Mitchell Overdrive

[Engineer127]

Hi Guy's,
I am building a 32 Roadster. I plan on installing a Mitchel overdrive unit. I am using a 37 transmission and a 37 rear end using the original 32 cross member and spring with 42-48 radius arms.
Attached is a sheet Mitchell sent me requesting dimensions.
Is there anyone out there that has done this and has the dimensions?

Thank You,
Jim Derickson
(925) 672-8431

[rotorwrench]

I would look for a 39 or later top shift gearbox myself or at least a set of gears from one of the later ones, side shift or otherwise. The older transmissions have a synchronizer that leaves much to be desired plus some have straight cut gears. The later gears will fit a 37 but the case isn't quite as strong. The double detent shift tower with the wide synchro fork is also recommended.

You will have to find out what the torque tube length needs to be for a 1932 chassis with a later model rear axle assembly installed. Normally the torque tube & drive shaft are shortened. This is one of those things that should be mocked up before you commit to a length. There can be other variables with these type modifications.

[Milt/Las Vegas]

Originally Posted by Engineer127

Hi Guy's,
I am building a 32 Roadster. I plan on installing a Mitchel overdrive unit. I am using a 37 transmission and a 37 rear end using the original 32 cross member and spring with 42-48 radius arms.
Attached is a sheet Mitchell sent me requesting dimensions.
Is there anyone out there that has done this and has the dimensions?

Thank You,
Jim Derickson
(925) 672-8431

I have a 39 trans.without the shifter,I don't know whether a 37 shifter would fit a 39.I'm in Las Vegas it would have to be picked up.

[mrtexas]

Your torque tube is likely not a stock length. Why not measure it? Or drive 100 miles to Colusa,CA to let Mitchell have a look see?

[raybee]

37 shifter will not fit the 39 trans without a 91A shift fork. Ray

[Mart]

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Advice re the gearbox, while good advice, was not really the focus of the question asked by the OP. I have a torque tube I shortened for a later axle in a 32. I'll put a tape measure on it.

Doing the set up in your own frame is the most reliable way, but I'll get a dimension for you.

Edit: I dug through to the back of the shed and measured the torque tube. It is 53-3/8" overall length. If you get 1 or 2 other people confirming a figure at or near that, you could probably use that length.

I can't advise re radius rod placement, unless you can get the stock measurement of a 46 rod mount bolt hole from the rear flange. Someone might be able to get that for you.

2nd edit: I just looked at the drawing on the Mitchell form and the dimension I quoted is the "C" dimension. The drawing is drawn very badly, the arrows should be just kissing the lines. Still, there's not much room for error so it's ok for this job, but from what I learnt 40 plus years ago in Technical Drawing at school, it's badly drawn.

Mart.

[mrtexas]

The result of not measuring the torque tube length correctly is that the radius rods won't fit.

[rotorwrench]

A person can use a 1935 through 1938 transmission or whatever they want but my recommendation for the 1939 or later is such that most folks traditionally used the later cog box for a good reason. Especially after the older types get lunched from a hammer hit with a warmed up flatty. The 37 rear axle is fine but the torque tube for a 37 will be longer. If you position the motor for the 32 cross member you could use the 32 V8 rear axle but things start to change with the later rear axles since the spring hangers, spring assembly, and cross member of a 1937 car are different.

The Mitchell uses its own torque tube that can be sized for whatever application a person would need. The late type radius rods can be attached to the Mitchell set up wherever they fit up on the tube. It would likely be in front of the Mitchell gearbox but the shaft and tube length is critical to get it to work. You can't be off by much or you start to put the rear spring in a bind. I'd mock up the rear cross member with the 37 rear axle without tube and measure it to the transmission in place. Any other way is a gamble.

[Engineer127]

Hi Guy's,
Thank you for all the good advice.

Jim Derickson

[Steve/IL]

Originally Posted by Engineer127

Hi Guy's,
I am building a 32 Roadster. I plan on installing a Mitchel overdrive unit. I am using a 37 transmission and a 37 rear end using the original 32 cross member and spring with 42-48 radius arms.
Attached is a sheet Mitchell sent me requesting dimensions.
Is there anyone out there that has done this and has the dimensions?

Thank You,
Jim Derickson
(925) 672-8431

Jim,

If I am reading the second sentence of your post correctly, you are using a 32 spring on your 37 rear end? If this is correct, have you actually installed the curved 32 spring on the 37 rear end? Without checking, I believe that the center to center dimension of the 32 spring eyes is too narrow for the 37 rear end spring mounts. If not, then you will also have another problem. The spring mounts on the 37 rear end are further back on the axle by 2 inch compared to the position of the 32 rear end spring mounts. IMO if you have mounted the 32 spring on the 37 rear end and installed the 32 spring in the 32 cross member, then the 37 rear end will be 2 inch too far forward!

If you want to use the 32 rear cross member, I suggest that you use the straight 37 rear spring and grind notches in the spring to allow it to fit the 32 cross member. this method positions the rear in the correct location.

I can not answer your question about the torque tube length. However the mounting face for the torque tube on the 37 rear end is further forward than on a 32 rear end, so you can not use the length of a stock 32 torque tube to get the dimension that Mitchell requires. I suggest that you do a Ford Barn search to get the difference in the length of the 32-34 banjo compared to the 35-40 banjo at the torque tube flange. This dimension has been discussed a number of times in this forum.