2015 IRS Hub Question

[JMan]

Hey guys, looking for advice here. I purchased a dropped out rear subframe from a 2017 GT PP mustang for the center section and knuckles. In the process, I purchased brand new hubs from LMR to replace the used ones from the mustang. I noticed they had a little "give" once they were all mounted up... I could grab the rear wheel and I could make it wiggle ever so slightly. Well, I took the car out for the first shake down runs and I've got maybe 5 miles on it now. She's back up on jackstands and I noticed that the rear wheels are way loose on the hub. I can grab the wheels a move it almost a solid 1/4" left-right & up-down. Not good.

What would cause the hubs to loosen up like this? All bolts are torqued & tight, brakes, park brake are all operational and look correct. They are the same on the right and left side.

TIA!

[mike223]

Tighten IRS axle nuts.

Not certain what the torque is supposed to be on the 2015 IRS axle nuts.

[edwardb]

Agreed. Sounds like maybe your axle nuts aren't tight. For the 2015+ IRS version, per FFR instructions and confirmation found elsewhere by searching: Torque Stage 1: 98 ft-lbs. (133 Nm). Torque Stage 2: Turn an additional 45°. Called Torque Turn to Tighten (TTT).

Otherwise, maybe you have the wrong hubs? Based on my info, should be FR3Z-1104-G. That's what LMR shows on their website, so suspect they're the right ones. But something to check. BTW, I get my parts from Tasca Parts. Quite a bit cheaper. What about CV axles? Using the ones from Factory Five? I've done two of these style rear suspensions, and both went together fine. First one with salvage knuckles (zero mile takeout, so used as is) and the second with brand new parts.

[JMan]

Thanks Guys, I'll double check this tonight after work. I don't recall the torque then turn to tighten step, so I must have skipped??

[edwardb]

Thanks Guys, I'll double check this tonight after work. I don't recall the torque then turn to tighten step, so I must have skipped??

Of course check it because that's the first thing to eliminate. I do have a hard time thinking that not doing the last 45° is causing you to have 1/4-inch of play though. On the ones I've done, the CV-axle stub was pulled tight with no slop during the first 98-ft-lbs stage.

[mike223]

I do have a hard time thinking that not doing the last 45° is causing you to have 1/4-inch of play though. On the ones I've done, the CV-axle stub was pulled tight with no slop during the first 98-ft-lbs stage.

+1

The Tbird IRS was 250 ftlbs torque.

The inner bearing races have to be squeezed together on the hub - captured between the hub and the axle.

I takes very little mileage for the axle nuts to loosen if everything isn't just right.


The least bit of slack (1/2 turn or less at the nut) will allow the inner races to separate on the axle shaft and cause (very) noticeable bearing slop at the wheel.


Typically it won't hurt anything if you catch it quickly.

[edwardb]

+1

The Tbird IRS was 250 ftlbs torque.

The inner bearing races have to be squeezed together on the hub - captured between the hub and the axle.

I takes very little mileage for the axle nuts to loosen if everything isn't just right.

The least bit of slack (1/2 turn or less at the nut) will allow the inner races to separate on the axle shaft and cause (very) noticeable bearing slop at the wheel.

Typically it won't hurt anything if you catch it quickly.

The 2015+ IRS hub is a completely different design than the Tbird IRS. Instead of bearings pressed into the knuckle, it has a bolt-in hub with the bearings factory installed. Four bolts to change the bearings. This picture hopefully gives an idea. https://cfc7329ad537523a5de1-b21544d...g_0463fb01.jpg. I've not noticed that the bearings move when torqued. But the CV-axle definitely has to be pulled tight per the torque spec. I've not heard of any instances on this forum or on the Mustang forums of the newer design nut loosening up like the old one. My Roadster certainly hasn't after three seasons of spirited driving, and I check them frequently.

[mike223]

The 2015+ IRS hub is a completely different design than the Tbird IRS. Instead of bearings pressed into the knuckle, it has a bolt-in hub with the bearings factory installed.

But the CV-axle definitely has to be pulled tight per the torque spec.

I've not heard of any instances on this forum or on the Mustang forums of the newer design nut loosening up like the old one.

Interesting - I haven't taken one of those apart, but it certainly appears to be a hub pressed through the inner race(s?) of the bearing.

On the old IRS - which definitely has two inner races - it's a very "light" press fit (hub to inner bearing race) - if the axle nut hasn't got the races tightly captured between the hub and the axle stub they quickly work apart (and cause slop).


I haven't heard any instances of the new IRS axle nuts working loose either - but I also do not recall ever hearing of OEM TBirds (or the old Cobra IRS, or the Lincolns) having axle nuts work loose - only when installed on the FFRs.

One of life's mysteries I suppose...

[JMan]

Of course check it because that's the first thing to eliminate. I do have a hard time thinking that not doing the last 45° is causing you to have 1/4-inch of play though. On the ones I've done, the CV-axle stub was pulled tight with no slop during the first 98-ft-lbs stage.

This was the issue, I must have not torqued them. They are now tight and have zero slop. I'm glad I'm doing a full run-through after first go-kart. Thanks edwardb!

[edwardb]

This was the issue, I must have not torqued them. They are now tight and have zero slop. I'm glad I'm doing a full run-through after first go-kart. Thanks edwardb!

Glad it was something simple and now resolved.