Help! Consistent pinion seal leak

So I took my mustang to the mechanic over a suspected oil leak, it would only smell like burnt fluids when I really got on it for an extended period of time. I took it to the shop. They diagnosed the pinion seal was leaking, spraying fluid on high rpms on exhaust. I hired them to replace seal. Supposedly they measured break away torque and rematched. I took it home and it was still leaking. So they suspected my driveshaft was the issue, so I bought a one piece drive shaft, took it in again and had them replace drice shaft and pinion seal again. Got it back yesterday, and it’s still leaking . What in the world, any ideas on why this pinion seal is consistently leaking?? Pinion flange??

To add, before he replaced it the first time it was noted there was slight scarring on pinion nut. I wonder if original owner miss torqued nut when replacing seal, and if that’s the case I wonder how one would go about finding right torque for it

Rolling Torque is 16-29 Inch Pounds. If the pinion flange itself is damaged that will cause a leak also.

You can measure rolling torque with diff sealed axles attached and tires on? Just inch pound wrench on pinion nut?

Replace the seal and the pinion flange. Also replace the nut and the crush collar. I don’t know how to set the pinion rolling torque with the carrier in place.

Midlife Crises said:

Replace the seal and the pinion flange. Also replace the nut and the crush collar. I don’t know how to set the pinion rolling torque with the carrier in place.

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You can't. All you can do is keep crushing the crush sleeve a little at a time and check for side play between each step. Once all pinion bearing play is gone, go just a tic more.

I have never replaced a crush sleeve without pulling the carrier. For just seal replacement, I just leave the old crush sleeve. Then just run the pinion nut down till it tightens, done.

Now for the persistent leak, agree with the possibility of the pinion flange having a grove worn in it from the seal, it happens. But I would also check to see if there is any side play on the pinion, as pinion bearing play will also cause a leak at the pinion seal.

Driveshaft causing a pinion seal leak? ummm, NO That is BS.

Juice said:

You can't. All you can do is keep crushing the crush sleeve a little at a time and check for side play between each step. Once all pinion bearing play is gone, go just a tic more.

I have never replaced a crush sleeve without pulling the carrier. For just seal replacement, I just leave the old crush sleeve. Then just run the pinion nut down till it tightens, done.

Now for the persistent leak, agree with the possibility of the pinion flange having a grove worn in it from the seal, it happens. But I would also check to see if there is any side play on the pinion, as pinion bearing play will also cause a leak at the pinion seal.

Driveshaft causing a pinion seal leak? ummm, NO That is BS.

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I agree with what you say about replacing the seal the first time. Some lock tite on the nut and tighten it just a bit more than it was.
The seal has been replaced several times so there is something wrong that is being overlooked.

Midlife Crises said:

I agree with what you say about replacing the seal the first time. Some lock tite on the nut and tighten it just a bit more than it was.
The seal has been replaced several times so there is something wrong that is being overlooked.

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I only see 2 possibilities: play in the pinion bearings or damaged pinion flange.
I would pull the carrier, replace pinion bearings, crush sleeve, pinion flange, and seal.

Juice said:

I only see 2 possibilities: play in the pinion bearings or damaged pinion flange.
I would pull the carrier, replace pinion bearings, crush sleeve, pinion flange, and seal.

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Gets my vote.

Put some sealant on the pinion nut and threads.......don't ask me how I know!!