1963 Differential to spring cover bolts

[Ray C.]

[Harry Sadlock]

Re: 1963 Differential to spring cover bolts

Ray, Paragon has two hits, 9 leaf is 6647K and 7 leaf is 6646K.

Did they send you the correct kit?

Harry

[Wayne M.]

Differential to spring cover bolts - Length

3.575" overall, minus head 0.355 thk = 3.22" insertion, minus thick lock washer. All 4 bolts were the same, regular suspension or F40/41 (IMO). Only 1.0" is threaded.

[Joe R.]

Re: 1963 Differential to spring cover bolts

Hi Ray:

Good for you for not torquing those two front bolts! They can punch through into the differential casing and cause trouble that you don't need.

I, too, used the Eaton spring and the Paragon bolts, and the bolt length required considerable attention. At the time I got my Eaton spring, the Eaton leaf material was slightly thicker than the OEM material (I've heard that this may have changed by now). The result was that the total thickness of the Eaton stack-up was about 1/4 inch more than the OEM spring.

I believe Paragon sells two different length bolts. I concluded that the short ones would not get enough bite in the differential case, and that the long ones would bottom out in the front two holes. In the end, I bought the long ones and ground the ends off to get the desired length.

You can calculate the desired length using a set of calipers or perhaps a good ruler. Measure the thickness of the assembled spring and add the thickness of the spring plate and lockwasher. This total dimension, which I will call the "clamping thickness," must be achievable with the front bolts before they bottom out.

With the spring removed, run the front bolts in until they bottom out, then measure the distance between the bottom of the bolt head and the surface of the differential. I shortened my bolts until the minimum achievable "clamping thickness" with the bolts bottomed out was about 1/10 inch less than the previously measured thickness of the total stack up.

Regarding the spring arch, the spring should be almost flat, but arched slighly downward (maybe an inch or so), with the full weight of the car on it. If I recall correctly, my spring bolts did have to overcome a slight amount of arch when I torqued them, even though the full weight of the car was on the spring.

[Gordon Peterson #4961]

Re: Differential to spring cover bolts - Length

Guys, I just opened a brand new box of p/n 6647K from Paragon (for the 9-leaf spring) and the total bolt length is 3.90" with a 3.55" insertion length. Thank you Paragon! I guess I'll be doing some grinding.

Pete