AA Underdrive
 

Hi Group, Has anyone heard of a "28/'29 AA Underdrive unit accessory?
Are the units worth anything? I would think an overdrive unit would be desirable.
Also I have a short driveshaft. Are they of any value?
Thanks for your reply.
Wayne Duprez Model A Club of Long Island

Re: AA Underdrive
 

The underdrive unit you have may be a standard Ford unit called a Dual High. In my opinion, highly UNdesirable. this gives you a stump puller. If the short shaft you have is the same length end to end as the dual high, it is VERY desirable...


Post a photo, please


Frank

Re: AA Underdrive
 

As mentioned, the Dual High term is a misnomer. It should have been described as a "dual-low." It is an "underdrive."

A typical Ebay price for an AA Dual High unit is $75 to $100.

I know. I explored briefly the possibility to install the Dual High BACKWARDS in a car rear axle propeller shaft assembly - and thus create an "overdrive."

Most large truck users of that era IF they wanted to increase the top speed of their AA trucks (typical 4 speed maximum road speed with a HIGH SPEED rear end is 45 mph) was to install a "Warford" overdrive transmission. This was a TRUE overdrive designed to replace the Dual High at the intermediate shaft location.

The Dual High was Ford produced and pretty much aimed at the 28-29 AA truck 3 speed truck market. The 30-31 and beyond AA 4 speed was usually provided with a "intermediate shaft" although there was room for the Dual High or something else, which could be applied. Methinks most went for the aftermarket Warford - which was available from Ford dealers. The Ford "Green Book" (published first pre-WWII and available until the mid-'50s) described the possibilities and parts required to set up a AA/BB & beyond truck to a users requirements.

Today there seems to be about equal number of extant Dual Highs out compared to extant Warford units - although today the Dual High can be had for less than $100 and the Warford sells for upward of $1000.

We drive faster today - that's why.

Joe K

Re: AA Underdrive
 

i have worked on an AA with a high/low range on the back of the normal 3 speed. Grain truck. if that is what you are talking about.

Re: AA Underdrive
 

According to my Dad, who drove the AA commercially, the "Dual-Hi" was nothing of the kind. It indeed was an Underdrive which allowed a 40hp motor to move huge loads, like 20 joints of 30' drill pipe. The first AA they owned didn't have a Dual high and had a road speed of under 30 mph, so they left it in the field when possible and rarely roaded it.