Replace 700R4 with 4L80E tranny in 1991 K5 ??

[Daddy Rabbit]

Hi All. I have a new-to-me 1991 K5 with a fresh 350 and a moderately worn 700R4 tranny. In the near future I hope to do a few basic modifications like perhaps a 4" lift, 35 12.5x15 tires, 4.88 gears, stronger axles, and a few cosmetics etc. Unfortunately, reverse in my tranny just gave up the ghost . Instead of having it rebuilt, I am considering replacing it with a stronger one like maybe a 4L80E or a 4L85E attached to a 205 TC harvested from one of the GM 4x4 heavy duty vehicles. Have you gentlemen had any experience with replacing a 700R4 with a 4L80E type setup? If so, what is involved in the switch? Is it a simple bolt on deal or is it a pain? ... Many thanks, Denny

 

[4X4HIGH]

Hi All. I have a new-to-me 1991 K5 with a fresh 350 and a moderately worn 700R4 tranny. In the near future I hope to do a few basic modifications like perhaps a 4" lift, 35 12.5x15 tires, 4.88 gears, stronger axles, and a few cosmetics etc. Unfortunately, reverse in my tranny just gave up the ghost . Instead of having it rebuilt, I am considering replacing it with a stronger one like maybe a 4L80E or a 4L85E attached to a 205 TC harvested from one of the GM 4x4 heavy duty vehicles. Have you gentlemen had any experience with replacing a 700R4 with a 4L80E type setup? If so, what is involved in the switch? Is it a simple bolt on deal or is it a pain? ... Many thanks, Denny

A 4L80E is a much longer trans than a 700R4 and in a short wheel base vehicle such as a blazer you will probably end up with rear driveline angle issues. Also the 4L80E will require a 800-1000 stand alone ECM. If it were me i would have your 700R4 rebuilt and use the heavy duty upgrade parts that the shop recommends such as The Beast sunshell, corvette servo and a few other mods then it should survive many years of abuse. I have a local trans guy (person friend) that built my 700R4 about 7-8 years ago and it's still going strong and i'm not easy on parts.

 

[dhcomp]

Also the 4L80E will require a 800-1000 stand alone ECM.

And by 800-1000, he meant $800-$1000

 

[Daddy Rabbit]

Thank you gentlemen for the advice. Accordingly, I found a local family shop here in NH with a few decades of exp who say they "specialize" in rebuilding transmissions to be much more heavy-duty than stock. They quoted me 1000-1500 including removal, reinstallation, and warranty to rebuild my 700r4. Do you all think that price is in the ballpark??

 

[Keitha]

The price seems reasonable on the surface, but like always: Ask questions! What is involved in the rebuild, what brand clutches and steels, what other parts do they replace etc.

 

[greywolf]

you could also look at the raptor 700r4, i think its $2000 with warrenty but you have to put it in.