Answer to 72 C10 cab mounts

[howzzzit]

Maybe someone has the answer concerning the cab mounting. Why did GM use 2 different diameter bolts and route one from the top to bottom and the other from bottom to top?

[Sheepdip]

Originally Posted by howzzzit

Maybe someone has the answer concerning the cab mounting. Why did GM use 2 different diameter bolts and route one from the top to bottom and the other from bottom to top?

Yes... the smaller diameter bolts are for the rear mounts and they face up from the bottom into a captured nut underneath your fuel tank, otherwise you'd have to pull the tank to change them out.
The larger diameter bolts are for the front, and they drop in from the floor board facing down.
Here's a reference video provided by Holley. The kit shown DOES NOT include radiator support bushings, they should be replaced at the same time.

https://www.holley.com/products/exte...6372962676&hsa

[LockDoc]

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Many times you will find that the head of the front bolts are tack welded to the floor recess. Probably to enable one person to install the nuts from the bottom on the assembly line.

LockDoc

[howzzzit]

Thanks. I know how they should be installed, but I am wondering why GM used 2 different size bolts and why is the front installed from the top and the rear installed from the bottom. Seems like the could have used cage nuts for the front as well as the rear. Must have been for their convenience? Just lay awake at night wondering. Ha.

[damnyankee36]

Any time I see a situation like this I figure it's purely an assembly line convenience as LockDoc mentioned.

And, as Sheepdip mentioned the rear are installed that way because of the fuel tank.

[RustyPile]

Originally Posted by LockDoc

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Many times you will find that the head of the front bolts are tack welded to the floor recess. Probably to enable one person to install the nuts from the bottom on the assembly line.

LockDoc

Mine were welded like that.. Normally, a floor jack can be positioned under the rocker panel to lift each side only an inch or two. Nothing has to be disconnected (fuel lines, ground straps, steering column, etc). Just loosen the bolts on the side not being lifted and remove the bolts on the lifted side.

Leaving the welded bolts in place, the body has to be lifted several inches... Lots of extra work.. Using a small Dremel and cut-off wheel, I cut the welds loose and removed the bolts.

[72c20customcamper]

The fronts can be replaced and tightened by one person with a little yoga involved I’ve done two trucks . The rear is because the tank was most likely installed before it was mated to the frame so they used cage nuts . They did it in a manner to facilitate ease on the line . No real regard for fixing them later .

[special-K]

On the front you want a bolt head up so there is a flat bolt head pulled down tight and not a bolt shank sticking up. The rear is because there is no bolt-through access without removing the tank. My guess is the tank is already installed in the cab before the cab is bolted to the chassis. Which is the opposite of how us home-built guys normally would do it.

[howzzzit]

Pulled back my carpet this evening. Guess I'm a really lucky guy. No tack weld on the front bolt head. Living right.