Thinking about Rear Axles

[David_Conwill]

I was daydreaming about my Falcon today, and came up against the rear axle question. The current 3.10:1 geared axle (7.5-inch or 7.25-inch, whatever it is), works okay with, and will probably live forever behind my 170/3-speed, but a mildly warmed up 200 and 5-speed will eventually reside in my Futura.

Seems like overdrive is almost unnecessary with the current (3.10) gear ratio, so I was thinking about locating a ‘60-‘61 rear axle with 3.56 gears to freshen up and install when the 200/5-speed combo takes residence.

Most people, though, are going for the Maverick 8-inch rear citing strength, and, to a lesser extent, parts cost. The downside is that the standard gear ratio for the Maverick axle is 2.79:1, and I’m not that big a fan of the freeways. Plus that would really make the 5-speed unnecessary. I think Currie does offer a variety of 8-inch gearsets, however.

I see a sprinkling of 8.8-inch rear axles in Falcons too, usually an Explorer axle that has had one side of the housing narrowed to center the pinion and make the axle the correct width for a Falcon. The 8.8-inch seems to be the “new” 9-inch, with a good variety of parts available in the aftermarket due to its use in lots and lots of Mustangs. The downside is that there are no 4-on-4.5-inch bolt-pattern 8.8s, so I would probably have to do a 5-lug conversion on the front.

So... What should I do?

1. Keep the Falcon 3.10
2. Go Falcon 3.56
3. Swap to Maverick 8-inch (recommended ratio?)
4. Swap to Explorer 8.8-inch (recommended ratio?)

Thanks for your help with my continually evolving plans.

-Dave

[rocklord]

I made a table of transmission gear ratios times the final rear axle ratio to determine overall gearing. I found out that a T-5 from a 4Cyl Mustang with a 3.00 rear axle were almost identical to a V8 T-5 with 3.55 rear axle.

4Cyl T5 with 3.00 axle
1st - 3.97 = 11.91
2nd - 2.34 = 7.02
3rd - 1.48 = 4.44
4th - 1.00 = 3.00
5th - 0.79 = 2.37
Rev - 3.70 = 11.10

V8 T5 with 3.55
1st - 3.35 = 11.89
2nd - 1.93 = 6.85
3rd - 1.29 = 4.58
4th - 1.00 = 3.55
5th - 0.68 = 2.41
Rev - 3.15 = 11.18

You're correct in that the 2.79 rear axle ratio is too tall for the T5, but not a 3.00 with the 4Cyl T5. The 4Cyl T5 is usually cheaper than the one for the V8, and the 3.00 rear gears are fairly easy to find for the 8-inch.

I have a 65 Mustang with a 2.77 3speed and a 7.25 rear end with a 3.20 axle ratio. I'm planning on using a 4Cyl T5 with a Maverick 8-inch rear and a 3.00 rear axle.

Hope this helps.

[David_Conwill]

Dan,

Thanks for the thoughtful reply, I hadn’t considered the 4-cyl Mustang transmission. This is similar to what I was thinking when I was still thinking about keeping my 170. My thought was to put an S10 4-cyl T5, with its deep first gear, between my 170 and my 3.10. The 170 isn’t a bad motor (though I’ve decided I really want all the mains found in a 200), but it doesn’t have enough low-end grunt to pull that 3.10 around town, and I think the 4-cyl T5 was GM’s solution to that problem with the 2.5L “Iron Duke” and the S10's weight.

Will a Mustang 4-cyl T5 hold up to a 200? I’ve zero experience with 200s, so I don’t know how much torque they’re really producing. Will the extra liter of displacement make a difference? I guess I didn’t think so when I was thinking the half-liter difference between the Iron Duke and the 170.

I guess I’ll keep my eyes peeled for a 4-cyl Fox body with a manual. Does anybody think I’ll have problems with my 195/75/R14s rubbing, given the extra width of a Maverick axle?

-Dave

[rocklord]

The 4cyl T5 is rated for 240ftlb of torque, more than enough to handle even a built NA 200. The Mustang 4Cyl T5 tail housing can be swapped out with the S10 T5 housing to move the shifter up. If you want to use a T5 out of an S10, read this article from richwrench about installing one in his 62 Squire wagon

http://www.rickwrench.com/index79.htm

If you use the S10 transmission, you will have to use the GM transmission yoke and corresponding driveshaft yoke, but since you have to shorten the driveshaft with either transmission, that isn't that big of a thing. Just make sure you get the GM yokes when you get the transmission.

[rbohm]

since you want the 3.00 rear gear, i would go with the 8" rear end, plenty strong and easy to find parts for, and if you grab one from a granada(75-80) it will fit your car with little effort. if you want to keep the four lug wheels, then grab an 8" from a maverick with the 250, 70-73 iirc. use the ford four cylinder T5 with the S10 tail shaft housing to move the shifter forward, then take the S10 T5 and the ford tail shaft housing bolt them together and sell that combination to someone who is swapping a chevy V8 into an MGB. that way you recoup some of your money from your trans swap. if you get the maverick rear end, you can still use disc brakes up front by going with the scarebird brackets.