Where should i look for rear end *thump* when putting into gear?
02-25-2011, 07:03 PM
#1
Race Director
Thread Starter
Where should i look for rear end *thump* when putting into gear?
Car has 120K miles, probably untouched rear suspension.
Gonna jack it up tomorrow and check things out.
Other than ring gear backlash being excessive, or a bunch of u-joints loose, would anything else cause a big old heavy THUMP from the rear when going into Drive or Reverse from park? Bushings somewhere? Maybe a pinion snubber of some sort?
Thanks,
Doug
Gonna jack it up tomorrow and check things out.
Other than ring gear backlash being excessive, or a bunch of u-joints loose, would anything else cause a big old heavy THUMP from the rear when going into Drive or Reverse from park? Bushings somewhere? Maybe a pinion snubber of some sort?
Thanks,
Doug
02-25-2011, 08:17 PM
#4
Burning Brakes
02-25-2011, 09:22 PM
#7
Race Director
http://www.volvette.com/SU42B.html
Pinion bushing may be loose or just need replacing. I am betting on bushing.
Pinion bushing may be loose or just need replacing. I am betting on bushing.
02-25-2011, 10:06 PM
#8
Le Mans Master
Something that happend to an older car(non Vette), is one of dif spyder gear's froze to pinion shaft, and broke the mounting bolt. The shaft started spinning in the dif case, wearing the mounting hole oblong, and acting as you described. Only seen this happen one time, but maybe another thing to check.
02-26-2011, 08:35 AM
#10
Race Director
Not saying this is not the problem but most of the time when the front TOP mount is bad, the complaint I hear is "when I let up on the gas I get a clunk". It seems to me it takes more than just idle rpm to get the differential to move enough to clunk.
That's my story and I'm sticking to it.
That's my story and I'm sticking to it.
02-26-2011, 08:49 AM
#11
Team Owner
Member Since: Sep 2006
Location: Westminster Maryland
Posts: 30,173
Likes: 0
Received 2,878 Likes
on
2,515 Posts
Hi Doug,
My eyes lit up when I read "untouched" in your post.
If it does turn-out to be untouched, there my be some nice old parts (like the shocks and spring) to hang on to if you decide to do some replacing.
Good Luck with your 'thump'!
Regards,
Alan
My eyes lit up when I read "untouched" in your post.
If it does turn-out to be untouched, there my be some nice old parts (like the shocks and spring) to hang on to if you decide to do some replacing.
Good Luck with your 'thump'!
Regards,
Alan
02-26-2011, 01:09 PM
#13
Race Director
Thread Starter
If this '72 car hadn't been recently repainted (correct color) and had mostly new interior put in, it would possibly be considered a survivor candidate., Though i believe the motor and trans may have been gone through at one time, but all parts are correct and original (except valve covers), though I see some rebuilders stickers on the vac booster and Q-Jet.
Thanks,
Doug
02-26-2011, 01:51 PM
#14
Race Director
Not saying this is not the problem but most of the time when the front TOP mount is bad, the complaint I hear is "when I let up on the gas I get a clunk". It seems to me it takes more than just idle rpm to get the differential to move enough to clunk.
That's my story and I'm sticking to it.
That's my story and I'm sticking to it.
02-26-2011, 04:10 PM
#15
Race Director
Thread Starter
Well, the Thump might have been a loose exhaust hanger, the rear muffler hanger was missing a bolt, and the muffler was swinging side to side.
But maybe not, will have to see over the next few days, it wasn't an everytime thing, anyway.
Strut rod bushings look new, front diff mount bushing looks new, I couldn't see any real movement up or down from the pinion input area from looking under the car when shifter was placed in D or R from N with car running and brake on.
No excessive backlash or U joint movement,a t least from turning one tire back and forth. No apparent wheel bearing sloppiness.
Interestingly enough, the fuel tank looks new,and all the diff mounting bolts are new. No evidence of any other repair back there, and no rust anywhere.
Posi lube tag is still on the diff.
Where are the numbers stamped for rear end ratio,a nd any other numbers that would be on the differential? It has 40 years worth of crud on it,and I was able to scrap some off, but without a lift, it is hard to maneuver under there to get a good look
But maybe not, will have to see over the next few days, it wasn't an everytime thing, anyway.
Strut rod bushings look new, front diff mount bushing looks new, I couldn't see any real movement up or down from the pinion input area from looking under the car when shifter was placed in D or R from N with car running and brake on.
No excessive backlash or U joint movement,a t least from turning one tire back and forth. No apparent wheel bearing sloppiness.
Interestingly enough, the fuel tank looks new,and all the diff mounting bolts are new. No evidence of any other repair back there, and no rust anywhere.
Posi lube tag is still on the diff.
Where are the numbers stamped for rear end ratio,a nd any other numbers that would be on the differential? It has 40 years worth of crud on it,and I was able to scrap some off, but without a lift, it is hard to maneuver under there to get a good look
02-26-2011, 05:31 PM
#16
Race Director
put the car in drive and switch from drive to reverse....if its in your drive line you will here it.....if its a clunk look to the front mount on the diff.
02-26-2011, 05:40 PM
#17
Instructor
Member Since: Nov 2010
Location: Hampton Fl.
Posts: 208
Likes: 0
Received 0 Likes
on
0 Posts
St. Jude Donor '11
Just replaced mine and it seemed to eliminate the clunk. The bottom looked OK , but the smaller piece above (that you can't see) looked tired.
02-26-2011, 06:03 PM
#18
I love this site, I have had that clunk for quite a while now . I am getting ready to replace all u joints (no grease fitting) and now will be looking at my diff mount grommett to boot. 
03-08-2011, 08:29 AM
#19
Melting Slicks
Check your trans. mount too. I had a clunk going on and on inspection, we noticed the trans mount was bad. Replaced it and diff front bushings too. Clunk gone. Not sure which got it. Diff. bushings looked bad but Trans. mount was broken...
03-08-2011, 08:20 PM
#20
8th Gear
Member Since: Feb 2011
Location: Dublin Ga
Posts: 8
Likes: 0
Received 0 Likes
on
0 Posts
I would also check the tail shaft on the transmission, I was checking my car for the same noise looking at U-joints on the shaft and noticed alot of play in the yoke on my tranmission (Turbo400) It was a bad tailshaft bushing cost about 70 bucks to get a trans shop to do or about 25 for parts if you replace it
