Recently bought a JDM evo 8 6 speed with 200,000 kms from interstate. The mechanic who I had look over it said rear diff bushed need to be done, other than that shes good to go. As such, I replaced the bushes with SuperPro poly bushes.

Since buying it, I've noticed a nasty grinding noise when letting off the throttle seemingly coming from the rear of the car - it stops immediately when the clutch is pushed in and/or when the car is in neutral. Seems to be more apparent in the lower gears but happens in all gears.

After doing a bit of research, I thought its likely a diff problem either the bearing is worn, or the crown & pinion are out of alignment. I've changed all the driveline fluids in the car, no metal was found in the gearbox, transfer case or rear differential but the noise persists.

I took it to a local evo specialist whos advice was "Driveline noise from gearbox, rebuild/replacement required". They apparently used a stethoscope to determine the source of the noise while the car was up on a hoist. I'm a bit skeptical of this finding as the car is basically stock and i haven't come across many issues with the 6 speed under stock power in my research. Furthermore, on the drive home I noticed a new high pitched whine coming from the rear of the vehicle above about 80 km/h.

Everything to me points to the diff being the problem, but i really don't want to cough up 2k on a new diff if the mechanic happens to be right. Maybe they were picking up the clutch chatter and just didnt decel from a high enough speed on the hoist. I know driveline noises tend to travel around under the car so from my point of view, really **** knows where its coming from.

Is there any other checks/ diagnoses I could do to pinpoint the problem or has anyone had similar issues?

 

those poly bushes are not great for folks looking for a comfortable ride. see if you can restore to stock quality and work from there.

 

It sounds like pinion and or bearing failure.

200k km of unknown use and maintenance. Perhaps trust an evo specialist if they scoped your gearbox, replaced fluids properly and car left with lesser/similar symptoms. There's no way to replicate drivetrain load whilst hoisted. Poly diff mounts in a suspected worn out rear and a new noise appears? Is the old one gone or are they both present? Also, when you say 6 speed are you refereeing to a 6-speed model Evo or has a 6sp transmission been installed? Did two different shops do the bushes and rear diff diag?

 

I've had the same thing for over 5 years, it's just an annoying sound, nothing ever affected performance. Replaced transmission and clutch, so it wasn't that. Exactly the same symptoms, only when decelerating, especially audible between 3-5k rpm off throttle. Sounds like loose bolts rolling around in a tin can. I tend to launch the car, so once the front diff eventually goes we'll see if the sound is gone.

 

@ViciousLSD - Not worried about ride quality, just want to make sure I'm not doing any mechanical damage by continuing to drive the car

@Kevin. - I have seen this diagnosis mentioned quite a bit for similar symptoms, ideally I want to confirm that is definitely the cause before opening the purse strings for new parts. Is there a way I can check if the bearing has failed without taking the diff apart? I know there's an inspection opening on the diff housing but I dont know how to check the pinion & crown contact with any confidence. I asked the shop to do this for me but they apparently aren't a gearbox/diff specialist so cant help me there this is an evo specialist workshop mind you, so yeah i wont be returning. "There's no way to replicate drivetrain load whilst hoisted" - my thoughts exactly. The mechanic who looked over the car initially (before i bought or drove the car) said the bushes were worn. So i replaced them myself when the car was delivered to me before I drove it for any real distance... so cant attest to whether they made the noise worse or not or if any new noises were added. Original 6 speed car from factory

@Name User - Also seen this sentiment around a fair bit. The noise does sound pretty brutal and I would honestly be scared to take the car out too far for fear of something ****ting the bed hard and doing more damage. Although a part of me was hoping for this on the drive home lol at least i could point to the culprit and say there it is right there!!!!

 

If it was mine, I'd disconnect the propeller shaft and spin and shake the flange of the rear diff to check for any play. spin from the wheels also. check also the mounting/bearing thingers of propeller shaft. then I'd fill that rear diff to the brim with 100% lucas diff lube and go for a test drive.