mattisnotrealc5

Hello all,

I've got a '99 Hatchback Corvette that I picked up in August. I had no issues with it and I drove it up until last month. I took the insurance off of it and stuck it in the garage with the crappy NY weather. Not to mention the 10-16 inches we're supposed to get tonight-tomorrow... Anywho.. When the weather began getting colder, I would notice this strange hissing noise that would happen until the car warmed up. Once the car was warm and I have been driving for a little while, no hissing noise. The hissing/ vacuum leaking sound sounds like it's coming from under the shifter. It's pretty loud and it goes away when I push the clutch in. As soon as I let the clutch out, it comes back. I can be moving or sitting still, but it's most prominent when I'm sitting at idle. It does get louder if I give it some gas too so I'm not sure exactly if it's a transmission/ clutch issue. If I drive, I hear it more in the lower gears, but I can hardly notice it in higher gears. Does anyone have any input? This noise has driven me nuts and I'm just curious if anyone has any indication as to what may be the issue. The car drives and shifts fine, no issues with the HVAC operation either. I don't think it's the throw out bearing because it's a different sound than the metallic rattle that I get when accelerating from 1st gear that I heard when I first got the car.


Thanks,
Matt

Cybermind

It's probably the normal sound of the driveshaft rotating within the torque tube. If the sound goes away when you push the clutch pedal in, then it is definitely torque tube related. As long as it's not a grinding noise, you're OK. There aren't any vacuum lines under the shifter and your shifter box is mounted directly onto the torque tube. You need to just make sure that your rubber shift boot is there and intact. It will make a racket if this boot is cut or missing.

dadaroo

How many miles on the car and do you know if any work has been done on the drive train?

mattisnotrealc5

Thanks for the reply guys. There are 49k miles on the car and I don't think any work has been done to the transmission/drivetrain. The car only has simple mods like LT headers, exhaust, and intake. The rubber shift boot is in tact, I actually installed a Hurst short throw a few weeks ago so I know that for sure lol. I'm not sure if it's exactly related to the driveshaft considering the car makes the noise even if I'm stopped.

dadaroo

Sorry but you don't understand how the system works. The drive shaft rotates with the clutch out. Think about it.

mattisnotrealc5

Thanks for the reply dadaroo, forgive me for my misunderstanding, but my impression of typical drive shafts were that if they were spinning, the wheels would spin as well. That being said, I'm assuming the operation on C5's are different considering the transmission is in the rear of the car.

Cybermind

Correct! It operates differently than a conventional front engine/ transmission setup. Our cars have torque tube. This is an assembly that connects the front engine/bellhousing to the rear transmission/differential. It is actually a structural component and hardmounted to the driveline. Within this tube there is a driveshaft that is held in place by bearings and rubber couplers at each end.

Your clutch disk is actually located in the front, right behind the engine flywheel. This means that when your car is in neutral, your clutch and driveshaft are constantly spinning. The neutral disconnect happens within the transmission, in the rear. Hope this explanation helps.

Here's an older thread with pictures:
http://forums.corvetteforum.com/c5-t...rque-tube.html

wcsinx

Does it go away immediately when you push the clutch in? If so, that probably rules out the torque tube since that keeps spinning for a few seconds after disengaging the clutch.

Also does it go away with light/partial pressure on the clutch pedal or not until it's fully disengaged?

mattisnotrealc5

Ah, very interesting! Thank you for the insightful information!

mattisnotrealc5

Yes the sound goes away as soon as I press the clutch in. I actually haven't checked to see if the noise goes away with partial clutch pressure. I'll go ahead and try that tonight and report back!

Eurotunerz5

I have the same problem in my c5z but it's not doing it at idle only when I'm in gear accelerating at low RPMs. Vacuum/hissing sound from the shifter tunnel.... Scratching my head.

mattisnotrealc5

Same here, Eurotunerz5. I presume it could be worn bearings/ bushings, but I figured it would be more of a rubbing vibrating sound.

Eurotunerz5

Me too did you figure it out yet? I'm thinking it's got to be the torque tube.