Axle Research

rice_man

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Mar 7, 2023
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I wanted to do a little research on the rear end I'd like to build. The ultimate end goal (years down the road, most likely) is a gen 3 coyote swap. In the meantime, I'm planning upgrades along the way, one step at a time.
The '82 GT had a 7.5 rear end. I want to eventually end up with a 5-lug 8.8 with 3.73 gears, a 31 spline carrier with fox length axles and trac-lok. Cobra brakes are in the works after that.
Junkyard parts are my drug of choice wherever possible.
If what I've read is correct (and this is what I'm trying to confirm):
1) Any 8.8 from 87-98 should be a more or less direct bolt in and be the same width as the current axle housing (shooting for a fox 8.8 if possible).
2) If I can find the an 8.8 carrier from a mid-90's explorer with t-lok and 3.73 gears, it should drop right in to a fox 8.8
3) There is no vehicle out there that has fox length 31 spline 5 bolt axles that'll work with disc brakes - I'll need to get Mosiers or something of the like.
4) Once I have the above sorted, I can follow the 5-lug swap thread stickied here in the forum to finish collecting the brake parts I want. I know I'll need a set of caliper brackets, but everything else should be easy enough.
Thanks for the help. I just don't wanna dork this up.
 
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If you are planning on running slicks I get going to 31 spline but if it will primarily be a street car then 28 spline will work just fine. I would upgrade to some Moser replacement axles but other than that just rebuild the stock trac-lok, new bearings, new seals, and swap gears.

The 8.8 housing is the same from 86 through 98. If you are starting from scratch what you are wanting is the complete rear end out of a 94-98 GT. This will get you the 8.8, rear disc brakes and will bolt into your Fox and you just need to swap gears and rebuild it. These rear ends are 3/4" wider per side than the Fox 8.8 however there will be alot of choices in 9" wide wheels for this combo. When you step up to 10" you really need to measure to get the correct back spacing and you will need to roll the fender lip and most likely use a BFH to massage the inner wheel whlls but you would have to do this with a Fox width rear end.
 
If you are planning on running slicks I get going to 31 spline but if it will primarily be a street car then 28 spline will work just fine. I would upgrade to some Moser replacement axles but other than that just rebuild the stock trac-lok, new bearings, new seals, and swap gears.

The 8.8 housing is the same from 86 through 98. If you are starting from scratch what you are wanting is the complete rear end out of a 94-98 GT. This will get you the 8.8, rear disc brakes and will bolt into your Fox and you just need to swap gears and rebuild it. These rear ends are 3/4" wider per side than the Fox 8.8 however there will be alot of choices in 9" wide wheels for this combo. When you step up to 10" you really need to measure to get the correct back spacing and you will need to roll the fender lip and most likely use a BFH to massage the inner wheel whlls but you would have to do this with a Fox width rear end.
I don't plan on running slicks, but I do plan on driving it like I'm mad at it. Plus, my luck is terrible. With a 3rd gen Coyote going in eventually, I want to fool with the rear end one time, do it right, and be done. I figure shooting for something good for over 500hp would be a good idea and from what I was reading, the 31 spline stands a better chance than the 28. If I have to buy axles either way, why not go bigger too?

My plan was to find a 94-95 cobra and rob parts off of it - this will get me front spindles and large discs on all 4 corners. I can use the axle housing off of it too.

My biggest reasons for posting was that I a) wanted to verify that my plan was sound and b) confirm that no vehicle ever brought to market had 31 spline fox length axles for a 31 spline carrier.
 
Yes, an 86-98 8.8 axle housing is the one to get. No changes to the housing itself, just the brakes and such bolted to it. You might be able to use a Mark 7 axle as well, but those seem to be harder to find these days as a lot of those have been scrapped by now.

There is a model explorer that does come with a 31 spline carrier. I don't know what model would have it though but that's an easy google search.

No fox-lenght 31 spline axles exist in the wild. I would go with some Moser's here as i've heard tales of the cheaper 31 spline axles twisting. Buy once, cry once.
 
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Yes, an 86-98 8.8 axle housing is the one to get. No changes to the housing itself, just the brakes and such bolted to it. You might be able to use a Mark 7 axle as well, but those seem to be harder to find these days as a lot of those have been scrapped by now.

There is a model explorer that does come with a 31 spline carrier. I don't know what model would have it though but that's an easy google search.

No fox-lenght 31 spline axles exist in the wild. I would go with some Moser's here as i've heard tales of the cheaper 31 spline axles twisting. Buy once, cry once.
Thanks! That's what I was hoping to find. Appreciate the info!
 
I think the Ranger (and explorer) had offset pumpkins.

Ranger 31 splines were 31.25" and 27.75" from a quick google search. Fox axles are 29.25"


I did all of 5 mins of google searching on this, so don't take this as 100% true yet.
 
I believe the Ranger had a 8.8 with 31 spline axles. It's been a while, but I think that is what I used in my Mustang back in the day. Would need to research it again.

I think the Ranger (and explorer) had offset pumpkins.

Ranger 31 splines were 31.25" and 27.75" from a quick google search. Fox axles are 29.25"


I did all of 5 mins of google searching on this, so don't take this as 100% true yet.

Based on my reading, you could use driver's side shaft from some Rangers and passenger side shafts from some Aerostar mini vans are Fox-length axles. I hadn't heard that any of them were 31 spline axles though. I'll do a bit more research to see. My local yard has a ton of Rangers and Aerostars, so that'd be awesome!
 
Based on my reading, you could use driver's side shaft from some Rangers and passenger side shafts from some Aerostar mini vans are Fox-length axles. I hadn't heard that any of them were 31 spline axles though. I'll do a bit more research to see. My local yard has a ton of Rangers and Aerostars, so that'd be awesome!

I believe those axles being references for 5-lug swaps are all 28-spline axles and from a 7.5" rear. They are 29 5/32" long.
 
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V8 explorer carrier will have 31 splines. Then a 86-98 mustang 8.8 housing. I’d recommend just buying a new set of 31 spline axles. They’re really not all that expensive from summit.
 
sorry, I'm acused of using short hand too often in my questions.
The swap-in idea.
What year/models will have an 8 inch rear. I can mod anything AND round here most stuff 10 yr old or older goes to the crusher (I get lucky sometimes, tho). That's Y I say - "any, all".
May B self explanitory: fox length, but again I can mod for my fox wagon.
I believe my '85 LTD hasa 7.5.
Rice man seeks the 8.8 so hope I'm not steppin on yer thread...
(Never seen them that I know.
Come to think of it I could puta 8 in chunk into the 7.5, MAY B, but seek the rest for a more strength. I just dont need 9 inch (or probably 8.8). I have the 9 in my '70 bronk).
Last, now I AM getting long winded - do the 8 inch have a good selection of gears (dont need LSD, lock, more than 28 spline, etc)? I see Strange has 2.79 - 5.43...
Even more confusing?
 
What year/models will have an 8 inch rear. I can mod anything AND round here most stuff 10 yr old or older goes to the crusher (I get lucky sometimes, tho). That's Y I say - "any, all".

Come to think of it I could puta 8 in chunk into the 7.5, MAY B, but seek the rest for a more strength. I just dont need 9 inch (or probably 8.8). I have the 9 in my '70 bronk). (No you can't, they're completely different animals.)
Last, now I AM getting long winded - do the 8 inch have a good selection of gears (dont need LSD, lock, more than 28 spline, etc)? I see Strange has 2.79 - 5.43...

Should really start a thread of your own if this gets more in depth, but the 8 inch was last used in a Mustang in 78 as @Mustang5L5 said. There are a decent amount of gear selections available as well as some differentials if you were to go that route. I have a Detroit Locker with 3.55s in mine. And the 8" come in a wide variety of cars from the mid 60s through the late 70s, although I'm not sure about when they were discontinued.

That's an old one. The Fox body and SN95 never got the 8". I think 1978 was the final year.

The Fox only got the 6.75" (very early 4-cyl) and the 7.5" and 8.8"

You are correct again, the Mark 7 will bolt in with nothing more than a brake and axle swap. Similar to the 94+ Mustangs, the axles are longer. The disc brakes are also the same as was used on SVO Mustangs iirc. I did some research on this about 10 years ago and have the disc brake setup that I intended on using on my 84 vert project that never come to fruition. I used a Mark 7 as a donor car and swapped the whole drivetrain minus the driveshaft for obvious reasons, but swapped the axles and brakes from the 7.5 that the vert had in it originally into the 8.8. And, if memory serves, any 8.8 from any Fox car should bolt into another Fox with minimal effort, but I advise you to do your own research on that.