'66 T-arm pivot bolts vs aft, front diff mount bolt; Different GM part numbers

[Gary B.]

Re: '66 T-arm pivot bolts vs aft, front diff mount bolt; Different GM part numbers

GM was consistent.

Gary

[Joe L.]

Re: '66 T-arm pivot bolts vs aft, front diff mount bolt; Different GM part numbers

Joe,

Once you acquire the NOS 3846867, please post the actual length. It's interesting that the stated length is 4-9/16", which is 1/8" longer than the Paragon reproduction. Attached is a photo showing a Paragon repro bolt installed in my '66 fame, and lightly torqued. As you can see, the hole for the cotter pin isn’t within the slot in the castle nut. So the cotter pin would not be properly captured by the nut. The ’67 AIM shows the addition of a lock washer which isn't shown in the '66 AIM. Nothing else changed in the AIM, so it must be the case that someone realized the cotter pin and castle nut did not function as designed and there needed to be a cheap and simple way to move the nut outward, hence the addition of the lock washer. Of course, a lock washer is not needed when a castle nut is used, so the lock washer isn’t doing what lock washers are normally supposed to do.

The fact that the length of the GM is 4-9/16", means the problem with the excess length would be exacerbated when using original GM bolts compared to the Paragon reproduction bolts.

It turns out the original pivot bolts on my '66 both had an outboard lock washer. So even though that lock washer was not shown in the '66 AIM, it appears the production line for late model year '66 was adding the lock washer before the AIM was eventually revised in 1967 to add the lock washer.

Gary-------


The GM #3846867 I'm getting will not be NOS. However, it will be a known-original removed from a 1965 Corvette. I'll report on its length when I get it.

By the way, the flat washer in your photo appears thicker than the GM #3693853. As I previously mentioned it is 3/32" thick.

[Gary B.]

Re: '66 T-arm pivot bolts vs aft, front diff mount bolt; Different GM part numbers

Joe,

Thanks for the tip on the flat washer. The washer in my photo is what came with the Paragon T-arm pivot bolt kit. It's about 0.117", or about 25% thicker than 3/32". Paragon has no excuse for not sourcing the correct washer, as AMK make a correct repro in zinc with the 0.09" thickness. I'll order some when I place my next order with them. Of course that will make the length problem slightly worse. But I think by adding the equivalent lock washer (GM #103328) that came on my '66 and is called out in the '67 AIM, I'll be OK.

Gary