8.8 rebuild

Flade · Dec 15, 2020

I am getting ready to rebuild the rear end on my 94GT. I am upgrading to 3.55 gears and replacing the bearing seals etc. At what HP point is it smart to move up to 31 spline Axles?

I have a 31 spline differential from a 97 Cobra, so the cost would be buying the axles and I assume I would need new ABS rings. I don’t mind spending the money if it’s needed, but if it’s not I can use it elsewhere.

Not sure how much horse I’ll have, I’m planning a mild build since this is a daily driver and won’t ever see the track. I have TFS 170 FAC heads, a mild cam, Larger MAF & TB, Cobra intake Shorty Headers, off road H-pipe, mag flow cat back. I am guessIng 300-325 HP

ttocs · Dec 15, 2020

if this is a racecar that your planning on track days, sticky tires and such then sure its possible to snap them. If its a street car on street tires on the street then your more likely to spin than break.

Flade · Dec 15, 2020

ttocs said:
if this is a racecar that your planning on track days, sticky tires and such then sure its possible to snap them. If its a street car on street tires on the street then your more likely to spin than break.

that’s a great point I hadn’t thought of. I have 17x10.5 rims, but will be running a good street tire, so unlikely to really hook up.

lwarrior1016 · Dec 16, 2020

Even if you hook up on a good street tire, it’s nothing like dumping the clutch at 5k rpm on drag radials. If you aren’t doing that, you’ll be just fine.

apsmith49921 · Dec 16, 2020

Agreed with the above.

Side note... are you sure that's a 97 cobra differential? I wasn't away any sn95 cars had 31 spline stuff. I know of people snatching explorer differentials because some of those got tlok 31 splines

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Randall Garner · Dec 16, 2020

Most gt models came with 31spline axles, the 7.5 had 28. Even if 28 unless your big hp they will handle it fine. Old 8" with 28 were behind 428 Fe and held up. There's other things that will break first. Like u-joints or you'll tear up control arm bushings. If your breaking axles. There's other things to look over if it pure drags. Ya c clip eliminators and possible 35 kit. Find a rpm you can launch on the street with minimal spin. Then that as a starting point for launch at the strip. Also with street tires. The more ya air down the more chance of cupping the tire and loosing traction. Most I've ever dropped street tires is about 5-10 below recommended setting.

Flade · Dec 16, 2020

apsmith49921 said:
Agreed with the above.

Side note... are you sure that's a 97 cobra differential? I wasn't away any sn95 cars had 31 spline stuff. I know of people snatching explorer differentials because some of those got tlok 31 splines

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I should have said out of a heavily modified 87 Cobra. Moser Axle, 31 spline differential, etc. unfortunately one axle was bent. Stupidly I threw them both away

Flade · Dec 16, 2020

Randall Garner said:
Most gt models came with 31spline axles, the 7.5 had 28.

Not true! 1979-2004 V8 Mustangs came factory equipped with 28 spline axles, except for 2003-2004 SVT Cobras which were 31 spline.

In 2005 Ford switched to 31 spline on all the GTs.

Thanks for other hints. I found one reference that says the 28 spline axles will support up to low 400s on HP so I should be fine.

apsmith49921 · Dec 16, 2020

I was tempted to go the junkyard route and start ripping up explorers some of them even had a t lok with 4.10s factory good rear end for a cheap price

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Frank.JD.Perez · Dec 16, 2020

i think you mean torque. high torque is what snaps shafts and requires higher splines. if i were you and i was building my diff there is zero reason to not upgrade to HD parts as it gives you more room for growth and its a peace of mind knowing that all the money you spent building the damn thing that it wont blow up on you. my car puts down about 300 wheel, but i have a 01 bullitt rear with a torsen t2r and 31 spine axles with extended arp studs and frpp 373s. the rear end is a stud and i have no worries other than if i start loosing fluid for whatever reason

Wmac · Dec 16, 2020

x2 with what Frank said. If you are ever going to track the car, upgrade now if possible. And all 2nd gen explorers were 31 spline. Some of the trailer towing pacs had 3.73 and some had 4.10 with tlok. But neither the axle housing or shafts fit a mustang.

Flade · Dec 17, 2020

Is it reasonably possible to remove the ABS tone rings without breaking them and move them to new axles or do I need to dish out an additional $100 for new ones?

ttocs · Dec 17, 2020

I am pretty sure when I swapped mine they were able to be taken off and then put back on.

tvsn95 · Dec 17, 2020

Tone rings swap easly. the 31 spline Strange axles cost it cheap. when you break the axle it can and will destroy the limited slit carrier. So you need a new carrier, Big $$.
I use a Torsen style.
the stock axles WILL NOT take much if your tires hook,,,But then neither will the Trans,, or drive shaft.
If you put a KILLER clutch in your car you WILL find ALL the weak links.
At the same time if you are just bolting on stuff and guessing you power,,,,your in fairy land

Frank.JD.Perez · Dec 17, 2020

just buy new abs rings. they arent that expensive and again, peace of mind. lmr sells them and i think theyre like 15 bucks a pop. also got new ones when i did my rear end build

Flade · Dec 17, 2020

Frank.JD.Perez said:
just buy new abs rings. they arent that expensive and again, peace of mind. lmr sells them and i think theyre like 15 bucks a pop. also got new ones when i did my rear end build

$40 each at LMR, so not too bad. Do they press on?

Frank.JD.Perez · Dec 18, 2020

I think they do, but you need to be somewhat careful. I took my car to the shop for the rear end. Thats one thing i wont do on my own car. Not to say i wont learn in a project car that doesnt see a lot of street time though

ttocs · Dec 18, 2020

I had a friend that told me he had swapped gears dozens of times so I felt good about having him around to help me. I can't tell you how worried I was when the first thing he wanted to do was watch a youtube vid a few times. It was pretty obvious he had not done dozens of times shortly into it when things were not turning smoothly so I ended up taking it into a shop to have them do it. The abs rings are nothing more than a metal ring with some notches in it that presses on/off the axle. There is no contact with anything on it so its not something that wears out unless its dropped or something. The only thing a new one will save you for $80 is the time to press the old one off which with a press only takes a few seconds.