Need advice with solid rear axle build

[Jonathan D]

For my build I'm going with a coyote and a tremec 600 and a solid rear axle. I'm thinking of building the rear myself and I'm looking for advice on what I need as well as gear ratio. Here is what I have for a build list so far:

79-93 mustang parts
-31 spline Moser axles
-31 spline Ford Racing Traction LOK Limited Slip Differential w/ Carbon Discs - 8.8
-Rear End Installation and Bearing Kit - 8.8
-Ford Racing 3.73 Gears
-Ford Racing Differential Cover

I installed 3.73's in my 2000 mustang gt and I really liked the way it pulled off the line and that car had under 300hp. I want the cobra to have that "take your breath away" pull off the line....do I need gears this steep with 400 hp or should I drop down to 3.55 or lower?

My number one question is with the axle housing itself. What are the options? Do I need to start calling salvage yards asking for a 79-93 mustang housing or will others fit? What is everyone else doing?

[rich grsc]

I would think 3:55 better choice, maybe even 3:27, this is a much lighter car.

[ClemsonS197]

I'm using a Tremec 3650 w/ a Coyote and I went 3.55's. I'm starting to wonder if I should have gone 3.27's and the car isn't even on the road.

[Jeff Kleiner]

The TKO 600 has a first gear ratio of 2.87 and a fifth of .64. With the 600 either a 3.73 or 3.55 should make a good combination providing a quick but useable first gear and a fifth that is comfortable for cruising without being too high to use below 70 MPH.

Conversely a 3650 has 3.38 first and .68 fifth. Combining a 3.27 or 3.08 rear ratio with it to tame the super short first gear results in a fifth gear combination that is hard to use below 70-80 MPH.

Jeff

[riptide motorsport]

I'd listen to Mr. Kleiner.

[Jonathan D]

Thanks everyone. After considering Jeffs points about the first gear ratio of 2.87 maybe I will drop to the 3.55's, should make the car a little easier to launch. Can anyone offer any advice on where to get the housing? Is salvage yards the only option? Assuming if I go this route I just need to measure and it should be 59.25” hub to hub?

[Jacob McCrea]

Jonathan,

I think the hub-to-hub measurement above is correct. I know that this issue has been discussed from time to time, so a search should show whether I am correct. Given all of the parts you already have, I would try to find a Fox-width 8.8 axle in a junkyard, on Craigslist, or the like. The correct years are 1986-1993, although you may find one retrofitted into an earlier Fox Mustang. Around here they are routinely for sale, complete, for $150-$300, so it is a nice opportunity to save some costs over a new one. My understanding is that some of the later 8.8 axle housings will work, but unless the correct-width axles are used tire and rim choices are not as vast. I don't know the minutia of all of that, but it has been discussed here from time to time. I would pick up a driveshaft from a Fox 5 speed car while you are at it. Between the "core" and having it shortened, with new u-joints, you should only have about $175 into it. Good luck!

[CraigS]

When you list the parts in your first post I am not clear if you already have those parts or if they are on your purchase list. On the width. No matter what you do mnake sure you end up at Fox width. It makes wheels so much easier. Someone will double check me on how late of an axle housing you can get but within reason you will be buying axles either way.Fox width was all 4 lug and I think all drum brakes so you need axles, calipers, and caliper brackets. Later axles had disc brakes but were too wide so you still need axles and caliper brackets. Look at their websites and talk to Richard Oben and/or Mike Forte for better details. Note that their websites have nowhere near all the stuff they have available so a call is good.
http://www.northracecars.com/
http://www.fortesparts.com/
Realize that the Coyote is a higher revving engine than most 302s or 351s so take that into consideration when reading recommendations on gear ratio.

[Rkloehn]

Fox axles go thru 93 then you get into sn axles which are 5 lug. Northrace cars makes really nice disk brake brackets and they work with c clip eliminators. Fox width axles from axle shaft flange to shaft flange are 59 5/8" with c clip elims and a little less with out. If i were you i would go 3:55 gears

[Jonathan D]

Thanks for all the info guys, it really helps. To CraigS, that is the purchase list I started, nothing purchased yet, trying to complete the list of what I need and see how much cheaper it will be than just buying the complete axle from FFR.