Questions about worm drive rear ends.

[midnite2336]

I am a new member and have a Sept. 28 built model AA. This truck has taken me more than 10 years to do. Now that I have it done and drive it on the road it is very slow. It has a worm drive rear end. I also have a 29 AA but I don't want to change the rear end and not have my 28 original. Can I get a higher speed gears for the 28 rear end? Can you tell me the gear ratio I have now and what gear ratio do I need and does anyone have these higher gears for sale ? You guys are great with your wealth of information on the model A and AA. Thanks, Midnite

[Chris Haynes]

The gear ratio is usually stamped on the speedometer drive grear.

[Neil Wilson]

The worm drive gears are the same for '28 and '29. So, if you have a '29 worm drive axle which is a high speed, then you can remove the gears and put them in the '28 axle. Your should expect to be able to go 40 mph (max of 45 mph) with the high speed gears.

Finding a good set of gears will be very hard and will cost up to $700.

If you are lucky enough to be looking at the gear set, divide the number of ring gear teeth by the number of worm/pinion teeth. Looking at the gears is also the only way to determine their condition!

If the rear axle is still assembled then the following procedure can be used to determine the ratio. Turn a rear wheel (with the other held stationary) for one turn and count the number of times the drive shaft or engine turns over. If you are counting engine turns, then make sure the transmission is in high (which is the 1:1 ratio or straight through position for the transmission). The count of turns times two is the axle ratio.

A 28/29 worm, high speed axle will result in slightly over 2-1/2 turns of the drive shaft (2.585 turns) to make the 5.17:1 ratio. When the drive shaft turns over 3-2/3 times the axle ratio is 7.25:1 (a low speed).

Also, keep in mind, that if your truck has a Ford "dual high" or other manufacture's over/under drive, then this extra gear box must be shifted so that it is straight through (i.e. a 1:1 ratio through the extra gear box).

[midnite2336]

Thanks Neil for the information. The 28 I have has a worm drive and the 29 has a conventional rear end. This is why I don't want to switch rear ends. I also don't know why I said I wanted 21" wheels as I know that they are 20". I am interested in the spook wheels you have but I don"t know how hard it would be to find the snaplocking rings. Can the locking rings for the steel wheels used on the later model be used on the spook wheels as I have some of them? I must have the 7.25:1 ratio rearend in it now. At 20 MPH the engine is turning pretty fast. My zip is 42153, thanks. Bob

[Chris Haynes]

The spoke wheels won't fit on the late '29 rearend.

[Neil Wilson]

Bob,
The '29 AA's originally had a worm drive axle (except for a very few with a unique bevel gear axle as shown in the picture below). The '28 steel spoke wheels can be used on the '29 axles.

Ford released the more common bevel gear axle starting January 1930. However, commercial vehicles (A and AA) continued to use the '29 cab and sheet metal until about May/June 1930.

The split rings used for the TT 20" wheels and wheels for '29 into '33 can all be used on the steel spoke wheels. Finding lock rings which are pit free is not easy.

The 7.25:1 worm drive axle will yield 27.8 MPH at 2200 RPM for the engine.

If you are interested in wheels without lock rings, send me an e-mail at wilsmor@juno.com with your request and zip code. I will send pictures and cost. To your zip, one wheel should cost $28.00 for shipping (Fedex).