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Old 11-01-2004, 12:48 AM
wielder of thor's hammer
Join Date: Jul 2003
Location: Long Island, NY
Posts: 321
Need help determining condition of flex discs 87 300e

I crawled under the car today and checked out the two flex discs that are connected to each end of the driveshaft. The rear disc seemed good. Bolts seemed very secure with no play. However, I did notice a number of tiny horizontal (when looking at the bottom of the disc) cracks in the disc itself. These cracks are very thin, not much thicker than a hair, and none of them make it to where the bolts go through the disc, they begin and end in between the bolts.

Are these cracks cause for concern? I definitely have a problem somewhere along the drivetrain, as the car clunks terribly, sometimes. Other times it shifts perfectly. It usually clunks worse from 3rd to 4th (with second gear start). The clunking is unpredictable otherwise.

Because it feels like it is coming from the rear of the car, and because it shifts perfect sometimes, I don't think it is the tranny itself.

The front flex disc seemed good as well, with secure bolts. I could only see the side of this disc that is metal(?), and I did not see any cracks. I need a dentist's mirror to see the other side, and I will look tomorrow.

There was one thing I thought was funny about the whole thing. I had the car backed onto ramps to observe the rear disc. I could turn the driveshaft about five degrees back and forth, with a metal clunking stopping me each way. This is how I could really tell that the bolts were secure. The odd part is that when I put the front of the car on ramps and observed the front flex disc, the shaft would not move at all. what's going on here? Is it just that the driveshaft is easier to manipulate further back from the transmission, maybe a leverage thing? Or is something not right here?

Thanks for your time.

headrivenoise... listen.
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Old 11-01-2004, 02:15 AM
Registered User
Join Date: Mar 2003
Location: Southern California
Posts: 2,282
The rear flex disk is very beefy and robust compared to the front flex disk, which is almost always the one that is bad. The minor cracks in the rear disk you report are probably not a problem.

Can't make any sense out of your driveshaft slack difference between the front and rear, but the way to check them is to get the car up in the air on four jackstands under the four jack pads so the suspension is hanging free and tires are off the ground. To check the front flex disk, place the trans in Park (or first or reverse on a five speed), parking brake OFF and rotate the driveshaft with your hand. The front disk is much softer and flexible than the rear and, if bad, will show air gaps between the bolt bushings and rubber as you torque the driveshaft back and forth. It's tough to see the front flex disk because it's in front of the vibration damper.

To check the rear, place the trans in neutral, firmly pull on the parking brake and torque the driveshaft with your hand looking for play.

I consider front flex disks to be automatically suspect if they have more than 60K miles or normal driving on them. They're basically a 60K mile service replacement item!

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Old 11-02-2004, 01:26 AM
wielder of thor's hammer
Join Date: Jul 2003
Location: Long Island, NY
Posts: 321
I realized when driving today that I can make the car clunk when I am going about 30-50 mph and let off the gas for a second and then punch it. There is a split second of delay, then a clunk and acceleration.

In my mind this verifies that it is the flex disc and not the tranny. Is there anything else it could be?

headrivenoise... listen.
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