91 Suburban Tranny

[mygmctruck1]

I have a chance to get a Free suburban auto tranny and transfer case .
in fact I can have the whole truck.
My question n.

will the tranny/transfer case fit my 68 K1500 4x4 GMC truck ok ?

will the radiator fit ?

[87Skier]

91 Suburban's came with 3 different automatic transmission options. 700R4, Turbo400 and 4L80E. All of these should fit, but may require a significant amount of work to get them in.

The radiator core is about the same size and the inlet/outlet is in the right place. You may need to modify the mounts, but it should fit in the hole.

[mygmctruck1]

Originally Posted by 87Skier

91 Suburban's came with 3 different automatic transmission options. 700R4, Turbo400 and 4L80E. All of these should fit, but may require a significant amount of work to get them in.

The radiator core is about the same size and the inlet/outlet is in the right place. You may need to modify the mounts, but it should fit in the hole.

The currant tranny is an O.D unit , should I assume it’s a 700R4 ?
You say a significant amount of work to install ? Can you give me a idea on what it would take ?
I already have a manual tranny with the transfer case ( Rockwell ) , I would have thought it would be pretty close to a simple swap out ?
I was original just going to put in a 700R4 period but this offer came along , so that’s the way I would like to go .
I’m actually wanting the automatic for the hilly city streets we drive on around the country.
Kind of hard with a stick when you have cars behind you on a steep grade .

[Mike C]

If it was the 4L80 that would be a score.

Is it a half ton? I have taken apart two different K20 subs to donate axles to Jimmy projects. 84 TH700 with 3.73 and an 86 that was TH400 with 4.10. You can use the front axle to convert yours to disc brakes but if gears don't match what you have, you will have to regear one end.

[mygmctruck1]

Originally Posted by Mike C

If it was the 4L80 that would be a score.

Is it a half ton? I have taken apart two different K20 subs to donate axles to Jimmy projects. 84 TH700 with 3.73 and an 86 that was TH400 with 4.10. You can use the front axle to convert yours to disc brakes but if gears don't match what you have, you will have to regear one end.

Not sure if it’s a 1/2 or 3/4 ton . But if it’s got the computer controlled tranny , i’m Not too excited about that .
I was hoping to keep the truck old school , much easier to work on for me.
This spring we went on a road rally , one of our friends has a 57 Chevy with modern fuel injection , tranny etc. he was having trouble the whole week we were out . Even though he had a reader , he still couldn’t get it right .

[87Skier]

It isn't a huge deal to swap it out for either one if you use the transfer case from the 91 Suburban. Probably the easiest thing to do is to keep the engine in the same place and allow the transfer case to move back. You will need to move the crossmember back and find or make a suitable mount to hold everything. The later transfer cases are a lot lighter and don't require the side mount or torque strut that was used.

You will also need to shorten the rear drive shaft. You might be able to get away with using the front driveshaft off the suburban. Exhaust might have to be modified. You may need to make a new shifter for the transfer case to get it to come up through the factory hole. The transmission will also need a cooler, so this will have to be added.

If the suburban is a 3/4 ton with overdrive it should be a 4L80. If it's a 1/2 ton, then it's a 700R4. Using the 4L80E will require either using the factory computer (wouldn't recommend), or to buy an aftermarket computer for around $500. The only external sensor these need are a throttle position sensor ~$40.

Swapping in a 700R4 will require the TV cable. Since it is behind a TBI suburban I suspect none of the bracketry will fit on your truck. If it's an early 4L60 (I don't believe any square body suburban's came with one) then the same controller and TPS would be required to make it work.

[mygmctruck1]

Just ran into a snag regarding the suburban tranny/trans case. My front pumpkin ,drive shaft is on the pass side. The suburban is on the drivers side . Which means , I would need to also use his front axle set up. For me not an option , unless the transfer case can be rotated 180 degrees ?

[Bigdav160]

Are you sure of the model year? 1991 Suburban should be a square body and IIRC are passenger side drops

[mygmctruck1]

Originally Posted by Bigdav160

Are you sure of the model year? 1991 Suburban should be a square body and IIRC are passenger side drops

I’ll have to clarify , owner says he thinks it’s a 92 but it could also be a 91 ?

[GASoline71]

Originally Posted by Mike C

If it was the 4L80 that would be a score.

I had a 1991 Suburban 3/4 ton with a 4L80E in it. Wish I still had that rig to thgis day.

Originally Posted by mygmctruck1

I’ll have to clarify , owner says he thinks it’s a 92 but it could also be a 91 ?

Bodystyle is completely different from 1991 to 1992 so it should be painfully obvious.

Gsry

[Patch]

Originally Posted by mygmctruck1

I’ll have to clarify , owner says he thinks it’s a 92 but it could also be a 91 ?

Well.....if it's a 92, that is a zero percent chance it will work for the front as you know it IFS.

[Ol Blue K20]

It would have to be a 92 to have a drivers side drop. This also means its an independent front end.

[mygmctruck1]

Ok , found out the suburban is a 92 , drivers side front drive shaft. Can I get a transfercase with a pass side shaft ? The tranny is a 700 r for sure.
It’s free and it sure would be nice to use it .

[Mike C]

You can adapt it to your transfercase. That's a $500 proposition though. There is no cheap way to do an OD swap in a 4x4.

You could get a TH700 or 4L80 from a 91 or earlier truck and adapt to your t-case. Or you could run it with the case it came with. Both solutions would require new driveshafts.

Do you have an integral or divorced t-case in your truck now? You could keep a divorced case and use a 2x4 trans, but none of the scenarios play out "cheap and easy" with the '92 donor.

[mygmctruck1]

Originally Posted by Mike C

You can adapt it to your transfercase. That's a $500 proposition though. There is no cheap way to do an OD swap in a 4x4.

You could get a TH700 or 4L80 from a 91 or earlier truck and adapt to your t-case. Or you could run it with the case it came with. Both solutions would require new driveshafts.

Do you have an integral or divorced t-case in your truck now? You could keep a divorced case and use a 2x4 trans, but none of the scenarios play out "cheap and easy" with the '92 donor.

My current tranny / transfer case is a new process manual set up . No way to adapt I don’t think .

[Bigdav160]

You can do a search on this site for TH700 or 4L60 and find out what it takes to fit.

I used an advanced adapter output shaft to mate a 4L60 to my NP205. I moved the engine mounts ~1.5 inches forward. I had to lengthen the exhaust, shorten the coolant hoses, move the shift linkage and install a different fan shroud. I like the driving experience but but isn't a easy direct swap.

[mygmctruck1]

What I am really looking to do is use the 700r for a 4x4 and get a transfercase designed for that tranny and a drivers side Shaft.

[Mike C]

I have an '84 square body suburban and it has a TH700R4 in it and what I would assume is a NP208 t-case. Not sure on that. So they are out there. You need to source from a square body solid axle truck though. Suburbans are usually the best (cheapest!) donor.

Your truck would have come with a Rockwell T-case originally and you won't find any adapters for one of those to a TH700.

[mygmctruck1]

Originally Posted by Mike C

I have an '84 square body suburban and it has a TH700R4 in it and what I would assume is a NP208 t-case. Not sure on that. So they are out there. You need to source from a square body solid axle truck though. Suburbans are usually the best (cheapest!) donor.

Your truck would have come with a Rockwell T-case originally and you won't find any adapters for one of those to a TH700.

Thanks