C2 rear leaf retaining bolt torque?

[Verne Frantz]

Regarding the metal retainer that bolts against the bottom center of the rear leaf spring, what is the recommended torque for those (4) 9/16 x 3.5" bolts?
Also, are the associated threaded holes in the rear casting blind?

Thanks
Verne

[ken edmunds]

Re: C2 rear leaf retaining bolt torque?

Verne, i do not know the torque but don't tighten the bolts until the wheels are on the ground and you have rolled the car back and forth a couple of times. If you tighten the bolts with the wheels off the ground you will break the rear and casting.

[Verne Frantz]

Re: C2 rear leaf retaining bolt torque?

Thanks Ken,
I had planned to do the job on a lift and unhook the leaf spring from it's end links so that it's static, under no load. One bolt is missing and I'm afraid someone may have already stripped the threads by doing it the wrong way.

Verne

[Alan Drake]

Re: C2 rear leaf retaining bolt torque?

From 63 Shop Manual Section 14, the Spring Center Clamp Plate is 55-75 ft.lbs.
Also see the AIM page D127 which mentions tourque on ground.

[ken edmunds]

Re: C2 rear leaf retaining bolt torque?

Verne, even unhooked from the trailing arm, there is still an arc in the spring under the spring plare.

[Verne Frantz]

Re: C2 rear leaf retaining bolt torque?

Thanks. Then that means an old fashioned drive-on lift, because no human being can crawl under a Corvette when it's on the ground.

Are the holes in the rear case blind, or do they go through an extended boss.? (sorry, but I can't recall seeing one dissembled before....) In case of potentially needed welding and retapping, I'd like to know if I need to buy a 9/16-12 bottoming tap ahead of time.......

Verne

[ken edmunds]

Re: C2 rear leaf retaining bolt torque?

Blind holes. A drive on is the way to go for this repair. Although, you can usually slither under the car on the ground far enough to tighten the bolts. I do and I am a big guy.

[Verne Frantz]

Re: C2 rear leaf retaining bolt torque?

Thank you Alan,
I'm surprised it's that high. This is a great and original driveline car and it deserves to be treated properly. I want to perform the best repairs possible. That's why I post my questions on this site.

Thanks
Verne

[Joe L.]

Re: C2 rear leaf retaining bolt torque?

Verne-----

Two other things besides what others have already mentioned:

1) You want to be sure to check that the spring center bolt does not have a head which is much higher than about 1/4". This could be a problem if either the spring or the center bolt has been replaced. The diferential cover has a hole in it into which the head of the spring center bolt must fit WITHOUT bottoming;

2) The 4 9/16" bolts that retain the spring MUST be the proper length----too long of a bolt will bottom and too short of a bolt will not allow enough thread engagement. The bolts should be the same as original length UNLESS the spring has been replaced. Some replacement springs are "thicker" or "thinner" in stack-up height than original springs, although they may otherwise perform perfectly. If the spring height differs from the original and you are using original or original length bolts, then the bolt length may need to be adjusted accordingly.

[Verne Frantz]

Re: C2 rear leaf retaining bolt torque?

Hi Joe,
Thanks for responding. After reading your post, I went out and checked things again. The car has a 7 leaf spring. (I always thought from reading that the 7 leaf was the HD spring, opposed to the 9 leaf). Anyway, the spring "appears" to be in the same shape as everything else, so for now, I'll have to assume it's original. Bushings are all dried up and the hardware has the same petina as everywhere else. I don't have any clues that it's been replaced.
I looked up through the hole for the missing bolt, and sure enough, there's the twisted off remains of the original bolt hanging out of the botton of housing. Now I know what I have to do.

Your first paragraph has stumped me though. You said "center bolt". Well, from the bottom there appears to be a center "stud" with a nut on it. Is that a bolt from above? Other than that, I'm looking at the flat steel retainer with 3 out of 4 bolts installed upward through it. The retainer is flat where the bolts and lock washers contact it. I see no recess for a bolt head. Maybe I misread your comment, but I really don't understand the issue you were trying to advise me of.

As for the replacement bolts, I was about to order a set for the 9 leaf spring, thinking that was the "standard spring", since there are no other clues that the car has any HD chassis equipment (master cylnder has been changed and I haven't pulled the drums). Given the 7 leaf (probably original) spring, what length 9/16th bolts do you suggest I should order?

Thank you as always for your help. The car thanks you too!

Verne

[Joe L.]

Re: C2 rear leaf retaining bolt torque?

Verne-----

The center bolt may appear to be a stud, but it's a bolt. However, it doesn't have a hex head. It has what they call a "fillister" head. This is just a round bolt head with no wrenching device. If you need to hold it (as when tightening the nut on the center bolt), you have to use a pair of vise grip or similar pliars. Most of the center bolts sold today, including the one from GM, have too thick a head for use on 63-79 Corvettes. The head has to be trimmed down to about 1/4" height. The only time that this bolt usually gets replaced is when the spring is disassembled for rebuilding. The new bolts are much longer than they need to be, but that's to make assembling the spring easier. The excess is cut-off afterwards. Most original springs have evidence of the bolt being rather crudely "chopped" off. NEVER use a washer under the head of the center bolt. This may interfere with the spring seating properly on the differential cover surface.

The 4 spring retaining bolts were the same for 7 leaf and 9 leaf springs. Usually, only F-40/F-41/FE-7-equipped cars received the 7 leaf. However, I have seen a few that were, apparently, originally installed on standard suspension cars. For example, I recall an absolutely known-original, very early 68 with base engine and THM that had a 7 leaf spring originally installed. I would use bolts that are the same length as the ones you removed as long as the spring is not being replaced.

[Verne Frantz]

Re: C2 rear leaf retaining bolt torque?

Thanks for the detailed explanation Joe. I understand the assembly now. I'll have to drop the spring to remove the broken retaining bolt, so at that time I can inspect the center bolt head to make sure it's not too tall.

What are some other clues to look for to determine whether this '64 has the heavy duty suspension? Front sway bar diameter? The shocks have been replaced.

Thanks
Verne

[Alan Drake]

Re: C2 rear leaf & F40 suspension

Went throught some of the same questions;

Front stabilzer d= .940
Front Spring d= .680 with a green tag marked as "EA"

The F40 spring will be shorter with a Free Height of 10.842 vs 15.40, however I have read here that the height does have other values - up to 12" as I recall.

Also believe that the rear shock shaft is different from regular suspension.

Hope these will start to help. It appears the real experts are at the show, so may be some more info will be posted tonight.