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Rear end noise on slow right turn after hwy use

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Rear end noise on slow right turn after hwy use

Posted: 9/14/25 11:35pmMessage 1 of 9
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Vette(s): 72 t top 350 77,000 miles

I have a 72 350 auto with 323 gears in back i believe.

after driving on hwy 20 miles or so i come to a stop and turn right i get a chatter type noise in the rear.

i had similar about year ago , changed the fluid and added the gm additive, it went away, but this year it came back, i only put about 400 miles on it and sat till june of this year.

 

it has 77,000 miles on it.

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Re: Rear end noise on slow right turn after hwy use

Posted: 9/15/25 7:05amMessage 2 of 9
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Duncanville, TX - USA
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Take it to a parking lot somewhere and do slow, tight circles in both directions for a few minutes. Might just need to distribute the posi additive after sitting for a long period. Anytime I hear one chattering after a long drive on the highway it is always the posi clutches. Another fluid change with additive might be needed, also, but try the slow circle thing first. After doing the circles get out and drive on the freeway for a few miles, exit, and take a sharp turn in both directions....see if that helps. 

Joel Adams
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Re: Rear end noise on slow right turn after hwy use

Posted: 9/15/25 7:47amMessage 3 of 9
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Burke, VT - USA
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Hey Double A - any benefit from doing the parking lot circles in reverse also?  I recall reading or hearing about adding those circles to the annual maintenance routine.

Jim Olson 

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Re: Rear end noise on slow right turn after hwy use

Posted: 9/15/25 1:04pmMessage 4 of 9
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Vette(s): 72 t top 350 77,000 miles

Thanks ill try that, your right it settles out probably, and they aren't slipping driving straight on hwy.

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Re: Rear end noise on slow right turn after hwy use

Posted: 9/15/25 3:30pmMessage 5 of 9
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Equinunk, PA - USA
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Vette(s): 1972 conv, 4-speed, 350, 200hp, numbers match, rally wheels, war bonnett yellow w/white top. good condition, nice driver.

Hello, Same effect, frontwards, or backwards.  AA beat me to the answer. 

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Re: Rear end noise on slow right turn after hwy use

Posted: 9/15/25 9:06pmMessage 6 of 9
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Duncanville, TX - USA
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Norsky said:

Hey Double A - any benefit from doing the parking lot circles in reverse also?  I recall reading or hearing about adding those circles to the annual maintenance routine.


No benefit at all in reverse....it does the same thing either direction. Makes one side turn faster than the other, which forces the clutches to "slip". The "slip" action breaks the clutches loose. On a long, straight-ish drive, the clutches can become stuck together, creating the chatter heard and felt on a turn. Normal, in town driving keeps the clutches from sticking as you drive around corners, or make hard turns. The posi additives just help with the sticking issue.....makes the clutches a lil less sticky. Nature of the beast, even in today's vehicles with clutch-type posi units. MOST rear gear oil these days also already has posi additives in them. Not all, but a lot of them do. Never hurts to add the GM stuff, tho. 



|UPDATED|9/15/2025 9:06:28 PM (AZT)|/UPDATED|

Joel Adams
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Re: Rear end noise on slow right turn after hwy use

Posted: 9/16/25 2:38pmMessage 7 of 9
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Loir en Vallee SARTHE, France
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Vette(s): 1978 L48 Auto. Red with Oyster Leather interior. Owned since 1990.

Personally, I'd change out the diff fluid again.  The current thinking seems to be to add TWO bottle of the GM additive, and top up with a good gear oil.   

Then, as said, take it to a parking lot and do at least 8 - 12 slow figure of eights.

Chevy used to say the diffs were "sealed for life", but the reality is that I usually change the fluid on our '78 every 7 or 8 years, so quite a few times in the 35 years we've owned it!   

Stephen J Irons
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Re: Rear end noise on slow right turn after hwy use

Posted: 9/20/25 11:52amMessage 8 of 9
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CHESHIRE, CT - USA
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Vette(s): 1969 350 4 spd drop top 1972 350 auto coupe

Posi chatter, common with the Eaton and Yukon posi's. Chatter depends on the clutch type and setup, possibly case wear. If you used a good gear oil, Eaton recommends only non-synthetic,  and one bottle of the current additive I would suck out about 4 oz and add another 4 oz bottle of additive. Fill with oil till it starts to weep out the fill hole. You can do the figure 8's in a parking lot to side load the clutches but normal driving will do the same thing. 

72 had the better posi cases but the weaker clutches. If the car was ever pushed hard, those clutches can break. If the chattering doesn't stop, you can try a relube again but most likely it won't matter.  I use Lucas 85-140 with 2- 4 oz bottles of gm additive in the diff's I build. You can use 80/90wt as well. Any quality gear oil will work, you do not need special HP oils.

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Re: Rear end noise on slow right turn after hwy use

Posted: 9/20/25 6:38pmMessage 9 of 9
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Vette(s): 72 t top 350 77,000 miles

Thank you 

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