This "straight cut gear" noise started from the back of my car yesterday all of a sudden. I think its getting louder plus now theres a loud howling noise at exactly 40mph (+/- 2mph). I just finished changing rear diff fluid before the vid. Rebuilt by sheptrans 9months/18k miles ago (12plate upgrade + REM) and always had oem diaqueen lsd. fluid swapped at 3k and 18k (today). 6 road track days and 1 very soft and 1 hard launch at 10k miles. Thoughts?


The fluid came out pretty clean. This is how the drain plug came out:



I'm almost suspecting somethings up with the driveshaft but I've never heard of that problem. The CV boots look like they're in good shape and all my wheel bearings are fine. I'm hoping someone knows exactly what this noise is!

 

bump! Can I get some help with this??

 

somethings grinding, hence is why you have all those metal shavings on the drain plug, that differential definitely needs opened up and looked at

 

If it is whining, then the ring and pinion are no longer aligned properly. Which means that it IS GOING TO FAIL soon.

Save yourself some time and money and have it repaired now, the longer the you wait the worse it gets and you could potentially hurt the diff case.

 

I recently had a rear diff pinion bearing go out and it sounded like truck tires, very similar to your sound. You seem to have located the problem in the diff, next step would be to remove it and check turning torque of the pinion and then tear it down and look for damage. Problem is Mitsubishi doesn't sell rear diff pinion bearing preload shims. So I had to make some on a lathe from some shims I matched up off McMaster Carr. That is if you have a pinion bearing issue.

 

Damn. Those are not the kind of problems I expect after sheptrans rebuilding it with a new r&p gear. I'm going to reserve judgement until I find time to take it in and get something definitive. But this is not encouraging.

 

I would have it checked sooner than later. If something is already grinding it is only a matter of time before it ends up failing completely on you.

 

For sure. I actually don't have to drive my car that much on an aveerage week. Its just bad luck that the noise started when I was out of town. Now I'm driving 300mi back home. If I can get within 120mi AAA wil take care of me.

And I got 80 to 110hr weeks ahead of me for the next 2 months....

 

I would check the driveshaft carrier bearing. Do you have aftermarket driveshaft support bushings like the Torque solutions one? I replaced my oem rubber support bushings with these aluminum ones and at decel down the track it whines making it sound like my evo is supercharged.

 

Yup I do but they've been in for 2 years now. This noise just started yesterday. How do you check the driveshaft carrier bearing?

Side note: made it home just fine. I'm not sure if the noise is getting louder. I chilled out and was just cruising (and got 29.5mpg in the process, lol).

 

You can reserve judgement all you want.

But 2 ASE certified EVO nuts have told you whats wrong already....

Also just because its shep built doesn't mean its unbreakable. All it takes is one wheel hop event to destroy it.

 

If thats so then its nothing but poor workmanship on sheptrans's part. I only ever launched twice with my car and that was 8k miles ago. And one was from 3000rpm and both times definitely no axle hop. I'm strictly a road course guy. I sent sheptrans an email.

 

safest way is on a lift. The idea is to be able to get under the vehicle safely while the drive shaft is spinning to hear if the carrier bearing is bad. I wouldnt recommend it on jackstands. If its obviously coming from the rear end then I would focus on that. does the rear diff bind up at all when you try to spin the wheels by hand?

 

Yea I'm gonna have my service shop take a look at it when I get a chance. I've done all I can to diagnose this.

 

I put the car on a lift today. 100% its the rear diff. Its going back to shep next week.