77 Bumping Noise

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Oct 27, 2007 | 10:14 PM

chucktn

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From: Oakland Tn

77 Bumping Noise

Got a 77 with new shocks and new u-joints front to back. Have noticed a bumping sound when I accelerate or if I accelerate and turning to the right. Sounds like it is coming from the right rear somewhere. Any ideas where to look? I've been all over the underside, could the rubber cushion bumpers be letting the car bottom out?

Oct 27, 2007 | 10:58 PM

tjhuyser

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From: Holtwood PA

then the sound would come from the left..if you are turning right and accelerating you are unloading the right front and right rear tire..is it only on acceleration or also decel and cruising?? does the thumping speed increase or decrease with speed? or engine or car?? "Johnny Five need input!!"

Oct 27, 2007 | 11:02 PM

colin75

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From: SHERMAN TEXAS

my car made bumping noise till i replaced pinion snubber bushings. i replaced with poly and they seemed a bit smaller but the noise stopped . just an idea

Oct 27, 2007 | 11:52 PM

chucktn

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From: Oakland Tn

77 Bumping Noise

TJ, only does it when hard accelerating and not everytime I turn to the right. Not consistent enough for me to pinpoint. Not saying it makes sense when I say it does it turning to the right and accelerating but that is when it seems to occur. Doesn't do it driving or cruising and the funny part it doesn't do it when I hit a rough spot in the road. I even when over some speed bumps to see if I could make it do it and of course it wouldn't.

Oct 28, 2007 | 12:46 AM

colin75

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From: SHERMAN TEXAS

i also experience occasional bumping caused by posi at beginning of takeoff and turning. been told that the clutches stick sometimes.

Oct 28, 2007 | 03:49 AM

Bob Onit

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From: Connecticut

Quote:

Originally Posted by colin75

i also experience occasional bumping caused by posi at beginning of takeoff and turning. been told that the clutches stick sometimes.

If it feels like a clunking when you start into a L or R turn, usually upon initial acceleration then my first guess would be the clutches sticking in the rear.

Pull the plug, suck out the old gear oil with a hand pump, add the 4 ounces of GM lubricant and fill it with new gear oil.
Very common issue in these cars and thankfully, very easy and inexpensive to cure.

Oct 28, 2007 | 12:17 PM

tjhuyser

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From: Holtwood PA

Quote:

Originally Posted by Bob Onit

even better top it with Lucas....that's where i was heading..if it only does it when power is applied an you have all new U-joints...I'm thinking posi..

Oct 28, 2007 | 12:50 PM

dobroman2001

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Joined: Jan 2007

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From: RTP NC

Quote:

Originally Posted by chucktn

I had something very similar on my '76. The only time the "bumping" sound would happen was when I was on an incline and turning either right or left. I ended up using a pump to remove the old rear-end greese. I can't remember the size of that bolt on the diff. but it is a 4 point bolt. I used a 8 point socket, removed the right rear wheel to gain access. I think I used something close to 12 oz of posi-track lubricant and 48oz's of 80-140 Mobile greese. It stopped the "bumping" sound for me. Good Luck,