1965 Rear Spring Center Bolt Tightening?

[James W.]

Is there are rule of thumb on how tight the center bolt/nut should be on the rear spring assembly?

Should it be tightened or snugged up after the weight of the car is on the spring? I'm getting ready to reinstall my rebuilt rear spring and wanted to get some input before I get started.

Thanks,

James

[Joe L.]

Re: 1965 Rear Spring Center Bolt Tightening?

Is there are rule of thumb on how tight the center bolt/nut should be on the rear spring assembly?

Should it be tightened or snugged up after the weight of the car is on the spring? I'm getting ready to reinstall my rebuilt rear spring and wanted to get some input before I get started.

Thanks,

James

James-------

There's no way to tighten the nut on the spring center bolt after the spring is installed in the car since there is then no way to retain the bolt head from rotation. It's completely unnecessary, too. Just tighten the bolt with the spring out of the car by retaining the round bolt head with vice grip pliers or similar tool and tighten the nut to standard torque for a 5/16-18 bolt of SAE grade 8 (about 20-25 lb/ft).

Also, make absolutely sure that the round head of the center bolt does not exceed about 7/32" in height. New center bolts, even those once available from GM, have a taller head. That can cause the cover to be cracked when the spring center plate bolts are tightened.

[Patrick H.]

Re: 1965 Rear Spring Center Bolt Tightening?

FYI, we used a new bolt when rebuilding the rear spring in the 63. It stripped at less than 20 lb/ft. And yes, we had already ground down the head to a usable height.

Reinstalled the old bolt and it worked just fine.

I use two clamps, one on each side of the bolt location, to draw the spring together and make it easier to tighten the center bolt to spec.

[Gary B.]

Re: 1965 Rear Spring Center Bolt Tightening?

James,

I’ve done what Patrick does, but with one C-clamlp holding the leaves tightly together. I, too, have sheared off a reproduction center bolt when shooting for 25 ft-lbs. The spring center bolt tightness is not critical once the spring is fully installed in the car, at ride height, with the four center spring bolts fully torqued.

Gary

[Joe L.]

Re: 1965 Rear Spring Center Bolt Tightening?

FYI, we used a new bolt when rebuilding the rear spring in the 63. It stripped at less than 20 lb/ft. And yes, we had already ground down the head to a usable height.

Reinstalled the old bolt and it worked just fine.

I use two clamps, one on each side of the bolt location, to draw the spring together and make it easier to tighten the center bolt to spec.

Patrick------

The bolt you used must have been a grade 5 (or, if marked grade 8, not made to grade 8 specification). Grade 5 torque spec would be about 13 lb/ft.

[Patrick H.]

Re: 1965 Rear Spring Center Bolt Tightening?

Patrick------

The bolt you used must have been a grade 5 (or, if marked grade 8, not made to grade 8 specification). Grade 5 torque spec would be about 13 lb/ft.

No matter what the grade, if they sell it as the rear spring bolt they should make it match the original specifications.
I know I ask a lot of the reproduction people.
They'd also make a short head to the bolt if they really paid any attention at all.

[Joe L.]

Re: 1965 Rear Spring Center Bolt Tightening?

No matter what the grade, if they sell it as the rear spring bolt they should make it match the original specifications.
I know I ask a lot of the reproduction people.
They'd also make a short head to the bolt if they really paid any attention at all.

Patrick------

Yes, I totally agree. However, even the spring center bolt that was available in GM SERVICE for many years had a too tall head. So, I expect what is being reproduced is the GM SERVICE bolt and not the one actually used in the manufacture of these springs. I have never seen a GM SERVICE bolt that was not of the tall head variety. I wonder how many differential covers were cracked over the years as a result of the use of these bolts?

[James W.]

Re: 1965 Rear Spring Center Bolt Tightening?

I'm using a repro bolt that I bought from LIC about a year ago since the threads on my original bolt were too badly damaged to reuse. I machined the bolt head down to match the original bolt length. I'll probably clamp the spring on each side of the bolt and torque it to 15 ft/lbs. and call it good. First picture - the original bolt on the bottom, repro machined to match the original in the middle and the size of the current repro that they send you on the top.



Thanks,

James

[Joe L.]

Re: 1965 Rear Spring Center Bolt Tightening?

I'm using a repro bolt that I bought from LIC about a year ago since the threads on my original bolt were too badly damaged to reuse. I machined the bolt head down to match the original bolt length. I'll probably clamp the spring on each side of the bolt and torque it to 15 ft/lbs. and call it good. First picture - the original bolt on the bottom, repro machined to match the original in the middle and the size of the current repro that they send you on the top.



Thanks,

James

James------

From what I can see of it, the repro bolt headmarking looks like it's SAE grade 5. So, 13 ft/lbs should be about right.

Also, the repro bolt obviously has a much larger head diameter than the original. The GM bolt once available did have a taller head but it was of the same OD as the original head. So, the repro bolt is not just a copy of the GM SERVICE bolt.