First, let me start out by saying I am not a professional mechanic nor do I claim to be an expert on transmissions.  Back in my racing days, I rebuilt a few transmissions out of necessity.  I rebuilt a T10 once and incredible as it may seem it actually worked afterward.  My current Ford is most likely the last old car I will ever own.  It's a culmination of all the things I always wanted when I was young; a 50s Ford, Y block engine, manual transmission and hot rod engine.  I bought this 55 TBird because it was a rust free west Texas car and it had a manual transmission. To my delight, it also turned out to be an Overdrive car because I had always heard Overdrive cars were faster, but I didn't know why.

When I first drove my TBird, I was confused about this transmission.  It freewheeled when decelerating without engine braking. I didn't like this as it was different than the 4 speeds I was used to. I actually thought it was broken.  After reading more about it, I learned this is normal. Once I figured out how O/D worked and how to drive it, I was hooked. 

Ford O/D was a wonderful idea years ahead of it's time. It allows the use of numerically lower rear gears without the disadvantages.  I'm not sure what rear gear is in my TBird.  People tell me it's either a 3.89 or a 4.11.  It takes off like a rocket running about 3,000 rpm at 60 mph in third gear.  I lift the gas pedal and it shifts into O/D and the tach drops to about 2,200 rpm.  It cruises along quiet and happy until I kick it out of O/D then the car changes personality.   I love it!!

Recently, my O/D stopped working.  This scared the heck out of me because I just had the tranny out for an engine rebuild.  A 55 TBird has a tiny transmission tunnel. The Ford T86 O/D transmission in my car barely fits. In order to remove the transmission without removing the engine, you have to remove the bell housing with it. Let's just say it's an experience you don't want to repeat too often.  I read everything I could find and started to troubleshoot the problem.  The mechanical O/D itself is actually pretty simple.  The wiring is not hard to access, but was difficult for me to understand at first. The hardest part to access is the governor.  It's at the rear of the transmission buried behind the frame.  If this part goes bad in a TBird, you most likely will have to take the transmission out.  All the governor does is ground the O/D circuit when the car reaches a certain speed.  I made a long wire with a 12 volt light at the end.  I lifted the car off the ground, connected the wire and light from the battery to the governor and started the motor.  Somewhere around 30 mph, the light went on.  As soon as I dropped below that speed it went off.  Hallelujah!  The governor was working.

Eventually I found the problem.  One of my electrical connections was not making contact.  I learned a lot about my O/D in the process. There are only a few simple components to this system.  The experts say most of the problems are wiring.  It was in my case.  I thought I would post my experience so someone else may benefit.  Old Fords are fun!!

Phil, THANK YOU. Real world hands on knowledge is VERY VALUABLE to everyone who works on these
old technology laden rust buckets. I see so much "hear say, speculation, and mis-information being passed
on as fact it is refreshing to hear some actual facts once in a while. Keep it up. Pete

It took me quite a while to fully comprehend how the overdrive works.  The wiring is simple enough, but it travels around the car and is hard to get to.  The best source of information I found on the web is at https://fifthaveinternetgarage.blogspot.com/2017/01/borg-warner-r-10-and-r-11-overdrives.html .  Randy sells a book that explains a lot.  I ordered his book, but didn't need it to fix my problem.  If you have one of these transmissions, you should be able to hear the click from the relay when coming to a stop.  In a TBird, it's on the other side of the firewall.  When I hear it, it makes me smile.  When I don't, I know I have more work to do.

I also love my 55’s BW OD trans., but one COULD make a career out of maintaining/repairing/mastering it! Just a few of the things I learned over the years that are not mentioned in the repair manuals:
1. The governor CAN be changed/serviced without removing the transmission, but good luck finding a short/thin wrench the right size. I finally had a machinist fabricate one.
2. NOS & rebuilt solenoids that bench test good, sometimes won’t function correctly under mechanical load. I had to construct a home-made loaded bench jig to test them properly.
3. Aging/corrosion takes a toll on electrical parts/contacts (especially magnetic coils), and current draw goes up. With the bright headlights, radio & heater fan on, sometimes there just isn’t enough 6V juice left over to operate an old solenoid pull-in coil or relay reliably. I had my OD relay converted to solid state, since FULL disassembly (to eliminate all contact corrosion) just wasn’t possible, even though the points WERE accessible with the cover removed.
4. When I first got my car, the OD wasn’t working. Turned out, the solenoid was full of lube that had flooded the points. The original seal was leaking, and the previous owner thought it would be a good idea to plug up the solenoid drain hole with silicon caulk (!?) to stop the leak. BTW: The solenoid CAN be installed upside down, so that it can partially fill with leaking lube. Maybe not far enough to cause failure, but if the thus-higher drain hole gets even slightly plugged with road gunk, said failure gets a head start.
5. ETC, ETC. When no good NOS 6V solenoid can be located, you will sometimes be left with the project of rebuilding your old one. THAT is a chapter for another day!

6 VOLTS/POS. GRD. NW INDIANA

"The governor CAN be changed/serviced without removing the transmission, but good luck finding a short/thin wrench the right size. I finally had a machinist fabricate one."

I use a small antique stillson wrench I inherited from my Dad, The jaws are flat, straight and adjustable, and it has a short handle. I've used it several times to remove and install the governor when the speedometer drive gear took a notion to slip out of position. Pull the governor, find the end of the drive gear with your little finger, insert a large flat blade screwdriver and push the gear back into place. I have no idea why the gear slipped and it's stayed in place for over 3 years now...

Before I discovered my problem, I suspected my governor was fouled with oil.   Not wanting to take the transmission out of the car again, I spent some time figuring out how I could get to the darn thing.    If you remove the seat, you could cut a hole in the floor to access it.  You could fabricate a sheet metal cover to go back over it.  Radical surgery I know, but it would work.  As it turned out I didn't need the operation.

My 55 Tbird had been converted to 12 volts before I bought it. I suspect the components including the governor are 6 volt.  While I had the transmission out, I re soldered the wires going to the solenoid.   The O/D was working fine until recently.   A bad male/female wire connector was the culprit.

Phil, not O/D related but possibly relevant. I have head that the 55 and 56 Tbird frame used a bolt in transmission support
X member. Is this true or not. The reason I ask is that some people claim to re-build the 55/56 FOM WITHOUT pulling the
engine and by removing this bolt-in cross member you can remove and the replace the FOM piece by piece.
What do you think? Pete

My 55 had a bolt in cross member, but that isn't the only issue.  I initially tried removing the O/D transmission without pulling the motor.  The governor and O/D solenoid stick out of the transmission and you can't move it back far enough for the input shaft to clear the bell housing.  The shifter gets in the way as well.  It is very tight under there.  I had my exhaust off too.  I can image what you would have to go through with the mufflers in the car.   The shop manual says you must remove the bell housing to get the transmission out.  Since I had to go that far, I just pulled the motor.  Funny thing is this led to a complete engine overhaul, which I needed anyway.

To me, it seems easier to pull the engine and put them both back in as a unit.  A 55-57 TBird has a long engine bay which helps a bunch.  The hardest part is getting the hood to line back up right.  You can easily fix this problem by drilling two 1/8 guide holes in the hinges before you take the hood off.

I once pulled the T85 OD trans from my '56 Bird without pulling the engine.  Besides the bolt in crossmember, I also had to slide the trans as far back as it would go, remove the bellhousing, slide it back to the front of the transmission, remove the clutch and flywheel, then bring out the bellhousing, then the trans.  As Phil mentioned, it is less work to pull the engine.  Besides, there is no way I could lay on my back and manhandle that T85 any more.  I can't believe how much weight that trans has gained in the last 30 years.

John - "The Hoosier Hurricane"

Brings back memories.  I once paid a guy to change the front transmission seal in a 1960 Starliner with a 352 and an automatic transmission.  We jacked up the car in a local parking lot.   He manually pulled the transmission down on his chest, then bench pressed the whole transmission back in the car by hand.  At the time, it didn't seem like that big of a feat.  I don't know what that old transmission weighed, but he was one hell of a man.