Upgrading from 3 to 4 speed tranny.

[LucasinAlaska]

I would like to put a 4 speed transmission in my 1989 Suburban 2500 4x4 350ci. It has a three speed in it right now. I searched the archives and could not find anything. Is this conversion possible and how hard is it to do?

Thanks

Lucas

 

[sled_dog]

you mean you want to go from an automatic 3 speed to a manual 4 speed or from the TH350 to the 700R4?

 

[LucasinAlaska]

I would like to go from 3 speed auto to a 4 speed auto, I'm sorry I don't know the tranny names. I'll assume the 3 speed auto is a TH350 and the 4 speed auto is a 700R4.

Thanks

 

[sled_dog]

your assumption is correct. sorry don't know much on this topic, I am sure someone can help

 

[RATAH]

KEEP THE 350

 

[Sparky87k5]

I seriously doubt if you have a T350 3 speed. 3/4 ton Suburbans of that year came with T400 trans 3 speed, and they are bullerproof compared to a 700R4 4 speed. For what it will cost you to swap, you can just about bolt in either a Gear Venders Overdrive or a US Gear 2 speed aux. trans.
Either option will give you the Overdrive you seek, plus the ability to use it in any gear, like having a 6 speed trans. Great for towing, I used a US Gear 2 speed in an 88 Suburban behind the T400 and what a nice setup.