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post #1 of 14 Old August 5th, 2015, 12:33 AM Thread Starter
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Building an 8.8 and need advice

I am looking to build up and beef up a 96 GT 8.8 Rear end. I want to have 31 Spline axles, 3.27 gears, and some limited slip posi,that obviously fit's the 31 spline axles and 3.27 gears and is not locked when turning. I am looking to have this still be a daily if I feel like it and handle 500 ft/lbs of tq.

If anyone could help point me in the right direction it would be much appreciated.

Thanks, Jon

---------- Post added at 10:33 PM ---------- Previous post was at 10:30 PM ----------

Also trying to maintain the ABS sensors
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post #2 of 14 Old August 5th, 2015, 01:19 AM
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Latemodel restoration sell a kit that has everything
1994-2004 Mustang Rear Axle 31 Spline Kits
Hope it helps
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post #3 of 14 Old August 5th, 2015, 01:24 AM
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The Cobra track loc 31 spline diff with the carbon fiber clutches works well up to 600 or 700whp and they are pretty affordable, around $250.

For best straight line performance run a synthetic oil with no friction modifier, the friction modifier makes the clutches slip more, not less and if you use a synthetic you don't need it.

Go with some forged 31 spline axles, I got the Mosers and they are working well, replace all the bearings and have the axle tubes welded to the center section and you are good to go.

The center section on 8.8's is cast steel, not cast iron so its an easy weld with a a tig or mig machine, no fancy nickel filler rod is needed.

If you take your time and do short welds spaced 180 degrees apart it won't warp the tubes out of alignment but if you are worried about that take it to a shop that has a jig for it.

The aftermarket axles allow you to put ABS rings on but its a pain, I'd go with the get it hotter than hell method to put them on, I cracked one trying to put it on without heating it.

With all that trouble, think hard about if you really want to stick with the 3.27's or go to lower gears while its all apart, the gears are pretty cheap, the Motorcraft ones are recommended as usually the same pinion shim works, making the installation faster.

With the overdrive gears in both the manual and auto trans in our cars a 3.73 gear is still real streetable and you'll get a nice kick in the pants out of that gear.

If you are going to be drag racing I'd also go with a Yukon solid spacer kit instead of a crush sleeve (tends to loosen on hard hits), the Yukon spacers are better made than the Ratech ones.

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post #4 of 14 Old August 5th, 2015, 02:25 AM Thread Starter
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Quote:
Originally Posted by CalBoy101 View Post
The Cobra track loc 31 spline diff with the carbon fiber clutches works well up to 600 or 700whp and they are pretty affordable, around $250.

For best straight line performance run a synthetic oil with no friction modifier, the friction modifier makes the clutches slip more, not less and if you use a synthetic you don't need it.

Go with some forged 31 spline axles, I got the Mosers and they are working well, replace all the bearings and have the axle tubes welded to the center section and you are good to go.

The center section on 8.8's is cast steel, not cast iron so its an easy weld with a a tig or mig machine, no fancy nickel filler rod is needed.

If you take your time and do short welds spaced 180 degrees apart it won't warp the tubes out of alignment but if you are worried about that take it to a shop that has a jig for it.

The aftermarket axles allow you to put ABS rings on but its a pain, I'd go with the get it hotter than hell method to put them on, I cracked one trying to put it on without heating it.

With all that trouble, think hard about if you really want to stick with the 3.27's or go to lower gears while its all apart, the gears are pretty cheap, the Motorcraft ones are recommended as usually the same pinion shim works, making the installation faster.

With the overdrive gears in both the manual and auto trans in our cars a 3.73 gear is still real streetable and you'll get a nice kick in the pants out of that gear.

If you are going to be drag racing I'd also go with a Yukon solid spacer kit instead of a crush sleeve (tends to loosen on hard hits), the Yukon spacers are better made than the Ratech ones.
Thanks for all the info! I am looking at buying one of these Cobra units from eBay, is there a way to tell if it needs a rebuild.
Ford Racing 31 Spline Diff Differential 8 8 Carbon Discs Cobra Mustang | eBay

1986 2014 Mustang or Cobra 8 8" 31 Spline Rear Traction Lok Differential | eBay

Do I need anything else other than the motorcraft 3.27 gears. I want these gears so I can stay in boost longer before shifting.

Also looking at these axles.
Moser 8 8" Ford Axles 31 Spline 1994 1998 Mustang 5 Lug with ABS Adapter | eBay

Please let me know what you think of this combination.

Thanks agian.

---------- Post added at 12:25 AM ---------- Previous post was at 12:01 AM ----------

Ford 8 8 inch Eaton Detroit Locker 31 Spline Mustang GT500 Part Number 187C145A | eBay

Also found this, said he took it out so he can dd his car, is there a reason not to use this unit while daily driving?
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post #5 of 14 Old August 5th, 2015, 11:36 AM
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Quote:
Originally Posted by CalBoy101 View Post
The Cobra track loc 31 spline diff with the carbon fiber clutches works well up to 600 or 700whp and they are pretty affordable, around $250.

For best straight line performance run a synthetic oil with no friction modifier, the friction modifier makes the clutches slip more, not less and if you use a synthetic you don't need it.

Go with some forged 31 spline axles, I got the Mosers and they are working well, replace all the bearings and have the axle tubes welded to the center section and you are good to go.

The center section on 8.8's is cast steel, not cast iron so its an easy weld with a a tig or mig machine, no fancy nickel filler rod is needed.

If you take your time and do short welds spaced 180 degrees apart it won't warp the tubes out of alignment but if you are worried about that take it to a shop that has a jig for it.

The aftermarket axles allow you to put ABS rings on but its a pain, I'd go with the get it hotter than hell method to put them on, I cracked one trying to put it on without heating it.

With all that trouble, think hard about if you really want to stick with the 3.27's or go to lower gears while its all apart, the gears are pretty cheap, the Motorcraft ones are recommended as usually the same pinion shim works, making the installation faster.

With the overdrive gears in both the manual and auto trans in our cars a 3.73 gear is still real streetable and you'll get a nice kick in the pants out of that gear.

If you are going to be drag racing I'd also go with a Yukon solid spacer kit instead of a crush sleeve (tends to loosen on hard hits), the Yukon spacers are better made than the Ratech ones.

^This guy... haha

Pretty much nailed it. Just to add to it, if you're a cheap bastard like me, go to a pick and pull and pull a 31 spline carrier out of an Explorer that has 3.73 gears already on it. Lots of Explorers had 3.73's and some with 4.10 posi, just check the door tags. Most of the V8 Explorers had the good stuff. Toss in the Cobra clutch packs and new bearings and you're good to go.

Also I went as far as having 9" ends welded on mine and got rid of the POS C-Clip design completely. Strange Engineering makes a kit that will retain your ABS and works with Cobra brakes. It was about $750 but I don't regret it, it's an amazing kit. Also don't weld the rear yourself, get it to a shop with a jig because they're all bent, and when you weld it it will pull. Do it once do it right.
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post #6 of 14 Old August 5th, 2015, 12:02 PM
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My 31 spline tracloc was fine up to about 500+ rwhp, but when I reached 600+, it needed to be rebuilt every 20 passes or so due to the spider gears chipping. But I'm sure that without the hard launches on slicks, it would have lasted much longer.

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post #7 of 14 Old August 5th, 2015, 02:00 PM
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Unless $ is really tight wouldn't mess with those used diffs (at least at those prices), they could have worn out clutches and by the time you put in new ones you are over the price of a new diff.

American Muscle sells the new Cobra one for not much more than those and it has free shipping, their prices on axles are pretty good also and their customer services is top notch.

They also have a 6% discount code for MM users, check your PMs.

But 69's tip on the Explorer diffs is good way to go if $ is tight and you want gears also.

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post #8 of 14 Old August 5th, 2015, 09:47 PM
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Quote:
Originally Posted by TonyG View Post
My 31 spline tracloc was fine up to about 500+ rwhp, but when I reached 600+, it needed to be rebuilt every 20 passes or so due to the spider gears chipping. But I'm sure that without the hard launches on slicks, it would have lasted much longer.
I ran one in my daily driven GT for 6.5 years. Put about 30k miles on it and 30 track passes in that time. 6 months before I pulled it out it started howling pretty bad. Was at 411/403 the last year and probably put 9 passes on it at that power level. Was at 360rwhp for 4 years before that. I always launched the car at 5-6k rpm on drag radials. It also took a decent beating on the street. When the diff came out the spider gears had multiple chips in them. I'll probably toss another one in my auto Mach which will be ~460rwhp since they are so affordable.

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post #9 of 14 Old August 5th, 2015, 09:56 PM
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Fellas, thanks for the info on the spider gears in the Cobra diffs.

I've had mine in for about a year and probably have made about 200 pretty hard pulls on the street with drag radials with an auto, not hooking as hard as it would at the track but still hooking somewhat hard, data logging was showing 0 to 60 mph times in the 3.6 to 3.8 range and zero to 60' times in the 1.6 to 1.8 range.

I'm going to be changing the diff gears soon, I'll take a close look at the spider gears and report back how they held up.

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post #10 of 14 Old August 6th, 2015, 02:03 PM
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Quote:
Originally Posted by CalBoy101 View Post
Unless $ is really tight wouldn't mess with those used diffs (at least at those prices), they could have worn out clutches and by the time you put in new ones you are over the price of a new diff.

American Muscle sells the new Cobra one for not much more than those and it has free shipping, their prices on axles are pretty good also and their customer services is top notch.

They also have a 6% discount code for MM users, check your PMs.

But 69's tip on the Explorer diffs is good way to go if $ is tight and you want gears also.
I do agree with the above. If you have the money don't even bother playing with the used diff. Just buy a new one. I kinda of regret it but it did save some money.


Far as spider gears, I'm sure the chips are from hard launches, if you're semi easy on the car it will probably be fine at most power levels.

When I say easy I don't mean drive like a baby, I mean make sure all drivetrain components are locked and have a hair of pressure on them before you let the clutch fly. Basically minor slip of the clutch to lock everything and then let her loose.
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post #11 of 14 Old August 6th, 2015, 03:39 PM
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Originally Posted by Kidd99 View Post
Latemodel restoration sell a kit that has everything
1994-2004 Mustang Rear Axle 31 Spline Kits
Hope it helps
i had mine rebuilt w/ this kit

Mustang 8.8" 31 Spline Heavy Duty Rear Axle Kit 3.73 Gears (99-04)

so far its held up just fine w/ MT ET Streets.
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post #12 of 14 Old August 6th, 2015, 07:27 PM Thread Starter
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Thank you all for your help, I have bought the following.

3.27 Gears
3.27 Mustang Gears - Free Shipping

Moser 31 Spline Axles
31 Spline Mustang Axles for 8.8in Rear w/ Studs - Free Shipping

8.8 31 spline LSD with carbon clutches
8.8 in 31 Spline Traction - LOK Mustang Limited Slip Differential w/ Carbon Discs - Free Shipping

Last thing I need to purchase is bearings and spacers/ shims. Does anyone have any suggestions on what is the best to use?

Again thank you all for your help.
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post #13 of 14 Old August 6th, 2015, 07:46 PM
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This Ford Racing bearing kit below is a good one, it also has the axle bearings and seals.

Mustang Ring & Pinion Installation Kit - 8.8in Solid Rear - Free Shipping

If you are going to use a crush sleeve the Ford brand one in that kit is better than the ones from Ratech.

But as I mentioned earlier if the car will be visiting the drag strip or will be making hard street hits with drag radials I'd go with a Yukon brand solid spacer kit instead of the crush sleeve, Summit sells those.

The solid spacer kits also make the installation easier if it turns out you have to change the pinion shim.

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post #14 of 14 Old August 7th, 2015, 07:25 PM Thread Starter
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I finished buying the rest of the parts, I ended up buying the Ford Racing rebuild kit and a solid pinion spacer. Now just need to wait for parts to arrive and the building process to begin!

8.8 Rebuild kit
Mustang Ring & Pinion Installation Kit - 8.8in Solid Rear - Free Shipping

Solid Pinion Bearing kit
Solid Pinion Spacer Kit 8 8" Ford | eBay
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