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Discussion Starter · #1 ·
Hi All

I'm new to this forum, but not new to forums.
I've spent time searching but can't find any cases where anyone went over the most simple approach to swapping out an open diff for a trac lock.

I have a '61 Ford f100 with an 8.8 IRS from a '97 Cougar.
(recently acquired the truck as is)
My hope is for a simple remove and replace of the differential.

Or

Would sourcing a mustang IRS unit fit.?

Upgrading would be smart due to power increase coming...but not necessary since it's not a drag vehicle and will keep a smaller tire on it.

Thanks
 

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If the complete IRS is from a 97 Cougar, then the easiest and cheapest way to get a trac-lok is to source one from an 89-97 Tbird or Cougar. 89-93 T-bird SCs all had the trac-lok, and all 89-92 cars with ABS also got the 8.8 Trac-lok regardless of engine. It was also an option on non-SCs and non-ABS cars, but avoid 89-95 non-ABS V6 cars because they got a 7.5" diff instead of the 8.8. Also if you don't want to dig into the diff to change gears, all 96/97 cars got a 3.27 ratio, as did all 89-93 Automatic SCs. If looking at a Mustang unit, it will have to be for a 99 Cobra. Only the 99-04 Cobra got the IRS, and the 01+ cars got a 31 spline axle instead of 28, which would require custom axles.
 

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Discussion Starter · #3 ·
If the complete IRS is from a 97 Cougar, then the easiest and cheapest way to get a trac-lok is to source one from an 89-97 Tbird or Cougar. 89-93 T-bird SCs all had the trac-lok, and all 89-92 cars with ABS also got the 8.8 Trac-lok regardless of engine. It was also an option on non-SCs and non-ABS cars, but avoid 89-95 non-ABS V6 cars because they got a 7.5" diff instead of the 8.8. Also if you don't want to dig into the diff to change gears, all 96/97 cars got a 3.27 ratio, as did all 89-93 Automatic SCs. If looking at a Mustang unit, it will have to be for a 99 Cobra. Only the 99-04 Cobra got the IRS, and the 01+ cars got a 31 spline axle instead of 28, which would require custom axles.
THANKS man...I have seen bits and pieces of what you had mentioned but now I see it gathered and makes SO much more sense.
I have done a differential before and it suuuuux...I still want to gag if I smell rear diff oil.
I suppose I can call around to some salvage yards and search the interweb for a diff to swap out.
OR spring for a new diff from Ford.
Apreciate it.
Brian
 

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The Parts Guy
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Sounds like you're calling the complete centersection a differential. Even if you swap out the whole centersection, you're going to want to change the oil in it, so you're going to have to get over your aversion to the smell.
 

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Sounds like you're calling the complete centersection a differential. Even if you swap out the whole centersection, you're going to want to change the oil in it, so you're going to have to get over your aversion to the smell.
That.

Or find a mechanic, and open your wallet and keep smiling as the mechanic helps him/her self to your money. ;)

That's Pournelle's Law as applied to DIY. Either pay a competent person to do the job and don't ***** about the money, or DIY and learn how, knowing there's a reason why the professional charges.

RwP
 
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If you truly have a 97 Cougar rearend (pumpkin), keep in mind it is 28 spline. So if you want to buy just a trak-loc unit to retrofit, or buy the whole pumpkin, make sure it's 28 spline. Almost everything newer is 31 spline, and if you went with 31 spline, you'll need the axles too.

Al
 
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Discussion Starter · #7 ·
Thank guys...good stuff.
I'm not above a differential fluid change...just hate being underneath and laying in it.
I sourced a sweet PUMPKIN from a Thunderbird SC in Texas...waiting to see if it works out.
 

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I would recommend a fluid change and rebuild of clutches and bearings at a minimum.
 
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Discussion Starter · #9 ·
I would recommend a fluid change and rebuild of clutches and bearings at a minimum.
Yeah...hate to admit it...but yeah.
I guess my logic was that it's going into a 1961 Ford low-rider...so even a used rear is new to the truck.
But if I'm going to do it...I should do my best to get it to hold up.
 

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Post some pictures of the truck if you can. I would like to see the whole setup.
 

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I’d do the clutches since that’s easy and the halfshaft seals. Bearings I wouldn’t bother with unless the pinion seal is leaking or a ratio change where it has to be stripped all the way down anyway. Those bearings are good for way longer than other components that usually put Tbirds and Cougars in junkyards
 

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Keep in mind, you might be getting a 2.73 diff from the SC, if it was a 5 spd. Pretty tall gears.

Al
 

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I'm familiar with Grannas, but his rears don't include axles. So you will also need 31 spline axles.

It would be a lot cheaper just getting a Yukon LSD diff and retrofitting into your Cougar housing. The clearances would need setup by a differential shop.

Al
 

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Discussion Starter · #15 ·
Another excellent point...
Grannas did quote me a 28 spline build...but with shupping and core charge was $2k.
My original logic of avoiding the tearing into the existing rear/cost/aggravation...may be erroneous 😬
I ‘ll try to research who could do it near me here in NY state.
I know it won’t be me. 👍
 

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The nice thing is you can take the pumpkin out and bring it somewhere. You can have a nice build with a quality center section for less than $1k. And that includes gear selection for you.
 

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Discussion Starter · #17 ·
The nice thing is you can take the pumpkin out and bring it somewhere. You can have a nice build with a quality center section for less than $1k. And that includes gear selection for you.
True...but at that point...I can also just drive the truck there and leave it. Fortunately I’m not needing to drive it everyday 😬
 

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Discussion Starter · #18 ·
True...but at that point...I can also just drive the truck there and leave it. Fortunately I’m not needing to drive it everyday 😬
If the complete IRS is from a 97 Cougar, then the easiest and cheapest way to get a trac-lok is to source one from an 89-97 Tbird or Cougar. 89-93 T-bird SCs all had the trac-lok, and all 89-92 cars with ABS also got the 8.8 Trac-lok regardless of engine. It was also an option on non-SCs and non-ABS cars, but avoid 89-95 non-ABS V6 cars because they got a 7.5" diff instead of the 8.8. Also if you don't want to dig into the diff to change gears, all 96/97 cars got a 3.27 ratio, as did all 89-93 Automatic SCs. If looking at a Mustang unit, it will have to be for a 99 Cobra. Only the 99-04 Cobra got the IRS, and the 01+ cars got a 31 spline axle instead of 28, which would require custom axles.
So i’m just scrolling through as I wonder...
I don’t see any tags and only a marking on the case “ F4LW-4033-AA”.
I just ordered a 3.55 Auburn limited slip entire kit for a 8.8. I have a fear it may be a 7.5.
Is the above code any indication?
 
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