Question: Possible differential problem

[tombird]

My '64 Corvette has developed a rather harsh humming noise the pulsates coming from the rear. It occurs on deceleration only,on road load and acceleration it is quiet. It also does not occur with the rear end jacked up and running.
I have examined all the U joints and all are tight. I disconnected the half shafts from the rear wheel spindles and could feel no roughness or play in the bearings. There is also no play in the differential output shafts. The differential oil is at the correct level and is dark brown in color.
My theory is that after 110,000 miles the ring and pinion are worn to the point that they have become noisy. However before I spend $900 for a rebuilt differential I would like to have some concurrence.
My question is: Based on the above info what do you think and have I overlooked anything?

 

[Hib Halverson]

I'm going to guess sort of the same...you have a rear axle problem, and it may or may not be failure of the gears. It could also be a bearing, either the pinion bearings, or the carrier bearings.

At 110,000 miles and, especially, if the lube has not been changed periodically, I would agree that you need to overhaul the diff.

 

[Verle]

Also, do not discount the possibility of a wheel bearing in failure mode.

 

[LVMYVT76]

I would think about rebuilding the complete rear area, with many miles on it(diff and rear wheel bearings).

 

[gmjunkie]

Half shaft U- joints are bad to get small serration's on the cross journals from the small needle bearings that will make the same type Humming under deceleration or acceleration your describing! You probly won't feel them in the U-joint by checking to see if there loose unless there real bad!! Visual inspection apart will be the only way!! Pinion bearing can make the same type noise,but usually will be accompanied by a leaking pinion seal!!Carrier Bearings usually will hum all the time usually accompanied with leaking axle yolk seals,and worn spider gears and pins can make the same type noise with a slight notable vibration in curves and under acceleration or deceleration with the feeling of excess slack in the differential between acceleration and deceleration!! Hope this helps!!

 

[hotmtrsports]

Whatever you do don't go for any rides. If it is the bearings and they seize, you're looking at more expense including locking up and sending the car to a skid etc...

Chuck M

 

[tombird]

Whatever you do don't go for any rides. If it is the bearings and they seize, you're looking at more expense including locking up and sending the car to a skid etc...

Chuck M

Thanks for the input, Chuck. Based on the noise analysis in the 1963 service manual I am pretty sure I am dealing with ring and pinion wear and not bearing failure.

 

[tombird]

Half shaft U- joints are bad to get small serration's on the cross journals from the small needle bearings that will make the same type Humming under deceleration or acceleration your describing! You probly won't feel them in the U-joint by checking to see if there loose unless there real bad!! Visual inspection apart will be the only way!! Pinion bearing can make the same type noise,but usually will be accompanied by a leaking pinion seal!!Carrier Bearings usually will hum all the time usually accompanied with leaking axle yolk seals,and worn spider gears and pins can make the same type noise with a slight notable vibration in curves and under acceleration or deceleration with the feeling of excess slack in the differential between acceleration and deceleration!! Hope this helps!!

Thanks for the input. The noise I am hearing is cyclic which according to the 1963 service manual is indicative of ring and pinion deficiency[wear]. There is no variation in noise on turns, however, all the differential seals are leaking and there is not excessive slack between accel and decel. AS for the U joints I think I will rebuild the differential and then if a noise persists look at them.

 

[tombird]

I would think about rebuilding the complete rear area, with many miles on it(diff and rear wheel bearings).

I do intend to do the whole rear end but I am not sure the rear wheel bearings are as old as the rest. There is no indication they are defective.

 

[tombird]

I haven't discounted the rear wheel bearings but I can find no evidence they are deficient. Besides I don't know they have not been replaced at some point. I have only owned the car for a little over a year.

 

[GTR1999]

Tom it does sound like gear lash and possible bearings. I would go about checking as you have but in the end I suspect you're going to be going through the diff. Makes no sense to try and isolate the bearing in the diff but to repace them all now. You can check the lash with the cover off and get a look at the pattern as well. If they are the original Gm gears they'll have a date code on them.

Look over my thread here to help you as all rebuilds are not the same. Hope this helps you.
http://www.vettemod.com/forum/showthread.php?t=167

 

[tombird]

Folks, I would like to close this thread but I don't know how. I appreciate all the input and I have achieved my objective of corroboration of the problem. I will rebuild the entire rear suspension. The differential gets new bearings, seals, positraction discs and if necessary new ring and pinion. The crossmember gets sandblasted, painted and new cushions. The control arms get new bushings. Thanks again for all your help.