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Topic: C3 rear thumping noise

C3 rear thumping noise (1/11)
 4/23/20 6:49pm
ahmtoys
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West Chester, PA - USA

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1972 Base model convertible yellow white top black interior 350 4spd


Joined: 4/16/2020
Posts: 4

Help, I recently had my trailing arms rebuilt in my 72 along with the 1/2 shafts.

Reinstalled the shims the same way they came out (new SS ones) Used all new hardware, shock mounts etc.

Have not realigned yet.

I developed a loud thumping noise from the P/S when moving in any gear or coasting, it sounds like an out of round condition that appears to happen at every 180 degree rotation.

I drained refilled & added the posi-lube to the rear no change, changed the snubber also. Differential mount bushing are tight.

I'm considering repositioning the rear spring it appears to be off to the P/S about 1/2" too far. The rear spring outer mounting bolts are not centered in the spring bushing, I believe this might be adding to the problem?

Does anyone have another suggestions? I'm at my wits end and hoping it's not a differential issue.

Alex






|UPDATED|4/23/2020 3:49:53 PM (AZT)|/UPDATED|
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Re: C3 rear thumping noise (2/11)
 4/23/20 3:11pm
manchestersharkLifetime Member
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Equinunk, PA - USA

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1972 conv, 4-speed, 350, 200hp, numbers match, rally wheels, war bonnett yellow w/white top. good condition, nice driver.


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Posts: 2011

Is P/S.  Propeller shaft?

Re: C3 rear thumping noise (3/11)
 4/23/20 3:21pm
manchestersharkLifetime Member
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Equinunk, PA - USA

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1972 conv, 4-speed, 350, 200hp, numbers match, rally wheels, war bonnett yellow w/white top. good condition, nice driver.


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Posts: 2011

IF you had the Drive/Propeller Shaft out of the rear, check to see if the end caps on the universal joint are properly seated in the pocket and the u bolts are tight on the caps. If you have side or up and down movement on the end of the propeller shaft, something is not tight, or not in correct placement.

Re: C3 rear thumping noise (4/11)
 4/23/20 4:34pm
BillHanna
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Cana, VA - USA

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1975 Stingray 71 350 engine Flat top pistons Sniper fuel injection Hyperspark ignition


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Make sure that the tailshaft of the transmission is on a parallel plain to the input shaft on the differential.  If these are not parallel, there will be a vibration since the driveshaft will speed up/slow down with every rotation.



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Re: C3 rear thumping noise (5/11)
 4/23/20 6:50pm
ahmtoys
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West Chester, PA - USA

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1972 Base model convertible yellow white top black interior 350 4spd


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Posts: 4

Thanks I plan on getting under the car this weekend and look. 

 

Re: C3 rear thumping noise (6/11)
 4/23/20 6:51pm
ahmtoys
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West Chester, PA - USA

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1972 Base model convertible yellow white top black interior 350 4spd


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MMM didn't think of that will check

Re: C3 rear thumping noise (7/11)
 4/23/20 9:49pm
Adams' AppleLifetime Member
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Duncanville, TX - USA

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#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas


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Check to see if the spring end is hitting on the rim, or a wheel weight. You should be able to see wear marks if it is...



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Re: C3 rear thumping noise (8/11)
 5/5/20 1:30pm
ahmtoys
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West Chester, PA - USA

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1972 Base model convertible yellow white top black interior 350 4spd


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Well guys thanks for all your help. 

I believe I did solve the issue, apparently when I had the local auto repair shop press in new universals on the 1/2 shafts, they had not properly secured the flange, needless to say it was bent at the top of the ears and this caused the thump at 180 degrees, the cap was not in line with the end of the universal and the retainer was not fully seated in the recess on the flange, I straightened the ear replaced the holding cap retainer with a new one test drove and all is fine so far.

Shame on me for thinking the local auto repair shop could do the job right. 

Re: C3 rear thumping noise (9/11)
 5/5/20 8:13pm
manchestersharkLifetime Member
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Equinunk, PA - USA

Vette(s):
1972 conv, 4-speed, 350, 200hp, numbers match, rally wheels, war bonnett yellow w/white top. good condition, nice driver.


Joined: 10/31/2007
Posts: 2011

Great!  I've been in that situation myself, and noticed the problem as I began the I installation.  Glad I could point you in the direction that I have encountered.  Be safe, drive it and enjoy it! 

Re: C3 rear thumping noise (10/11)
 5/5/20 8:14pm
manchestersharkLifetime Member
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Equinunk, PA - USA

Vette(s):
1972 conv, 4-speed, 350, 200hp, numbers match, rally wheels, war bonnett yellow w/white top. good condition, nice driver.


Joined: 10/31/2007
Posts: 2011

Great!  I've been in that situation myself, and noticed the problem as I began the I installation.  Glad I could point you in the direction that I have encountered.  Be safe, drive it and enjoy it! 

Re: C3 rear thumping noise (11/11)
 5/12/20 10:43am
73shark
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Overland Park, KS - USA

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1973 Orange Metallic Coupe (orig owner), L82, 4 spd (WR), PS, (A/C & PW (I installed from wrecked 73)), leather, AM/FM Stereo, ran with '65 FI unit earlier & will again some day.


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manchestershark said:

Is P/S.  Propeller shaft?



I think it's Passenger Side. I first thought it was Power Steering until I read farther. 



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1973 L-82 4 spd

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