Noise from engine compartment

[redsho]

All,
RE: 95 MTX @ 98K miles

I'm seeking some advice as to what is causing this sound. It's kind of a rattling noise that seems to be coming from the tranny/clutch area. The clutch was replaced exactly 1 year ago. The noise is really only audible under two conditions: heat/ac turned on & car in netreul. The noise goes away when heat/ac on, but clutch pedel depressed. Let go the clutch pedal and noise comes back on.

The first guess is it's a clutch problem, so I took it back to the shop that installed the clutch. They inspected & said it could be the tranny? However, they can't be positive until they take the tranny apart & diagnose. They also indicated that my water pump is leaking. Could this just be the cause of the problem? I do not notice my tranny having any signs of problems and the car seems to be running fine.

Thanks for any guidance!

 

[K-Dawg]

What throw out bearing is on the car?

 

[redsho]

What throw out bearing is on the car?

I dunno. All I know is that the replacement clutch kit was made by LUK. It's an OEM replacement.

 

[redsho]

Bump :sun:

 

[87hurricane]

Most standard transmissions make a little noise when in neutral with the clutch out, how much noise are you talking about? For a rattle, I'd start with the exhaust, could be that letting the clutch out, or enagaging the AC is dragging your idle down just enough to hit that perfect resonance. Start from you manifolds, and work your way back, either tapping on them with your fingers to listen for a buzz, or simply let the car run and isloate the sound.

 

[sdpatt]

The connection with the heat/AC being on is the one that confounds me. The only affect that would have is to engage the A/C compressor when the climate control is set to any setting but OFF, VENT and FLOOR. This should have no effect on the transmission when the engine is in neutral except for a slight variation in the engine rpm. It would not add or reduce load on the transaxle. You could get the same effect by manually changing the engine rpms as done when the compressor is engaged. It should result in the IAC valve bumping the rpms up a hundred rpm or so. This may change the sounds due to the different engine speed.

The SHO has a known condition in the trans with gear rattle. When you let the clutch out/up in neutral, the engine is coupled to the trans and the main shaft and all gears spin. The only things not spinning are the output shaft and the reverse coupling gear. the throwout bearing should always be spinning and in contact with the pressure plate fingers. If not, pull up on the clutch pedal and then fully depress the pedal to take up any slack in the cable. The owners manual says to do this every 5,000 miles. When you depress the clutch pedal, the throwout bearing is in more forceful contact with the pressure plate springs.

When you depress the clutch pedal, does the noise reduce in rate in conjunction with the trans shafts and gears coasting down or does it stop instantly? If it matches the coast down scenario, it must be a component in the trans. If it stops instantly, it is likely related to the throwout bearing.

 

[redsho]

Most standard transmissions make a little noise when in neutral with the clutch out, how much noise are you talking about? For a rattle, I'd start with the exhaust, could be that letting the clutch out, or enagaging the AC is dragging your idle down just enough to hit that perfect resonance. Start from you manifolds, and work your way back, either tapping on them with your fingers to listen for a buzz, or simply let the car run and isloate the sound.

In the last 2 days, I've noticed my exhaust being very loud, as if it has a hole in it. I don't know if this relates to the problem I have or not. It certainly seems like a separate issue though. I'll have to tend to the exhaust & troubleshoot some more.

 

[redsho]

Well.... fixed the exhaust leak... but that rough engine noise sound is still there, so I don't think it's related to the exhaust at all. Would a slowly leaking water pump make this kind of noise?

 

[87hurricane]

Most water pumps that I have heard fail, squeaked first, then usually just failed completely, either dumping all the coolant out at once, or a steady drip. I've never seen a waterpump bearing get bad enough to grind or rattle, usually once there is any play in the bearing, the seals fail. Plus, the waterpump is on the opposite side of the engine, far away from your trans.