The guide to Fox Chassis Rear Axles

[blake4591]

I've been doing a lot of research on axles and figured I should share what I've found. I'm sure most of its been posted before, I'm just putting it in one easy to find place.

So to start out

All 7.5 and 8.8 housings from 78 to 98 are the same width (this may or may not include the few 6.75s). They all also came with the same 28 spline pattern on the carriers. This means that any axle shaft can in theory be used in any housing assuming the correct brake hardware for the shaft is also used.

The 8.8 axle was released in '83 and made its way into the fox platform in '86.

Factory Mustang and other fox body cars.
Housing width is 59.25" with zero center section offset. Axle shaft length is 29.25"
Brakes are 9" or 10" 4 lug Drums

Gear ratios from factory are normally
2.26 for 4.2L v8 auto 78-82
2.47 for 5.0l v8 auto 79-??
3.08 for v8 all trans 82-84/5ish?
2.73 for v8 manual 87-93
3.27 for v8 auto 87-93
3.27 in 7.5" for N/A 4 cylinder
3.45 in 7.5" for turbo 4 cylinder (except 85 and 86 SVO and below 87-88 TC)


Popular Swaps
**All numbers below are based on comparison to factory fox body mustang.**

87-88 Turbo Coupe and 93 Cobra 8.8" axles are basically the same with 30" (3/4" longer) axle shafts meaning, they are 1.5" wider overall.
brakes are 10" 4 lug vented rotors

Gear ratios from the factory:
3.55 for the manuals
3.73 for the autos
3.08 on the 93 Cobra


87-92 Lincoln Mark VII 8.8 axles are 30.5" (1.25" longer) per side, meaning total width is 2.5" wider.
brakes are 10.5" 5 lug vented rotors
gearing is normally 3.27 or 3.08

SVO and 87-93 Saleen shared these axle shafts.


94-98 SN95 8.8 and 7.5 share the same 30" (3/4" longer) axle shafts, meaning they are 1.5" wider overall.
have two options for rear brakes

GT and v6
10.5" 5 lug non-vetned rotors
cobra (non IRS only?)
11.65" 5 lug vented rotors


99-04 SN95 housings are 3/4" longer per side, and the axles are 1.5" longer per side but they continue to share the 94-98 rear brakes.


Door tag Axle codes for fox body (missing the code for 3.55s)

Conventional or "open" rear ends break down as follows:
8-2.73, Y-3.08, 5-3.27, F-3.45, 6-3.73.

Locking or "Traction Lok" break down as follows:
M-2.73, Z-3.08, E-3.27, R-3.45, W-3.73.

7.5 is approximately 40lbs less than a 8.8 when similarly equipped.

Please add other useful information and correct any thing I have wrong.

Blake

[mudgepondexpress]

Don't forget the old 3.08 ratio (I have never seen an 82 5.0 V8 with anything but a 3.0.

Kenny

[Black97Tbird]

I was wondering on the source of the 3L08 rear that was swapped into our 86GT auto. I had the date code, not not sure. I swore it was july 88 or so, does that sound right?

[blake4591]

Added years for the v8 ratios. I don't think the earlier v8s had the ratio consistency the later years did.
The 3.08s where available in the 87-93 but they had to be optioned and as far as I know aren't that common.

[1986Saleen]

The SVO axles are the same length as Mark VII.
(Also used on 87-93 Saleen Mustangs.)

[gotboost?]

1. 84 SVOs had 3.45s
2. 85-86 SVOs had 3.73s

[xctasy]

Your info is perfectly summarised, but you missed the funniest and quite common odd ball ratio ever, the open wheeler 2.29. Its the worlds tallest gear ratio axle ever, and our Foxes got it with the Ford 7.5 inch 2.29 axle, 78 to 82 V8 on all Foxes. It was mostly with the single and dual exhast D code 4.2 engine 80 to 82 engine, but some F codes from 78 to 82 might have gotten it. The 5.0 F code was an option on the Cougar, XR7 and T bird in 1981, but not the other Foxes. When it didn't have an AOD, it got the C4 OR or C5 with the moon shoot axle.

Be aware that Fords with SROD 4 speed boxes in the non V8's were quoted as overall 2.49 top gears in some publicity blurbs, but there is no 2.49:1 axle. Fords copy editors were playing with as.

When a 3.08 axle ratio 7.5" diff got an SROD , it got the small 0.81:1 top gear four speed with the 2.3 or 3.3, and it was called an 2.49:1 overall top.

With The "Boss Is Back" 5.0 2-bbl and SROD 4 speed 5.0 4-bbls, they got widder 0.70:1 tops, and a 2.16:1 over all top.

As far as I can tell, the 7.5 only has the 2.29, 2.73, 3.08,3.27,3.45, 3.55, 3.73 and probably 4.10 options (in the Ranger) from the factory, but a whole swoop of aftermarket ratios.


The vast majority of 1980's 7.5's are 2.29:1 ratio ratios found behind the 255/4.2. In 1981 to 1982, there was no auto V8 option and from 1978 to 1981, almost unbelivable to conceive, no Traction Locking diff option at all. How anyone coped with an open wheel non locking axle on any frozen American pavement even with 85 hp let alone 119, 132 or 139 hp is totally beyond me. WOT WER FORD THINKIN?

If you wanted an auto with a locking diff, it was from 1981 to 1982, only the 255 4.2 liter engine and 3.08:1. The W code Turbo package had the 3.45 as a locking diff option, if I recall.

[blake4591]

Updated again.

I have come to the understanding that the earlier year fox axles are not nearly as documented as the later years. Probably because everyone throws out the early axles to replace them with the later stuff. Also if I want to go set a land speed record I can use a 7.5. Haha

[FoxChassis]

The 2.29:1 ratio is actually 2.26:1. (Standard with the Capri/Mustang 4.2L in '80 and '81, unsure about other models.)

There is also a 2.47:1 ratio. (Standard with 5.0L/C4 Capri/Mustang in '79, unsure about other models.)

The 2.26:1 and 2.47:1 ratios were "open", at least in the Capri/Mustang. Traction-Lok wasn't available in the C/M until the '81 model year, and not available with the 2.26:1 ratio anyway. If you wanted T-L with the 4.2L in '81 you had to get the 3.08:1 ratio.

[mcfairmont]

My 79 Mercury Zephyr Z7 is a 302 auto,and has the 2.26 ratio. My old 78 Fairmont 2 door sedan, was also a 302 auto, but it came with 2.47s, as did my buddys 79 Mustang Ghia HB, 302 auto. My 78 Fairmont race car was origionally a 2.3 4 cyl. and 4 speed, it had 3.08s in a 7.5, yet my 79 Fairmont 2 door sedan Ghia, was a 200 cube 6 cyl. auto, yet it had the 8 bolt cover 6 3/4" rearend, like a Pinto, or early 6 cyl. Falcon or 65-66 Mustang.Kinda odd that the 4 banger had a bigger diff than the 6.

[xctasy]

Okay, revise that to 2.26 and 2.47. How cool is that? I bow to superior knowledge!

The first Fox had a 7.5" diff, but the 6.7/6.875" 8 bolter was an inclusion into the lighter Mustang and then some of the standard duty Fairmonts. If it had a blue color high mount 3.3 engine, with a C3 or it needed a 2.73 or 3.08:1 ratio, it would be downgraded to the clunky, very early Round Body Falcon/Pinto/Mustang II derived 23 spline diff. A lot of 3.3's got saddled up with it too. I'd guess if its got a V code for the trans, chances are 50 % or greater that its got the Sterling 6.7 code on the diff.

The 2.3 was variously going to be a turbo option, so it got the 7.5 often, but not always.

[Black97Tbird]

Lots of great info here, but I have a few questions.

I've known about the bonneville ratio axles for a while, but I always just assumed that it was to make up for the early transmissions without overdrives. So are these all in the smaller diameter axles? Was there ever any ratio(s) below 2.73 in the 8.8s?

[webestang]

Added years for the v8 ratios. I don't think the earlier v8s had the ratio consistency the later years did.
The 3.08s where available in the 87-93 but they had to be optioned and as far as I know aren't that common.

My 88 5.0 LX vert has a 3.08 ratio.

[tiptopss]

So would the longer axles (94-9 slide right into a 79-93 factory rearend? Think my car would look better with an additional 1.5" on each rear tire.

[1984mustanger]

A simple question, what is the optimal gears for a 302 with T5? Not looking for a highway driver, just best for torque and HP.

[mcfairmont]

A simple question, what is the optimal gears for a 302 with T5? Not looking for a highway driver, just best for torque and HP.

With such little information, its hard to say. On my drag 85 Mustang I run either 4.88s or 5.13s, I ran 3.55s in my daily driver 302 5 speed Fairmont, but would have gone deeper if I didnt need to drive on the freeway to work every day.

[n2omaverick]

A simple question, what is the optimal gears for a 302 with T5? Not looking for a highway driver, just best for torque and HP.

My 83 has a T5Z with the .63 overdrive so i just installed some 3.89 gears and i must admit that it was a great decision! It allowed me to change the speed of the opening of the secondarys, increase the speed of the pump cam / discharge nozzel size and some other fine tuning! Glad i changed the upper and lower control arms because traction would have been a huge issue!

[xctasy]

Lots of great info here, but I have a few questions.

I've known about the bonneville ratio axles for a while, but I always just assumed that it was to make up for the early transmissions without overdrives. So are these all in the smaller diameter axles? Was there ever any ratio(s) below 2.73 in the 8.8s?

The moon shot gearing in 2.26 and 2.47 is 7.5" diff stuff, not 8.8 or the 23 spline Sterling 6.7/6 3/4 axle. It is indeed there to compensated for the lack of SROD and AOD in all 1978 to 1979 Fox cars. When the 80-82 Thunderbird got the AOD in 5.0 engines, the ratios in the 7.5" axle were down to 2.73 and 3.08. With the 4.2, it was 2.26 or 2.47. The itty bitty Sterling 8 bolter for the 3.3 was 2.73 or 3.08. But the diff could be 7.5 or 6.75...the 2.73, 3.08 and 3.45 ratios were common to both.

A simple question, what is the optimal gears for a 302 with T5? Not looking for a highway driver, just best for torque and HP.

Not easy, because Ford standardised three gear sets, and you can't mix and match the o/d 5th and intermediate ratios idealy, but for a 225 hp 5.0 engine with the E303 cam or a modified 2 or 4-bbl GT 5.0, and 25.6" tall 225/60 15 tires, I can prove

2.73 ( 2.47 ), with narrowest ratio 85.5 SVO 4cyl ratio T5, early 2.3 NA T5 0.81 top
3.27 (3.08 ), with narrower ratio V8 Chevy/Ford T5 ratios and a 0.72 top
3.45 ( 3.27 ), with the narrowest Viper T56 first four ratio gears, but the 0.68 top.

Each do best possible for a 1/4 mile and top speed. The 3.45's are the hit pick, 3.27 and 2.73's can work if you can reduce the overdrive on the 5th gear. The bracketed values are for the factory gears that could be used if you went down to 225/50 15, 23.9" tall tires.

See this other post so blake4591 keeps this post intact

http://vb.foureyedpride.com/showthre...16#post1506016

[blake4591]

So would the longer axles (94-9 slide right into a 79-93 factory rearend? Think my car would look better with an additional 1.5" on each rear tire.

Yes, I personally have '97 axles and rear disk in my '82 housing. Slide right in dropped in the C clips and never looked back. This does force you to change to 5 lug. You could use the TC axles and brakes to stay 4 lug.

[Jack Hidley]

Fox axles are 29.16" long.
1994-98 axles are 29.91" long.
1999-2004 axles are 30.63" long.
SVO/Lincoln axles are 30.41" long.

Some 1979-81 2.3l na cars had 6.75" axle assemblies.

Ford incorrectly lists a 2.45:1 gear ratio for the 7.5" in 2.3l turbo and 2.8l with 4-speed. Whoever filled out the documentation should have written 3.45 (the gear teeth are 11 and thirty eight).

[xctasy]

In all instances, it was when Ford used the 6 cyl 0.81 or V8 0.72 overdrive in the SROD, or the 0.79 in the 2.3 T5. Stock axle was 3.08, so it got listed as 2.49, 2.22, or 2.45:1 final drive in the over driven top. All the time, they had the stock 3.08 diff, although there were other ratios on offer.

Proof was the magazine articles like Motor Trend and Car and Driver who just copied Fords details...and got it wrong!

Ford soon stopped this when the 5.0 came back, and started talking about performance differentials.

[redse]

New to the game here I have a 1984 LX 5.0 HO with carb and been tying to figure out what all this car has, when I was putting the new original coil springs on the back because it was lowed before it got it. Anyway the tag is still on the rearend and reads as follows: WGX S 3MO3 273 A75S275D can anyone on tell me what I have for the rearend and thanks in advance!!!

[Quicksilver]

My '84 GT CFI/AOD car came with 3.27 gears in the 7.5 diff.

Also, a lot of the manual transmission '87 to '93 5 litre cars around here came with either 2.73 or 3.08.

[FoxChassis]

Is there a letter or a space between "2" and "73"?

[redse]

Pretty sure no space and is really clean I didn't even have to wipe the tag at all!!! Just like the cam I have no idea what cam is in it and a holly 600 or 650 double pumper with mechanical secondary's??? I'm just trying to figure out what I have?
Thanks again