Differential substitutions for higher speed
Differential substitutions for higher speed
I confess this is a rookie question. Has anyone found a substitute differential/axle that can replace the stock 30-31 differential/axle to increase the highway speed? And, do with without "extreme" modification of rear suspension, torque tube, etc.
Or even better, is there a substitute for the differential itself (ring and pinion gears) that would fit inside the stock case of the 30-31?
Comment: I spent an afternoon inside the shop of a hot rod builder, and those guys really think outside the box, while I look for bolt on replacement NOS type stuff. Perhaps an AA restorer has come up with an idea to increase highway speed.
Or even better, is there a substitute for the differential itself (ring and pinion gears) that would fit inside the stock case of the 30-31?
Comment: I spent an afternoon inside the shop of a hot rod builder, and those guys really think outside the box, while I look for bolt on replacement NOS type stuff. Perhaps an AA restorer has come up with an idea to increase highway speed.
- Chris Haynes
- Posts: 2203
- Joined: September 7th, 2003, 5:18 pm
- Body Type: 82A
- Model Year: 1930
- Location: Camarillo, CA
Re: Differential substitutions for higher speed
There are two different gear ratios for the AA. How to easily find out which you have depends on whether yous is a worm drive or ring and pinion. You mention ring and pinion so I will assume that is what you have. There might be a metal tag bolted towards the top of your case. If not remove the speedometer drive from the drive line. The ratio will be stamped on the drive gear. The "High Speed" gears used on the '30/'31 AA were also used on a WWII White Scout Car. These gears can sometimes be found at dealers of WWII truck parts.
- Chris Haynes
- Posts: 2203
- Joined: September 7th, 2003, 5:18 pm
- Body Type: 82A
- Model Year: 1930
- Location: Camarillo, CA
Re: Differential substitutions for higher speed
There are two different gear ratios for the AA. How to easily find out which you have depends on whether yous is a worm drive or ring and pinion. You mention ring and pinion so I will assume that is what you have. There might be a metal tag bolted towards the top of your case. If not remove the speedometer drive from the drive line. The ratio will be stamped on the drive gear. The "High Speed" gears used on the '30/'31 AA were also used on a WWII White Scout Car. These gears can sometimes be found at dealers of WWII truck parts.
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- Posts: 478
- Joined: June 3rd, 2013, 6:15 pm
- Body Type: 186-B stake
- Model Year: 1931
- Location: LHC Arizona & UP Michigan
Re: Differential substitutions for higher speed
I have had a couple high speed '30-31 differentials. One had the ratio tag on one of the bolts near the bottom. Another just had the ratio stamped on the case.
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- Joined: September 30th, 2009, 8:02 pm
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- Location: Massachusetts
Re: Differential substitutions for higher speed
It would take some research to find the right custom gear company to make brand new ring and pinion sets, but it's not impossible. As discussed, the Ford AA high speed ratio is 5:14 to 1 , (7 teeth on the pinion, 36 teeth on the ring gear). A custom gear manufacturer could copy the bearing diameters and other essential dimensions from a good Ford set, so that it fits properly in the case, but make a new ratio such as 3:85 to 1, (7 teeth on the pinion and 27 on the ring gear.) The truck would need a strong engine, more than 40 hp to pull properly at low speeds, but it would have a great top-end, probably hit 60 mph. A Stipe camshaft, a good distributor set-up, a downdraft carb, and a 6:1 head would probably do the trick to provide enough power to cover all the bases.
How many people would order a set to get the price down? Could the shop quote 12, 25, and 50 sets?
How many people would order a set to get the price down? Could the shop quote 12, 25, and 50 sets?
- emf
- Posts: 115
- Joined: March 21st, 2016, 5:21 am
- Body Type: Firetruck
- Model Year: 1928
- Location: Hudson, NY
Re: Differential substitutions for higher speed
I would almost guarantee that custom gears would cost more than a Mitchell. Why re-invent the wheel. Since I put a Mitchell on my truck with high speed rear, I can easily do 45 to 50 on the highway.
Frank
Frank
Re: Differential substitutions for higher speed
Emf can you expand more on the "Mitchell" I too have some Interest about my 29 3 speed w direct/under drive. I'm not sure which gear ratio in my work gear rearend.
- emf
- Posts: 115
- Joined: March 21st, 2016, 5:21 am
- Body Type: Firetruck
- Model Year: 1928
- Location: Hudson, NY
Re: Differential substitutions for higher speed
My truck is an early with 5:1 rear. I put a 36% Mitchell overdrive in and could not be happier. I can cruise at 45-50 all day long just jumping from 3rd to overdrive and back. The install was easy and all the parts fit as advertised. You just have to anticipate your stops a little more in advance...
Frank
Here is a link to the earlier discussion: viewtopic.php?f=1&t=5898
Frank
Here is a link to the earlier discussion: viewtopic.php?f=1&t=5898
Re: Differential substitutions for higher speed
Thank you EMF
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- Posts: 43
- Joined: May 19th, 2009, 7:19 pm
- Body Type: 82 B ?
- Model Year: 1931
- Location: Bonita springs Fl
Re: Differential substitutions for higher speed
65mph@ 2600rpm.built engine,BRAKES,Mitchell Overdrive .ran 50/55 today 60miles one way with the ac on today it can be done.have around 2000miles so far and run that speed all the time.but the devil is in the details
Build it to make you happy NOT other peoples opinions.
- blgitn
- Posts: 201
- Joined: July 6th, 2013, 6:36 am
- Body Type: 275-A
- Model Year: 1931
- Location: West Point, VA 23181
Re: Differential substitutions for higher speed
31SWFL,
You have my attention; how about some details?! Maybe some pictures?
You have my attention; how about some details?! Maybe some pictures?
R/ Roger.
- blgitn
- Posts: 201
- Joined: July 6th, 2013, 6:36 am
- Body Type: 275-A
- Model Year: 1931
- Location: West Point, VA 23181
Re: Differential substitutions for higher speed
Beg pardon. Just saw them in the other thread!!
Very nice!
Very nice!
R/ Roger.
- Chris Haynes
- Posts: 2203
- Joined: September 7th, 2003, 5:18 pm
- Body Type: 82A
- Model Year: 1930
- Location: Camarillo, CA
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- Posts: 43
- Joined: May 19th, 2009, 7:19 pm
- Body Type: 82 B ?
- Model Year: 1931
- Location: Bonita springs Fl
Re: Differential substitutions for higher speed
No doubt you can do 50 with5:14 and tires but why twist the engine that hard when you don’t have to.my truck with me in is very close to 3900#’s (38 and change depending on witch holiday )and one other note i’m Not running a bushing u joint,i’m Running needle bearings and there is pictures of it already posted some time ago.my main reason for doing what I did was the majority of people said it can’t be done and I lost track of smiles per mile
Build it to make you happy NOT other peoples opinions.
- emf
- Posts: 115
- Joined: March 21st, 2016, 5:21 am
- Body Type: Firetruck
- Model Year: 1928
- Location: Hudson, NY
Re: Differential substitutions for higher speed
I guess when I mentioned the speeds I achieved, I implied that my engine was running at a speed that would keep it together. With standard engine components for the A, your engine must be running over 3000 rpm. Go for it...
Frank