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Rear diff whine after oil change


RegularGuy

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The question, pulled from the end: Even if the differential was suppose to get 80w-90, why would it be so noisy all of a sudden?

Bit of an odd frustrating day I had, needed the gear oil changed on my rear axle. Having priced things out, I took it in to a lube shop, they look up the vin which indicates 75w-140, the second tag is missing though and so they put 80w-90 in the axle. After three hours of back and forth between myself, the lube shop, and Ford who verified over the phone that it was in fact a torsen, they (presumably) drained the differential and (I can only hope) filled it back up with 75w-140...

Driving the truck home however, the differential made one horrible whining sound. I plan on opening up fill plug to see if they didn't just empty it and send me on my way but the question remains..... Even if the differential was suppose to get 80w-90, why would it be so noisy all of a sudden? Is this normal? Should this be cause for concern?
 


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Dirtman

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No it's not normal and it "WAS" designed for 80w90. Ford later changed their spec on ALL truck differentials past and present to use 75w140. Either fluid would work fine with a friction modifier. Check the fluid level immediately.
 
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rubydist

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All of the torsen rear ends require 75W140. They will not last with 80W90. You need to be sure it has 75W140.
 

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All of the torsen rear ends require 75W140. They will not last with 80W90. You need to be sure it has 75W140.
I don't know where you got this information but Ford uses 75w85 in the mustang, and Torsen themselves uses 80w90 at the factory.
 

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It said in my manual and was confirmed by the Ford tech that the truck should get 75w-140. In both cases, the shop didn't add friction modifier. When brought up, they acted offended at the idea of using such a product
 

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I don't believe a Torsen uses a friction modifier...
 

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Why all this guessing?

Screenshot_20201006-100521_Chrome.jpg


Screenshot_20201006-100445_Chrome.jpg
 

RegularGuy

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Cracked it open to find the diff was filled to a proper level, it smells considerably different than my jug of 80w90... Would that be enough to assume they put the synthetic in the second time around? It feels the same in my hand but 80w versus 75w, I'd imagine it would.

At this point I'm seeing my options as either dumping friction modifier in the pumpkin (lube shop did not) or doing the whole job over again from the beginning myself
 

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Adding friction modifier to your fluid is going to do nothing. Don't waste your time or money there. As a side note, a lot of gear lube now comes with friction modifier in it already...the bottle will say "for limited slips" or something to that effect.

Friction modifier and synthetic fluid definitely do have a more pungent smell than standard 80w90. I guess I would take their word for it that they put the right fluid in.

As to your question of why it's just now making noise... I do not have a good answer for that. Running 80w90 in an axle that calls for 75w140 will not hurt it in that short time period you described, and really it probably wouldn't even matter. 75w140 is just thicker at higher temperatures. Too many unknowns to give you a diagnosis over the internet but pretty safe to say that as long as it was not run empty, it should be OK before and after the fluid change.
 

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Yeah, that friction modifier smells horribly all by itself. Anyhow, when I changed the differential cover on my Lightning, I bought the 75W-140 at my local Ford dealer, who also said to get the friction modifier. So I guess not all of it has the stinky stuff in it. The bottle of friction modifier says it's for noise reduction purposes.
 

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As per Ford's recommendation I added the friction modifier and after a few miles of mixing it quieted down. It's still noisier than before the gear oil change but I can no longer hear it with the windows down
 

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Glad to see you have solved the problem. Next time, if you want to, get a differential cover from G2. As I can recall, it was not that expensive. I purchased one for the simple fact that I can drain and fill the rear diff without having to take the cover off. I know that the service intervals are quite long for axle fluid, but I usually change it a little bit more often.
 

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My issue has returned! The diff has become incredibly noisy over the last week. I pulled the cover to finding the oil to be very dark (moly perhaps?) Checking the magnet revealed quite a bit of black buildup. The cover was black except where the ring gear throws oil. I can say with certainty now, it's for sure the torsen differential. Not sure what to make of this wear pattern on the gears though. Of the teeth I felt, the was no scoring or apparent chipping

After much research, I've purchased some royal purple and the xl-3 (xl-3 had to be shipped) for the next 24 hours I'm just waiting for the rtv to cure. I plan on having a sample of the drained oil tested to find out just what it was they stuck in there.... Being that it started getting louder, I can only assume there's some damage

Looking at the second photo, there appears to me like some pretty serious pinion wear

IMG_20201103_145416.jpgIMG_20201103_145445.jpgIMG_20201103_145439.jpgIMG_20201103_145428.jpgIMG_20201103_145411.jpgIMG_20201103_145407.jpgIMG_20201103_145403.jpg
 
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One tire low in pressure causing it to be a different diameter?
 

RegularGuy

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I wouldn't rule it out just yet, I have the pressure checked 3 times every two months though so it shouldn't be the issue
 


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