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Old 06-25-2017, 03:07 PM   #1
Nick in Fayetteville
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Default Mitchell Overdrive Question

I am thinking about putting a Mitchell Overdrive in my '31 Tudor. Presently, I have a 3:54 high speed rearend in it. Will the Mitchell work with my present rear end or should I change back to the original stock ratio? What would be the biggest problem with the Mitchell and my high speed rearend working together? Thanks.
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Old 06-25-2017, 03:11 PM   #2
1931 flamingo
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Default Re: Mitchell Overdrive Question

Not sure BUT do a search as the Mitchell and it's ratios have been covered buku times.
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Old 06-25-2017, 03:14 PM   #3
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Default Re: Mitchell Overdrive Question

or call Mitchell, they would be glad to help.
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Old 06-25-2017, 03:32 PM   #4
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Default Re: Mitchell Overdrive Question

Mitchell is a 26% or 36% overdrive depending on what you choose,a 3.54 is about a 10% increase in road speed over a stock 3.78..so basically if a stock A is happy at fifty mph,yours does 60 with the 3.54 and say you buy the 26% OD you would top out at close to 80 mph..heres the neat thing about the Mitchell,you can 'split' gears so instead of three you now have six..so the additional torque load of the 36% or (46% if you choose)on the engine is moderated by six gear combinations..you might shift more,but keep in mind the mitchell is syncromesh,you can actually never have to shift the flat gears against load again..I was on the fence till I looked at it..

http://mitchelloverdrivemfg.com/

Not anymore..
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Old 06-25-2017, 04:53 PM   #5
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Default Re: Mitchell Overdrive Question

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Originally Posted by Railcarmover View Post
Mitchell is a 26% or 36% overdrive depending on what you choose,a 3.54 is about a 10% (actually 6.3%)increase in road speed over a stock 3.78..so basically if a stock A is happy at fifty mph,yours does 60 (53.2)with the 3.54 and say you buy the 26% OD you would top out at close to 80 mph(67)..heres the neat thing about the Mitchell,you can 'split' gears so instead of three you now have six..so the additional torque load of the 36% or (46% (32.3%)if you choose)on the engine is moderated by six gear combinations..you might shift more,but keep in mind the mitchell is syncromesh,you can actually never have to shift the flat gears against load again..I was on the fence till I looked at it..

http://mitchelloverdrivemfg.com/

Not anymore..
ACTUAL changes in red but the point is pretty much the same as a standard diff with a 33% O/D. I think it would be quite acceptable if your motor has been upgraded some.
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Old 06-25-2017, 04:58 PM   #6
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ACTUAL changes in red but the point is pretty much the same as a standard diff with a 33% O/D. I think it would be quite acceptable if your motor has been upgraded some.
Yeah like I was saying..except the caveat of 6 speeds,even with a stock engine you can find a happy combination..
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Old 06-25-2017, 05:04 PM   #7
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Default Re: Mitchell Overdrive Question

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Originally Posted by Nick in Fayetteville View Post
I am thinking about putting a Mitchell Overdrive in my '31 Tudor. Presently, I have a 3:54 high speed rearend in it. Will the Mitchell work with my present rear end or should I change back to the original stock ratio? What would be the biggest problem with the Mitchell and my high speed rearend working together? Thanks.
My sedan is setup that way and it really does not work well unless you have a very strong engine, I am going to put 16" wheels on my car which should help, if not I am going to change back to a stock 3:78 rear.
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Old 06-25-2017, 08:44 PM   #8
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Default Re: Mitchell Overdrive Question

One of the guys in our club has the Mitchell 26% in a coupe with 3.54:1 rear end ratio. Even with the smaller 16" wheels, it is a little anemic. On flat ground, once it gets going, it is great!
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Old 06-25-2017, 10:17 PM   #9
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Default Re: Mitchell Overdrive Question

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Yeah like I was saying..except the caveat of 6 speeds,even with a stock engine you can find a happy combination..
Yup, high second is a very handy gear, especially when towing. In one of my cars, I also have the Mitchell gearbox. I change between high second and ordinary third in one motion - move both sticks at once.
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Old 06-25-2017, 11:26 PM   #10
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Default Re: Mitchell Overdrive Question

I have the 26% on a Mitchell tranny and 3:54 rear end, 600 X 16's on the ground. This is on a light roadster with a "Touring Engine," inserts "B" grind on cam and Police head, Fairly well balanced engine with pressure oiling (Could have been better balanced, I believe) and it pulls the mountains here in CA quite well. In my opinion on a light car this is a good combo. Mitchell told me more ideal would have been 36% with a 4:11 rear. That is what I intend to put in the coupe. It also has 600 X 16's on the ground.
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Old 06-26-2017, 01:36 AM   #11
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Default Re: Mitchell Overdrive Question

Synchro, How do you shift both at the same time? Mine are not close enough. Did you modify the Mitchell lever so it's closer?
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Old 06-26-2017, 02:33 AM   #12
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Default Re: Mitchell Overdrive Question

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Synchro, How do you shift both at the same time? Mine are not close enough. Did you modify the Mitchell lever so it's closer?
foxfire42, Remember, our cars are RHD so the Mitchell shift lever is in a different position. I have one car that was LHD and the lever position makes that impossible so I made up a cable shift for that one. I did consider modifying the lever but went cable instead. I think modifying the lever would have been easier.
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Old 06-26-2017, 03:35 AM   #13
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Default Re: Mitchell Overdrive Question

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One of the guys in our club has the Mitchell 26% in a coupe with 3.54:1 rear end ratio. Even with the smaller 16" wheels, it is a little anemic. On flat ground, once it gets going, it is great!
Thank you so very much for the feedback, have the 16s getting powder coated so will give them a try, then if it is still struggling will change out the rear, my engine has the 5.4 heads and is balanced, not really potent so most likely will not work well with just the 16s, I screwed up!
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Old 06-26-2017, 09:38 AM   #14
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Default Re: Mitchell Overdrive Question

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Thank you so very much for the feedback, have the 16s getting powder coated so will give them a try, then if it is still struggling will change out the rear, my engine has the 5.4 heads and is balanced, not really potent so most likely will not work well with just the 16s, I screwed up!
With a stronger motor, you will be just fine. Enjoy!!
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Old 06-28-2017, 11:07 PM   #15
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Default Re: Mitchell Overdrive Question

With all the Mitchell comments, while in Coos Bay last week I saw a tudor from ID with TWO Mitchells in the drive line!! Not sure what the reason was as didn't see the owner but the engine had a OH valve head on it and other upgrades. The shift levers were mounted just ahead of the seat and parallel with the seat. Looked like a nice job but why?
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Old 06-29-2017, 02:08 AM   #16
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Default Re: Mitchell Overdrive Question

Im trying to do the math and its making my head hurt. That is to say that I doubt he uses them simultaneously. Maybe one is geared for speed and the other for torque?
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Old 06-29-2017, 02:17 AM   #17
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Default Re: Mitchell Overdrive Question

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Im trying to do the math and its making my head hurt. That is to say that I doubt he uses them simultaneously. Maybe one is geared for speed and the other for torque?
If both are 26% units, using both at once would give him 59%.
If both are 33% units, using both at once would give him 77%.
Wonder what diff ratio he was running!
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Old 06-29-2017, 05:53 AM   #18
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Default Re: Mitchell Overdrive Question

Maybe one Mitchell is in reverse for hill climbing.
Like Bill says about the pinto engine car.

A pinto (never seen one, but used the engine in a Cortina for some years) needs to run flat out to make power.
With an overhead valve it would allow more revs.
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Old 06-29-2017, 06:29 AM   #19
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Default Re: Mitchell Overdrive Question

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Maybe one Mitchell is in reverse for hill climbing.
Like Bill says about the pinto engine car.

A pinto (never seen one, but used the engine in a Cortina for some years) needs to run flat out to make power.
With an overhead valve it would allow more revs.
One installed forward and one backwards would end up the same ratio as having none, only more power lost on the way to the back wheels.
Also never seen a Pinto but I believe they are not he world's best motors which fits with "need to run flat out to make power". The Lotus motors in the Cortina - well that's a whole different story.
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Old 06-29-2017, 07:16 AM   #20
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Default Re: Mitchell Overdrive Question

If you call Mitchell, they will tell you that the 26% reduction with a 3.78 ring and pinion set up I ideal.
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