Overdrive

B

Bob 37

Member
Does anyone have any input on overdrive units that are available for early V/8 Fords? A friend has a basically stock '39 coupe that he would like to make more highway-speed friendly.
 
If you want OD with the closed drive, you would do best to get the Mitchell OD unit. If you have (or plan to install) an open drive rear end, the 49 or 50 Merc OD would be the easiest way to go.
 
I have Columbia ODs in both my model A s.Each has ratios of 4.11 & 2.94 .I adapted both myself & no lathe work was required. I have used one since 1960 in over1/2 doz A s & modified abt 15 yrs ago to fit a 33 coupe.Modified it a 2nd time a couple yrs ago to fit my A coupe.My A sedan has a 46 columbia that i had to narrow by taking 15/16"out of the Columbia hsg & used 36 axles & spider gears.For me the 4.11s give the best OD ratio even when in the 33 with the 59A.I think 3.78s would be to high geard for my likeing--unless you live in the prairies or the US midwest.
 
There is a possible downside to each of the above options.

The Columbia rear axle is expensive and finding all the correct controls for your year car can get interesting. It is the most correct option for a 39 and will get no points off at judging if done properly. Everything needed is findable, just open your wallet or spend a while searching or both.

The Mitchell is a nice unit. I have ridden in an A with the Mitchell overdrive and Mitchell synchro A transmission and was impressed by both. The downside to the Mitchell is it may not fit under the floor. All the pictures I have seen of a Mitchell under a 33 and later passenger car had the floor under the truck / back seat area cut out and raised to clear the overdrive. I have seen posts where people say they have a Mitchell with no floor cutting needed in a passenger car, but no pictures. If a Mitchell can be installed in a 37-40 passenger car with no floor cutting, I will end up installing at least two in my and my dad's cars.

The F-150 transmission is longer than the stock 3 speed and every picture I have seen of one installed in an early V8 included a cut cross member. Again, I have seen posts that say these transmission can be made to fit with no cutting, but no pictures.
 
I've got a Mitchell in my 41 pickup. Running a SBC with stock Ford ****** and 3:54s in the banjo, 26% Mitchell overdrive. I love it. Much easier than converting to open drive and a T-5. Two guys and four hours .. easy swap.
 

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The f150 kit comes with new rear transmission mounts. the stock rear cross mount comes out and the new ones bolt in. driveshaft and tube needs to be shortened a couple of inches. everything else bolts in.
 
Have a Mitchell in our 37 sdn with 3.78 rear and 28% od and it is the cats meow. Bullet proof unit and great people to deal with.
Don
 
I installed all of mine with the body off frame when I was doing the car so it was easy and I put a full Bradley floor in it.I think I have some pics I"ll see
 
Can the Mitchel be installed in a Business coupe/Opera coupe? I don't think so because of the extended elevated floor pan. Now on a 5 window coupe it can be installed. My 1940 5 window has one in and it was easy to install. I am doing another 5 window and it will have a 36% Mitchel OD.

Jerry
 
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