Help Diagnosing Damaged Differential

[tdstuart]

Need some help diagnosing my damaged differential. Wanted to see if any experts in here might know what is wrong since I know next to nothing about differentials.

Car is a 2015 mustang gt, 6r80 with the 3.15 differential. ~125k miles on diff.

Started noticing noise when going from drive to reverse. Progressively got worse, eventually car would make a loud bang when flooring in 1st due to the differential case flexing up and hitting the gas tank. Noticed very worn differential bushings so I replaced them with aftermarket polyurethane bushings. Fixed the differential case flexing but the noise is still there and even more pronounced.

Sounds like a gear-grinding noise. Happens when down-shifting, stopping, starting from a stop, and when going from drive to reverse and reverse to drive. Specifically, when going from drive to reverse and back you can see the suspension loading and the car makes multiple clicking noises coming from the differential.

When I drained and replaced the fluid after installing the bushings there was some metal sludge sitting at the bottom of the case.

Jacking the car up I can make a similar clicking sound by slightly turning the wheel back and forth. It will click but the driveshaft will not move unless I put a little more force and turn further. Happens with both wheels.

The car also makes a lot of clicking noises after parking the car when hot. Definitely not just exhaust cooling down, the differential seems to distinctively make a loud click every few seconds.

Any feedback or opinions are greatly appreciated! Trying to find the most budget-friendly thing to do. Not sure if I can just replace ring/pinion gears or the actual differential gears.

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[WD Pro]

A few random comments from me :

• 125k ? At what point is the diff considered ‘end of life’ (accepting that you have also put multiple high speed runs on it).
• You drained the oil, what went back in ?
• In my experience (Tracloc with 2.5k mounted with Steeda’s red bushes), putting in the wrong oil (or missing the friction modifier) can make the diff real noisy.
• Any gear noise from your diff, will now be exaggerated (all else being the same) after adding the new / stiffer bushes.
• I believe swapping gears is expensive. If you’re not fussy, putting in a low mileage pumpkin is possibly a better option ?
• Tracloc or Torsen ? If you want to do the work and open the casing, Tracloc units are (or were) surprisingly cheap from Ford Performance - but it’s labour intensive and you will also need to budget on a fitting kit.

Your ‘budget friendly’ final comment would lead me to suggest :

• Be sure to rule out a bearing failure - not an uncommon problem and I believe some can be done with the diff in situ.
• Low mileage secondhand pumpkin.
• New oil (preferably with a bottle of Fords friction modifier).
• Do the swap yourself (if capable).

Whichever option you choose, I hope you get it fixed up OK

WD

 

[tdstuart]

A few random comments from me :

• 125k ? At what point is the diff considered ‘end of life’ (accepting that you have also put multiple high speed runs on it).
• You drained the oil, what went back in ?
• In my experience (Tracloc with 2.5k mounted with Steeda’s red bushes), putting in the wrong oil (or missing the friction modifier) can make the diff real noisy.
• Any gear noise from your diff, will now be exaggerated (all else being the same) after adding the new / stiffer bushes.
• I believe swapping gears is expensive. If you’re not fussy, putting in a low mileage pumpkin is possibly a better option ?
• Tracloc or Torsen ? If you want to do the work and open the casing, Tracloc units are (or were) surprisingly cheap from Ford Performance - but it’s labour intensive and you will also need to budget on a fitting kit.

Your ‘budget friendly’ final comment would lead me to suggest :

• Be sure to rule out a bearing failure - not an uncommon problem and I believe some can be done with the diff in situ.
• Low mileage secondhand pumpkin.
• New oil (preferably with a bottle of Fords friction modifier).
• Do the swap yourself (if capable).

Whichever option you choose, I hope you get it fixed up OK

WD

Low mileage complete pumpkins are several hundred dollars + several hundred in shipping usually. My ideal solution would be to figure out what the internal problem is in the diff and just switch out those gears with new ones.

And yes I’m sure the stiffened bushings amplified the noise, especially when shifting.

I put in some valvoline gear oil. Probably should add friction modifier but I’m sure it’s not the cause of the noice as it was happening before and instantly after the bushings and fluid change.

 

[Jaymar]

No amount of metal in the diff oil is considered normal, something made those shavings and it isn't going to get any better. You should probably do a diff rebuild before it gets worse and takes something else out with it. A bearing and seal kit isn't much and you should inspect the ring and pinon while you are there. All in, rebuilding now even with a new gearset will be far cheaper than if something else goes wrong. You could even use the opportunity to get rid of those 3.15s now.

 

[tdstuart]

No amount of metal in the diff oil is considered normal, something made those shavings and it isn't going to get any better. You should probably do a diff rebuild before it gets worse and takes something else out with it. A bearing and seal kit isn't much and you should inspect the ring and pinon while you are there. All in, rebuilding now even with a new gearset will be far cheaper than if something else goes wrong. You could even use the opportunity to get rid of those 3.15s now.

Never said the metal was normal haha.

But I agree on it needs to get fixed eventually.

So there is a bearing inside the diff? Like I said not super knowledgeable on differentials. My guess is the internal gears are damaged. My understanding is there is the ring and pinion gear set and differential gear set also called spider gears.

What do you think I should replace? Also about swapping ratios Im confused on what’s required to swap the 3.15 to another ratio. Do you need a new housing or just different differential internal gears? Thanks!

 

[Jaymar]

Never said the metal was normal haha.

But I agree on it needs to get fixed eventually.

So there is a bearing inside the diff? Like I said not super knowledgeable on differentials. My guess is the internal gears are damaged. My understanding is there is the ring and pinion gear set and differential gear set also called spider gears.

What do you think I should replace? Also about swapping ratios Im confused on what’s required to swap the 3.15 to another ratio. Do you need a new housing or just different differential internal gears? Thanks!

Take it to someone, a differential isn't a "my first job" kind of thing. They will get you an estimate for a rebuild. My main point was that any amount of metal in diff oil is a problem. You have an opportunity to possibly take care of that problem now but if you wait things may get much worse.

Don't worry about changing ratios, it's more involved. It was just something to consider if it was already on your radar.

 

[tdstuart]

Take it to someone, a differential isn't a "my first job" kind of thing. They will get you an estimate for a rebuild. My main point was that any amount of metal in diff oil is a problem. You have an opportunity to possibly take care of that problem now but if you wait things may get much worse.

Don't worry about changing ratios, it's more involved. It was just something to consider if it was already on your radar.

I rebuilt my motor in my garage and did the bushings myself. I’m sure I can figure out the differential, just need some guidance on what I should be looking for.

 

[Jaymar]

I rebuilt my motor in my garage and did the bushings myself. I’m sure I can figure out the differential, just need some guidance on what I should be looking for.

I'm not trying to poop on your abilities, 30 years ago I was in a cold garage with a 302 taken completely apart wondering if I was in over my head too. We all have to start somewhere. With that experience plus the intervening years, I can tell you that you don't want to tackle a differential. The tools to do it properly will cost you more than having the job done. There are shortcuts around some of those tools but those require the experience that comes with having done that job many times before. If you knew enough about the differential to figure it out, you'd know mostly what those noises are that you are hearing. Again, nothing against you, those things come with experience that you will gain along the way.

Unless the Mustang is a project car and you have the disposable income to do the job multiple times if you go wrong then take it in to have it done. There will be plenty of maintenance jobs on this car to get you that experience as well. If you want to lean the ins and outs of more complicated jobs in a consequence free environment, pick up an old Mustang or Ranger as a second car you can wail on in your free time. It's always good to have an ugly Ranger around that you just don't care about.

 

[Buldawg76]

Here is a thread on the 8.8 rear ends that are in our mustangs. Lots of good info .

Inside the "Super 8.8" Rear End | 2015+ S550 Mustang Forum (GT, EcoBoost, GT350, GT500, Bullitt, Mach 1) - Mustang6G.com

BD

 

[WD Pro]

I rebuilt my motor in my garage and did the bushings myself. I’m sure I can figure out the differential, just need some guidance on what I should be looking for.

I have the full rebuild instructions, pm me your email and I can send them to you on Monday (they are on my work pc)

WD

 

[tdstuart]

I have the full rebuild instructions, pm me your email and I can send them to you on Monday (they are on my work pc)

WD

The ford service workshop ones? I have those but thank you for the offer!

 

[tdstuart]

I'm not trying to poop on your abilities, 30 years ago I was in a cold garage with a 302 taken completely apart wondering if I was in over my head too. We all have to start somewhere. With that experience plus the intervening years, I can tell you that you don't want to tackle a differential. The tools to do it properly will cost you more than having the job done. There are shortcuts around some of those tools but those require the experience that comes with having done that job many times before. If you knew enough about the differential to figure it out, you'd know mostly what those noises are that you are hearing. Again, nothing against you, those things come with experience that you will gain along the way.

Unless the Mustang is a project car and you have the disposable income to do the job multiple times if you go wrong then take it in to have it done. There will be plenty of maintenance jobs on this car to get you that experience as well. If you want to lean the ins and outs of more complicated jobs in a consequence free environment, pick up an old Mustang or Ranger as a second car you can wail on in your free time. It's always good to have an ugly Ranger around that you just don't care about.

Not trying to rebuild the entire differential but people commonly do gear swaps and it’s something I am confident I can do. I have all the ford service docs on rebuilding the diff and I work at a ford dealership so I can get the special tools and advice from others.

Trying to see if anyone thinks I can just replace the pinion/ring gears or the differential unit.

 

[ice445]

Just replace the whole unit. Replacing the pinion and pinion bearing and setting preload is a huge pain and requires some special tools. If you get it wrong it will destroy itself in just a few miles. Plus you have to set proper backlash with the ring gear which is doable but still annoying.

There's some things that are fun to DIY but this isn't one of them. I'm impressed a trak lok made it that far in the first place. Usually the steels are trashed by 100k with how most people drive.

 

[Buldawg76]

Until you diagnosis what is causing the noise there is no real advice/direction any of us can provide to help you determine how to proceed further with fixing your car. Removing the rear housing cover will give you a closer look at the ring and pinion gear teeth and spider gears as well. You should also be able to see possibly what is moving/worn that could be causing the noise.

If you don't want to tear into the housing to determine the issue, then just replace the whole unit with used/new pumpkin.

BD

 

[tdstuart]

Just replace the whole unit. Replacing the pinion and pinion bearing and setting preload is a huge pain and requires some special tools. If you get it wrong it will destroy itself in just a few miles. Plus you have to set proper backlash with the ring gear which is doable but still annoying.

There's some things that are fun to DIY but this isn't one of them. I'm impressed a trak lok made it that far in the first place. Usually the steels are trashed by 100k with how most people drive.

Previous owner just drove it as a daily for 91k miles and pretty lightly based on mpg. I have violently abused the car for the last 35k haha

Thanks for the advice

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