I recently got a 12 bolt 3.55 posi rear for my 69 Camaro. I just bought some new drums for it from NAPA because of problems with the other ones. Towards the back of the hub, there is a ridge and maybe 1/8 of an inch before you get to the back of the hub. The new drums don't back up to the back of the hub, just to the ridge. Also, the person that had the 12 bolt put longer studs on it.

My question is does the drum need to rest against the hub or is the "gap" ok? I can have the drum drilled out to make it fit, but didn't know if I should. I've enclosed a photo of the hub and you can see the ridge.

Thanks for your help.

Rick
duskblue69

I could be wrong but if I understand you correctly, I think you're talking about "shoulders" on your wheel studs. They are slightly thicker (35/64) than your remaining studs (1/2) and prevent the drum from sliding all the way back so it can seat itself. I had a similar issue with my rear disc setup. My rear end came with thicker as well as longer wheel studs. I had to drill the rotors (drums in your case) out so they would seat themselves properly. Yes, I would recommend drilling them out as you want the drum to seat itself correctly. Also, in my case the studs were too long so I had to shorten them about 1/4 inch as my lug nuts were not deep enough. See thread below for details.... Last, finding a 35/64 drill bit in Denver was like finding a needle in a haystack, I had to order one. Hopefully you'll have better luck.

http://www.camaros.net/forums/showthread.php?t=154835

There are some "shoulders" around the studs but I'm not sure that the are going to cause me an issue right now. There is a raised part at the back of the hub (the center piece) that you can see in the photo. The center of the drum won't slide over it.

The studs are the longer ones and that too may cause an issue. The previous drums that were on the car cleared this without incident. However, the idiot that put the rear end in my car slid the drums on and rather than enlarge the center hole of the drum, he pounded the drum onto the axle causing the center to bulge out and cause vibration issues and ruin the drum.

Since all of the rear-end is supposed to be original, (except the studs), I'm wondering why the replacement drums are having the same issue. Can anyone tell by looking at the hub/end of the axle, if this is what they should look like or are these some type of replacement.

Rick

This issue relates to hub centric where drum and wheel should true up to the axle hub, I am not sure if the inside edge of the drum shouldnt be chamfered a little to clear the ridge. If you are using stock wheels you should notice that your wheel center also just fits over the hub which centers the wheel (hub-centric) vs if the lugs center the wheel (lug-centric), I would get the drum machined to fit over the ridge so you will have a true center and shouldnt have any vibration issues

My question is does the drum need to rest against the hub or is the "gap" ok? I can have the drum drilled out to make it fit, but didn't know if I should. I've enclosed a photo of the hub and you can see the ridge.

Rick
duskblue69

Yes, the drum does have to rest against the hub and a gap is not okay. You should modify the drum to fit the hub. The hole is too big to use a drill bit, it needs to be cut on a milling machine, or opened up by spinning a die grinder stone around the inside. The difference is probably minimal and you won't have to take much metal off.
Do you have the tools to measure the hub and drum bore diameters? A 6" caliper would be sufficient.

After reading a couple of replies, I tried putting the drum on the opposite way, to see if it would hang up on the studs. It did. The studs are the long ones, installed before I got the rear. So before I start drilling anything, I think it's time to go to the standard wheel stud first. Otherwise, I'd be drilling the holes for the studs and probably for the center.

Maybe after replacing the studs with the standard ones, I'll get lucky and the drum will slide on the hub all the way flat. The previous drums cleared the studs but didn't fit all the way on the hub.

Sometimes working on these things gets so aggrevating that I think of selling the car. But every time I go to the garage and see it the car sitting there, I'm glad I didn't.

Rick

Sometimes working on these things gets so aggrevating that I think of selling the car. But every time I go to the garage and see it the car sitting there, I'm glad I didn't.

Rick

Nah, you just can't let it get it to you. It doesn't have to be done today as your other car will get you to work and the grocery store. It's a hobby so take your time and enjoy it.

I don't know if you can go backwards to a 7/16" stud after a 1/2" stud has been installed. If it's not sliding on the stud at all, drill out the holes with a 1/2" bit first. Then if it hangs on the shoulder right at the axle just get a 35/64" bit and buzz the backside of the holes in the drum until it will slide on all the way. Matt and I both had to do the same thing with our disc brake rotors.

I don't know if you can go backwards to a 7/16" stud after a 1/2" stud has been installed. If it's not sliding on the stud at all, drill out the holes with a 1/2" bit first. Then if it hangs on the shoulder right at the axle just get a 35/64" bit and buzz the backside of the holes in the drum until it will slide on all the way. Matt and I both had to do the same thing with our disc brake rotors.

Good advice, you can't downsize the studs back to stock size, stick with the 1/2" studs, they are safer than stock 7/16" anyway.

........stick with the 1/2" studs, they are safer than stock 7/16" anyway.

X2...Dave is correct, 1/2" studs are stronger and safer than the stock 7/16" studs. Keep 'em!!!!!!

David F.

The studs on the car are 7/16. They are just longer than the stock ones. So I'm just going to replace them with stock ones that are shorter.

I got an email from Freddie (big gear head). He said that the hubs on the axles were either 2.780 or 2.810. So what I'm going to try and do is find some drums that are already 2.810. If I can't, then I'll have them drilled out to that.

I got to thinking after I saw the post from icpop. What lead me to look at the drums was because of vibration from the rear. I took the car to Driveline of Norcross, just north of Atlanta. We took out the driveshaft and when they spun it up to 3000 rpm, it didn't look like it was moving. Also got the pinion angles checked. 2 degrees down on the transmission, 1 degree up on the rear. Also, we pulled the drums and put the car through the paces. No axle problems.

That left drums and tires. And that was where I saw a problem with the drums. Also, I have Wheel Vintiques on the rear (originals up front) and they are lug centric and not hub centric. There is about a 1/4 inch gap between the wheel and the hub. After doing some searches, I saw where Eric Kammerer had a similar issue with ralley Wheel Vintique and them being lug centric.

I have some original 15 inch rims that I need to clean up, paint, and then I'll have the tires taken off of the Wheel Vintiques and put on the originals. Hopefully between getting the correct drums and original hubcentric wheels, I'll get rid of the vibration in the rear.

Rick
duskblue69