1929 150-A rear axle ratio
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Joe K
Well-known member
My truck when I got it had the 4.11 rear. A little slow in real life, I changed it out to good effect (the truck is light without a load) to a 3.54 - which I would recommend for ANY Model A - providing you have a strong engine.
The only SURE way to confirm which of the two original ratios you have is to block up one rear wheel and then using the crank, turn over the entire system starting at the engine end. Count the number of turns in at the crank versus the number of turns out at the wheel - then account for the fact that a differential will make the rear wheel turn twice as fast if you're only turning one wheel of the two.
However, and since you're talking about a commercial vehicle, check your torque tube on the rear axle. If it is "straight sided" for the rearmost 2/3rds of the tube, then you have a 3.78 rear. If it is tapered uniformly between transmission and punkin, then it's likely - but not assured - to be 4.11.
We've discussed this issue years ago on the old Ahooga site - and while I can't confirm this from others, it is what I found on my CCPU. It would make sense that Ford would need a way to tell the 3.78 axles from the 4.11 axles while being assembled to the chassis. A tapered torque tube would do that.
Good luck with that 150A. My third choice of Model A to own After my own 82A CCPU and the 76A RPU.
Charlie Bass, our distinguished ex Congressional Representative from NH owns a 150A. He tells stories of apple picking while standing on the roof of his.
Joe K
The only SURE way to confirm which of the two original ratios you have is to block up one rear wheel and then using the crank, turn over the entire system starting at the engine end. Count the number of turns in at the crank versus the number of turns out at the wheel - then account for the fact that a differential will make the rear wheel turn twice as fast if you're only turning one wheel of the two.
However, and since you're talking about a commercial vehicle, check your torque tube on the rear axle. If it is "straight sided" for the rearmost 2/3rds of the tube, then you have a 3.78 rear. If it is tapered uniformly between transmission and punkin, then it's likely - but not assured - to be 4.11.
We've discussed this issue years ago on the old Ahooga site - and while I can't confirm this from others, it is what I found on my CCPU. It would make sense that Ford would need a way to tell the 3.78 axles from the 4.11 axles while being assembled to the chassis. A tapered torque tube would do that.
Good luck with that 150A. My third choice of Model A to own After my own 82A CCPU and the 76A RPU.
Charlie Bass, our distinguished ex Congressional Representative from NH owns a 150A. He tells stories of apple picking while standing on the roof of his.
Joe K
Thanks for the replies, but my question was not how to determine the ratio, as that topic has been discussed on this forum previously. Here is my question: What ratio was installed new, at the factory, on a 150-A? I understand that 3.78 was standard on most cars, and 4:11 was optional and was used on trucks, but how did the 150-A fit into this puzzle? If anyone has an original 150-A that still has the factory-installed differential (and you are 100% sure of this), please respond. Thank you.
Ron in Quincy
Well-known member
If the speedometer drive gear is still in place on the drive shaft it will be marked, for example, 9-34 which equates to 3.78, 9 teeth on the pinion and 34 teeth on the ring gear. The speedometer drive gear will have 19 teeth. If you divide 9 into 34 the answer is 3.78.
The speedometer drive gear on my very early 28 is marked 10-37; it has 18 teeth on the drive gear. The rear end ratio is 3.70; 10 teeth on the pinion and 37 teeth on the ring gear. This was the standard rear end ratio for most 1928's.
In late 28 Ford came out with the 3.54 ring and pinion, but it was only recommended for the Roadster which was the lightest A made. A 18 tooth speedometer drive was used with this ratio.
Ron
Ron
The speedometer drive gear on my very early 28 is marked 10-37; it has 18 teeth on the drive gear. The rear end ratio is 3.70; 10 teeth on the pinion and 37 teeth on the ring gear. This was the standard rear end ratio for most 1928's.
In late 28 Ford came out with the 3.54 ring and pinion, but it was only recommended for the Roadster which was the lightest A made. A 18 tooth speedometer drive was used with this ratio.
Ron
Ron