Mustang GT S550 diff issues

[ikocijan]

Hey all,

I have 2021 GT, PP1 with LSD. The car has only 20 000 miles. EDIT: This is EU version of the car so it has 3.55 gear ratio and it has LSD, but not torsen.

It appears that I have an issue with my diff. It started when I bought the car 6 months ago. From time to time when driving slowly and turning left or right I would hear a slight grinding noise from the back. It sounded like tyre rubbing. Since it happened rarely and was not that loud, I wasn't able to pint point when it's happening.

Now I lowered the car with steeda min drop springs and it's happening constantly when turning at low speed and it's louder.

The Ford dealership checked the car and said that there isn't anything wrong with the suspension. They say that for some reason the diff blocks the wheels, but they don't know why. They called in a guy who only works on diffs to see if he can figure anything out. They said they don't want to pull out the diff until they are sure there is something wrong with it. The guy says that the problem could be the oil and the additive which is added to it. He said it's common on these kind of diffs that either there isn't enough oil or the additive is missing so it grinds. He proposed to change the oil and add additive as the first step.

I've attached a video. You can hear the grinding when I'm turning left at the beginning and end of video.

Does anyone know anything about these diffs? Could this really be the issue because of the oil? I will change the oil, but if that doesn't fix the issue I want to know what else I could check before disassembling the diff because it's hard to believe that it's dead after only 20 000 miles. The car was regularly serviced once a year at Ford and it literally still has original tyres from 2021 on it. So I doubt that the previous owner trashed the car.

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[MidwayJ]

When my '19 GT had gear failure in the diff it made a very different sound. It was more of a high pitched whining or ringing sound. It was not a PP car, though, so it didn't have the Torsen. Also, there were metal shavings in the fluid that seemed easy to identify without disassembly.

 

[Brokestang]

Maybe someone changed the differential fluid and didn't put friction modifier back in. I changed the rear differential fluid in my ford expedition & used valvoline gear oil with friction modifier already in the lube & the rear made a similar sound when turning. Especially when accelerating in the turn. Was told to put the ford motorcraft friction modifier in to fix it. After putting it in no more noise.

 

[ikocijan]

When my '19 GT had gear failure in the diff it made a very different sound. It was more of a high pitched whining or ringing sound. It was not a PP car, though, so it didn't have the Torsen. Also, there were metal shavings in the fluid that seemed easy to identify without disassembly.

Ah, I'm sorry about that. Did they figure out why it failed?

I forgot to write it down so I edited the post: I don't haven Torsen. My car is EU spec and although it's PP1 it has 3.55 gear ratio and normal LSD, not Torsen.

 

[ikocijan]

Maybe someone changed the differential fluid and didn't put friction modifier back in. I changed the rear differential fluid in my ford expedition & used valvoline gear oil with friction modifier already in the lube & the rear made a similar sound when turning. Especially when accelerating in the turn. Was told to put the ford motorcraft friction modifier in to fix it. After putting it in no more noise.

This is a good point. I have some old invoices from it's service so will check and I will ask the Ford dealership which sold me the car if they know anything about changing diff oil.

 

[MidwayJ]

Ah, I'm sorry about that. Did they figure out why it failed?

No but fortunately, it happened at about 4.5 years and 57k miles so it was covered under the powertrain warranty.

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