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View Full Version : TH350 swap into a 90 gmc sierra



onebadsierra
10-04-2005, 06:59 PM
Ive got a 1990 GMC Sierra, currently it has a 700r4 tranny in it. I am considering swapping in a 350 turbo tranny in it b/c it is not a daily driver and it would work well with plenty of power and my future plans as well. What i am curious about is can i use the stock crossmember, or do i need to get a different crossmember? Also i realize i will probaly have to get a slip yoke for a turbo 350, but are the u joints the same series so i can use my same driveshaft? Thanks for any help.

ChevyGuy350
10-04-2005, 10:15 PM
the stock crossmember will work but you will have to get an adapter for the tailshaft housing...it is too short. i think you may be able to get it at advanceadapters.com. also you have to make sure the TH350 is for the application you need, 4 wheel or 2 wheel.

onebadsierra
10-05-2005, 06:24 PM
i looked on advandeadapter.com and they have all this stuff for 4x4, my truck is a 2wd, will i still need the adapter?

ChevyGuy350
10-05-2005, 06:49 PM
im not sure ... maybe not. would have to measure. i dont have a 2wd i have 4wd. is the tranny for a 2wd or 4wd?

onebadsierra
10-05-2005, 10:41 PM
yes, my truck is a 2wd.

ChevyGuy350
10-05-2005, 11:24 PM
what did you get the tranny out of?

onebadsierra
10-06-2005, 09:22 AM
I havent gotten a tranny for my truck yet. There a dime a dozen around here, so i just wanted to find out the info on the swap before i go out and buy one.

Pauly
10-06-2005, 01:38 PM
Some turbo 350 tranny's come with a long tailstock which make them the same length as the 700 r4, the driveshaft neednt be shortened and the sme yoke can be used. The mid 80's GM trucks came wuth a th 350-C, this is called a metric th350. It comes with a TCC(torque converter clutch) that allows the trans to lock the converter. Using this trans will net you about 1-3 mpg better than using the conventional th 350. They dont make shift kits for the th350C, only the standard non-lockup thm 350's. The metric trans uses the same electric signal that the 700r4 used in your truck to lock the torque converter clutch. My 1984 GMC sierra came stock with a metric th350 with a locking TC.
The standard car thm 350's have a shorter tailstock and output shaft than the truck trans do. If you use 1 of these tranny's you will have to lengthen the driveshaft.

The 1990 700r4 crossmember will work for the th 350, but the driveshaft will not unless the trans is from a truck originally.. Find a truck THM 350 and you can use your driveshaft, slip yoke and crossmember. i am pretty sure about tyhis if my memory serves me correctly.

Pauly

onebadsierra
10-09-2005, 09:28 PM
Some turbo 350 tranny's come with a long tailstock which make them the same length as the 700 r4, the driveshaft neednt be shortened and the sme yoke can be used. The mid 80's GM trucks came wuth a th 350-C, this is called a metric th350. It comes with a TCC(torque converter clutch) that allows the trans to lock the converter. Using this trans will net you about 1-3 mpg better than using the conventional th 350. They dont make shift kits for the th350C, only the standard non-lockup thm 350's. The metric trans uses the same electric signal that the 700r4 used in your truck to lock the torque converter clutch. My 1984 GMC sierra came stock with a metric th350 with a locking TC.
The standard car thm 350's have a shorter tailstock and output shaft than the truck trans do. If you use 1 of these tranny's you will have to lengthen the driveshaft.

The 1990 700r4 crossmember will work for the th 350, but the driveshaft will not unless the trans is from a truck originally.. Find a truck THM 350 and you can use your driveshaft, slip yoke and crossmember. i am pretty sure about tyhis if my memory serves me correctly.

Pauly


I was looking through the jegs catalog and they have the th350 trannys with either a 6" tailshaft or 9" tailshaft. Im guessing if i bought one new through them or some other company then if i got the one with the 9' tailshaft it would work with my factory cross member and ever ything else? Also if i just get one out of an older truck is there any certain year to look for that might be a little bit better.

ChevyGuy350
10-09-2005, 10:11 PM
the shorter tailshaft i beleive is for fourwheel drives and the longer one for 2 wheel drives. the cases are the same length so the stock crossmember will work either way.

YummY
10-09-2005, 11:51 PM
Crazy, i made a thread about this not too long ago, I have a 90 gmc sierra 2wd and blew my 700r then bought a turbo350 but just rebuilt my 700r..... ill try and find the links thats tells all the difference and what mods ya gotta do.

onebadsierra
10-10-2005, 04:54 AM
Crazy, i made a thread about this not too long ago, I have a 90 gmc sierra 2wd and blew my 700r then bought a turbo350 but just rebuilt my 700r..... ill try and find the links thats tells all the difference and what mods ya gotta do.


That would be awesome if you could find the links to the info on what all i need to do.