View Full Version : Mustang IRS Differential Question
Opinions needed from knowledgeable folks. I have come across a 2019 Mustang differential in a local boneyard, 3.55, Trac-Loc at a really good price. The car it was removed from has 50K on the odometer.
So, with 50,000 miles on it should I go for it or pass?
If I go for it, should I plan on freshening it up a bit, like replacing the clutch pack and spring?
Or just bolt it in and feel good about it?
I did a quick search yesterday and found a lot of parts available for the old 8.8 solid axle diffs, but few parts for the Super 8.8 IRS units. Is there a clutch pack kit even available for the IRS units?
Thanks for any advice!
Hoooper
03-02-2023, 11:27 AM
The diff itself would be fine as far as the gears and such, the clutches may not be. Really depends on who owned the car before and since it was in a mustang chances are... If you are planning on not tracking the car its likely fine/doesnt matter. If you are planning on tracking the car it doesnt matter since the clutches will be toast pretty quickly anyway even if theyre new. Mustang guys who track their cars burn through the clutches pretty quick.
If you buy it, I'd bring it to a trusted gear shop to check it out. It's short money, especially for some peace of mind (and preventing you from installing something you'll curse later on). I bought a 3.55 Torsen unit with 10k miles for $300, but paid about $200 for the shop to inspect, reseal, and install new axle seals. So I'm still ahead by about $500 give or take.
If you buy it, I'd bring it to a trusted gear shop to check it out. It's short money, especially for some peace of mind (and preventing you from installing something you'll curse later on). I bought a 3.55 Torsen unit with 10k miles for $300, but paid about $200 for the shop to inspect, reseal, and install new axle seals. So I'm still ahead by about $500 give or take.
That was a real deal!
CraigS
03-03-2023, 07:42 AM
I suspect that it will be fine as is. But, if you can find the clutch pack rebuild kit it is not a bad idea to do it now while it is out. Research the procedure a little because it comes to my mind that you may need to make up a case spreader tool. My memory is real vague but it may depend if it is an iron or aluminum case.
BradCraig
03-03-2023, 09:23 AM
Mine was salvage and pulled at 30k, the only thing I did was replaced the shaft seals just for insurance. These things are fairly bulletproof.
rich grsc
03-03-2023, 10:11 AM
I suspect that it will be fine as is. But, if you can find the clutch pack rebuild kit it is not a bad idea to do it now while it is out. Research the procedure a little because it comes to my mind that you may need to make up a case spreader tool. My memory is real vague but it may depend if it is an iron or aluminum case.
A case spreader shouldn't be needed for a clutch pack rebuild, but will be for a gear change.
CraigS
03-04-2023, 08:03 AM
Glad you chimed in here Rich. As I say my memory is pretty vague because it was a friend who needed the spreader. Just didn't want the OP to be surprised.
I hit the boneyard this morning and purchased the differential. It came out of a Mustang GT, 5.0 that had a close encounter with something solid in the front end. It is an iron case unit. I am planning on removing the cover, replacing the clutch pack, and putting in new half-shaft seals. I did some more checking, and it appears the Trac-Loc clutch pack is a Ford dealer item, Part FR3Z-4947-A. I have seen the kit for $29.36 online.
Thanks to all that responded!
Railroad
03-04-2023, 06:10 PM
Soak the fiber clutch disk before stacking them in the carrier.
CraigS
03-05-2023, 08:01 AM
I ran Mobil1 75-90LS gear oil in mine w/ no additional additive.
https://www.mobil.com/en/lubricants/for-personal-vehicles/our-products/products/mobil-1-syn-gear-lube-ls-75w-90
Soak the fiber clutch disk before stacking them in the carrier.
Soak them in friction modifier, I assume?
Have you replaced the clutch pack in the IRS diff? Any surprises when I start this?
Railroad
03-05-2023, 02:57 PM
Soak them in friction modifier, I assume?
Have you replaced the clutch pack in the IRS diff? Any surprises when I start this?
Just use Syn lube. Sny lube sometimes negates the need for friction modifier. If you would rather not crawl under there to add later, put it in on fill.