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Old 07-10-2011, 07:40 PM   #1
SkeksisNV
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3/4 to 1/2 ton conversion

I have a 1971 GMC 2WD 3/4 ton pickup that I am considering switching to a 1/2 ton for 5 lug wheels and possibly lowering and bagging. I have a 1980 GMC Sierra Grande 1/2 that is pretty much scrap. Can I use the '80 for as a donator truck and use the suspension to make the conversion? If so, what is all involved? I have seen some conversions on here using late 80's models for their parts, I wasn't sure if the '80 would work fine.

Also the '71 and '80 both uses leaf springs. I see a lot of ppl using coils and trailing arms on there half tons. Is there any advantages/disadvantges to using coil/trailing arms vs leaf springs?

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Gary
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Old 07-10-2011, 07:58 PM   #2
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Re: 3/4 to 1/2 ton conversion

SkeksisNV this is a really common conversion. You can do it several ways using the donor parts. If the motors are coming out already, you can swap the entire front crossmember. If your not pulling motors, its easier to swap to the later control arms. You can also convert using your existing control arms, but you will need to change balljoints to match.

In the rear, trailing arms were more common on Chevrolet's and leaf springs were the norm on GMC. Either brand was available with the opposite on C-10s, but the coil spring was the most common set up.

There is nothing wrong with either system, so you decide.
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Old 07-10-2011, 08:27 PM   #3
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Re: 3/4 to 1/2 ton conversion

Thanks for the info N2Trux. Just went down and looked at the crossmembers and looks like it would be pretty easy. Not a big deal to pull these engines on these trucks either.

Anything I need to know about taking the dana rear end out and putting the 12 bolt in?
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Old 07-10-2011, 09:01 PM   #4
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Re: 3/4 to 1/2 ton conversion

The '80 rearend will have different shock mounting points.
You may have to remove the shock mounts off the 3/4-ton rearend and weld them to the '80 1/2-ton rearend.
You will need to bend up a few new steel brake lines as well.
Alot of people before you have done this swap.
So it's nothing new.

If I were you,...
I would install a set of ECE's (3/4 to 1/2 ton) conversion spindles.
They bolt right on your 3/4 ton front end.
Swap nothing else.
They allow you to use 1/2 ton rotors and calipers.
Simple for what you are wanting to do.
Are you lowering it as well?
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Old 07-10-2011, 09:26 PM   #5
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Re: 3/4 to 1/2 ton conversion

I haven't made any decisions for what I want to do yet. Right now I am just kicking around some ideas. If I go from 3/4 ton to 1/2 ton, then chances are I may end up lowering and bagging the truck. I really don't know much about suspension so it will be all learning. Right now, just doing some research. I have that 80 truck and figured I would ask here to get some ideas and little learning in the process. I also may switch to rack and pinion steering once I actually learn what that does vs power steering. I am not a big fan of how these trucks steer with the power steering. I asked on these forums about a month or so ago about looking to change the steering so it acts more like vehicles do today with steering rather then how they do now stock and someone pointed me to another thread showing the Flaming River bolt in rack and steering. It didn't really explain what that does.
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Old 07-11-2011, 06:59 AM   #6
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Re: 3/4 to 1/2 ton conversion

Adding a rack style steering can be an expensive mod.
Have you ever thought about switching to a "quick ratio" steering box?
AGR make some nice steering boxes.
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Old 07-13-2011, 05:51 PM   #7
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Re: 3/4 to 1/2 ton conversion

Also with the spring perches for the leafs on the rear axle are different I do believe. They are a different width so you'll need to move them out around 1 1/2" on each side. The distance might be a little different it's been a couple of years but I know they are a little bit off.
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Old 07-14-2011, 12:42 PM   #8
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Re: 3/4 to 1/2 ton conversion

Here is pics of my drop with 1974 Chevy 1/2 ton front suspension. I used my crossmember from my truck and the front suspension and the 12 bolt out of the 1974 1/2 ton Chevy truck. You won't need to move the leaf spring perches. You might not even have to move you shock mounts, you'll have to check once you mock it up.Lolife aka Keith was my main source of info for my conversion.
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Old 07-14-2011, 12:46 PM   #9
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Re: 3/4 to 1/2 ton conversion

I thought I had some pics on my phone. I will send some when I get home
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Old 07-14-2011, 08:30 PM   #10
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Re: 3/4 to 1/2 ton conversion

Here are some pics of the old rear end that was in my truck, it was a 14 bolt corporate rear end of a 1973-1985 Chevy truck, I swapped it with a 12 bolt rear end out of a 1974 Chevy 1/2 ton. I also have the flip kit installed in the pics with the 12 bolt. The green rear end is my 12 bolt with etching primer on it before i painted it black. I did remove my axle shock mounts because they didnt line up with my frame shock mounts and there wasn't anywhere I could move my shocks to the frame that would give me the travel I needed for the shocks to work properly with the factory shock mount setup on the 12 bolt axle ( whew, that confuses me...lol) l
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