1970 Rear End Cover

[Stephen B.]

The JG state's that the aftermarket rear end covers feature thicker casting bosses in the area of the threaded holes for the spring mounting bolts. I'm not sure how thick the bosses are suppose to be for a frame of reference. Does anyone have pictures, measurements, etc?

[Joe L.]

Re: 1970 Rear End Cover

Bunky------

The easiest way to tell an aftermarket cover from a GM cover is to check for the presence of the GM casting number. It's easily observed from the rear of the car. If there's a casting number there, it's GM; if there's not, it's aftermarket. Yours should have a 7 digit number beginning with "38". A 6 digit number beginning with "4" is a later GM SERVICE cover, also used in PRODUCTION for 1978-79 Corvettes. In that case, the cover will use 7/16" bolts for spring retention.

[Stephen B.]

Re: 1970 Rear End Cover

Thanks for your help Joe. What's the bolt size for the original 1970 cover?

[Joe L.]

Re: 1970 Rear End Cover

Bunky------

1970 originally covers use 9/16" bolt size. This size was used from 1963 through 1977.

[Stephen B.]

Re: 1970 Rear End Cover

Thanks again, Joe.

[Chuck R.]

Re: Yours look like this?

Ain't pretty is it

[Stephen B.]

LOL. Maybe after a few power shifts!!! *NM*

[Terry M.]

Re: LOL. Maybe after a few power shifts!!!

Actually I don't think power shifts will do that, unless something else is worn or broken. However, not reading and following the instructions in the FSM WILL do that when installing the rear spring.

[Wayne M.]

They're Special Bolts

As Joe has said, they are 9/16" shank. Also 12 threads to the inch and 3_1/4" long, per 1970 Corvette P&A30B GM catalog; Gr. 7.529, part # 3833486; although one's I've measured are about 1/16" shorter than that.

Note the short threaded section (only 1_1/8" threaded) "WB" headmarks are all I've ever seen on C2's, but there may be others.

Be sure not to use bolts that are too long, especially on the forward holes, as you may break through the blind hole machined into the bottom of the carrier and into the oil chamber. The short threaded section may have been designed to avoid this error.

[Stephen B.]

Re: 1970 Rear End Cover

Where exactly is the casting number on the rear end cover?

[Joe L.]

Re: They're Special Bolts

Wayne------

These bolts are long-ago GM-discontinued. I believe that the supercessive part number is also discontinued. As far as I know, they are not reproduced in any headmarking.

One thing that I long ago considered was obtaining a longer bolt with an unthreaded shank length about the same as these bolts. Then, cut off the threaded end to match the bolt's total length. The problem is I could find no longer bolt with an unthreaded shank length about the same as the unthreaded shank on these bolts----they were either too short or too long. So, my "clever idea" went for nought. However, I haven't given up yet. There might be some longer bolts out there with the correct shank length.

[Joe L.]

Re: 1970 Rear End Cover

Bunky-----

To tell you the truth, I've forgotten it and I'm away from home. There were only 2 or 3 castings used from 1963 to 1977, though.

[Patrick H.]

Re: They're Special Bolts

Joe,

Paragon item number 6647K

See link below

Patrick




http://www.corvette-paragon.com/cata...5-1AC358B8E835

[Joe L.]

Re: They're Special Bolts

Patrick------

Well, it's good to know that they are being reproduced. Now I don't have to "dink around" trying to modify standard bolts to get the correct configuration. Plus, one gets the correct headmarking as a bonus.

To be honest, I don't even know why I was messing around with the "clever idea" I mentioned, anyway. I have original bolts in excellent condition on my car and several sets of NOS original bolts "in reserve" in my collection [none for sale]. So, I'd have to live until I'm about 500 years old to possibly require more bolts. It's very doubtful I'll live that long.

[Wayne M.]

Upside down on flange attach to X-member

This one's a "303" cover ( '63 thru early '65 --- actually a "hybrid cover" from my early '65 with the coarse thread tapered filler plug of later '65 and up).

But the later "375" cover casing # is in the same place, and also upside down.