Hi guys, really could do with some guidance on an issue I have at the moment. Have been Googling it a lot but so far not able to come to a firm conclusion.

 

CAR

'91 Jap Import 2+2 300zx TT

 

ISSUE

Noise coming (I believe) from the rear of the car.

Noise is consistent with road speed, not engine speed.

Starts around 20mph and gets louder with speed.

Throttle and braking does not seem to affect the noise.

Turning left makes the noise disappear instantly, it returns when you straighten up. This is either a slight left at high speeds or a sharper left at low speeds.

Wheels are not noticeably warm/hot after a long drive

 

THINGS DONE TO THE CAR

I've changed the diff oil - this did not affect the noise

Fitted C-cups to the rear subframe mounts - this did not affect the noise

Inspected CV joints on drive shafts - no obvious issues, i.e. not split

Replaced the passenger side wheel bearing - this has not affected the noise

I've been reliably advised that the prop shaft bearing is gone, however I'm not convinced this fits the noise? (thoughts appreciated)

Car has standard suspension but is running negative camber on the back - despite the adjuster being all the way out

 

Any thoughts, help or similar stories appreciated!

 

Thanks.

My thoughts from the noise that you describe would be a wheel bearing. Was it the pax side rear bearing that you have replaced already?

Yeah I replaced the passenger side. Neither side has (had) any play or other signs of the bearing being gone. Car has done 80,000 miles btw.

How would you describe the noise - rumble, grating, screech etc? Is there any vibration occuring at the same time?

 

Have you checked the brake shoes for wear/adjustment? The same for the pads, OEM pads have metal wear tabs which

rub on the discs when worn down.

Edited January 24, 201510 yr by AndrewG

Rumbley whir... There is some vibration coming through the chassis, worse at higher speeds although I think it peaks around 45-50mph.

 

Have check p/s shoes and pads, all good. Handbrake adjustment feels good.

 

I've taken a video with my phone on the p/s rear seat floor - not sure if it'll help at all!

 

The vibration is likely related to the worn centre bearing.

Could be worn propshaft support bearing as Joel says. Have you had that checked for play when up on a ramp?

The rubber support for the bearing can fail allowing the propshaft to vibrate.

 

*** I see from your OP that you have been advised that it has gone***

 

Location and pictures here: http://www.pexcom.com.au/z32cms/e107_plugins/content/content.php?content.420

 

When you drained the diff, did you notice any metal particles in the oil?

Edited January 24, 201510 yr by AndrewG

Andrew,

 

The prop shaft bearing does seem likely, but I'm not sure why the left turns would silence it?

 

I've spoken to Jeff at ZedWorld and intend to replace the prop with one of his lightweight single piece ones to get rid of the problem, so maybe I should just suck it up and get that done! I guess the other option is removed the spacers on the prop bearing to raise it and see if that affects the noise at all. At least that way I might get an indication if it's related.

 

I don't think there was anything odd in the diff oil, but I can't remember how closely I inspected it.

 

Thanks,

 

Jynx

Did you inspect the tires ? (eg. for sidewall damage/pothole damage/heavy cupping) or maybe one of the wheels is not fully round or out of balance in some way ?

 

A propshaft that is out of balance or has a failed center bearing usually only causes vibration at a certain speed and then fades out at higher/lower speeds.

A center bearing that is completely shot makes a knocking sound (usually at low speeds only).

Thanks for the info on the centre bearing, it doesn't quite seem to fit.

 

The tyres are very worn on the inside edge due to the bad camber I mentioned previously. I'm trying to arrange to get another set to try from wchestnutt, so maybe that will shed some light.

If you can get it on a ramp and run the drive train up to speed and closely listen to each wheel bearing, diff, prop bearing etc. only thing is as it won't be under any load the noise may not be present or reduced, also put your hand on the relevant components, taking care not to loose any fingers of course, and feel, sometimes you can feel the problem before you hear it.