Trailing Arm Question

[Joel T.]

Hi All;

I have an ongoing problem with my 1963.. Some time ago I posted a question looking for general suggestions/causes of this "thump" I get from the right rear. Recently I replaced the rear end (not related to this) so I know that everything back there is tight and in most cases new/rebuilt.

The "thump" happens a)the first time I back up and hit the brake and b)directly afterwards the next time I go forward and hit the brake. I can get the sound to repeat pretty much at will.

I've checked everything in the entire rear assembly. Yesterday I pulled that right rear wheel and checked the shims which align the trailing arm with the frame.. They were in place and had zero rotational movement except via a prybar... The trailing arms were replaced in 2007.

Here's the question... are there different size trailing arm bushings; i.e to accommodate different size trailing arm bolts? I'm just wondering if I might have the wrong size bushing which results in this thump... In my 1963 the trailing arm bolt has a 5/8 head and an 11/16 nut.

This issue has been driving me nuts for some time now.. and I gotta believe that it is something subtle which I have missed...

Thanks!!

Joel

[Timothy B.]

Re: Trailing Arm Question

Joel, When you had everything apart did you replace the front differental rubber mounts and torque the bolt?

Also, did you check the frame for weld brakes where the sombaro is welded. That's the piece that holds the large bushings in the crossmember.

[Joel T.]

Re: Trailing Arm Question

Hi Tim;

I did not replace the front differential rubber mounts this time around. I did replace them; mounts, bolt, washers etc. when I first replaced the rear, so they are basically new. That bolt is torqued to 60# and I can see nice compression on the mounts. The front mounting bracket is also "new" and is one of the later styles which has the reinforcing bars welded to the sides so I do not suspect any shifting there.

On the sombreros, I did not specifically look for breaks in the welds but did a quick visual go over and saw nothing out of the ordinary...

Originally I thought that I had an exhaust problem, making contact somewhere. Now I am reasonably convinced that there is something shifting back there.... shifting based upon a change in direction and braking. As I said, I can get it to "thump" now basically at will, so I got to believe that it is something rotational in nature... If I back the car up say three times in a row and apply the brakes (as if I were adjusting),I will get the sound the first time only. Similarly if I the go forward and hit the brakes three times, I will get the sound only the first time... If I had a sombrero problem I suspect it would happen each time I applied the brakes.

Do you think I might have play in the rear brake backing plate (elongated holes)?? I still have an issue with the car pulling to the right when braking hard...

Thanks!!

Joel

[Wayne W.]

Re: Trailing Arm Question

You might try looking at the brake shoes, but the most common cause of thumps in a 63 rear is wear in the bolt holes that holds the snubber to the rear end. There were many updates in this part over the years.

[Jeffrey A.]

Re: Trailing Arm Question

Joel

I had the same problem with mine and the brake shoes. I changed them out along with (NOS brake shoes) and all the fastners and it fixed the problem. I drive the car sometimes and I had not had the noise since. Jeff

[Jerry G.]

Re: Trailing Arm Question

Joel:


I agree with Jeff. It's sound like a brake shoe is grabbing and sticking when released. It may just need an adjustment in how soon it contacts the drum.

[Jeffrey A.]

Re: Trailing Arm Question

That is exactly what was happening in my case. I hope this helps, when I was reading his post, I knew what the isssue was from my own personal experience.

[Joel T.]

Re: Trailing Arm Question

Guys;

Thanks for the suggestions... Last winter I re-did the entire brake system; rebuilt master cylinder (SS sleeve), all hoses, cylinders, brake parts and shoes. The only thing I did not change was the steel lines but they were flushed and blown dry.

That right rear brake seems to run hotter than the other three.. I've replaced the wheel cylinder twice since rebuild. I've even replaced the emergency brake cables to eliminate the potential for a dragging rear shoe. The springs and other parts are new..

The brake shoes came from LI Corvette.. Any suggestions for another provider... At this point I'm open to anything.

Joel

[Jeffrey A.]

Re: Trailing Arm Question

Joel

I am going to talked to a close friend of my that works with me on my vette. I will pass your issue accross to him and see what he thinks. I get back to you in a couple of days.