OD on a 1951 Ford
- Thread starter roadster
- Start date
blucar
Well-known member
The O/D units, transmissions w/OD attached are without a doubt one of the slickest options ever added to a automobile, light truck.. As I recall the units that Ford used were Borg/Warner.. Could not swear to that though..
OK now the nuts and bolts of how they work:
As a general rule an OD equipped vehicle will have a slightly lower rear end gear ratio as compared to the normal gearing.. i.e. my '59 Ford F100 w/OD had 3.89 ratio in lieu of the standard 3.73..
The OD transmissions have a free wheeling feature, that allows the driver to shift without the use of the clutch at speeds below about 35.. The one disadvantage to the free wheeling feature is that when the throttle is released at low speeds the engine does not, can not, assist with slowing the vehicle down...
Reading the owners manual on an OD equipped vehicle will reveal that the OD unit should be manually disengaged, via a lever mounted to the bottom edge of the dash, when traveling in mountainous terrain. Of course this is also true of the modern OD equipped vehicles... I know... It is not cool to read the Owners Manual before operating a vehicle..
I have had a lot of experience with vehicles that had the trans OD.. I found them to be very reliable.. Ford was late in embracing the trans OD's, Chrysler, Studebaker, and several other manufactures came out with OD units in the late '30's..
If you are thinking about converting a vehicle to an OD, it is best to find a unit that is already in a vehicle, that way you can get all of the linkage, etc. required to install the unit..
The OD's found in the Ford cars, '49 and later are generally the same as the units used in the F-1/F100 pickups...
In 1955 a friend and I installed a '55 Merc Y-Block in his '40 Ford coupe. We put an OD trans from a Merc behind the Y-Block using the banjo center section from a Ford pickup.. That was a really nice '40.. It was great on the highway... "Hot Rod Magazine" did a full page article on the car in 1955...
OK now the nuts and bolts of how they work:
As a general rule an OD equipped vehicle will have a slightly lower rear end gear ratio as compared to the normal gearing.. i.e. my '59 Ford F100 w/OD had 3.89 ratio in lieu of the standard 3.73..
The OD transmissions have a free wheeling feature, that allows the driver to shift without the use of the clutch at speeds below about 35.. The one disadvantage to the free wheeling feature is that when the throttle is released at low speeds the engine does not, can not, assist with slowing the vehicle down...
Reading the owners manual on an OD equipped vehicle will reveal that the OD unit should be manually disengaged, via a lever mounted to the bottom edge of the dash, when traveling in mountainous terrain. Of course this is also true of the modern OD equipped vehicles... I know... It is not cool to read the Owners Manual before operating a vehicle..
I have had a lot of experience with vehicles that had the trans OD.. I found them to be very reliable.. Ford was late in embracing the trans OD's, Chrysler, Studebaker, and several other manufactures came out with OD units in the late '30's..
If you are thinking about converting a vehicle to an OD, it is best to find a unit that is already in a vehicle, that way you can get all of the linkage, etc. required to install the unit..
The OD's found in the Ford cars, '49 and later are generally the same as the units used in the F-1/F100 pickups...
In 1955 a friend and I installed a '55 Merc Y-Block in his '40 Ford coupe. We put an OD trans from a Merc behind the Y-Block using the banjo center section from a Ford pickup.. That was a really nice '40.. It was great on the highway... "Hot Rod Magazine" did a full page article on the car in 1955...
Dale Fairfax
Senior Member
Quick reply to original question: With the lockout handle pushed in (O.D. enabled), drive the car normally-using the clutch and accelerator just as you would in a non O.D. car. When you want to shift into O.D. (at somewhere above 26 m.p.h.) let up on the throttle and the O.D. will automatically shift into gear. This is usually done in 3rd gear and at highway speeds. It reduces engine R.P.M. at a given road speed by approximately 30%. However, the O.D. unit doesn't know what gear the transmission is in-it only knows if it is at or above 26 m.p.h. thus it can shift into gear while in 2nd gear or even 1st gear. There is no practical reason to shift into 1st O.D.-it's only to show off loud pipes. 2nd O.D. can be a nice compromise gear for urban cruising (It's inbetween 2nd and 3rd in the transmission). The only downside is the freewheeling. if you'r running in O.D. and wish to shift back into conventional drive you push the accerator to the floor which momentarily grounds the ignition (to remove any load off the driveline) and sends a signal to the O.D.s shifting solenoid to shift out of O.D.
Dick Webber
Senior Member
you can leave the lever pushed in (overdrive engaged) all the time. However it will free wheel below 26 mph which is hard on brakes (and you won't hear the duals pop). But the big problem is parking. Park in reverse only, otherwise it will roll away. I always used mine locked out in town--it was hilly and the exhaust music was great. For highway cruising it is a great accessory. On my 49 Mercury the stock rear end is 3.91. With OD the rear is 4.11.