The Stovebolt Site Forums The Shop Area Engine Shop overdrive !

Hello people Iam looking where to find an overdrive unit for a 1963 gmc four speed,I have heard about them but never seen one,any tips or links would be much appreciated!

I was going to post some ideas, but looked at your profile and found this is for a Napco 3/4 ton, and the suggestions won't work for a 4WD.

You can regear both differentials or replace the tranny with an overdrive unit, the most popular is the 700R4 automatic.

thank's for the reply,why won't it work on the 4x4,is it because of the tranfer case?.Iam probably just going to run taller rubber if the overdrive can't be done,that should get another ten mph! which is all she really needs

There isn't enough space between the 4-speed and the transfer case to put in an overdrive, even though they are a divorced setup.

You MIGHT be able to fit a Ranger overdrive (Advanced Adapters) between the motor and transmission but it would significantly shorten the divorced driveshaft unless you moved the divorced transfer case. This would cause you to modify the length of both driveshafts. You MAY be able to convert your 4 speed and transer case (probably need to swap to a later NP-205 if you have the Rockwell T-221) to a married style, this would give you room for the Ranger and wouldn't cause too much change to the driveshafts.

You could possibly put a overdrive after the transfer case, but you could only use it in 2wd, and you would have to modify the length of the rear driveshaft. I don't know if those planetary gear overdrive will mate to the output of a transfercase or not.

thats fine! if it can only be used in 2wd,cause that would be the only time it would be used(on the hwy!).there isn't any room between the engine and trans,but aft of the trans case seems like the place ,any info on were to find these units would be great!thanks for the input!!

if you have a 3 speed OD, the tailshaft can be used in place of the 4 speed. i'm not sure of the saginaw or muncie specifications. but i beelive someone has done it on here. or maybe its on inlinrs. i'm not sure. check out the archives, with a search top be sure.

http://www.usgear.com/dual_range.htm

http://gearvendors.com/4x4.html

https://eshop.advanceadapters.com/c...category_id=1198&czuid=1131510062250

You are looking at $2500 for the first two, $1500 for the Ranger. You will find that ALL overdrives are expensive, without exception.

You can also make an overdrive similar to what Jolly did. http://www.6066gmcguy.org/spicer-5831-b.htm

thank's for all the great info guy's,now I've got somewhere to start,and that's down in the shop to make some cash to aford one of these babies!!!