1953 overdrive transmission interchange

sawzall

sawzall

Senior Member
Ive been familiar with the early 50s overdrives for some time.

recently I purchased a 51 ford car that currently has a stock 3 speed I am thinking that adding a Overdrive would make a great addition.

with hershey on the horizon, what should I be looking for? obviously want to find the most complete setup, however I am wondering what year overdrives would interchange? i believe ford 49 thru 51 ford are identical, can I find a merc overdrive? can I use later overdrives if so what years?
 
'49-'50 are different from '51 because they moved the transmission mounting pad in '51 to accommodate the new Ford-O-Matic transmission. I would think the Merc units (even if they are compatible) would have the same problem. I don't know if later ones will work either; bring a ruler.

The hard parts are the relay and other assorted bits. Luckily, most (the wiring harness, kickdown switch, and lockout cable are available on the aftermarket. I had a hell of a time finding the bracket that holds the rear of the lockout cable to the transmission.
 
I believe 51 through 56 will interchange. I've bought , rebuilt, sold or installed so many and never really new what specific year they were. If you have a bellhousing like a 53 I think the only difference could be the rear mount position as far as actually bolting in. I have seen two different styles ,one a top loader and the much more common side loader. Both of these fit in my brothers 53 sedan . The man who knows the facts on this subject is Mac Van Pelt. Hopefully he will chime in here.
 
The '49-'51 Fords are the same overall length, but differ in mounting as tubman stated.



The '49-'50 and early '51 Mercs are completely different with '32-'48 round pattern cases, but regular production '51 Mercs are the exact same as the 4-bolt '51 Fords except for shift levers. The convertible OD tail housings may be different because of relay locations between F/M.



The '52-up Fords/Mercs will work but overall length may be different than '51, requiring drive shaft mods. The '49-'51 side covers do have an extra boss that supports the brake and clutch pedals and should be interchangeable with some later B/W trannys, but

I would contact VanPelt for more info on later year compatibility.
 
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You need to retain the side shift assembly since your clutch linkage bolts to it. I think you need a 51-54 overdrive transmission, they have the transmission mount in the correct place and have interchangeable side shifters. Measure your existing transmission length, measure the location of the transmission mount, take note of the side shifter bolt pattern and size, and take note of the bell housing bolt pattern. Any overdrive that matches these should work for you.
 
The 1951 shift cover housing may be the hard part. As was mentioned, it is part of the old type pedal & equalizer assembly. Swing pedals came out in 1952 and up. The shift cover has a mechanism to operate the internal reverse lock out on the OD transmissions. 1951 and later transmissions have the new style gears and there is interchangeability there for 51 and up transmissions. Mercury cars changed over to the new style transmission around February of 1951 and they have a one year only cast iron bell housing that was set up to use the old style pedals on it. In 1952 all the 259 series transmissions were basically the same as equipped in Ford or Mercury cars. They all used the same cast iron bell housing with the lever type clutch release.
 
I think shift cover problem is solved by combining parts from the transmission in the car and from the overdrive transmission. The cover casting and outside shift arms from the 51 transmission get combined with the inside shifter parts. You want to take the side assembly apart anyway to install new seals and clean up the lockout ball area.
 
The lock out mechanism was only available on the OD transmissions and the 51 is a bit different than the 49 & 50 transmissions but a person might be able to make that side cover style work.
 
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