AA Truck Auxiliary Trans question

[alsfarms]

Does anyone here have experience with the Model AA auxiliary transmission?  I would like to speak with you.

Al

[alsfarms]

Does anyone here have an AA truck with the two speed gear box?  If not, where is the best place to talk to Model A truck guys?

Al

[Dave Mellor NJ]

I had one that I sold at Hershey about 10 years ago. It was an underdrive within the driveshaft on 28 -29s. It had a kickdown switch in the floor to activate it. Looks kind of like a peanut. It was replaced in 30 with the 4 speed trans.

[alsfarms]

Dave,  Do you recall what the gear reduction was when shifted into under-drive?  Also, did this particular box make the very traditional "whine" when run in under-drive?  I have such a box and am considering doing some home-brew engineering to reverse the box making the out-put to be the input and run it in reverse making it function as an overdrive box.  Do you or anyone else have enough experience with the Ford AA Aux. box to share an idea on my thinking?

Al

[alsfarms]

I am sure I am not the first person to dream up a change of direction for the Ford AA aux. box.  If you know of a Doodle bug or anyone that has made  the alteration I suggest above, it would be nice to hear from you.

Al

[Dave Mellor NJ]

Al I probably know less than you about these things. They have AA chapters within the Model a clubs that would know. As for doodlebugs, the whole purpose is to get low speed power to have a cheap tractor.I have seen AA outputs into a TT input

[jpage]

I doubt that switching the gears around would benefit you in any way. They were designed to be an underdrive system for more pulling power. Most of the trucks with the 2 speed tranny were also equipped with a worm gear rear axle which is inherently slow and noisy in itself. Before I ruined a good 2 speed trans, I would just switch to the regular 4 spd tranny and change the rear axle to a ring and pinion. Still, even with that mod, you'd be pressed to get more that 45 mph out of the truck. I really don't know why so many folks want to change and update these historical vehicles, but that's just my opinion.

[alsfarms]

Hello JPAGE,  Your point is taken.    I have seen a few interesting similar gear boxes originally designed for use on the TT trucks, reversed.  In farm country they would be used in what ever fashion would render the truck more useful.  Yes, some creativity was involved to reverse or make a double under like in Doodlebug applications.  It is not my intent make an AA into a F-350 Superduty, but to help relax the engine a bit so I can further and safely enjoy the old girl, with a little better road speed.  Further, I do like them for what they are 'antiques' that can still be used for fun or some light farm duty.  It is a bit off topic, but I also use a 1947 (first series) GMC 1-1/2 ton dump truck.  (This truck has an after-market Brownie under-direct and overdrive transmission installed in the dive-line).  I have more fun with Jimmie than I do my modern trucks and am still able to accomplish farm work at the same time and with a bit better road speed.  I also have a John-Deere 70 as my back-up baler tractor that I enjoy as much as the newer tractors and funner to run.  The neighbors all like to hear an old popping john working in the field and have told me so.  The AA instead of having a direct and under will just have a direct and over.  I will post my determinations and if the trans reversal can work on the AA later.  Any other thoughts on this subject.

Al

[oldford]

I recently installed a two speed Mitchell overdrive unit in my 28 AA. I went with the 36% unit and could not be happier. It's not cheap, but it fits the bill. Not sure where the 2 speed discussion came from, but with an AA, it does not matter if you have the 3 speed or  4 speed transmission, top gear is still 1:1. What is nice about the Mitchell is the fact that the entire torque tube drops out and is replaced by another with a box in the middle. It's really a bolt on unit that doesn't change these 'historical vehicles.'  With the Mitchell, I can enjoy my firetruck and move along at 45 mph without worrying about some jerk driving up my back-side.

 

Frank

Edited November 24, 2017 by oldford (see edit history)

[alsfarms]

Frank, how much gear howl are you getting from the Mitchell conversion?  What you are telling me is exactly the same as I am trying to achieve for my project but maybe using the original direct and under aux. box reversed.  I realize that I will need to get crafty with some machine work, but that is a creative part of machine work.  Have you ever run or been around a truck with the original aux. box?

Al

[oldford]

I cannot notice any gear howl from the Mitchell, since the Ford worm drive rear is noisy enough. I have the original dual high gear box for the truck but have never used it. I think the dual high is either straight through in one position and underdrive in the other position. It was used to lower the ratio for trucks that only had the factory three speed in conjunction with the high speed rear (5.8:1). The installation of the Mitchell could not have been easier. Drop the old torque tube and driveshaft out, put the new Mitchell with its own torque tubes and shafts in. Easy-Peasy...

 

Frank

[alsfarms]

Frank,  Is your truck a 1928 or 29?  Did you ever run the truck with the factory aux. direct/under-drive?  I am trying to use original pieces and come up with an overdrive unit by reversing the in-put to be the out-put. 

Al

[oldford]

My truck is a 28. The dual high that I have came from a donor and I never ran it. It appears complete with the control pedals and all...

[alsfarms]

Do you know what the  under drive ration is on these aux boxes?  I wish someone, with a manual, would speak up.

Al

[oldford]

This chart came off the AA Ford information web site (http://fmaatc.org/aa-fords)

It shows the ratios for each of the different auxiliary transmissions available at the time. It looks as though the ratio of the dual high box is 1:1 in high and 1.47:1 in low...

[alsfarms]

Hello Frank,  Do you know why Ford used the terminology : Dual high?  I had also thought that the Ford Aux box was a direct and under.  What I am seeing on the chart is the Aux box is an under and a double under?  Do I see that correctly?
Al 

[oldford]

I think the two columns at the far right side of the chart are for two different rear end ratios. The low speed rear was 7.25:1 and the high speed rear end was 5.17:1.

[alsfarms]

Yup Frank, you are right, I missed read that bit of information, so my original thought was correct, direct and under for the Ford Aux box.  It appears to me that if the box was to be reversed, (the input becomes the output) you would add about 8 MPH instead of reducing  the MPH by 8.  Does my assessment appear correct?   Thanks for taking the time to read and respond to my inquiry about these AA aux box under-drive transmissions.

Al

[oldford]

That's how I would read it too... I'll check tomorrow to see how different the input is from the output. Not sure if you can just reverse it without some machine work being done.

[alsfarms]

I envision needing an adapter replacement for the in-put and out-put castings to make it fit back into the driveshaft torque tube.  I am not sure how to deal with the rocker shifter but I am certain that something could be worked up to shift the thing.

Al

[viv w]

Hi Al,

 Have a look at Fordbarn.com and see if there is anyone on there that can offer advice,

Regards

Viv.

[alsfarms]

Thanks Viv, I have been over at that site, not to much action for the AA trucks let alone one with the under-drive transmission.

Al