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Old 03-13-2019, 08:41 PM   #1
bill boz
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Default Mitchell transmission or overdrive

I would like to improve the drivability of my 31 closed cab pickup. Originally I was thinking about a Mitchell overdrive but now I’m wondering if I would be better off with the Mitchell synchromesh transmission. The truck has a strong engine and 3.56 rear end and 19 inch wheels. Most of our touring is at 45 to 50 we seldom run much higher. Our terrain is flat to rolling hills. My thinking is that the 3.56 rear end gets us going fast enough, seems like it would be great to have the easy up and down shifting from a synchronized transmission. I know this transmission is only synchronized in 2nd and 3rd gears that’s what I’m used to with my 40’s vintage cars. I wonder about your experience with either the transmission or overdrive and what other factors I might be overlooking. I have read as many past threads as I could find and am still pondering.

Thanks
Bill

Last edited by bill boz; 03-14-2019 at 06:42 AM.
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Old 03-13-2019, 09:14 PM   #2
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Default Re: Mitchell transmission or overdrive

Buy the overdrive..actually its a splitter box,the first time your wring out second low and shift to second high you'll be sold.
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Old 03-13-2019, 09:27 PM   #3
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Default Re: Mitchell transmission or overdrive

I have one car with both the MItchell transmission and O/D. We do lots of miles towing a camper behind that one. I have another 3 cars and all of those have the original cog house and a Mitchell O/D (gear splitter). One of those also has a 3.54 rear end (1928 Tudor) with a B engine fitted with a downdraught carby. That car doesn't handle hills all that well but I can sit on 60 mph easily enough in it on the flat. I think I prefer the standard rear end with O/D. The original gearbox is fine.
In your case, I'd go the O/D
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Old 03-13-2019, 10:57 PM   #4
Dick Steinkamp
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Default Re: Mitchell transmission or overdrive

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Originally Posted by bill boz View Post
I know this transmission is only synchronized in 1st and 2nd gears ...
I think you mean 2nd and 3rd.
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Old 03-14-2019, 12:11 AM   #5
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Default Re: Mitchell transmission or overdrive

I have the F150 OD with 3.78 rear. This gives me Synchronized gears plus OD. Does very well on the flat or hills.
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Old 03-14-2019, 04:41 AM   #6
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Default Re: Mitchell transmission or overdrive

We have a 31 Tudor with a strong engine, Mitchell overdrive 26% and Mitchell gearbox with 15% higher 1st and second. Diff is 3.78 and tyres are 16 inch on V8 rims.
This is a nice car to drive, but every now and then on really steep 180 degree uphill bends needs first gear to avoid straining. On the other hand on long uphill pulls in the hills where top gear is too high, overdrive second really speeds things up.
Our Roadster with a very strong engine cannot go as fast up these hills where second gear is needed without going over my 2600 rev limit. But it pulls the very tight uphill bends in second gear ok. It has 19 inch wheels with Excelsior sport radials 155X19. Gearbox is standard Model A, overdrive is 26% Mitchell and rear end 3.78.
Both are a delight to drive and impossible to say which is best.
Reading this to myself I think the message is stay with 3.78, put in 26% Mitchell o/d and if your gearbox needs any kind of attention put in the Mitchell synchro internals. For a strong engine ( higher compression, better camshaft, larger carb.) go for higher first and second gear ratios. For a standard engine I am not sure on this last point. One can up the ratio on either or none of first and second gears.
I put a plus 15% first and second in a friends cabriolet with standard diff and tyres. His only comment is "it goes very fast in reverse now, especially in backing out of my shed". He is 85 and a rather slow driver.
SAJ in NZ

Last edited by SAJ; 03-14-2019 at 03:51 PM. Reason: Changed 12% to15%
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Old 03-14-2019, 06:41 AM   #7
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Default Re: Mitchell transmission or overdrive

I have the 3.54 rear with the Mitchell synchro tranny, was going to get the overdrive, but don't think its needed since I just cruise at 60mph.
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Old 03-14-2019, 09:08 AM   #8
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Default Re: Mitchell transmission or overdrive

I ordered a 26% Mitchell two weeks ago for our Tudor with stock 3.78 rear end gearing. . I've had an old Borg Warner overdrive in the car since the late 1980's. Last fall the Borg Warner made a terrible clunk and then nothing. Permanent neutral. Tow truck ride back home. No more Borgs for us. Thanks for the great info guys! Makes me feel good about ordering a Mitchell.
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Old 03-14-2019, 09:13 AM   #9
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Default Re: Mitchell transmission or overdrive

Have a 36% Mitchel for the cabriolet but also have a cut down Columbia in the '28 pickup with 3.78's and REALLY like being able to split the gears.
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Old 03-14-2019, 03:24 PM   #10
bill boz
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Default Re: Mitchell transmission or overdrive

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Originally Posted by 1929 View Post
I have the 3.54 rear with the Mitchell synchro tranny, was going to get the overdrive, but don't think its needed since I just cruise at 60mph.
Did you opt for th 15% higher 1st and 2nd gear?
Thanks
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Old 03-14-2019, 04:03 PM   #11
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Default Re: Mitchell transmission or overdrive

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Originally Posted by 1929 View Post
I have the 3.54 rear with the Mitchell synchro tranny, was going to get the overdrive, but don't think its needed since I just cruise at 60mph.
I'm sure I wouldn't be driving at that speed even with the higher ratio diff and without an O/D.
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Old 03-14-2019, 05:44 PM   #12
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Default Re: Mitchell transmission or overdrive

A Model A has so much torque (125 ft lbs) relative to its weight that I can't see how splitting gears would be an advantage. The owner's manual wants you to get into high gear at 12 MPH.

I also agree that being able to cruise at 60 and better is not something that I would do without a modern brake and tire upgrade.

These are great cars, but they have their limits.
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Old 03-14-2019, 05:50 PM   #13
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Default Re: Mitchell transmission or overdrive

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Originally Posted by bill boz View Post
Did you opt for th 15% higher 1st and 2nd gear?
Thanks
I don't remember, it was 4 years ago, I just did what the Mitchells recommended. The receipt says ratio #3.
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Old 03-14-2019, 05:52 PM   #14
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Default Re: Mitchell transmission or overdrive

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I'm sure I wouldn't be driving at that speed even with the higher ratio diff and without an O/D.
Iam under 3000rpms at 60
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Old 03-14-2019, 05:55 PM   #15
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Default Re: Mitchell transmission or overdrive

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Originally Posted by Dick Steinkamp View Post
A Model A has so much torque (125 ft lbs) relative to its weight that I can't see how splitting gears would be an advantage. The owner's manual wants you to get into high gear at 12 MPH.

I also agree that being able to cruise at 60 and better is not something that I would do without a modern brake and tire upgrade.

These are great cars, but they have their limits.
Dick, my 16s stop on the dime, with all new brakes and good thick shoes from Randy.
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Old 03-14-2019, 06:23 PM   #16
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Default Re: Mitchell transmission or overdrive

If you do go with just the tranny, consider instead of a higher 1st and second, go with just the second. First is pretty high, especially for parades etc. Then there is a big jump to third. We opted to keep 1st as it is then a 15 percent higher second. Initial test drive, we liked it but winter hit before we could test it much.
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Old 03-14-2019, 11:34 PM   #17
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Default Re: Mitchell transmission or overdrive

Bill, Is this with your Roadster or Town Sedan?
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Old 03-14-2019, 11:41 PM   #18
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Default Re: Mitchell transmission or overdrive

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I am under 3000rpms at 60
Can we assume your engine is not stock? 3000 rpm is pretty high for a Model A engine.
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Old 03-15-2019, 01:10 AM   #19
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Default Re: Mitchell transmission or overdrive

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Bill, Is this with your Roadster or Town Sedan?
That is in the roadster.
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Old 03-15-2019, 06:19 AM   #20
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Default Re: Mitchell transmission or overdrive

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Can we assume your engine is not stock? 3000 rpm is pretty high for a Model A engine.
Inserts, 6-1 Head, Ross forged pistons,counterbalanced crankshaft,lightened flywheel, etc.
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