Clunk noise

Thomas95SC

Registered User
I noticed that sometimes when I put my car in drive or in reverse it will make a clunk noise. It sounds like its coming from the rear somewhere. It doesnt do it all the time... mostly when its not on flat ground. Someone told me it could be a U joint or slack in the differential????
 
sonicman1634 said:
I noticed that sometimes when I put my car in drive or in reverse it will make a clunk noise. It sounds like its coming from the rear somewhere. It doesnt do it all the time... mostly when its not on flat ground. Someone told me it could be a U joint or slack in the differential????

Does it shift hard, or is it just the noise? Usually when cars face up inclines, they drop into gear pretty hard. That might be all, but maybe not. Don't quote me on that, cuz I'm not too mechanically inclined when it comes to stuff like this.
 
It doesnt seem to shift hard at all when doing normal driving. Although sometimes when I gun it really hard it red lines before it will shift out of first.
 
AODs are (in)famous for this... Particularly in truck applications where the fluid can become dirty and gunkey quickely. You can swap out an accumulator spring to fix the problem if it is really bad and most transmission shops that rebuild AODs will know what I'm talking about. Don't force the tranny into 2 by going from 1 to D back to 1 quickely when racing as this makes it worse.

The problem could also be slack in the driveline somewhere aft of the tranny, although I doubt it because you'd hear a grinding sound (like gravel rolling in a tin can) coming from the back of the car that increased with road speed.
Check the fluid for filings by sticking a strong magnet on the fill plug and driving around for a bit. Pull the plug with the magnet still on there and check for filings. If you have slack in the diff, it will be COVERED because your diff is on it's last legs.

Check the U-Joints for leakage or pull the driveshaft and check for free movement (they should move like butter).

The super-easy-yet-dangerous way to check is to place a mirror so that you can see the driveshaft while in the car (or have a helper). Move the shifter btw reverse and drive, letting the tranny engage each time. The driveshaft should not buck or turn more than 4 degrees (which will barely be noticeable.) You can mark the pinion if you want to check the movement more accurately and your helper is very brave/trusting.

Hope this info helps. If you want/need to rebuild the tranny, please have a look at some of the aftermarket input shafts and valvebodies available for the AOD. They are kinda hard to find, but the OD input shaft in particular is very small on our automatics. Shift kits or aftermarket valve bodies will increase the life of your bands, particularly the OD band a LOT and give you a tenth or 2.
 
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