U-Joint question

black88coupe

black88coupe

Club Member
I have a clunk coming from the rear of my car that sounds a lot like a bad u joint. The rear joint/ mounting flange (8.8 Mustang) feels tight when I try to wiggle it back and forth. I also pulled the rear diff cover off and everything seems in order with nothing really obviously wrong. It clunks when it is going into third until light throttle. It doesn't clunk when I put it into drive or reverse but my foot is almost always on the brake at that time. I don't have any vibrations in the driveline. Just this weird 2-3 shift clunk. Its a FRPP aluminum shaft with sealed 1330 u- joints. The shaft has been sitting around for quite some time so I'm wondering if the grease has gotten crusty and is therefore allowing it to clunk even though it doesn't feel loose like when the joints go bad. I'm guessing that the grease is there to provide a small amount of cushion as well as lubrication. Also the rear control arm bushings seem to be in good shape as well.
 
Last edited:
Billydroveit said:
is there a flare between the 2-3 shift? My c4 had a small flare and under cruise would clunk on the shift.
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No shift flare. AOD is fresh. Im thinking the posi is probably bad. Im changing the joints for good measure but Im thinking the problem is a bad posi. There is a small amount of slop between the spider gears and the side gears.
 
I would recommend checking the backlash in the rear end but you would notice it from drive/reverse moreso than 2-3 shift. It doesnt really sound like its a u-joint issue.
 
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