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1/2 ton verses 3/4 ton 91 Suburaban

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tch777

1/2 ton status
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So what are the differences in a 1/2 verses a 3/4 ton 1991 GMC Suburban?
I know the rear axles are different 10B verses 12B and the rims on the 3/4 ton are 16 inch with 8 lugs.

Is the frame the same?
Are the braking systems the same?
How are the brakes different?

Basically I want my 1/2 ton to be a 3/4 ton. And I have too much in this 1/2 to sell it and start over.

Also I searched but couldn't find the whole answer:
If I find a 90 to 91 sub or truck with a 350 and a 4L80E what is needed to drop the tranny in and mount it to my 241 transfer case?

Thanks

Tim
 
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Actually the 3/4ton has a 14BSF some are 6 lug, but most are 8 lug. While you're swapping anyways, you'd be better off using a 14BFF, since if you break an axle your wheel wont go flying down the road. You can also change your front to 8 lug pretty easily or just swap it too. There's a ton of writeups on the 8 lug conversion, if you can't find them let me know. The braking system is larger and more powerful. IIRC the MC is larger, and the rotors in front are larger, as well as the drums in the rear. I don't know about the frame, but I've heard people argue about it before. I think some years are different, but some are the same. For the motor tranny you'd need the computer that controls the 4L80e also, but I'm not sure if you'd need anything else.
 
12 bolts are 1/2 ton rear axles.

A 3/4 ton would have a 14BSF in the rear as was said. The 4L80E is a th400 so it should bolt up to a np241 that has 32 splines(your th700r4 does not, should be 27 splines)

Brakes are physically bigger. That's why the 3/4 ton has 16" wheels, because the 15" wheels would not fit up front with out grinding the calipers.
 
i think they nailed the 'biggie' differences.. (brake system & axle)...
front roters (dia. x thick) 11.86 x 1.29 vs 12.50 x 1.29
facing contact: 37.63 vs 42.98 (think this is also called 'swept area')
rear drums (dia x width) 11.15 x 7.75 vs 13.0 x 2.5
facing contact: 107.42 vs 116.73
I think the 2500 also had a hydro brake option as well.

but my 91 spec book also lists some frame differences. (I think it's partly in 'engineer speak). The side rail wideth & depth are the same, but thickness is .177 vs .192
The section modulus (rails only, cu in) is 3.57 vs 3.88
the RMI (NFI what that is) is 139,230 vs 151,320 lb/in

I think part of that extra beef contributes to the larger numbers for tow-ratings. Towing also adds in the tranny & engine oil coolers. Krazy enough, it also advises the speed control & comfortilt steering wheel!

I can give u the exact numbers for engine/axle combos if ya want..
 
Thanks for the information.

That fills me in very well.

Looks like I will just make this Sub a HEAVY half ton and be happy with that.

Later

Tim
 
I am pretty sure that the 4L80E didn't appear to 1991 and is worth skipping the 1990's for.
 
91 lists the RPOO codes MX0 for both 4L80-E & 700R4 and indicates the 4L80-E was only in R (2WD) models & 8600 GVWR.
 
If you're saying the 4L80E was only in 2WD, that's incorrect, there's a '91 3/4ton 4WD in my driveway with a factory 4L80E, but maybe I just misunderstood your point. The '91 1/2ton version had a 4L60E (aka700R4). For '90 the 1/2ton had the 700R4, and the 3/4ton had the TH400 (basically a 4L80E minus the overdrive and electronic control). I agree, cc, the 4L80E is well worth skipping the '90 TH400's, I get crappy milage even with overdrive, and can't imagine what I'd be getting without it.
 
FYI
My 1991 GMC suburban has a 700R4 not the 4L60E. I checked with the tranny id guides and mine is a 700R4 even asked the tranny guys when they serviced it the first time and he confirmed it.
 
mini_mull said:
It's the same tranny, they just changed the name.
Click to expand...
no its not

700R4 was changed in name in 91/92 to the 4L60, then in 93/94 it went to electronic controls, name changed to 4L60E

Turbo 400 was hydraulic shift 3 speed, in 91, a 4L80E became avalible, it was pretty much a Electronicly shifted T400 w/the addition of OD
 
tch777 said:
FYI
My 1991 GMC suburban has a 700R4 not the 4L60E. I checked with the tranny id guides and mine is a 700R4 even asked the tranny guys when they serviced it the first time and he confirmed it.
Click to expand...
4L60E was not in trucks till at least 92, but they are discusing the 4L80E
 
tch777 said:
FYI
700R4 not the 4L60E.
Click to expand...

I said these are the same. We AGREE! I know we were discussing the 4L80E before, but then tech777 mentioned he had the 700R4 not the 4L60E as quoted above. Which we both said was just a name change when they added the electronic controls. ;)
 
4L60E=700R4 auto OD with electronic controls and a new name
4L80E=TH400+overdrive with electronic controls

A lot of guys hate 700R4s cause they break. However, a lot of other guys run "built" 700R4s and never break them (like the ones from bowtieoverdrives.com). A stock TH400 or 4L80E is much tougher than a stock 700R4, which is why they came standard in the 3/4tons. Both need to be kept cool in order to not bust which is why the most important tranny upgrade is a tranny cooler and maybe a gauge. (Boy I'm getting good at regurgitating all the info I've learned on CK5, thanks for schooling me guys.)
 
Thanks... Im am running a 4L60E in a 91. Whith out a bunch of major work what favorable upgrades can be applied in steps in need be. I have a cooler (AZ) and due to my interest in a quad trailer or somthing multi purpose I dont want to be un prepared. Already looking into a 14b ff .. Thanks J.
 
Everyone has missed another important difference: springs. With the long wheelbase, the 1/2-ton sub rides pretty good, but the 3/4-ton version adds 62 leafs to the pack for dump-truck ride :haha: (oh yeah, and increased load capacity).

Some of the 3/4-tons also featured the adjustable proportioning valve in the back that adjusts rear brake pressure based on load (squat)
 
Yeah those 8-10 leaf rear packs realy stink for ride quality. I wouldn't exactly call the ride good though in my 1/2 ton, but that might have been because the leafs were too tired. IMO, all stock rides stink. The difference between load capacities is substantial and should be noted. I was planning to do air helpers to make up the difference while towing when I had my 1/2 ton.
 
Also, isn't it a good possibilty that the rear axle is actually a 14b full floater, as opposed to the semi float someone mentioned?

John
 
I thought the 3/4ton 4x4 burbs were all SFs, and the FFs were only in the 3/4ton 2wds (maybe w/BBCs). Confirm?
 
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