AA Transmission Replacement

[Cape Codder]

Is it possible to change the AA Transmission with a F-150 transmission? the truck presently has 5.16 rear end. Will this help to get the truck up to 50 mph with less RPM then original trans.?

[Mike Peters]

High gear on any AA transmission is 1:1, the 28-9 three speed or the later 4 speed. You will need an overdrive transmission to lower RPMs at 50 MPH. You already have the high speed rear end. Also, AA trucks weigh nearly twice as much as cars, and powered by the same engine, so speed is not their strong suit.

[Bob C]

Here is a picture that was posted of an F150 OD trans set up for a
AA firetruck.

[Cape Codder]

So then is the answer to have a lower number ring and pinion gear made? Or what is the modern alternative to this other than a Mitchell Overdrive?

[Ernie Vitucci]

Good Morning...Others may correct me...however, I don't think that expecting an AA with anything like a stock engine to be able to cruise at 50 miles an hour, except down hill, is a bit much. With a rebuilt engine, over-bore, main and rod inserts,
and a weber carburetor, you would be perhaps able to hold 40+ on fairly level roads...Ernie in Arizona

[Don Conklin]

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Alternatives would be a Laycock or BorgWarner overdrive unit. I have both both. They fit in the torque like a Mitchell. The Laycock shifts with a switch. The BorgWarner offers “more” overdrive but requires more controls and has a position where it will freewheel

This site probably lists people who can do this modification.

[David R.]

Overdrive would be likely be most effective way to get higher top speed but that would only help down hill or on level. You will still end up down shifting on hills any way. Keep on back roads and wave and smile when they pass you.

[Cape Codder]

First, I to thank you three for your responses and suggestions.
So let me get this correct, what you guys are saying is even if I had a new Ring & Pinion made (lower Number i.e. 4.11) because of the weight of the truck I'm not going to get any more speed.

Thanks again for the response.

[Don Conklin]

Another posibility would be the complete rear axle from middle thirty’s Ford truck they may have a lower numerical ratio. I think the bell on the torque is compatible and brakes are rod operated thru 1936.

Check, don’t take my word on this!!

[Bob C]

Originally Posted by Don Conklin

Another posibility would be the complete rear axle from middle thirty’s Ford truck they may have a lower numerical ratio. I think the bell on the torque is compatible and brakes are rod operated thru 1936.

Check, don’t take my word on this!!

Even into the 40's 5.14 was the high speed axle.


Bob

[nick c]

About 4 months ago I finished a complete restoration of my 29 AA. I installed a F150 - RTS 170 with 41% overdrive. The engine is rebuilt and mostly stock except for the single barrel downdraft from a Ford 300 inline 6 eng. and a centrifugal distributor. I cruise 50 mph at 2000 rpm's. has a 160* thermostat and temp gage and does not run hot. and I'm not lugging the engine when I shift from 3 gear to OD at 35 mph then run up to 50 and there's still more left to accelerate.
It was a lot of machining. When I bought the tranny, I didn't know which OD it was then later someone on the FB posted the letter code so you can decode the name plate on side of tranny to find out which OD it is.

[rotorwrench]

Back in the day, folks used the over and under gear boxes. There were kits supplied by the manufacturers to fit them into the drive line. The Warfords were likely the most common type.

[emf]

Originally Posted by nick c

It was a lot of machining. When I bought the tranny, I didn't know which OD it was then later someone on the FB posted the letter code so you can decode the name plate on side of tranny to find out which OD it is.

It doesn't get much easier than the Mitchell. I installed a 36% unit in my 28 AA in less than a day's work. Raised on the lift, dropped the torque tube, installed the Mitchell, drove it away. The hardest part was making the shift linkage because I did not want the cable shift. I can cruse at 45 without any problems, other than wondering if the brakes will be good enough to stop if some nut pulls out in front of me.


Frank