C2 periodic bump when driving?

[brumbach]

I've asked this question before and thought I found the problem but...

Every so often, I'll be making a righthand turn when pulling out and there will be a bump (or thud) sound that comes beneath the passenger side of my 65 convertable. Can't find anything loose or missing. Probably not enough info provided but wonder if you have any ideas as to what might be making this sound. I've checked out motor mounts, u-joints, exhaust, transmission bolts. All seem in good order. Suspension appears tight too. Have observed no marks or rubs on the under carriage to point me to the culprit. Welcome your suggestions.

 

[Mikey1]

Have you checked for loose wheel lugs ? also check screws on the a arm. check for lost shims.

 

[BarryK]

I had what sounds like the same thing on my drivers side in the rear. Turned out it was some of the rear alignment shims had fallen out on that side allowing the trailing arm to shift on turns and make a "clunking" or 'thudding" noise. It didn't make the noise on every turn, just sometimes.
You may want to look underneath to make sure all your shims are in place.

 

[67HEAVEN]

These guys may be right. Check #29B on this link.

http://licorvette.com/pdfcatalogfiles/cat22/51.pdf

There should be no gaps on either side of the trailing arm. If shims are missing, the trailing arm will move left or right on the bolt.

 

[hansenisu]

Could also be your posi clutches catching in the rear end

 

[brumbach]

These guys may be right. Check #29B on this link.

http://licorvette.com/pdfcatalogfiles/cat22/51.pdf

There should be no gaps on either side of the trailing arm. If shims are missing, the trailing arm will move left or right on the bolt.

Thanks guys. I think you might have nailed it. I'll check it out this weekend and let you know. Bill

 

[BarryK]

oh my god!! you mean I may actually have been right about something and possibly helpful to someone on here??!!
Damn, it's about time I was able to contribute some help for a change. I guess all my own bad luck with my car and everything I've had to do with it over the last few months have been somewhat useful for something afterall.
LOL

 

[studiog]

I am leaning toward the posi rearend as the problem. If the shims are OK this would be my next try. I would change the posi fluid with new gear oil and the GM posi additive.

 

[Gerry]

If you still haven't found the problem check the ears and/or bolts that locate the rear suspension to the frame. Mine was broken and did exactly that except it was drivers side. Welding in new ears was a PITA but necessary.

Best regards,
Gerry

 

[brumbach]

These guys may be right. Check #29B on this link.

http://licorvette.com/pdfcatalogfiles/cat22/51.pdf

There should be no gaps on either side of the trailing arm. If shims are missing, the trailing arm will move left or right on the bolt.

Checked it out this weekend. On the side that the thumping or bumping occasionally occurs, there were three shims (#29B) all together on the same side. They were loose, with plenty of room for additional shims. I also examined the left side trailing arm and found no shims at all but there appeared to be no space that would allow for any either.

As I reported, the thumping noise comes from the pasenger or right side of the car (the side with loose shims) when making a right turn. Does this seem to explain the problem and possible solution? Is it odd that shims are all together and only on the right side of the car?

Thanks,

Bill

 

[67HEAVEN]

Bill,

This does not sound right at all. I've never seen a C2 / C3 completely without shims on the trailing arms.

I think you've found your problem.

 

[BarryK]

yep, sounds like you found the problem. on the side with the loose shims and the space for others. that additional space will allowing the trailing arm to shift and the noise you hear is the training arm hiting the sides of the frame. looks like you lost some shims on that side.

As Bob mentioned, it's odd though to not have any shims required on the other side.

You need to get the car into a good alignment shop that is familiar with these old cars and get a good 4-wheel alignment done. I had to do just the same thing for the same reason just a few weeks ago on my '65. Just to be on the safe side I ordered the shims from LICS to take to the shop with me not knowing if they would have proper shims for a car of this age - the complete set was only about $40 or so and was worth it so there wouldn't be any problems or delays at the shop.

Be glad it wasn't anything more serious

 

[brumbach]

yep, sounds like you found the problem. on the side with the loose shims and the space for others. that additional space will allowing the trailing arm to shift and the noise you hear is the training arm hiting the sides of the frame. looks like you lost some shims on that side.

As Bob mentioned, it's odd though to not have any shims required on the other side.

You need to get the car into a good alignment shop that is familiar with these old cars and get a good 4-wheel alignment done. I had to do just the same thing for the same reason just a few weeks ago on my '65. Just to be on the safe side I ordered the shims from LICS to take to the shop with me not knowing if they would have proper shims for a car of this age - the complete set was only about $40 or so and was worth it so there wouldn't be any problems or delays at the shop.

Be glad it wasn't anything more serious

Thank you, everyone for the advise. Forgive my ignorance but what does LICS stand for? Does this supplier have a webpage?

 

[BarryK]

Thank you, everyone for the advise. Forgive my ignorance but what does LICS stand for? Does this supplier have a webpage?

LICS is Long Island Corvette Supply. They are an excellent vendor for parts for midyear Vettes.
Their website is: http://www.licorvette.com/
Go to their website and look at their online catalog under section #51 and find parts #29B - those are the shims you need.

 

[JohnZ]

Checked it out this weekend. I also examined the left side trailing arm and found no shims at all but there appeared to be no space that would allow for any either.Thanks,
Bill

If the trailing arm on that side (no shims and no room for any) doesn't move laterally when you reef on it, either the frame pocket has been partially collapsed by over-tightening the bushing through-bolt instead of installing the correct shim pack, or the front bushing was replaced and the inner steel sleeve wasn't properly peened over with the bushings compressed. I'd have someone who knows Corvette rear suspension take a close look at it to see if Bubba has been there. Both trailing arms should have at least some shims on both sides of their bushings, through-bolts should be tight (without distorting the walls of the frame pocket), and each through-bolt should have a castle nut and cotter pin on the outboard side.

 

[brumbach]

If the trailing arm on that side (no shims and no room for any) doesn't move laterally when you reef on it, either the frame pocket has been partially collapsed by over-tightening the bushing through-bolt instead of installing the correct shim pack, or the front bushing was replaced and the inner steel sleeve wasn't properly peened over with the bushings compressed. I'd have someone who knows Corvette rear suspension take a close look at it to see if Bubba has been there. Both trailing arms should have at least some shims on both sides of their bushings, through-bolts should be tight (without distorting the walls of the frame pocket), and each through-bolt should have a castle nut and cotter pin on the outboard side.

I've ordered one shim kit. Since one side is totally without and the other is obviously in need of additional shims, will one kit do or should I order two kits? Quantity of shims per kit were not specified. I ordered from Paragon @ $36 per kit.

 

[BarryK]

one kit should be enough for both sides.
I only ordered one kit and they did both sides of my car and still had a number of shims left over

 

[brumbach]

These guys may be right. Check #29B on this link.

http://licorvette.com/pdfcatalogfiles/cat22/51.pdf

There should be no gaps on either side of the trailing arm. If shims are missing, the trailing arm will move left or right on the bolt.

Shims have been ordered and due today. I've located a mech who supposedly has the techical background of midyears. One question, the existing shims have the bolt running through the top hole of the shim but the lower hole is not secured by anything. Is this correct?

 

[BarryK]

Shims have been ordered and due today. I've located a mech who supposedly has the techical background of midyears. One question, the existing shims have the bolt running through the top hole of the shim but the lower hole is not secured by anything. Is this correct?

be sure he has the equipment to get the car up on a proper alignment machine!
Also, if you are interested, when I went through this a few weeks ago JohnZ gave me all the proper alignment specs the car should be adjusted to. You may want to give these specs to your shop who will do the alignment for you.
assuming you are running modern radial tires and not original bias ply, the specs you want the car set up to are:

Rear:
1/16" total toe-in, split equally across the thrust centerline (1/32" per side, exactly), and zero to 1/2-degree negative camber.

***Rear toe is the most critical setting on the whole car, particularly getting it evenly split to both sides across the thrust centerline.

Front:
zero camber, 2.5 degrees positive caster, and zero-to-1/16" total toe-in.

Note: on the caster, 2.5 is perfect for good tracking and returnability but increases static steering effort. 1.5 – 1.75 is a better setting with manual steering.

I hope this helps!


Barry

 

[67HEAVEN]

Shims have been ordered and due today. I've located a mech who supposedly has the techical background of midyears. One question, the existing shims have the bolt running through the top hole of the shim but the lower hole is not secured by anything. Is this correct?

On your car, yes. The C3's started using a very long cotter pin to hold the shims from falling out......to cure the exact problem you have experienced. The shim holes were also modified slightly.

I drilled my frame and inserted the cotter pins.