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post #1 of (permalink) Old 01-10-2001, 11:50 AM
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Difference between 1/2 ton or 3/4 ton rear springs

This one is puzzling me....

I have a 1984 3/4 ton Chevy 4x4. Stock it had an 8-lug 14 bolt SF rear axle but I installed a 14 bolt FF in its place. My truck has 7-leaf rear springs.

The donor truck that I got the 14 bolt FF from was a `79 Chevy 3/4 ton. It had 9-leaf rear springs. I saved the springs, as they were in good condition. Now, here's the rub - I parted out a 1/2 ton Chevy 2WD (5 lug wheels) a couple of years ago that I also saved the rear springs from -- and they are of the 7-leaf variety. I thought they had fewer leafs, but noticed they were 7-leaf last night when I was moving some parts around.

Does my `84 3/4 ton have 1/2 ton rear springs in it or is the spring constant of the springs in the `84 higher (ie stiffer springs) to make them 3/4 ton springs???

Thanks for any insight.

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post #2 of (permalink) Old 01-10-2001, 02:02 PM
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Re: Difference between 1/2 ton or 3/4 ton rear springs

Just a thought but the springs from the 79 could be heavy duty springs.
However I just went outside and looked at the springs on my 81 3/4ton and it has 7 leafs and an overload spring,and I know it has heavy duty rear springs.
Ahh talking out loud now,but could chevy and gmc have changed the number of leafs in 81 when I know they changed a bunch of other stuff on the trucks?Anybody else have any ideas?

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post #3 of (permalink) Old 01-10-2001, 02:28 PM
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Re: Difference between 1/2 ton or 3/4 ton rear springs

I know that the newer vehicles have fewer but thicker leafs. My '85 K20 (8600lb GVW) has 7 leafs plus the overload. My old 1980 K10 also had 7 leafs plus the overload. Big difference in spring rate though. 1500lbs in the box would flatten the 1/2T down clean to the overload. Only drop an inch and a half in the K20 with 2000lbs. A guy I work with here has an '87 K20 (7200lb GVW) and it has only 5 leafs plus the overload. Also a big difference in spring rate, 1500lbs puts it down the overloads too - he put on those hellwigs to compensate. Another guy I work with has a '96 Dodge 3500 dually. It has only 3 leafs plus overload. It drops 1 inch when loaded with 1500lbs in the back. I'm not sure how the leafs affect ride quality, but I think that more thinner leafs give a better ride and that fewer thicker leafs are stiffer, but I could be wrong. Materials used have improved over the years as well.

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post #4 of (permalink) Old 01-10-2001, 02:32 PM
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Re: Difference between 1/2 ton or 3/4 ton rear springs

The 1/2 ton chevy you parted out was probably what is refered to as a "Heavy Half".
They (GM) put 3/4 ton springs on 1/2 ton trucks. Some trucks even had factory stickers on the bed that said "Heavy Half", very simular to the "Z-71" stickers

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post #5 of (permalink) Old 01-10-2001, 03:42 PM
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Re: Difference between 1/2 ton or 3/4 ton rear springs

I think you are on the right track with the spring constant. The total number of leaves in the spring packs does not necessarily make one spring pack the same or different from another. You can take a spring pack with two leaves and make it much stiffer than a pack with nine leaves......it all depends on the thickness and the length of the leaves.
After all of that, there is a chance that the springs you have are the same. It's pretty common, at least around here, for people to swap in 3/4 ton springs on their 1/2 tons.......or as already mentioned it could of possibly have been a factory option for the "heavy half".

post #6 of (permalink) Old 01-10-2001, 05:26 PM
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Re: Difference between 1/2 ton or 3/4 ton rear springs

here's a kick in the pants, i just counted mine and it has 4 leaves and a overload spring. 84 swb.1/2ton 4x4.

MIKE.S 84GMC,454
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