My 51 F-1 with 16" tires/wheels has the 4.27 rear end and I wanted something a little better for highway speeds so my optimum rear gearing I figured should be around 3.7 +- so in searching for a 9 inch rear end I settled for one with 3.50 gears.

I cleaned it up and painted it but not installed yet, I may have found a 51 F-1 parts truck with the 3.92 rear end and have started to think I might have better acceleration with the 3.92
I am going to use a T-5 trans with I beleive the .86 overdrive (5th gear) behind a rebuilt 49 Mercury flathead.

I know there are replacement/parts brakes bearings etc available for the stock rear end but is there any other things I am not thinking about that could be advantageous by using the 9 in rear end?

I would rather to have a better acceleration around town than the top speeds on the freeway, as long as I can do 65 comfortably and maybe up to 75 if need be would be good but this truck is going to be mostly stock other than the transmission so maybe I don't even want to ever get up to 75 ??
If you read this far thanks for listening to me ramble on!

Josh

 

Well, from a parts availability standpoint, both for the rear and the brakes, I would say the 9" has an advantage.

As far as power you shouldn'd have a problem with the T-5 in the lower gears giving you the zip you need around town.

Here's an RPM calculator I have used and found to be right on the money. Be sure to measure the "roll out" distance of your back tires. An accurate measurement there really helps.

Gear Ratio Calculator

 

Advantages of the Ford 9inch; gear ratio choices, shock geometry, brakes and sway bar if you want one.

Ok, I have very limited experiance with my truck so far but, I did go for a ride of 60 + miles yesterday. At 2200rpm I'm rolling down the road @ 55mph, and I'm pretty happy with that. I feel I need to do some more work on the frontend before I'll go faster.

The gear ratio I have in the truck right now was not my first choice. I was looking for a 3.25 gear, but because the 9inch had a 3.50 I would go with that, one less thing to buy and if I didn't care for it I could away change it later. It's still to early to say for sure right now, but yesterday I kinda wish I had a 3.70. Again to early to say for sure. So stay tuned.