The Stovebolt Site Forums The Shop Area Engine Shop overdrive for 61 1/2 ton shortbed

Hi Guys, I have a 61 1/2 ton with a six and three speed. The engine runs great and is reailable transportation for my son. However it's geared so low its only good for about fortyfive mph. I know they used to have overdrives at that time and I've read stories about passenger car o/d units used in trucks. But this truck has an x crosmember that is very close to the end of the trans and it seems as if it would not allow for the extra length of the overdrive unit.Has anybody done one of these? Or do you have any other suggestions?

Tony:
I have one in my 57 chev pickup. I like it very much. It drops about 23% rpm at highway speeds. My experience has been very good with the 3 speed OD trans.

Just finished installing a Borg Warner T85N O/D in my '61 Apache 10. The tranny is exactly the same length as the original three speed thats in there. Didn't have to modify the drive shaft length. Simple bolt out, bolt in install, just a little wiring to do afterward. With the stock 3.90 rear end, running 235/75/15 tires the old 235 straight 6 should turn about 2400 rpm at 75 mph.

Tony, the 55-65 GM car or truck 3 spd OD is the same length as the 3 spd non OD tranny,it's a bolt in other than the controls for the OD.

Does the shifter linkage require any changes or modifications?

What about the clutch, the original one is fine?

Northern, Clutch and shift linkage is the same as stock, if you use the Borg Warner T85N Overdrive. If you want to use a floor shifter, as I did, some careful setup is required to get the shift rods around the solenoid, but it can be done. As the floor shifter on the stock tranny is very close to the front edge of the bench seat, with the over drive the shifter position will be an additional 1.5" toward the rear. You will have to lose the bench and go with bucket seats. If you retain the column shift all remains the same, other than installing a push/pull cable for the freewheel lockout on the O/D unit.

Yacht,T-85N? is that the overdrive unit? The trans itself is a GM built Muncie.

It's the BW designation as far as I can tell. Yes the front part is a muncie unit, on the later O/D units, after 1966 thru 1987,the front portion is the three speed Saginaw unit, fully synchronized. The O/D unit itself (the tail section containing the governor, solenoid and planetary gears) is designated "R 10 H". Put the Muncie, or Saginaw together with the R 10 H, and you get a T85N. The R 10 H was put together with other trannys of different manufacturers (F##D, Mo*#r, etc. and given different designations). BTW, if you look around on the web, you can find an article, where a guy took a R 10 H tail and with a few modifications, was able to mate it to a FOUR speed Saginaw, with gear splitting in all four gears. Which you can do with the three speed version if you wire it correctly.(Gear splitting, that is) Again I refer anyone with questions about this tranny to this site http://www.speedprint.com/Deves50/OverdriveIndex.html (fixed link)

Great link, what a wonderful resource.

Are both the Saginaw and Muncie basically the same when put together with the overdrive unit?

I guess I have been timid about searching wrecking yards because I am not sure which one I need.

I have a 1966 Saginaw 3spd OD in my 37 truck, the T-85 is BW's code for a heavy duty long tailhousing 3 spd used in the 50-60's for larger engined Fomoco's and some Mopars.The T-85 is the tranny that the T-10 4 spd was devoloped from in 1957.I've always heard the T85N was the OD version of the T85.Be careful of using OD on first gear,it's not designed to carry a great deal of torque.
NortherenGMC, the two trannys are the same length, same front spline and bolt pattern,but the 55-64 Muncie has a non syncro low gear and has the small 4 bolt side cover.The later Saginaw has a finer rear output spline and it's all syncro and some what more rugged.The OD internals are allmost identical, but the cases are different.

so a transmission designed for a **** or mopar will bolt to a 235 chevy?

Truckedup:
I just installed what appears to be a Saginaw 3spd OD in my 57 Chevy pickup (came from a 63 pickup). One of my existing shift rods is too short (reverse & first). Did you run into the same problem with your install? If so, what did you do?

Thanks for all the advise. Now that I know that its possible to install one of these overdrives all I need to do is find one. Does anyone know where I can find them preferably in so Cal. and what is a decent price for one that is running good.

Thanks
Tony

OD transmissions are scarce and expensive, and if you're wrecking-yard scavenging, try to get the OD relay and kickdown switch off the donor vehicle with the transmission, if possible. (Not the solenoid attached to the trans, the relay in the vehicle wiring harness). New ones aren't available, to my knowledge. It's possible to cobble up a relay using newer parts, but it's difficult. You'll need a heavy-current relay with normally-open and normally-closed contacts. Good luck!
Jerry