The Stovebolt Site Forums The Shop Area Driveline overdrive question

I have a 58 half ton apache with a 235. It has the standard 3 on the tree with a 3.90 rearend. I just came across some transmission parts of which one is a tail section of a borg warner overdrive.It spins free and looks like it is all there. My question is will this tail section and spacer work on the front half of a regular three speed to make a complete overdrive unit.

No. The overdrive version of the SM318, the SM319, has a different case and much shorter mainshaft.

The difference in the OD case is that it is drilled for the reverse OD kick out. One could drill a case if needed.
I suspect you got the main shaft with the OD.
I should also say the OD will only work on your 58 trans if the OD is from a 1955-63 trans.

Are there any codes on the tail sections to determine the year it was built? I don't want to get rid of it in case I can locate a complete overdrive unit later. I may need spare parts.

I have not been able to find any date codes on the BW units I have worked on. A general rule would be: 55-57 cars & trucks did not have a rear mount on the OD unit. 58 up cars used a rear mount and the mount holes were drilled out. 58-65 trucks would have the mount boss but some were not drilled. They were all the same basic unit and will interchange. If you have a transmission case that has the extended casting area you can drill the hole for the reverse shaft. Your 58 case should be OK. Some of the cases will not work.
Fred

The next question is , are all the brackets and switches necessary. Is it possible to connect a toggle switch to supply voltage to the solenoid to engage the overdrive? I found a wiring diagram on line for the borg warner T 85 and there is a lot of parts to complete the overdrive circuit.It will be like looking for hens teeth.

I have setup a number of them with just a toggle switch to power the solenoid.

Fred...I have found so far that case number 3845122 is almost always 55-57 with no back mount.

Just some unscientific research from looking at quite a few of them online.

I have mine set up with a DPDT switch in lieu of the kickdown switch and a Bosch relay. You will need the governor and solenoid made for the tranny.

A governor is not really necessary if you wait to turn the switch on once you reach 35 MPH.
If you have a good governor it is easy to hook up though.

I want to get it up and running with bare bones. If I can get her going with just the solenoid I will kick it in after 35 mph , I do not have a problem with that. If I happen to run across any more of it I will save it as a later option. The truck is running fine after 6 years of rebuilding and I drive it and use it as a truck but I would like to drop the rpm for less strain on the engine while on the open road.

You'll have to remember to turn it off when you go below 30. Sounds like a lot of remembering to flip switches to me. Have fun.

I agree with cletis. With a wire loom, an aftermarket switch and relay you can make it work like the factory intended for under $50. Good insurance to avoid tearing it up.
Fred

What is a DPDT switch and who sells it?

A DPDT switch is a double pole double throw switch. It is a 3 position switch with 2 circuits.

In this application it is wired between the relay and governor on one circuit and between the #6 terminal of the solenoid and the coil on the other circuit.

You can get them at automotive stores, hardware stores, Radio Shack, etc.