Howling from the Differential help!

Originally Posted by kbc749

Hello everyone!



I have daily'd my Z for over 4 years and put about 65,000 miles on her since I purchased her. One of the first mods that I did was polyurethane bushings from Whiteline. The diff is the stock-non sport (read non-VLSD) diff. With no gear changes or installed LSD of any kind.



A few weekends ago I was doing some aggressive driving here in Ohio at a place called Hocking Hills trying to keep up with a C6 Z06.



It was about 90 degrees out and we drove hard for probably 3 hours on and off. (as in sometimes there would be a car in front of us and we would slow down or the road wouldn't be curvy and we'd just cruise, but always in constant motion, just not aggressive driving at all times).



Anyways as we go to stop for lunch I'm starting to notice a louder than average gear noise coming from my Z. After lunch I decide to call it a day and drive back home. On the drive on the interstate on the way back it becomes evident that I am hearing a howling from some part of the drivetrain.



I tested several things on the drive home:

-Did the noise change with speed?

-Did the noise change with Gear?

-Did the noise change with RPM (free revving with the clutch pedal pushed in)

-Did the noise change with wheel speed? (go fast, push clutch in and coast)

-Did the noise change with trans speed? (go fast, put the car in neutral and let the clutch out)



And my results were:

-changed with speed, the faster I got the louder it got

-changed with gear, but only to get faster mostly

-does not change with RPM

-does not make noise when the clutch is disengaged. (IE when the pedal is pressed in, the noise is gone)

-the noise gets louder if you are in a low torque area trying to dig out of the low torque area.



So then I got home and parked and found some drips on the ground and found the subframe was wet with what smelled and looked like gear oil.



So now everyone reading this is like: "boom your diff is F'd and leaked fluid and now you damaged the gears in the diff" which is also what I think.



But upon further inspection, none of the seals are leaking and all of the gear fluid appears to have exited the diff out the breather hose. The breather hose appears to be tucked into the rear subframe. And out of the rear subframe is where ALL of the fluid came from. The entire diff was bone dry on the exterior when I inspected it.



So on the recommendation of my coworkers, I drained and checked the fluid. The fluid was not glitter filled. The drain plug did have some metal shavings in the goop that was on it but I see that seems pretty regular based on reading other peoples changing of diff fluid threads. After draining the fluid, I refilled with the Motul 75w-90 gear oil that is recommended and drove the car.



The noise is still evident. I think that this means that the gears were damaged by the lack of fluid and the heat of driving.







SO after that long back story, my questions to you all are:

1) How did the fluid get out? It is my understanding that the fluid will heat up to the point that it will stop lubricating and then the diff will heat up itself and go boom. I've not found descriptions of the fluid like boiling over and coming out the breather...

2) How long do I have until the diff goes boom? I have a track day here in two weeks and I want it to survive at least through that event.

3) Could I have misdiagnosed my issue and the noise is coming from the trans? I think not but I didn't change my trans fluid when I did diff fluid.



I would really appreciate some input on this situation because the search function keeps finding people saying "Just put a diff cooler on it" and "you'll know when it fails because it will go boom". Which is very correct but doesn't help my analysis much.



Thanks!