[MidLifeCrisis]

Hi,

My GTV has been running great so I haven't been on the bb much, but recently it started making a strange sound. It kind of goes like this...

"vum vum vum vum vum..."

If you say the above without hesitating between "vums" but without hurrying you will duplicate the sound I'm hearing. This only occurs in 4th gear and only at about 40-45 MPH. If I drive at the same speed in 3rd or 5th gear the sound goes away. If I pop it into neutral the sound goes away, even if I maintain the same revs. If I drive below 40 MPH in 4th gear the sound goes away.

I was sure it was the driveshaft support bearing so I replaced this, but the sound is still there (definitely needed one anyway). I have installed new motor mounts, a new tranny mount, and a new quibo.

Anyone have any ideas?

Thanks,

Michael.

 

[italiansedanman]

Have you ever had the tail shaft balanced, or checked the UJ's for play?

Odd that it goes away when you coast in neutral though.

 

[MidLifeCrisis]

Thanks,

I've never had the shaft balanced, but this sound didn't exist before... it kind of evolved. I did check the universal joints for play when I was replacing the support bearing and didn't sense any at all. I should point out however that my differential seems to have more play than it should... a good quarter-turn of the driveshaft.

The neutral thing has me puzzled and makes me think it has something to do with the transmission, but I can't imagine what.

 

[5yearplan]

if the clutch isn't slipping, and the trans fluid is good, and the trans shifts well I'd say prob the diff, did you check the fluid?

 

[MidLifeCrisis]

I definitely have minor leaks in the tranny and diff, but I'm keeping both topped-off. I think the fluid levels are, and have been, ok.

 

[rogerspeed]

Does the frequency of the sound vary between 40 to 45 mph in fourth gear? Any chance it is a sympathetic vibration either exhaust or rear suspension? I've had 105/115 coupes and sedans that make a weird vibration noise at various speed in certain gears which seem to be have something to do with the rear springs! If nothing else works try swapping the rear springs side to side. Also check the axle splines for wear? When you depress to clutch at speed and the sound goes away the "load" on both the driveline and the suspension changes. Not sure, but I think it would also change the "load" on the exhaust system.

 

[MidLifeCrisis]

Interesting...

The frequency does change with speed between 40-45 mph while in 4th gear. Lately while jacking up/down the car I've been hearing a 'pop' in the rear suspension like the springs are sliding laterally as they're released/compressed. I have the IAP springs and I think the rear is an inch or two too high so I was going to lower it this winter.

Are you suggesting that the springs can act like tuning forks?

 

[rogerspeed]

The rear springs do have a tone. As suggested I'd work from the trans back: d/s balance and u-joints, any chance the e-brake rubs against the d/s? rear axle splines and outer bearings. trailing arm and trunion/diff bushings. Do you have the rear axle rebound straps installed?