How can you tell when a flex disk is bad?
 

Hi,

I just bought a 1994 E320 and I'm giving it a good once over. It has a light clunk when I abruptly chop the throttle and it goes from accelerating to decelerating.

Once I find a 14 mm hex socket, I'm going to do a differential lube change. I've chosen to replace whatever is in there with Mobil 1 70/95 synthetic. I don't want to start up the debate over synthetic vs. petroleum, but that's what I decided to get.

I climbed underneath last night to inspect the flex disks. The front disk was obviously new, but the rear was not. There is some slight cracking of the rubber around the thicker areas where the bolts pass through. I didn't see any indications of separation though and I couldn't flex it by twisting the driveshaft by hand. I also put both wheels in the air and spun the diff by the driveshaft, then each wheel. There was no excessive slop or clanging.

I am hoping that the new gear lube will do the trick, but can anybody tell me how to tell if the flex joint is good or bad?

Thanks, Dennis

I just picked up the 14mm hex key at a local industrial hardware supply shop. That's issue #1 taken care of.

Can anybody give me advice on how to tell if the flex disk needs to be replaced?

Thanks again...

I am a diyer so get a techs input because they have seen alot more of these flex disk than I have and I probably have never seen one that is worn out. Looking at the book it seems that the disk is worn out if the holes that the bolts go through are "wallored" out. That is, they are no longer round. I can't tell you if this would cause the klunking though.

Regarding the FLEX DISC - try this.

Go to this sites SEARCH function - upper right hand corner on most screens.

- In SEARCH BY KEYWORD key in FLEX
- In SEARCH FORUMS select SEARCH ALL OPEN FORUMS
- Click SEACRH TITLES ONLY
- Click PERFORM SEARCH

Lots of info on the subject.

Or I can just post an answer.
The rear driveshaft has a rubber coupler, not a actual "flex disc" in terms of this topic.
To check the front flex disc (it's just called the "front" flex disc, even though it is the only one on the car), the car should be off it's wheels to allow the drive shaft to move. The drive shaft is then twisted back and forth and looseness is looked for between the front yoke of the driveshaft and drive yoke of the transmission. Essentially, you are looking at movement between the 3 bolts that hold the flex disc on to the transmission, and the 3 that hold it on to the driveshaft.
The flex disc absorbs torsional load shocks from the driveshaft and is considered a wear item. The rear coupler it's a good idea to keep an eye on, but it's really rare to see a failure of it. Since it's mostly rubber, it may be normal to see a slight amount of weather-checking or small cracks. I do remember replacing one once where it had larger cracks on the sides and had what looked like tire cords coming out of the cracks, some sort of reinforcement threads.
Gilly

Thanks for the advice. I did the search also and I'll check my center support bearing this weekend. I can see that the front flex disk is new and the rear coupler doesn't look bad.

I'll let you guys know what I find.

Dennis

If the drive train seems to be in order, you may want to check the rear suspension torque arm bushings/arms.
They are the weak link in the diff. suspension and the new ones are beefier.

Problem found! There are 2 big "cush mount" bolts that go through the frame into the rear of the differential. It was obvious that the rubber cushion part is shot. Especially the one on the driver's side. Now I will have to go back to my local store and buy a 12 mm hex key (no problem - I love tools!).

I changed the diff gear oil in both the 300E and the E320 in probably 20 minutes each. What a piece of cake. If you need to do yours don't hesitate - it's really easy.

Thanks for the help.

Dennis

Caution!
 

Dennis,
I think you are describing the rear differential mounts. If that is the case, it is not as easy as you think. You need a special puller or you will have a hell of a time trying to remove them. I know, changed those suckers myself!
The mounts are around $10 each, the tool is around $100. I discussed this topic before, do a search.
Big difference afterwards.

Thanks for the warning J.H.!!!

I see that you and many others have been down this path :)

Being a glutton for punishment and a cheapskate, but armed with what I consider to be an excellent shop setup, I will go the home fabricated tool route.

I'm glad that Performance Products posted a picture of the tool - it gives me ideas...

I will report the results and if I remember, I'll snap a picture of the puller setup I come up with, since many others have asked for similar advice.

Thanks again!!!

Dennis

Added links
 

http://porsche996turboblog.blogspot.com/2011/03/iui-clack-when-lifting-accelerator.html

http://www.dtmpower.net/forum/e36-3-series/168420-worlds-worst-guibo-flex-disc-not-kiddin.html

http://www.m5board.com/vbulletin/attachments/e39-m5-e52-z8-discussion/109684d1277943243-my-flex-disc-guibo-tore-out-my-o2-sensor-connections-need-replace-them-wrecked_guibo.jpg

http://i12.photobucket.com/albums/a226/Pikstarr420/flexdisc_1.jpg

http://moonpatrol.org/~craig/bmw/guibo.jpg

http://www.ltdlx.org/albums/cage/guibo.sized.jpg

http://forums.bimmerforums.com/forum/showthread.php?p=7273957

IMHO this sounds more like a carrier bearing support than a flex disk.

-J

10 years since, I wonder how the car is doing. From the most recent posts, I guess it's still running.

Oh lol, I didn't look at the dates of the posts...