Does anyone know the size and length of the bolts that attach the rear spring and plate to the differencial ?

 

The length depends on the thickness of the spring. Just make sure the front two bolts are NOT to long. If they are, when you tighten them you will destroy your rear end.

https://www.zip-corvette.com/63-77-9...8aAurGEALw_wcB

 

I'm guessing I might have already done that ! when I took one out the grease started running out !!!

 

Per the P&A 7.529, bolt PN 3833486 measures 9/16 x 12 x 3 1/8”. No differentiation between 7 or 9 leaf spring.

My P&A covers 68-75 but I believe the bolt dimensions are the same all the way up to 1979.

 

Yep, that cover is done. You can get a HD replacement for about $150. Do not drive that car until it's fixed.

 

Can the cover be replaced without removing the whole thing ?

 

Not really. It's a whole lot easier to remove the differential with the crossmember. Besides, there's no way to get at the top bolts unless the crossmember is removed. And double check the bolt length. Do not trust what a supplier gives you to be correct.

 

No difference between the 7 leaf and the 9 leaf spring thickness,,,,, really? Depending who makes them, how they make them, the supplier, even one 9 leaf can be different than another 9 leaf. This is why people destroy their covers.
I put the spring in position, start the two rear bolts snug, make sure the spring is straight and flush, with car weight on it, then measure the total depth of the bolt. I found that you don't have much leeway for thread depth until it bottoms out. The two front grade 8 bolts I got had to be cut down a bit. Make sure you use the correct torque for the bolt size and year of car, they are different........ What you don't want to hear,,,,,"crack"!

 

This is straight from Eckler's..... Hummmmm.

IMPORTANT NOTE: Due to variations in the thickness of the springs and liners between original and replacement springs, it is recommended that you measure the thickness of your spring "stack", along with mount plate and lock washer thickness, plus penetration into the rear covers to determine correct bolt length. Excessive bolt length can cause damage to the differential cover.


1968 torque spec for center spring,,,, 55 to 75 ft/lbs with full weight on the rear. I think the later year cars were different.

 

Just a quick note for clarification. Our '68 has F41 - the 7 leaf spring had never been removed. I removed it last winter as part of an overall suspension rebuild and can tell you for sure that 2 of the bolts were shorter than the other two. I was also cautioned by Mike at America's Finest Corvettes (restored spring) and by Van Steele (restored the rear and other stuff). Best, Paul

 

New question.....if I remove the spring will the differencial stay up ? And it looks to me like there is enough room to get the top two bolts out of the cover without removing the cross member ! There is at least an inch and the bolts look like they should slide straight out unless they are really long !

 

I believe the answer to your question is 'no can do'. The only way to drop the diff without the member is to drill a hole saw from above and drop it that way. Some have done it, and will likely chime in. But dropping the diff/member isn't that bad. A few really good youtube vids, and lots of help here.

 

The diff is bolted to the cross member above the cover. There are four 7/16-14 bolts into the top of the cover. The cross member is bolted in to what many refer to as the Sombrero mounts, also by 7/16-14 bolts.

The old manuals, 40+ year old, have a procedure to remove the rear cover in the car. In fact that is the way they show to remove the diff, it is a bad one. Yes it can be done but you have to understand the diff is 100lbs of dead weight with almost 2 qts of vile disgusting gear oil in it. You can suck out a lot but you won't get it all so splitting it in the car will give you a nasty surprise. However, that's not the main concern, it's the safety factor. The diff is held in by the rear cover and the front snubber bracket so you better support the diff securely.

The best and safest way is to remove the diff from the car, keeping it bolted to the cross member, then work on it on the bench and reinstall as it came out. Yes I am aware of the old hack way of cutting the floor out over the 4 bolts in the crossmember, I never liked that method but it has been done for 60 years by some.

If you are going to go through all the trouble of pulling the diff, do your homework on what to look for inside with the cover off, it might save you a job later. 76's had issues with loose RG bolts, weak clutches, and bad axles.

 

OK....thanks for all the info & help !

 

Hole saw? I just have to love these guys! Thanks, but NO Thanks!

 

OK, I guess I'm going to have to replace the differencial cover. It's not going to be fun for an old guy with serious COPD ! I now there are videos and posts about how to do it but......will someone post the procedure start to finish so I can print it out before I try doing this ????

 

Maybe you should have someone do it for you. Step wise, it's pretty simple, but it heavy, and getting the crossmember to release from the bushing caps might be labor intensive, especially it it's original. If you want to tackle it, we can provide you with the info.

 

You want someone with a lift and a transmission hoist doing this. It's simple to do with the right tools. Dangerous to do without.

 

Is there a way to leave the axles and shafts hooked up, remove the crossmember bolts, then lower the diff just a few inches to get to the bolts on top?

 

Agree. Not all that bad with the right tools.



It can actually be a bit of fun with the right tools. Removed and installed ours with the help of a good trans jack and our son. As the videos show, loosen but don't remove the two cross member bolts; soak the bushings with penetrating oil; use a pickle fork and a 3 lb hammer; and it'll drop onto the bolts. This pic is after install and safety chains removed.