67 Corvette Trailing Arm Bolts Through the Frame Spacing

[Mark E.]

Re: 67 Corvette Trailing Arm Bolts Through the Frame Spacing

Gary,

It's hard to believe GM would allow an undocumented departure from the assembly instructions to go on for years. Especially an operation as critical as this one.

Maybe there are revised work instructions/AIM that we don't know about.

[Joe L.]

Re: 67 Corvette Trailing Arm Bolts Through the Frame Spacing

Mark,

The cotter pin in Alan's photo is not fully in a slot of the castle nut. It's hanging in the breeze. That is the problem. And yes, I think it was a potential safety concern until resourceful workers on the assembly line started to add an additional spacer, which in the case of multiple unmolested 66s that I've seen, including mine, was a 0.140" thick lock washer. Which as Joe points out, is not the ideal way to fill that space. But it works.

Next, we should talk about that same dog nose bolt, but used at the forward of the two horizontal bolts that attach the tongue/snubber mount to the front of the rear differential. The '66 AIM calls for two 103328 lock washers, each 0.140" thick, one next to the head of the snubber front bolt and one next to the castle nut. In that case, there simply is not enough space to use those two lock washers and still be able to insert the cotter pin.

So, GM was 0 for 2 in terms of accuracy in the AIM with regard to the proper use of that pilot tip bolt with castle nut and cotter pin.

Gary

Gary------


Yes, as seen in Alan's photo, the cotter pin would only prevent the slotted nut from coming completely off the bolt. It would do absolutely nothing with respect to preventing the nut from loosening which is the whole purpose of the slotted nut and cotter pin when installed properly and per UPC 0 of the AIM.

In fact, this "foible" might be the root cause of trailing arm shim loss reported on C2 Corvettes.

[Larry M.]

Re: 67 Corvette Trailing Arm Bolts Through the Frame Spacing

Gary------


Yes, as seen in Alan's photo, the cotter pin would only prevent the slotted nut from coming completely off the bolt. It would do absolutely nothing with respect to preventing the nut from loosening which is the whole purpose of the slotted nut and cotter pin when installed properly and per UPC 0 of the AIM.

In fact, this "foible" might be the root cause of trailing arm shim loss reported on C2 Corvettes.

Joe:

You can't just lose the "two-hole" shims.........without losing the bolt. Certainly the shims may loosen up a bit and the rear end of the car may get "squirrelly" if the bolt loses tension, but the shims won't fall out.

Probably about 2 bolt threads free play until slotted nut contacts the cotter pin and stops.

Larry

[Joe L.]

Re: 67 Corvette Trailing Arm Bolts Through the Frame Spacing

Joe:

You can't just lose the "two-hole" shims.........without losing the bolt. Certainly the shims may loosen up a bit and the rear end of the car may get "squirrelly" if the bolt loses tension, but the shims won't fall out.

Probably about 2 bolt threads free play until slotted nut contacts the cotter pin and stops.

Larry

Larry------


I should have said C2 that have been converted to slotted shims. In my 1969 with slotted shims and the nut and cotter pin installed properly, I never had any loss of shims in hundreds of thousands of miles of driving. No cotter pins were ever installed to retain the shims, either.

Also, it takes only a fraction of a turn of the nut before the assembly loosens. In addition to the other problems created, once the assembly loosens the bushing no longer acts as intended and, essentially, becomes non-functional. When it loosens, the trailing arm movement is around the bolt, not within the bushing.

[Gary B.]

Re: 67 Corvette Trailing Arm Bolts Through the Frame Spacing

Gary,

It's hard to believe GM would allow an undocumented departure from the assembly instructions to go on for years. Especially an operation as critical as this one.

Maybe there are revised work instructions/AIM that we don't know about.

Mark,

I've always thought that the AIM was revised regularly whenever a change was needed. But I don't know what really took place on the assembly line when the workers found an issue that wasn't dealt with in the AIM. The flawed design of the pivot bolt in terms of length might have been something that the line workers dealt with on their own and for whatever reasons a change didn't make it into the AIM until 1967. So, yes, years went by before it was officially addressed in the AIM.

I've always heard people say, don't restore a car or judge a car based solely on what the AIM says. Restore it or judge it based on how it left the assembly line. I've seen enough 66s to know that the T-arm pivot bolt and the front differential mount pilot bolt were not assembled as they are shown in the '66 AIM in terms of the washers or lack thereof.

Gary