's article to assist![:0] :? [:p]      

[George Des]

Finally replaced the flex disk. The one I pulled out was really torn apart badly--I'll pots a picture when I get a chance. The toughest part of this job is working under the car and having to remove so much to get at the darn thing. I did slightly enlarge the holes on my heat shield to allow a socket to fit thorugh so at least that piece as well as the exhaust doesn't have to come off should I have to do this job again. I did notice that in order to get the flex disk to install without distortion, I had to remove one of the shims under the rear transmission mount. This allowed the transmission to sit ever so slightly lower in the rear to take the twist out of the disk. The engine and tranny had previously been rebuilt over twenty years ago by MB-Kaiserslautern and I can only assume that while using the original engine and tranny mounts that they had compressed slighlty and the shims were used to bring things in line. When I did my restoration, I replaced all the mounts with new and this may have caused things to ride slightly higher. Took it for a test drive and there are no vibrations coming from the drive line. I did follow the advice to settle the suspension before tightening both the d/s slip joint and the center bearing mount this time. Still not too happy with the TimeValve SS exhaust--I believe the down pipes are a few inches too short and this makes it almost impossible to hang w/o some very close fittings to body parts with resulting vibrations. Almost ready to go back to stock, but that's a project for later.

George Des

[Ben]

I made the mistake a few years back of installing the d/s and tightening everything whilst the car was in the air. I couldn't believe the vibration that came through the car when driving !

Anyway I realised the fault and loosened then re-tightened everything whilst on the floor and it was fine afterwards !

Regards,
Ben in Ireland.
'64 230SL 4sp.