I am looking for an aftermarket overdrive unit to put onto my stock 4 speed 1978 ford bronco 4x4.
Does anyone have any suggestions?
I need to drop the RPMs on the highway.
Thanks Joshu

 

Is your TC married to the trans?

Which trans do you have, T18?

https://www.gearvendors.com/4x4.html

 

Thanks for the reply
I'm pretty sure the TC is married but I'll go outside and confirm. The tranny is a 4speed stock with granny gear. I'm not sure how to tell the exact model of the tranny. It doesn't look like the VIN identifies the tranny but I could be wrong. I'll have to do more research unless you know how to tell the specific tranny by looking at it.
Thanks for your help.

 

The TC is not divorced
Still working on the tranny info.

 

Yes, it is a T-18 transmission

 

Swap in a ZF 5-speed and TC from a newer truck.

 

Duh....x 2 on the above. Less expensive to boot.

 

Why do you need to drop the rpm's?

 

I want to drop the RPMs because I need to drive over an hour one way a couple times a week. If I drive 75mph which is the speed limit, the increased RPMs cause increased gas consumption and is harder on the truck. I was hoping to keep the original equipment since it is so clean and just add on an overdrive if possible. I could change the transmission and TC to a newer one but I since it is so original and that 4 speed is bullet proof I would like to keep it stock. I guess I could put on bigger tires and drive slower but was looking for an overdrive option. I might consider changing the gears but that would not be the best thing for off road.
Thank you

 

I might consider that. Thanks.

 

There is no value in keeping the truck all original it's not like it's going to be worth anything to anybody else, and you're going to have to get an overdrive ratio in there and drive slower to see significant milage gains.. 75mph is to fast for a vehicle with the aerodynamics of a tool shed.
If you were to put a GearVendors OD unit in the truck you would need a custom rear driveshaft which isn't going to be cheap and those GearVendors are violently expensive too, so finding a donor truck to pull a ZF+ T-case and both driveshafts from would likely be the most economical solution. But even then you would need to find and buy a parts trucks for a couple hundred dollars for this to really be viable, because it will take a long time to recoup $1000 to $1500 or more in gas savings if you were to spend that much on either option.

 

^^ And it still wouldnt be nearly as off road capable as it is now.

 

I appreciate it. I know it's not a collectors item or anything, I just like how tight it is with no vibration and original equipment. The top has never been taken off so it's quite a grandpa barn find.
I think I might just put bigger tires on it and pay the extra gas, or just drive slower.
Thanks for all the help.

 

Drive slower With my '95 I rarely go above 60 with the speed limit being 65, and in the one or two places I go (rarely) where it's 70 I hover around 65.

Don't forget you'll have to recalibrate the speedo if you go with significantly bigger tires.

 

Thanks, good reminder