Gearing noise on 4th gear deceleration ( No throttle)

[2slow2go]

So i just got an sr20det 240sx and i was driving home and i hear a 4th/3rd gear grinding noise from the transmission tunnel area. It only happens when i cruising off the throttle in the gear in specifically those gears.

Any ideas?

[e1_griego]

Presumably the car has an aftermarket clutch?

It's probably just drivetrain harmonics coupled with stiffer-than-stock mounts.

[jedi03]

could be worn bearings...change gear oil and will tell you...could just be bad harmonics too tho...the tranny is close to you and not very well insulated for noise...

[2slow2go]

yeah aftermarket clutch i believe. I've read online and they say it could be harmonics and maybe the frequency of the diff and tranny together or syncro bad or aftermarket setup. Another said it might be the bearings like the input but i dont see any sound diff in neutral when i push the clutch in and out.

At first I thought it might be an unbalanced driveline but that would mean it would make noise at accel and decel.

It also odd that it mainly does it in 4th gear.

Haven't saw you forever E1_griego. NWN is dead..

[e1_griego]

Yup, 100% dead. I even deleted the NWN link from my bookmarks bar since it wasn't worth going any more.

4th gear is 1:1 ratio so that's why it's the noisiest. All my 240s have done it. Scary at first, but years and years later it's just the cost of doing business with aftermarket parts.

[Def]

Yep, it's diff harmonics due to the 1:1 ratio of 4th. It's loudest at about 2.5-3k RPM or so.

A stock clutch disc will have almost zero noise in this situation.

[canadians14sr20det]

Backlash in the transmission in 4th coupled with a worn input shaft bearing makes this noise.

It's annoying, but won't hurt anything. Every used transmission I've owned for my SR makes that noise. The noise never killed a single one of them.