Help! overdrive swap 80' K5 ?'s

dUke><dUb · Dec 10, 2006

the search was down so don't get to angry if this is a common post.

I own aand daily drive a 1980 K5 and the gas mileage is killing me, it has a th350 tranmision which is a three speed and I want an overdrive.

What I want to know is ?...If any one could direect me to a write up on this swap or what is envolved in changing the trany out. Also what kind of fuel gains would I be looking to gain be doing this swap ?

thanks, the truck has 35'' tires, and I have no clue about the gear ratios, the truck seems super slow with the 3 speed auto

4xjunkie · Dec 11, 2006

Well I don't know of any articles.

But the swap should be pretty straight forward for a 700R4, it is a little longer so the drivelines with need to be changed.

Bolt patteren on the back of the trans is the same, but I am not sure if the shaft size and splines are the same.

The 700r4 also has a lower first gear with will help with around town.

I take it back , quick google search turned this up

http://www.oldengine.org/unfaq/leadfoot/th350in.htm

http://www.smokemup.com/tech/700r4.php

http://www.pirate4x4.com/forum/showthread.php?t=433906

bobracing · Dec 11, 2006

If you rig is already sluggish, an OD swap may not be the ticket. I have a 700r4 in an '88 Blazer with 3.08 and 31" tire, this combo makes the OD useless unless headed downhill with a tail wind. I'd check the gears and make sure you aren't under geared already.
If you already have 35s, then a 4.56-4.88 with OD will allow the engine to work less getting up to speed and will run down the highway at a reasonable rpm.