Rear end ?

[70GMCer]

Why did GM make 2 different types of rears for these trucks? That is, why are some leaf spring, and others are coil spring. Mine is leaf. What is the mounting of choice, and why? This is something I'm curious about......

[tomatocity]

GMC came with leafs standard with the coil option. Chevy came with coils standard with the leaf option.

[cableguy0]

not completely sure why they did it but the coil sprung trucks handle a ton better and are much better for planting the power to the ground dont have problems with spring wrap or wheel hop

[flip66]

I think it was the coil road and handled better and the leaf can handle more load.

[Longhorn Man]

leafs and coils in 10 and 20 seriews are both rated for the same amount.
Not ALL GMC's of the era came with leafs standard, my old 69 Short/Fleet had coils, and no mention of it on the listing...I've seen quite a few GMC tru7cks with coils and not being listed...and even a leaf sprung GMC, that had it listed in the option list.
The coil set up that actually started in 60 if I recall, was put into use so GM could use that set up on the stock car circuit. Back then, stock cars had to be pretty close to stock. (go figure) Your typical car wasn't really long enough to handle those huge trailing arms, so they said stab them under a truck. I think it's the bush cars, still have this set up today.

In all reality, for what most of the ppl on this board are looking for (good ride, lowered ride height, added morse power) the coil spring set up is WAY more desirable. Those trailin arms act like traction bars... so wheel hop is pretty much not going to be an issue.

One day, I may just have to slap the coil spring set up under the old longhorn. I do like the idea of being able to load what ever I want in the back and pretty much not worry about it, however, in all reality, it is a bit on the overkill side.

One draw back on the coils... in my observations, mine didn't tow worth a dam. True, it was a 1/2 ton, SWB truck, however, above 55 even with U-haul's smallest closed top trailer, it became a white knuckle ordeal.
Granted, that is the ONLY coil spring truck I have towed with, and it did have 500,000 miles on it and from the looks of the rotted and partially missing bushings... they looked original.

[70GMCer]

So, is a coil spring rear a direct replacement to a left spring rear?

[Joe67]

It is if you weld on the rear trailing arm mounting brackets

[pjmoreland]

I've heard that since leaf springs are farther apart on the axle than coil springs, the leaf springs do a better job of handling tall loads that want to tilt side to side (like big campers).