Rear axle Performance Upgrades?

[Subzero]

I just picked up a 1972 9 in rear axle with 3.00 gears for my 1968 F100 with 3.25 gears. I'm replacing all wear parts and bearings, brakes too. Noticed there's a lot of performance stuff out there for these such as mini spools and entire trac-loc third members online. I'm not sure if it's a 28 spline or a 31 or how to tell. The truck is a daily driver for the most part but I don't mind it being a little fun too. Are there any good upgrades for these to be able to make the truck spin tires better? How much of a difference will I notice now that I have a 3.00 instead of a 3.25?

[ultraranger]

If you're wanting 'performance,' you went backwards in going from the lower 3.25s to the higher 3.00s.

All Bumpside F100 9-inch rear ends had 28-spline axles and 28-spline differentials. The ONLY Bumpsides that had 31-spline axles were the '68-'72 F100s with a Ford 9-3/8" rear end.

Spools/mini-spools are fine for drag racing (straight line driving) but, aren't good for street use.

Bumpside F100s weren't available with Traction-Lok differentials until 1968.

I installed 31-spline axles, from a '71 F100 9-3/8" rear end, in the 9-inch rear end housing under my '69 F100. With that, I was able to install an N-case 9-inch 3rd member with a 31-spline Traction-Lok differential with 3.50 gears I pulled from a '75 F150 4x4 pickup.

'69 F100 9-inch 28-spline axle on the left. '71 F100 9-3/8" 31-spline axle on the right.



'69 F100 9-inch 28-spline single track 3.50 3rd member on the left. '75 F150 9-inch 31-spline Traction-Lok 3.50 N-case 3rd member on the right.







Bumpside F100s with a 9-inch are 28-spline. Some Dentside trucks have 28-splines but most Dentside F100s/F150s have 31-spline axles. All Bullnose ('80-'86) F100/F150 9-inch rears are 31-spline. You are more likely to find a Traction-Lok 3rd member in a Dentside but chances are it will have 31-spline axles/differentials, and it's definite if it's from a Bullnose that it will be 31-splines.

[youngone]

Hi Steve when you install your 5.0 ho and auto transmission what gears are you going with? You going for power or economy, just curious what mpg s you expect to get. I plan on going a similar way but with a carb.

Thanks Pat.

[HIO Silver]

3.50 gears, a locker, and, if ya want, disc brakes. A 28-spline is fine.

[ultraranger]

Hi Steve when you install your 5.0 ho and auto transmission what gears are you going with? You going for power or economy, just curious what mpg s you expect to get. I plan on going a similar way but with a carb.

Thanks Pat.

Plan is to run the 3.50 gears I have. My '69 F100 isn't my daily mode of transportation so, I'm not terribly concerned about fuel mileage although, I figure with EFI and an overdrive it'll get between 18-20 MPG (guessing). If it gets more, great. If it gets less, I'm not torn up about it.

....I also have a 3.89 gear set I could install in one of the 9-inch 3rd members I have. I also have a 3.25:1 9-inch Traction-Lok 3rd member as well as a 2.50:1 ratio 9-inch 3rd member (at one time, I had a really high 2.47:1 ratio 9-inch 3rd member). --I guess the 2.50s would be good if I wanted to make a high-speed pass at Bonneville.

[sargentrs]

I installed a Richmond PowerTrax No-Slip in mine. Limited slip with your original carrier and axles. A little pricey at $500 but an easy install into the stock original carrier. http://www.fordification.com/forum/view ... &start=165

[69timemachine]

I have an Eaton TrueTrac differential in my 9". It was in the $500 range as well, but I highly recommend it since it works so smoothly and seamlessly. It feels like an open diff in turns, but sends power to the tire with the most traction when there's slippage.

I had a PowerTrax in my '76 El Camino I used to have, and my buddy had one in his '89 GMC pickup. We were both having trouble with wheel hop for some reason. Also had tire chirp on the inside tire when making a turn since they are basically one-wheel-drive in turns. The good thing about PowerTrax is that on a C-clip style rear end, you can install it without having to remove the carrier.

The Eaton TrueTrac is the best in my opinion.