Another Mitchell Overdrive question - 26% or 36%?

[SDJason]

Hi all,

Long story short - I'm planning to have a Mitchell Overdrive installed.
I have a 1930 Town Sedan, with a Snyder's 5.5 HC head and 3.78:1 rear end.

The local Model A folks who will be installing this recommended I get the 36% OD. From reading various threads here, it looks like 26% is what most folks get and recommend.

So - just want to pick the collective brains here: why should or shouldn't I get a 36% overdrive vs. a 26%?

Thanks!

[Big hammer]

Originally Posted by SDJason

Hi all,

Long story short - I'm planning to have a Mitchell Overdrive installed.
I have a 1930 Town Sedan, with a Snyder's 5.5 HC head and 3.78:1 rear end.

The local Model A folks who will be installing this recommended I get the 36% OD. From reading various threads here, it looks like 26% is what most folks get and recommend.

So - just want to pick the collective brains here: why should or shouldn't I get a 36% overdrive vs. a 26%?

Thanks!

I would call Mitchell :-) and see what they recommend! Your $ their business
They will want you to be a happy customer.

[[email protected]]

I had a 30 Town Sedan with a 5.5 head and a 3.78:rear end. It easily cruised at 55-60 mph
and worked very well when I took it up in the mountains. I have never owned or driven a 36% car but I was very happy with the combination I had.

[daveymc29]

What size tires you running? I talked with Steve Mitchell at length about the different combinations. He felt that the ideal was a 4:11 rear with the 36% unit for my roadster with 600 X 16's on the ground. However, I already owned a 26% and used that with a 3:54 ring and pinion. That worked well for me with a Model A tranny. I bought the Mitchell tranny with the 15% increase in first and second. Not quite so good as the stock box on really steep climbs but on normal mountain roads here in Calif. it is quite satisfactory. I just drove it from the Bay Area to Sonora a couple of days ago and it pulled all but the steepest part of 108 in third over. Had to go to direct on the steepest and in one place I went to second over. Maintained in excess of 45 MPH on the entire trip with out any overheating or lugging. Most of it between 55 and 60 on the open road.

I drove the roaster to Texas with the 26% Mitchell and 21 inch tires. I had no problems with the combination, altho I had a loose wire to my 6V+ground alternator that gave me fits. Found that a couple of years later. I would lose number 2 cylinder at speed and if I went faster then I would also lose number 3. For some reason I could enrich the mixture on the choke a turn and a half out and the car could then run satisfactorily but not 100%. More like 70% of normal, and as with most loose wire things, it came and went so the majority of the trip I was Okay. Wish I knew how to send that story and pictures, it's pdf and I'm lost there.

I had a pickup with Borg Warner 36% but I didn't check the differential. Probably 3:78 with a "touring" engine. Would cruise 60/65 all day and had a lot of oats from an overhead by Cragar, the old Iron one. Made it quite hot in the cab when warm outside. Sorry to say I sold it. It had 600 X 16 radials on it and was quick as a cat.

[Tom Endy]

The 26% work best with a 3.78 ring & pinion. A Snyder 5.5 head enhances it. I believe the 36% is too high unless you have a hot rod engine installed. Back in the days when the only overdrive that was available was a cottage industry 33% Borg Warner and they were too high. Many changed out the ring & pinion to a 4.11.

Tom Endy

[sphanna]

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Tom Endy is right, I believe. I have a Fordor 1930 and used to cruse at 50 mph before installing my Mitchell 26%. 50 mph with a 3.78 rear end gives you about 2200 rpm. The 26% OD will give you 63 mph at 2200 rpm. That is fast enough. Any more and the engine labors too much with any incline. On the expressways, if I try to not hold up traffic , I can cruise all day at 65 and I still have enough power to climb gentle hills. A 36% will give you only 5 mph (68) at 2200 rpm and the stock engine with a 6:1 HC head will disappoint you at 36%.

[TerryH]

I also have a 1930 Town Sedan, with the 5.5 HC head, along with the Mitchell 26%, and stock 3.78 rear end. Have had this combo for over 10 years now, and I feel it is ideal for most uses. I drive S. California freeways frequently, so being able to cruise easily at 60-65 is very nice. But I also drive surface streets quite a bit, and like the response this combo gives. I personally feel the 36% would be too high for my liking and would not yield much, unless, like Tom Endy said, you have added more power than the HC alone head provides.

[Y-Blockhead]

Originally Posted by TerryH

I drive S. California freeways frequently, so being able to cruise easily at 60-65 is very nice.

Wait!! What?? Go 60-65 on a SoCal Freeway??

[SDJason]

thanks all!
I've got some things to think about. I think my most common use would be using 2nd gear with OD on hills, and maybe an occasional foray onto a freeway (would want to be able to comfortably do 65 to do that).

[BILL WILLIAMSON]

Sometimes, in our haste, we might tend to OVERGEAR our car. Like, BIGGER is BETTER. Are we tryin' to do 65 @ a FAST IDLE???
Trivia: Ted has a Coupe with a PINTO! He put in a Mitchell O.D. BACKWARDS, so he could climb REAL STEEP mountains. I don't know what rear end gear he used???? (We have some REALLY DUZZY Mountains, here, like TIOGA PASS, WHEW!) If you DON'T know how to DOWNSHIFT, you might come home in a BOX!!!
Bill Careful

[TerryH]

Originally Posted by Y-Blockhead

Wait!! What?? Go 60-65 on a SoCal Freeway??

I don't normally drive the 405 during rush hour in my Model A, but during later morning until early afternoon, 60-65 is no problem.....at least in Orange County. Have also made several trips down the 5 to San Diego, with few problems....

[Y-Blockhead]

Originally Posted by TerryH

I don't normally drive the 405 during rush hour in my Model A, but during later morning until early afternoon, 60-65 is no problem.....at least in Orange County. Have also made several trips down the 5 to San Diego, with few problems....

Yeah, 405 is what I was referring to. We have a couple of "windows" where you can get on the 405. Between morning rush hour and lunch hour and after lunch until evening rush hour.

[mrtexas]

Originally Posted by Y-Blockhead

Wait!! What?? Go 60-65 on a SoCal Freeway??

In the middle of the night on a holiday weekend maybe.

[Arlyn Bieber]

S Jason, Here is my suggestion, come to the Ramona Garage and I will let you drive my heavy slant window sedan with the 36% and 3.78 rear end. I guarantee you will never want anything less. Now keep in mind you need a strong engine for the 36%. If your engine is half worn out then the 26% might work best. All I know is from experience, over the last 15 years we have installed bunches of Mitchell overdrives all 36% except for a couple and those people wish they had installed the 36%. You should see our stack of used driveshafts! Yes, when I climb Scripts-Poway expressway which is a 7% grade I drop out of overdrive, no big deal, when I get to the top of the hill I shift back into overdrive. Arlyn Bieber, Hansen Ford Garage

[Benson]

Do you have a Stipe IB330 or UN-reground original stock Ford cam in this engine?

[Arlyn Bieber]

My engine has a "B" camshaft that has not be reground. Since good "B" cams are hard to find most of our engine rebuilds have the Stipe IB330 camshaft.

[SDJason]

Thank you Arlyn, I'll give you a call. Since you guys pretty much built my car, I'll assume it has the Stipe cam.

[Benson]

Originally Posted by Arlyn Bieber

My engine has a "B" camshaft that has not be reground. Since good "B" cams are hard to find most of our engine rebuilds have the Stipe IB330 camshaft.

Arlyn,

Thank You ... I figured that you must have one of those low-end torque cams to have enough low end torque to pull the higher gears!

In 1976 I built a B engine with reground cam ... I was very disappointed when I found the lack of low end torque when shifting from 2nd to 3rd when compared to my other stock Model A engine with un-reground Model A camshaft.

It was years later that I found out why the B engine was so "gutless" at lower RPM.

[Jim Brierley]

Get the 26%, anything higher will lug your engine down and possibly even damage it, especially with your heavy sedan. I use a 23% from Ryan, and with the 3.78 rear end it is very nice. Aim for about a 3:1 final drive ratio.

[larrys40]

Arlyn always has a good handle on things as well as Tom Endy. Like Tom I run an older 23% Ryan and a 3:54 rear in my 30 tudor along with a 5.5 head. It's a good highway cruise and does well in town as well. With the 330 cam and hc head and 3.78 with 36% you should be good. I have to say it's one of the best upgrades you can do to make them cruise easier with today's traffic. Yes, the rest of your drivetrain, steering, brakes etc have to be up to snuff... but then you would want them to be anyway.

Arlyn, looking forward to getting back out your way sometime and driving that SW Town sedan!

Larry Shepard