Hi speed aftermarket rear end?

[Del in NE Ohio]

Went this AM to help a friend who had just removed engine and transmission from a '31 pickup. We plan to dive into the rear axle assembly tomorrow. As we discussed possibly changing the ring and pinion for a higher ratio, we decided to try to determine what rear end ratio is in the truck. So, we jacked up the truck. A complete 360 degree revolution of the rear wheel resulted in slightly less than 2 revolutions of the drive shaft. Seemed odd, so we did it again. What do we have here?

Been on meds lately, so I am reluctant to do the math. Seems like a really high rear end ratio, or am I still in a pharmaceutical fog?

[Sparky]

When you hold one wheel stationary don't you double the ratio through the differential? So it sounds like you have the standard 3.78:1. 3.78/2 = 1.89 which is about what you say you measured.

[Fullraceflathead]

Yes it is doubled when turned one completed revolution with other wheel locked from moving.

[Tom Wesenberg]

Yep, with one wheel turning, it will turn twice as fast, so you need to make two revolutions of the tire and count the revs of the engine. Or, an easier way is to hand crank the engine 3.78 turns and see if the rear tire makes exactly two turns.

[BILL WILLIAMSON]

A 3.78 ratio is a quite decent ALL AROUND RATIO. I, personally, would not change it, like, how fast do we need to go?
Bill W.

[BRENT in 10-uh-C]

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My experiences is a Model-A with a high-speed Ring & Pinion greatly enhances the drivability. At minimum, we typically install a 3.54 ratio and often install the 3.27 ratio. These two ratios are good for another 4-7 MPH at cruising speed. While that does not sound like much, it takes an engine that likes 45 mph and turns it into roughly a 50 mph vehicle. Often times this is just what is needed to keep from holding-up traffic.

[BILL WILLIAMSON]

Originally Posted by BRENT in 10-uh-C

My experiences is a Model-A with a high-speed Ring & Pinion greatly enhances the drivability. At minimum, we typically install a 3.54 ratio and often install the 3.27 ratio. These two ratios are good for another 4-7 MPH at cruising speed. While that does not sound like much, it takes an engine that likes 45 mph and turns it into roughly a 50 mph vehicle. Often times this is just what is needed to keep from holding-up traffic.

GOOD point you made, Brent,
"Maybe" these inputs will help Del consider what is the best for HIS NEEDS.
3:78's are fine for ME, as I'll be mostly in Big City driving.
Bill W.

[CarlG]

3.78 is fine by me as well. 80% of my driving is city driving as well. For the long haul open highway tours, I just slip it into overdrive, sit back and let the engine loaf!

[TinCup]

I think for me more importantly 354 gears would take a car that likes to run 45MPH and reduce stress on the engine by reducing rpm's. The added benefit is the extra 4-7 when you need it.

[Del in NE Ohio]

Thanks guys! I completely forgot about the X2 if rotating the one wheel. 3.78 is what I would expect to find. I installed the 3:54 in my truck a year ago. It did make things a little less effort at 45-50 MPH. If I had it over, I might have opted for the 3:27, but that is some serious $. Thanks again!

[Mitch//pa]

I put 3:54's in Lucy ( Tudor) with an HC head, it does relieve the R's but would go with 3:27's next time around. I'm not looking to blow any axle keys out of the hole

[modelAtony]

I put 3:27 gears in my 31 Tudor back in 2001 and turned my car into a great driving experience. They advertise that the gear will give you 10 mph extra speed. Wrong it will be 7 mph but 7 extra mph is really great in a bone stock A. Through the years have added other up grades, check my avatar info. Have fun modelAtony tony white Lafayette, LA

[Tom Wesenberg]

I put 3.27 ring and pinion in my friend's pickup, and would also like to build a 3.27 rear end for my car.