Okay, my therapist, 74 corvette, is giving me problems. I have a thump in the driver rear after it heats up. It does not occur when it is cool. I have replaced the half shaft and just changed the diff lube. It sounds and feels like a brake grabbing. Could it be the parking brake grabbing. It only occurs when applying the brakes and then starting again. When torque is on the rear end going forward there are no thumps after it first starts. When rolling start/stop it does not occur. Okay, I am trying to be complete. L48, Auto, 74….

 

In problems like this. I usually stand outside the car and have my helper start off and I listen and watch to see if I see movement in the trailing arm bushing ( which I have) and it can cause a "thump"...but usually all the time.

I also have experienced the four bolts that secure the half shaft to the inner flange were not correctly tightened and did not have the french locks on them.

I removed the rear brake hose from that side and installed a plug so i do not loose brake fluid and check it in the shop parking lot or shop. I did this when the noise was there...and when the brakes were disabled...the noise went away...which would confirm your thoughts. DO NOT be an idiot and do what I say and go drive your car on the STREET. Bleeding the brakes will be required...naturally...if you remove the hose.

I hope you replaced the universal joints when you did the half-shaft. Hopefully with ones that have NO zerk (grease) fitting in them. Solid universal joints is what came in the car from the factory...and it is all I will use. Universal joints are cross-drilled and actually weaker.

Unless you remove your rotor on that side...it is hard to say of the parking brake springs are broken and allowing the shoes to move. Parking brakes are separate from your brake calipers. So pressing your brake pedal has nothing to do with the park brake operation.

DUB

 

Dub - thank you for your response. I did not replace the universal joints on the drive shaft. They both have zerts which means they have been replaced? The front looks new and the back has no play. I only replaced one half shaft, the driver side. The rear drums have been drilled out. However, I did not remove the rotor. The noise is inconsistent. Sometimes it thumps more in reverse, but is not an always thing. Someone, a previous owner has worked on it. Fortunately there is only surface rust and the interior is repairable. It apparently sat out for a while but does not appear to be bad at all. I probably spent too much but it runs great. More money then brains and got it for 6k.

I bought the car very used and the engine runs great. I did so just to have something to work on, my 97 only has 35k on it and does not need much so this is the toy.

 

Sounds like the classic posi-clutch chatter. Change the rear fluid with the correct posi lube and two bottles of additive.

 

check you trailing arm where it mounts to the frame ,maybe a bushing is bad .jack the up the rear of the car and pull and push on every suspension part real hard .

 

I just changed the fluid. Used the GM lube with the additive in it. Would you add more additive to the diff?

 

Will do tomorrow. It is a very inconsistent thump but when it goes it goes! Stood outside as Dub suggested but could not tell a thing.

 

I am not aware of GM lube with additive in it, may be something new, but it needs two bottles of additive.

 

I also was not aware of the limited slip additive being in the gear oil. I always buy them separate.

I have also experienced a bushing at the lower shock mount area being bad or the nut is loose. this will cause for a noise...maybe not what you are hearing...but I have encountered it numerous times and a simple tightening up on the nut stopped the noise. And then sometimes I have to replace the lower bushing.

Hopefully the strut rod bushing located below the rear differential are still good. I have had some that the rubber was completely gone and the "eye" of the strut rod was moving around. This is usually noticed when you raise th car...or the fact that the rear tire(s) are leaning inwards at the top due to the lack of rubber in the "eye" of the strut rod.

DUB