AA Pickup diff query

[Kiwimagoo]

We are restoring a '28 AA pickup for a customer. He'd like to have a better diff ratio (and be able to travel faster than 40mph !) than what is available with the standard worm drive diff.
Can someone please advise what conversions or modifications can be done to achieve this? We still want to retain the original suspension etc.
Any ideas appreciated.
Thanks

[Steve Plucker]

Ford never made a AA pickup that I know of AND the rear axle you show does not look like a Model AA worm gear axle to me...is it?

More photos....

Pluck

[Neil Wilson]

The worm drive AA rear axle came in a 7.25:1 or 5.17:1 ratio. The 5.17:1 ratio yields about 40 mph. So, it sound like the truck referenced has the 5.17:1 gear ratio.

The next step to gain additional speed is to install an overdrive. There was a Warford transmission (replaced the coupling shaft) which was a three speed (underdrive, 1:1 ratio, and overdrive). The overdrive yields about a 30% increase in output.

You can likely get more AA responses at http://forums.aa-fords.com/.

[jhowes]

Jack up the rear and give the crank turns while counting the turns of the cank until the wheels make one turn. This will give you the ratio that you have.. Meanwhle can you post pictures of the truck so that we can see what it is.

[Joe K]

The Warford overdrives can be quite pricey - think $400 to $800 - but their advantage is they replace the "intermediate shaft" directly with little intervention.

Some have problems with the universal joints on these as they require a "mixed" yoke assembly - which can be ordered as parts, or combined from two other Spicer universal joints.

I have heard tell that it is possible to "reverse install " the commonly found and not necessarily expensive Ford "Dual High" (which despite the name is actually a 'dual low') But this can be problematical since the dual high is made to replace the AA intermediate shaft directly - and reversing it requires modification of the dual high casing - or the universal joint housings.

A better solution may be to buy into the Mitchell Overdrive transmission. You may have a standard 3 speed Model A transmission now (since you're talking "early" AA) and substitution of the Mitchell unit should be simply a matter of unbolting one and bolting in the other.

Agreed that 40 mph is hardly competitive in todays roadworthy world.

I would say about twice a year a Warford Overdrive is seen over at the AA Ford Forum classified. It's still cheaper than a Mitchell.

Joe K

[modelAtony]

Sponsored Links (Register now to hide all advertisements)

Originally Posted by Kiwimagoo

We are restoring a '28 AA pickup for a customer. He'd like to have a better diff ratio (and be able to travel faster than 40mph !) than what is available with the standard worm drive diff.
Can someone please advise what conversions or modifications can be done to achieve this? We still want to retain the original suspension etc.
Any ideas appreciated.
Thanks

I believe Mitchell Overdrives are now ava for the AA. Have fun modelAtony Lafayette,la

[modeleh]

You had better do some legwork to find the best running wheel and tire combos you can and balance them. There is alot of mass in an AA wheel/flap/tube/tire combo. The 28-29 may be a little lighter due to the spoked wheel, but may be harder to find wheels that run true. 30-31 ran discs or Budd wheels, heavier but more sturdy. When you get going over 50mph you may get a bad case of shaky fenders. Stopping will be no problem, but running fast in an AA may not be as fun as you think. Been there done that.

[Bob C]

Mitchell does not make an OD for the worm gear rear axle. How about
an overdrive transmission like this.

Bob

[BrianBurkert]

I have a '31 AA with the 5.14:1 bevel axle. I can concur with Neil's speed assessment with similar 5.17:1 ratio. 40 mph is cruising speed clocked with gps. I have a flatbed body, dual wheels, on 157" chassis, so I am heavier than an express "pickup." Unless you do something with an overdrive, the old truck just doesn't got very fast.

[KCTA Chris]

I've been questioning the same here as I'd like to put my truck back on the larger AA chassis. With 4 years of daily driving on a car chassis it would be hard to slow down a little. I looked at welding a 9" ford center section but when you factor quality machine work and axle fab it's more than the Michell unit.

[Kiwimagoo]

Thanks guys. Appreciate the quick responses. Please keep the suggestions and experience coming !
Will the overdrive units that are used in the regular Model As work with the AA?

[Kiwimagoo]

Originally Posted by Bob C

Mitchell does not make an OD for the worm gear rear axle. How about
an overdrive transmission like this.

Bob

KCTA Chris - did consider the versatility of adapting a 9" centre section, but aside from the work, change in driveshaft angle etc, customer does want to maintain the originality. In looks anyway.

Bob C - What is that overdrive out of?

[CarlG]

Originally Posted by Kiwimagoo

Bob C - What is that overdrive out of?

That looks like the F150 4-speed OD tranny that was installed in an AA Firetruck.
http://www.modelaonly.net

[Tom Wesenberg]

Originally Posted by CarlG

That looks like the F150 4-speed OD tranny that was installed in an AA Firetruck.
http://www.modelaonly.net

I gree with Carl that this is the firetruck tranny, and that looks like the best solution to more speed for the AA. Just be sure to paint it Ford green.

[dumb person]

Is that a model T worm drive in the picture?

[Steve Plucker]

Originally Posted by dumb person

Is that a model T worm drive in the picture?

I was thinking the same thing and it also looks like it is in the vehicle up side down??? OR...Maybe that is just the way the photo was taken the more I think about it???

Pluck

[spdway1]

Originally Posted by Tom Wesenberg

I gree with Carl that this is the firetruck tranny, and that looks like the best solution to more speed for the AA. Just be sure to paint it Ford green.

This is what I am going with!!

[Brian T]

Originally Posted by dumb person

Is that a model T worm drive in the picture?

It is a AA probably 29, you can see the service and emergency brake toggles and rods on the left side, which the TT truck didn't have, what makes it look like a TT is that someone as added oil cups to the rear bearing cover and the end of the torque tube for improved lubrication.

[Kiwimagoo]

Definitely a Model A. Pic attached of the truck before being dismantled for restoration. Thanks for all the help - we've decided in favour of the F-150 gearbox.

Next issue to resolve is with modern roads, and this vehicle in all likelihood never being destined to carry much of a load on the back again, should we remove some of the rear leaf springs for a softer ride?????

[Tom Wesenberg]

Originally Posted by Kiwimagoo

Definitely a Model A. Pic attached of the truck before being dismantled for restoration. Thanks for all the help - we've decided in favour of the F-150 gearbox.

Next issue to resolve is with modern roads, and this vehicle in all likelihood never being destined to carry much of a load on the back again, should we remove some of the rear leaf springs for a softer ride?????

That truck didn't look like it needed to be taken apart and restored. From that one picture, it looks really nice.

I wouldn't remove spring leafs, and haven't heard of it being done on any AA's. I figure a truck should feel like a truck, and today's roads are pretty good, unless you're driving on the Minnesota potholes. On the news today it was reported that one guy hit a pothole and it made his airbags blow, sending the driver to the hospital and declaring his Geo Metro totalled.