I got a 79 gmc 4x4 with th350. can I put a 700r4, its out of a 88 chevy. will it work? or am I crazy?

This is where I would start. I'm sure they can answer any questions you may have.

http://www.700r4.com/faq/faq.shtml

I got a 79 gmc 4x4 with th350. can I put a 700r4, its out of a 88 chevy. will it work? or am I crazy?



Been there, done that. It can be done.

I'm ASSuming the tranny you take out of the 88 is a 4x4 tranny.
You can use a 2wd version with and AA shaft or a custom spacer.

You can buy a special output shaft from advanced adapters ($$$$) to mate to your t-case (assuming you have a NP203 seeing as how it's a 79 and TH350, but can also be done with an NP205), but I would not do it that way. I did and found the driveshaft CV to 700r4 pan clearance was negative (it hit a stock pan). I had to mod the pan and that sucks. Others have run a spacer between the trans and t-case and that seems to work best. Either way you will most likely have to shorten the rear driveshaft and lengthen the front so be aware of the added costs of that. You will also have to modify your t-case shifter as it will sit farther back. I cut mine and welded in a lateral spacer to push the top of the shifter foward but keep the bottom portion the same (mine was an NP205 t-case though).

I had a local tranny builder modify and warranty my tranny as the 700's are not know for being super strong. I run mine daily towing a 18' enclosed landscape trailer and run in the street legal truck pulls. I love the lower first gear and my wallet likes the overdrive mpg's. I will say that I am saving and planning on swapping in a 4L80 as I know the 700 will not last a long time doing what I am doing (plus I just swapped in a healthy BBC).

What are your plans after the tranny swap? Reason I ask is it may be cheaper to start with a 4L80 if you plan to flog it. The 700 can be made to take some moderate abuse assuming the builder knows what he/she is doing, but they do have their limit.

PM me if you have any specific Q's about the swap.

I have had nothing but probs with the th350. I got the 700 so I thought what the heck! the only thing that I'm not sure about is there is some sort of electical fitting on the trans, I think for overdrive but not sure. how long did it take you to do the whole project? and cost$$ without labor?
plans are to drive it and hove some fun in mud, nothing hard core.


and would a th400 be easier to do and they are 4 speeds right? because I want to drive about 75mph for about 1500 miles.

TH400 is a 3 speed. It is considered a heavy duty trans (used primarily in one tons and almost always when a big block was used back in the day). It will be stronger than the TH350 but will be expensive to swap as it is different in size, uses a different style adapter and t-case and possible driveshaft mods.

The electrical connector on the trans (if it's a 700R4 and not 4L60E) is for the torque converter lockup. The overdrive is not electronic, it's mechanical/hydraulic and selected with the gear shift.

My 700R4 swap cost me ~$2500, but yours can be much less.

Here is the breakdown of mine:
700R4 cost (bought used for $200)
700R4 rebuild with new converter ($700 and a few favors)
Wiring to lockup converter ($15 homebuild system)
New Driveshafts from High Angle Driveline ($1000)
Crossmember and frame mods (Free...just my time tools)
Reworked T-case shifter (Free...just my time/tools)
Exhaust mods ($100 My custom duals hit my relocated t-case and needed fixing, yours my not)
Fluids ($??)
Tranny Cooler ($75?? I bought the B&M extra large stacked plate cooler and adding cooling is a MUST for a 700R4)

Again, I did it for two reasons:
1.) Added MPG as I use this truck daily
2.) I have a tranny builder who is really good with 700's

I also new going in that at some point I would change again as I only had a slightly modded SBC 350 and good gearing (4.56's with 33-35" tires).

Now that I have a BBC 454, I know I'm on borrowed time


I have had nothing but probs with the th350. I got the 700 so I thought what the heck! the only thing that I'm not sure about is there is some sort of electical fitting on the trans, I think for overdrive but not sure. how long did it take you to do the whole project? and cost$$ without labor?
plans are to drive it and hove some fun in mud, nothing hard core.


and would a th400 be easier to do and they are 4 speeds right? because I want to drive about 75mph for about 1500 miles.