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  #1  
Old 04-27-2003, 09:18 PM
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Unhappy 300E clunking in reverse

I have an '88 300E with about 180K. It started making a clunking noise in reverse. It doesn't make any noise going forward and drives fine.

Is this likely a u-joint or a cv joint?

I'm trying to decide if I want to tackle it or send it to a shop. I've done both these jobs but on other cars. Any advise?
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Old 04-27-2003, 09:27 PM
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At the front of the driveshaft, there is a rubber coupler, called the "flex disc", instead of a U joint. They are in a way considered a "wear item". I wouldn't be surprised if this is the cause of the clunk. The rear of the shaft typically has a hard rubber coupler, and they seldon wear out, but the front one has some cushioned rubber areas around all the bolts which hold the coupler to the transmission output yoke and the driveshaft yoke. It helps make the drivetrain power transmission softer, which helps make a more comfortable ride and absorbs shocks in the entire driveline.
When the cushioning wears out, it makes the driveshft kind of sloppy and can cause the clunk when shifting from drive to reverse/reverse to drive (change in shaft direction).

Gilly
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Old 04-28-2003, 02:37 AM
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Thank you for the reply. Maybe I should be more specific.

I don't really notice a clunk going from drive to reverse. But when I do go in reverse, the clunk-clunk... starts about the speed of a marching band, and if I hit the gas, the clunk-clunk speeds up with the car's speed. All is quiet when switching to and moving in drive.

Does that change your diagnosis?
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Old 04-28-2003, 08:35 AM
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It's easy enough to verify if it's the flex disc or not just by getting it on a hoist. There actually is an inspection interval for the front flex disc, I believe it's every 60,000 miles it's supposed to be inspected. It could also be what is called the "mid ship" or "mid shaft" bearing. The car has a 2 piece drive shaft, and this is the bearing that supports the middle of the driveshaft. OR it could also be the mid ship bearing support, which is a metal support for the middle of the driveshaft which also has a rubber collar inside which is known to wear out.

To inspect the front flex disc, just get it up on a hoist. Make sure the parking brake is NOT set. Grab the driveshaft and twist it back and forth (at the front of the shaft if possible, sometimes there's not much room, depending on the exact model, and a helper needs to twist the driveshaft back near the differential while you observe the front flex disc). While the shaft is being twisted back and forth, watch the 2 sets of bolts that hold the flex disc to the driveshaft and transmission (3 bolts for each job).
When twisting the shaft, there should be only a small amount of motion between the 2 sets of bolts. Also with a good light, you should see that the rubber surrounding each bolt is intact. If the rubber around the bolts is gone, you know right away it's junk.

To inspect the midship bearing and support, grab the driveshaft as close to the middle of the shaft that you can (usually from the rear of the shaft, you can get closer to the middle fron the rear) and try moving the shaft up and down and see if you can detect any movement.

To do either of these jobs is pretty involved, it almost has to be on a hoist. You need to be able to spin the driveshaft to access all the bolts, and it really helps to take off the transmission mount, which involves having the car in the air, and holding up the transmission with a transmission jack or pole jack (screw jack) of some kind.

Gilly
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Old 04-28-2003, 11:41 AM
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Thank you, thank you. A drive line, I can handle. But I busted too many knuckles changing cv joints on my 928. And, I don't recall what kind of noise they made when they were going.

I immediately remembered the same clunking noise from friend's cars with front wheel drive when making a tight turn if the cv joints were bad.

It sounds like the 300E's cv joints don't give much trouble?

Thanks again.
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  #6  
Old 04-28-2003, 02:48 PM
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Sounds to me like the foward clutches are worn out and the apply piston is hitting the front drum. Simple to fix, hard to find.




Joe
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  #7  
Old 04-28-2003, 03:31 PM
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The only cv joints on this car are on the rear half-shafts. They only flex with suspension movements, since the rear wheels don't turn (left/right) the wear on the rear cv joints is minimal.

Gilly
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