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88-91 Suburbans

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kpanza

1/2 ton status
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Lake Forest, Orange County, California
Ok guys, quick question - I'm pretty sure that you could not get a Suburban 2500 4x4 with the 454 engine, right? Only 2wd 3/4 ton with 454?? I don't know the reason, maybe someone on here does...

Also, what trans did the 88-91 2500 4x4s come with? Did they ever come with the 4L60??

Thanks, trying to help my brother find a Suburban - has to be a straight axle, wants fuel injection, wants to eventually lift it and bigger tires - also wants it to tow his Jeep and other vehicles. Anyone have any suggestions?

Also, does anyone know if it would be smog legal to swap a 454 into a 3/4 ton Suburban 4x4??

Thanks
 
10 bolt front, and 14 SF rear. Most were 4.10 gears. The 88 came with a 700r4, 89-90 came with 4L60 (same as the 700r4), and the 91s came with the 4L80E.
 
On the smog legal Q.... unless it came from the factory with it, then here in CA you would have a hard (or impossible) time smogging it.... but honestly, when I have gotten smogs, they enter in the vin, but never even check what I have in there. It passes, I paid and they didn't even care, so might be worth looking into. Unless you actually have to go to a smog place to have it inspected where they check everything throughly, then I am betting you can pull it off. The guys that get $6.25 an hour to run it through don't care....
 
From what I've seen the 3/4 tons of '88-90 get the TH400. The '91s get the 4L80E.
My '88 has the TH400, that's why I bought a gearvendors OD.

Why not get a 454 2wd model and make it a 4x4? I guess it just depends on how much work you want to put into the project.
 
Oh, the 91s came with the 4L80e?? Cool, that is much heavier duty than the 4L60e (if I remember right it's an electronic version of the T400 with OD). So they came with the 14bsf, huh? Well, a swap to the 14bff wouldn't be too hard if he ever wanted to that anyways...

What about the 454 in a 4x4? Did it ever happen or is it true that you could not get it? Thanks for the info, this will help him start off with the best mechanicals as a base!
 
Yea they did come with the th400s too. I forgot to mention that. Some even came with a Gear Vendors unit as well. (not sure if its actually Gear Vendors, or another company)
 
Ok, so the 88-90s had the Turbo 400 and the 91 got the 4L80E? Sounds good...

Yeah, I brought the 4x2 to 4x4 conversion up to him, but I don't think he is too keen on all that work - plus he lives in a new housing tract, and they would probably sh*t their pants if they even saw him changing his oil! ha,ha /forums/images/icons/smile.gif
 
GM didn't offer the 454 in a 4WD Suburban until the IFS rigs came out. /forums/images/icons/frown.gif Until then it was a 2WD only option.
 
Kieth I know of a real cheap donor K5 that you could use to make a 2wd into a 4wd. The guy that bought my Blazers is about ready to get rid of the chassis. It's an 85 K5 with a 10Bolt front.
 
Thanks Richard, but my brother isn't very interested in doing such a swap...he doesn't have the tools, time or space to attempt anything like that. So I think he is fine with the 350 in the 2500s...I'll have him throw on some Vortec heads, a cam and stuff and he'll be happier. He is trying to find a 91 with the 4L80E, but if not, I almost have him talked into throwing on a Gear Vendors overdrive unit on a regular Th400! /forums/images/icons/smile.gif I guess he has spotted a clean 89, so we might go look at it this weekend...
 
The gear vendors is a really nice unit. I put one on my '88 K30 crew cab, 6.2L diesel, and it made a world of difference. Mostly in driveability. Fuel mileage increased some as well.

Holley makes a supercharger kit for the TBI motors. Complete kit is about $2900, said to add 100 HP. Flowmaster is the only company I found to offer a exhaust for the '88-91 'burbs. I have it on my '88 and like it, 3" manderal bent with a big block series muffler. So far all the headers are for the IFS trucks, manifolds dump in slightly different angles with crossover too the RH instead of LH side.
 
I just talked to a guy at Gear Vendors, sounds like one sweet unit and fairly easy to install also. You lose some length in the rear d-shaft, but the Burbs are long enough that it isn't that big of a deal...if he ends up going with a pre-91, I think I can talk him into getting the GV unit. Supercharger, huh?? /forums/images/icons/smile.gif I can get a discount on Holley products...hmmm!! *Big smile sweeps across my face* ha,ha
 
Before you go all out with the Gear Venders unit, check out US Gear @ <a target="_blank" href=http://www.usgear.com>http://www.usgear.com</a> Their's is a true 2 speed aux. transmission. Gear Venders is an overdrive unit and has been known to have reliability problems and can not be used in an underdrive design as the US Gear can.
 
Mine is a 1990 with a T400 but the shift indicator has P, R, N OD, D, 2, and 1. I think one of the previous owners swapped out the OD tranny. Another gear would be nice. Mine is a 3/4 ton with a 350.
 
If yours is a 3/4 ton, I don't believe the 700R4 trans was available. I'm sure that the T400 was the only available trans in a 3/4 ton. 4L80E was available in 91 and it's possible that yours could have had one of these, but unlikely. I built an 88 3/4 ton Sub with T400, NP208 and US Gear overdrive aux trans with 1 ton 4.56 axles and a 513 Caddy engine for towing my 29' trailer. US Gear unit was just awsome and worked very well for towing. Can't go wrong with the US Gear unit.
 
One draw back of the US Gear unit is that it can't shift under power. The GV unit can shift under full power. I had a doug nash unit, early us gear, and I still prefer the GV design. The GV unit uses a constant mesh planetary gear set, same design as an automatic trans. Also the US gear unit can fail between gears, if the electric motor jams, shorts out etc. If the actuator on the GV were to fail(its a simple solenoid) the shift mechanism is spring loaded to return to direct drive.
The down fall of the GV is that it costs more.
 
my 1989 3/4 has a th350 and a 8-lug 10b and a 8-lug 14b sf, 3.73 gears, most i've seen have 3.73s and th trannies not 4L blah blah blahs. the 4L trannies are elcetronic TH trannies are vacuum.
 
does the gv od go between the trannie and t case or behind the t case? how is it shifted? do you have a separate shifter or does it work with the column shifter? thanks,
jason
 
The GV unit mounts standard on the rear of the t-case. The person I talked to at GV says they can supply adapters to mount between if you want. Seems some customers in alaska have them mounted between the 'case and trans.

Shifting is done by a button. In my case I use a flow mounted dimmer style button. It also has an auto function that kcks in at 45mph.

As far as trans designations go:
GM changed how they identify transmissions several years ago.
TH400=3L80
TH350=3L60
TH700R4=4L60 w/electronics is a 4L60E
TH440T= 4T60 or 4T60E etc.
 
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