1963 "Thump"

[Joel T.]

Hi all;

I have a strange problem with my 1963 which I am hoping someone can shed some light on... Here's how it goes...

When I back it out of the garage and step on the brake the first time, I hear a "thump" coming from the right rear. Sounds like it is coming from the brake but I can't be sure.

After driving the car a bit, like I did yesterday, I'll stop the car in the driveway just to check out the sound. If after going forward, I put the car in reverse, back up, and step on the brake, I get the "thump" again. If I then put it in first and move forward and step on the brake again, I get the "thump" again. As may times as I go forward and back and step on the brake I get this "thump".

I've had the car up off its wheels a few times but I can't find any evidence of a problem. Everything back there is basically new or rebuilt and nothing appears to be rubbing.

Last symptom.. When I brake hard, the car pulls to the left. This continues in spite of a complete brake job this past spring and me adjusting the brakes a few times.

Any thoughts will be greatly appreciated!

Thanks,

Joel

[Timothy B.]

Re: 1963 "Thump"

Joel,
I would look carefully at the differental front rubber mount for the thump, there is a torque with the bolt at this location. The rear can flex up-down with torque and cause this.

[Tom H.]

Re: 1963 "Thump"

Joel,
I would look carefully at the differental front rubber mount for the thump, there is a torque with the bolt at this location. The rear can flex up-down with torque and cause this.

Exactly my thoughts ! I would say you have two seperate problems. The thump and the pull.

Most here will advise you to inspect the front brake hoses for deterioration. I had the pull issue on mine too, but solved it with new wheel cylinders. There are several other things you can do as well while tracing the pull. Inspect the drums to be sure they are in spec. You may also want to switch them, left to right to see if you notice a difference. Take your time and go over everything thouroughly, and you'll find the issue.

[Joel T.]

Re: 1963 "Thump"

Hi Tom;

Thanks for the input. This past winter I rebuilt the entire braking system. The master cylinder was rebuilt (Apple), all rubber hoses replaced, wheel cylinders replaced, all new brake hardware (springs, etc..). The drums are reproductions.. The originals were cut too thin already.. I had the new drums cut a bit basically because they were out of round. I have not tried swapping drums around, that's a good idea.

I had a problem with that right rear brake dragging. I would drive the car and when I got back to the garage that right rear drum would be HOT. I traced this to the parking brake cable (which was original) and replaced that too. I'm wondering if that excessive heat could have "hardened" the drum??

Joel

[Joel T.]

Re: 1963 "Thump"

Joel,
I would look carefully at the differental front rubber mount for the thump, there is a torque with the bolt at this location. The rear can flex up-down with torque and cause this.

Hi Tim;

Thanks for the input.. I swapped the rear this spring and then had to go back in and replace that front bracket because the holes were too elongated. Let me go back in there and check that front bolt torque as you suggest.

Thanks!

Joel

[Stuart F.]

Re: 1963 "Thump"

Joel;

For what it is worth, I rebuilt my brake system on my 63 this past spring and tried reproduction drums as well. I was replacing the metallic brakes and got the drums before hand as I was told by many that my original drums would be junk after 40k miles with the metallic shoes. I installed Matrix Ceramic linings, but could never get them to adjust right with the repro drums. They were of a generic type w/o grooves for the anti-chatter springs. I finally went back to my originals and had them resized (cut) and even then I had to return them to their original positions to get a good adjustment for straight stopping (no pulls).

My conclusion on the repro drums was that it appeared they have a different dimensional relationship between the hub mounting surface and the brake friction surface, i.e. the linings do not position right in the drums. I did not do any sophisticated measuring to verify this, but you could see by the eye ball the drums did not fit up to the backing plates like the originals, i.e, a slight gap. The originals seem to engage or overlap the backing plates.

I was able to get the correct drums matched to their hubs because if you look close they each leave their own unique print or impression - inside of drum to hub.

I don't know how my experiences can help you and I can't offer any specific suggestions or recommendations, but perhaps they may provide you with some ideas on what else to look for.

Stu Fox

[Joel T.]

Re: 1963 "Thump"

Joel;

For what it is worth, I rebuilt my brake system on my 63 this past spring and tried reproduction drums as well. I was replacing the metallic brakes and got the drums before hand as I was told by many that my original drums would be junk after 40k miles with the metallic shoes. I installed Matrix Ceramic linings, but could never get them to adjust right with the repro drums. They were of a generic type w/o grooves for the anti-chatter springs. I finally went back to my originals and had them resized (cut) and even then I had to return them to their original positions to get a good adjustment for straight stopping (no pulls).

My conclusion on the repro drums was that it appeared they have a different dimensional relationship between the hub mounting surface and the brake friction surface, i.e. the linings do not position right in the drums. I did not do any sophisticated measuring to verify this, but you could see by the eye ball the drums did not fit up to the backing plates like the originals, i.e, a slight gap. The originals seem to engage or overlap the backing plates.

I was able to get the correct drums matched to their hubs because if you look close they each leave their own unique print or impression - inside of drum to hub.

I don't know how my experiences can help you and I can't offer any specific suggestions or recommendations, but perhaps they may provide you with some ideas on what else to look for.

Stu Fox

Hi Stu;

As always, I appreciate your thoughts. Unfortunately, my original drums found their way into the "round file" probably two years ago... I had brought them to my local machine shop to have them cut but they told me that they were already cut too thin so there was no point in hanging on to them... What's in there now are four drums from Paragon. I had picked up four additional drums from LI Corvette but they were too far off to use... they did not even have the adjusting slots, and I was not about to go drilling holes in the front of drums, not at those prices!

I know what you are saying about the alignment of the shoes/backing plate to the drum. As I recall there is that slight gap you mention. I guess I am going to need to do some careful detective work to see what is going on. You know, I had the trailing arms rebuilt last year too so I am wondering if there may be an issue with that work...

I guess it is time to get the car up on blocks (again) and begin to see what's what.

Be well,

Joel

[Paul J.]

Re: 1963 "Thump"

Joel:

As unlikely as it seems with new wheel cylinders, what you've described sounds like a piston sticking in a cylinder. Usually the thump is when the shoe breaks loose from the drum. Take the wheel and drum off and have someone slowly work the pedal. Watch for the shoe to return. It could also be your springs. I'd start with the left rear.

Paul

[Joel T.]

Re: 1963 "Thump"

Joel:

As unlikely as it seems with new wheel cylinders, what you've described sounds like a piston sticking in a cylinder. Usually the thump is when the shoe breaks loose from the drum. Take the wheel and drum off and have someone slowly work the pedal. Watch for the shoe to return. It could also be your springs. I'd start with the left rear.

Paul

Hi Paul;

Thanks for the reply. I've swapped that wheel cylinder already (2nd new one in there!), as well as the rubber hose, and all the springs, just in case. Do you think it could be the parking brake sticking?? I had a problem with that left rear wheel getting HOT while driving... you could actually feel the heat and smell it cooking. I swapped out the parking brake cables which seemed to help.... but it could still be sticking.

Joel

[Bob R.]

Re: 1963 "Thump"

I think I experience the exact same thump sound on my 63. I only notice it on initial start of the engine and backing up the car then apply the brakes. It sounds like the sound is coming from the rear right wheel. I don't seem to notice the sound after the initial backup. I heard the sound before I worked on the braking system. Since then I have replaced the entire system, steel lines, wheel cylinders, wheel spring kit, rubber hoses, drums and new linings, rebuilt original master cylinder. The carhas a power glide transmission. My car does stop straight and the brakes feel firm. I thought the noise was caused by the brake shoes moving against the drum after sitting for a while.

[Paul J.]

Re: 1963 "Thump"

Joel:

I'm not sure about the sticking parking brake. It would have to be the lever assembly at the wheel. The central lever, equalizer, and cable would only be a possibility if you heard the clunk each time after using the parking brake. You can check it two ways. You can remove the drum and watch the action of the lever when someone presses the pedal, or you can try to get the car to do it (like when you first back up) and stop everything, remove the wheel and use a lot of persuation to get the drum off. If you can catch it in the failed position you'll know exactly what the probelm is.

There is also a slight possibility that there is a blockage in the line. This can slow the back flow of fluid and cause the piston to be extended too long. However, I've never seen this happen and it's probably a long shot.

Paul

[Bob R.]

Re: 1963 "Thump"

I know it can't be a blockage in the system on my car. I had the noise then replaced everything, I mean everything and the noise is still there.

[Bill M.]

Re: 1963 "Thump"

One more LONG shot: Check the pads on the backing plates that the shoes sit on. They do wear and get grooved. It may be possible for a shoe to get hung in a groove? Never had it happen...

[Paul J.]

Re: 1963 "Thump"

Joel:

There is enough interest in this that I have put a question into my "Guru", specifically asking if the parking brake at the wheel can cause dragging and thumping and how it would do that. Right now I have to get to him from a third party so it will be a few days.

With respect to the cables, the service manual says to lubricate them. I've read this in more than one place, so it might be a possiblity that the cables are sticking. You indicated that you had replaced the cable at one point and it was better.

I've also thought about Tim and Tom's initial answer. Thier answer might explain the thump, which in this case would be unrelated to the brake issue. I've never had any probelms with Corvette bushings, but there's a Volvo in my number 1 bay waiting for new sway bar bushings. Certain model Volvos are a thumping nightmare. Strut, subframe, and sway bar bushings are always issues in these cars. Changing the attitude of the two parts that the bushing holds apart can create a distinct thump, like moving forward and stopping, and then backing up and stopping.

Paul

[Gene M.]

Re: 1963 "Thump"

Do you have the star wheel adjuster in backwards?