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Old 02-05-2014, 05:40 PM   #1
w0ivb
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Default Best overdrive

] What is the best way to obtain near hiway speed; overdrive or overdrive transmission for a model A ?
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Old 02-05-2014, 06:35 PM   #2
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Default Re: Best overdrive

Mitchel Gear splitter. many advantages over a 5 speed . least thats for me .
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Old 02-05-2014, 06:42 PM   #3
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Default Re: Best overdrive

You need to do your own research, then read what others like and then decide.
There are 3 methods in common use.
5 or 6 speed transmission, top gear being OD.
Middle of the driveline OD. As with Mitchell, Ryan or Volvo type.
Integral with rear end as with a Columbia.
All are expensive and all require machine work to install.
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Old 02-05-2014, 07:14 PM   #4
Art Bjornestad
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Default Re: Best overdrive

Also Borg Warner
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Old 02-05-2014, 07:14 PM   #5
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Default Re: Best overdrive

There is a lot of information here and on the HAMB. It would take you a solid weekend to digest everything the you can find doing a couple of searches.

Start here:

http://www.fordbarn.com/forum/search...archid=3639519
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Old 02-05-2014, 07:24 PM   #6
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Wink Re: Best overdrive

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I've got a Borg-Warner over drive, but the next one I get will be a Mitchell. Any O/D is good if it is built right and treated right. But the
Mitchell is built simpler and more foolproof to me. The 4 and 5 speed newer car/truck transmissions are nice too, so I'm told by the owners.
But the old crash-box Model-A Ford tranny's are part of the true Model-A
experience to me. And I'm going to stick with mine.

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Old 02-05-2014, 07:41 PM   #7
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Default Re: Best overdrive

Quote:
Originally Posted by Pete View Post
You need to do your own research, then read what others like and then decide.
There are 3 methods in common use.
5 or 6 speed transmission, top gear being OD.
Middle of the driveline OD. As with Mitchell, Ryan or Volvo type.
Integral with rear end as with a Columbia.
All are expensive and all require machine work to install.
One more you didn't mention was the F150 4-speed OD. Required no machine work to install. Kit was completely bolt in.
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Old 02-05-2014, 07:46 PM   #8
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Default Re: Best overdrive

Quote:
Originally Posted by CarlG View Post
One more you didn't mention was the F150 4-speed OD. Required no machine work to install. Kit was completely bolt in.

Maybe I am misunderstanding but how is there was no machine work involved in retrofitting one to be installed in an 'A'? The ones I have seen required several hours of machine work. What am I missing?
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Old 02-05-2014, 07:47 PM   #9
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Default Re: Best overdrive

I have the F150 and love it! Ron W
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Old 02-05-2014, 07:50 PM   #10
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Default Re: Best overdrive

Brent, is there no work in the others? It's a matter of who does it. Ron W
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Old 02-05-2014, 08:13 PM   #11
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Default Re: Best overdrive

In answer to Brent's post. I am one of several that build the F150 OD. I cannot answer for how the others build their kit, but for my kit, this is how I do it. I do all the machine work - and there is lots of it. When the customer gets the "kit" all the "machine" work is done. All the customer has to do is the final installation. I even include the extra and unique bolts and nuts required as well as the gaskets (U Joint cover and TT to Banjo gasket.).

Now to address the initial inquiry. Before anyone buys or install any kind of OD for their "A" I recommend they do all their homework. Research every type and style of OD, then analyze your driving requirements and driving style, then make a decision. Not everyone needs an overdrive. Also if one wants and OD in order to drive faster be very sure your engine and equally as important their brakes can handle the extra speed.
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Old 02-05-2014, 08:25 PM   #12
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Default Re: Best overdrive

Quote:
Originally Posted by BRENT in 10-uh-C View Post
Maybe I am misunderstanding but how is there was no machine work involved in retrofitting one to be installed in an 'A'? The ones I have seen required several hours of machine work. What am I missing?
Hee hee. I guess if you just whip out your wallet and have someone else do the job, there is no work involved.(for you)

Oh, I didn't mention the F150 conversion because I consider it the absolute least desirable of the choices.
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Old 02-05-2014, 08:41 PM   #13
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Default Re: Best overdrive

let us know how you make out
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Old 02-05-2014, 09:35 PM   #14
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Default Re: Best overdrive

I have 3.54 gears in my '31 RDPU and don't feel it is worth the money to go to an overdrive. I run mine comfortably at 55. What do you consider "highway speed"? Anything over about 55 and the fenders act like airplane wings making the car uncomfortable to drive. If you are passed by an 18 wheeler pushing a lot of air you will find yourself in the next lane without moving the wheel.

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Old 02-05-2014, 09:54 PM   #15
Kevin in NJ
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Default Re: Best overdrive

Do you really need an overdrive?

People seem to miss the point that the A was designed to be driven 60 MPH. See the original ads. Read some of the stories about the A's being driven when new. They got 50,000 to 80,000 miles on an engine before redoing the babbitt.

Of course that requires the engine returned to its original specs such that it is tightly balanced which many are not very close these days.

If you are not going to be putting thousands of miles on your car each year then an overdrive is not needed to be able to run 60 to 65 for extended runs on a regular basis

There is a lot to getting the A running 65 comfortably. Most is attention to details with getting the original parts back to factory tolerances. A properly set up back to original A is a pleasure to drive at 65 and a dream at 45.

You will be putting out some serious $$$ for the overdrive. Before you do that you should be perfect comfortable with your car running 65 as it is. If the car is not running nice then it will not be better with an overdrive.

Keep in mind I am not saying the overdrive is bad. Just that it is probably only worth the money for people who do some serious miles on their car.
Anyway something to consider.
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Old 02-05-2014, 10:05 PM   #16
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Default Re: Best overdrive

My recommendation would be a Mitchell 26% overdrive. It is not difficult to install and does not molest the Model A, except for a small slot in the wooden floorboard and floor mat of carpet. It is easy to operate and will work well with the standard 378 ring & pinion, and covers just about all driving conditions. Even though it is a $2200 investment it holds its value. It adds that much value to the car, or can be removed and sold for close to that value. They are well built and the manufacturer stands behind them and the Mitchell folks are nice people to do business with.

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Old 02-06-2014, 12:04 AM   #17
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Default Re: Best overdrive

Several years ago we reviewed the various overdrives that went into the torque tube. Each has a plus but the Mitchell seems to be more versatile because you can shift in and out of overdrive at any time, where the Borg Warner you need to have the ability to "coast" slightly when engaging it, which means that you can't shift into overdrive if you are climbing a hill. We like being able to engage 2nd high on some of the passes we have encountered. But the Borg Warner is nice on the flat lands. We have around 50,000 miles on the Phaeton with the Borg Warner and about 25,000 miles on the sedan running the Mitchell. The other plus to the Mitchell is it is all new nothing to machine or work on just pull the old torque tube and install the new one with the Mitchell.
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Old 02-06-2014, 12:40 AM   #18
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Default Re: Best overdrive

I guess is if you have one of the rare stock Model A's that really can cruise effortlessly at 65 mph, than you really do not need an overdrive..... I have never seen one in our local club, so the folks who do want cruise at 55-65 mph, and have their cars in good running order, do install some form of overdrive. I would suggest riding with someone who already has one first, and see for yourself how they work. I rode in a friends nicely restored Roadster, with a Mitchell OD, and came away very impressed, and immediately had one installed in my car, and have never regretted it. With the stock 3.78 rear end, the 26% ratio is about perfect and the unit is bullet proof.
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Old 02-06-2014, 12:44 AM   #19
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Default Re: Best overdrive

I guess we can put "Best Overdrive" on the list with:

What kind of oil
Which Radiator
Alternator vs generator
12 volt vs 6 volt
Anitfreeze or water
etc vs etc
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Old 02-06-2014, 01:02 AM   #20
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Default Re: Best overdrive

On page 102 of Schild's "Restorer's Model A Shop Manual" it shows a chart with multiple torque, HP, compression, and speed curves, from a 1930 factory catalogue. 60 MPH corresponds to 2800 RPM. At 2800 RPM you have fallen way off peak HP and torque, meaning the engine has to really labor to make 60 mph happen. If I drove any Model A I have ever come across at 2800 RPM I would vibrate the teeth right out of my skull. I have run a temporary tach in many of these cars so I can know exactly what the RPMs are doing. However Ford did the original factory crank/flywheel balance no one seems to be able to duplicate it today. Plus the universal joint is a single joint, not one on each end of the drive shaft as was done later. Thus there is a constant fast/slow component to the rotation of the driveshaft and thus the tranny components and crank. This, too, sets up an oscillation. Plus there were few roads where you could actually accomplish 60 mph back then, unless you were on a track, so to me the 60 mph was a lot of hot air to accomplish some nifty advertising.

Remember, these are long-stroke motors, very unlike the short stroke high-revving engines of today. A long stroke motor has all its torque at the low end. Study the HP and torque curves, and study them again, and get your head around what those curves are trying to tell you.

If there are any Barners who have driven stock Model As out there at 60 mph for thousands of miles without engine damage let them come forward. To me, a stock A redlines at 2000, maybe 2200 rpm. I never run mine over 2000. (I have a full time tach).

IMO anything over this and you are shortening the life of your babbitt, especially the center main, which gets the most wear anyway.

I had a 3.54 gearset, but if you do the math, this is only 6% OD. The Mitchell is 26% OD and gears can be split depending on the road conditions, such as using high second in the mountains. I switched to the Mitchell and back to 3.78 and I am much happier I never need to go over 2000 and I can do about 65 mph at that rev. on level ground. I don't like to go that fast in an A but those of us who live in metropolitan areas sometimes have to use the interstate to get out to the more rural areas.

I want my babbitt to last a good long time. Choose your priorities, do your research, and make your choices accordingly.

And Terry has a great suggestion about riding with others who have the various forms of OD to see what they are about.
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