Alright guys, what's the real difference between 1/2 and 3/4 ton 67-72 trucks?

[turbobuick1]

In terms of parts the factory put on? Are the control arms different? How are the frames different, if they are at all? How about steering knuckle/spindles? Brake calipers, master cylinder?

I've tried searching the board a little, I was hoping someone could point me towards a good reference. I wonder if the factory service manual specifies the differences?

Share the knowledge with a newbie guys!

[sameyrasmea72]

Originally Posted by turbobuick1

In terms of parts the factory put on? Are the control arms different? How are the frames different, if they are at all? How about steering knuckle/spindles? Brake calipers, master cylinder?

I've tried searching the board a little, I was hoping someone could point me towards a good reference. I wonder if the factory service manual specifies the differences?

Share the knowledge with a newbie guys!

The difference = .25 ton I may be wrong on this, but I will take a shot.
Control arms same with different bushings
3/4 ton frames are a little thicker (I think)
not sure about the steering
spindles, brakes,master cylinder are all different, more heavy duty on 3/4 ton

[stich626]

I don't really know, but by looking at the 3/4 trucks and my 1/2 ton
I'd say rear axle and springs haven't seen a 3/4 with coil springs.. in the rear..
frame, I'd think is the same, but again not sure..
I also never seen a 1/2 ton with rear leafs ..
tho. 73 up they all do..

[greenbd71]

I am interested also in this info. I have a 1972 3/4 ton custom fleetside. If parts are more heavy duty then I am glad I have one.
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[60ratrod]

i've seen plenty of half tons with leafs. not all the half ton 67-72 chevy/gmc trucks got coils on all 4 corners. IIRC some half tons had 4 corner leafs. but the brakes, rear diff, spindles, and MC/prop valve were different along with the suspension, to allow hauling heavier loads

[Jessechop]

I have a 68 coil sping 3/4 ton, these are the differences I see:

Rear axle
Spindles
Hubs/drums/brakes
Booster
8 lug

I assume the springs are different (heavier rating) but mine has different springs in it so I cant compare

Otherwise I think they are the same. My truck has been rebuilt with a good share of stock 1/2 ton parts with no issues what so ever

[turbobuick1]

Well just to help out a little I have a '72 Custom C-20 truck, and if you go on rockauto.com to look up parts for any vehicle, by clicking on the blue part number you can see what vehicles the part fits. I can see that between a 1/2 ton and 3/4 ton:

1) The master cylinders are different.

2) Rotors / Hubs are different.

3) Brake booster is different.

4) The upper control arms are different.

5) The lower control arms are different according to LMC trucks and Brothers trucks.

5) The rear coil springs are heavier duty, as are the front.

Frame differences? Steering Knuckle differences? I don't know.

And what about rear axles? I'm used to the newer 10 and 12 bolt rear ends, and I'm under the impression my truck has a Dana rear axle. What's the facts on 1/2 and 3/4 ton axles?

[stich626]

Originally Posted by 60ratrod

i've seen plenty of half tons with leafs. not all the half ton 67-72 chevy/gmc trucks got coils on all 4 corners. IIRC some half tons had 4 corner leafs. but the brakes, rear diff, spindles, and MC/prop valve were different along with the suspension, to allow hauling heavier loads

in my post I listed that 73 up where all leaf..

figuring he's asking about the 60-72 set up....

[oldgold70c10]

The 3/4 ton frame is supposed to be made of slightly thicker material, though I've never checked mine to confirm. The frame has extra braces. If you've got drums all the way around, they are different front to back, and are a lot more powerful than 1/2t. Different master cylinder than 1/2. If you have rear coil springs, the control arm are reinforced. 4.10 ratio was as low as you could get (though I've read that some 4wd & big block could get 3.55 ratio in 3/4 ton). Full-floating axle in 3/4. And one of the cab mounts is different on 3/4. Other than that, body sheet metal and engine and transmission choices were the same.

[70truckguy]

I had a '69 3/4 ton side by side with my '70 1/2 ton. The front springs were taller, rear coils were thicker. The 3/4 had overload leaf springs on the back. I swapped springs to stiffen the ride. The front springs were either light or heavy from the factory (3/4 ton or big block were heavy). I did all of this 20 years ago when gm had factory parts available so it wasn't a problem to look it up. I remember the 3/4 ton having power brakes and 8 lugs, but can't recall anything else.

[Shyguy]

The 3/4 ton rear cab mounts on the frame are lower so thicker bushings are used to give a smoother ride in the cab.

The 3/4 frame is slightly thicker.

The trailing arms has a plate on them for added strength.

There is extra frame bracing on the cross beam that the trailing arms bolted to.

I am sure there may be afew others, but I can not remember.

[Spoof]

Sounds like a question for Special K.

[DaHos]

ttt
???

[DeadheadNM]

For 4wd applications:
1) longer rear leaf springs for 3/4 ton
2) Dana 44 front for both with the "big hub" 8-lug for 3/4 ton
3) 12 bolt rear for 1/2 ton while 3/4 Chevy's came with an Eaton HO52 and 3/4 GMCs a Dana 60

Not sure if frames are thicker: I have both here will check

[darush01]

my 72 custom 20 has all listed above and of course bigger wheels and tires I believe mine had 16.5 stock now has 16

[Mike C]

I think all leafs were 52" eye to eye, regardless of 3/4 or 1/2, it wasn't until the later square bodies that the 56" leaves came on the scene.

Four wheel drives got 2 1/2" wide leaves while two wheel got 2 1/4". Whether 1/2 or 3/4 ton. The exception was the Longhorn trucks that had 2 1/2" wide springs. Balljoints and spindles different on 3/4 ton trucks in addition to aforementioned extra bracing, thicker frames, and completely different braking systems.

Most 3/4 ton Chevrolet's, as well as some GMC's, had the HO5200 Eaton while some received the HO7200. Most GMC's and some Chevrolets had the Dana 60. I've seen leaf and coil versions of both.

My two '70 GMC parts trucks both had 4.57 gears in their leaf spring rear Dana 60's. One was a 4 speed Longhorn with a 350 and the other a 6 cylinder 3 speed. The big block truck was a 7500 GVW truck while the Longhorn small block was 6600 and the 6 cylinder truck 6200.

I'm sure there are even more differences than those covered here.

My '70 Sierra Grande big block truck had 3.54 gears.

[DeadheadNM]

Thanks Mike C - no difference in leaf spring length 3/4 vs 1/2 T 4wd: 52" on a 3/4 ton HD spring here at home: 2.5" wide at narrowest point.

[Mike C]

Another fact, 2 wheel drive trucks had spring perches on 42.5" spring centers while 4x4 had 40.5" spring centers. Once again, except Longhorns which also had 40.5" spring centers, so the Longhorn axle should be a bolt in 3/4 ton swap for a Blazer/Jimmy.

73-87 4x4 and 2x4 1/2 and 3/4 ton trucks had 42.5" spring centers while the one ton trucks were 40.5".

[Longhorn 70]

As for the Longhorn compared to half ton, ball joints have larger diameter tapers as well as the tie rods so spindles are different. Bearings in the front, rear ends, and sway bars are heavier on the 3/4 ton. I have noticed the frames are heavier on the Longhorn but I don't know if the width and thickness are the same as other 3/4 tons.

[SS Tim]

Here are the frame section and modulus numbers, 39k psi carbon steel through C30s. Note the increased section height, flange width and thickness changes of the frame as the series step up.

C Blazer
C10 115
C10 127 6.04" height 2.53" flange width 0.156" thick 2.98 section modulus

C20 127 6.11" height 2.46" flange width 0.194" thick 3.71 section modulus

C30 133 C20/30 Longhorns 7.20" height 2.77" flange width 0.194" thick 5.05 section modulus

C30 157 8.18" height 2.97" flange width 0.224" thick 7.29 section modulus


K Blazer
K10 115 6.02" height 2.71" flange width 0.141" thick 2.70 section modulus

K10 127
K20 127 6.09" height 2.75" flange width 0.186" thick 3.48 section modulus

[1972RedNeck]

Originally Posted by SS Tim

C30 157 8.18" height 2.97" flange width 0.224" thick 7.29 section modulus

That's a good frame.

[Mike C]

Great info Tim. I would have assumed that C and K frames had same rails, just different crossmembers. Interesting to see choices made by GM and all of the different components that had to be in the supply line.