Quiet thump in rear end - FFCars.com : Factory Five Racing Discussion Forum

 
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post #1 of 5 (permalink) Old 04-21-2017, 10:17 AM Thread Starter
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Quiet thump in rear end

When pushing the car around the shop I can feel a light thump in the rear end every foot or so. When lifted with the frame on jack stands and suspension at drive height there is no thump. Only when on the ground. I hear nothing while driving. It is a '87 limited slip with new axles and friction modifyer. Any thoughts??

Thanks

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post #2 of 5 (permalink) Old 04-21-2017, 11:14 AM
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what is the pinion angle set to at ride height


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post #3 of 5 (permalink) Old 04-21-2017, 11:43 AM Thread Starter
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Thanks for your reply.

Just measured it. 5 degrees up in the rear at ride height.
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post #4 of 5 (permalink) Old 04-21-2017, 07:17 PM Thread Starter
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UPDATE:

Took it for a 15 mile run. Loud whinning noise in rear end while driving. Parked on the driveway and as I pushed it by turning the wheel, it shuttered every few feet. I was sure I had teeth missing from the ring gear. Then I put the rear of the car on jack stands with the suspension drooped and turned the wheels (both in the same direction) with NO noise or shuttering of any kind! ??!!??

Could it be the pinion angle which is at 5 degrees, measured at the flat spot on the side of the housing? Any thoughts would be appreciated.

Thanks!
Bob
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post #5 of 5 (permalink) Old 04-22-2017, 01:29 PM
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This is very likely NOT your problem but it was mine. I had a thumping when driving that was making me crazy. Only when driving, never when it was lifted up and moved by hand. Ended up the driveshaft bolts mounting it to the rearend had worked themselves loose and that was causing my problem. Tightened them and everything was fine after that. Again, likely not your problem but.....
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