drive train noises

[Jiggerachi]

I've had two separate unrelated drivetrain noises. I've had both for at least a year or two, probably more. Anyway driving today I've noticed strange things about them, strange enough to make a thread.

1. I've got a rattley, diesel truck sound at idle. First thought it was an exhaust shield, then noticed it goes away when I push the clutch in. Then I thought it was obviously the pilot or throwout bearing. After my clutch job it's still there. Same thing. I then thought, well either it's normal, or it's the supposed noise related to lightweight flywheels, or I've got a bad pilot / TO bearing again(both replaced so unlikely).

This morning I turn off the AC at a light, the noise goes away completely. Hit the AC button it's back full force. Push in the clutch pedal, noise goes away, let off the clutch, noise is back full force. Now it's got me head scratching...what the hell would be related between the clutch and the AC system? Any ideas? (edit to note: I also have an exhaust shield rattle, I've got a broken bolt on the bracket that holds the pipe after the header, but it's a seasonal, louder, more abrasive noise. This diesel sound at idle is reliably there, and reliably alternates with the AC button and clutch.)

2. Seems like my car has always had a SSSSSSSSSS noise while at speed. Not real loud, but annoying and can be heard above the road noise on quiet pavement. Sounds exactly like someone filling up a tire or helium ballon, that hollow hissing/ringing sound. Sounds like it's coming from the rear. I always figured it was a loud diff or some drivetrain part combined with miata style sound deadening. Today at lunch I notice the noise completely goes away when I apply the brakes. So pulled the hand brake slightly and same thing, goes away.

Naturally I would think i've got the rear brakes adjusted too tight and need to loosen them...but actually quite the opposite. I think they're not tight enough, my hand brake barely works in driving, and with it cranked all the way on an incline I can push the car and the brakes creek and almost move. (note the lever is adjusted to around 6in of movement, not too loose or anything) Noise has been the same through the crappy no-name Vatozone pads the car came with, the OEM value pads, and now Hawk HP street pads. Any ideas? Probably the adjustment isn't right and the pads are dragging, but I followed the procedures to adjust them exactly, and still the same, both noise and crappy hand brake.

Sorry for the novel of a post, I'm stumped on both of these and figured I didn't want to make two threads.

[jrj512]

Probably the drive shaft.

[goofygrin]

for #1: http://forum.miata.net/vb/showthread.php?t=241009

[Jiggerachi]

Probably the drive shaft.

Can I borrow your extra one for testing?

[brandonmpace]

I've had the same sound for a while that comes and goes under the same conditions.
I thought it had to do with my clutch, but it works just fine.
I've learned to ignore it, and will only be concerned if it gets worse.

[Jiggerachi]

for #1: http://forum.miata.net/vb/showthread.php?t=241009

Interesting. That pretty much nailed it. I thought for a second it could be harmonics related to idling, but then I though...nahh, couldn't be.

I searched a few times on M.net, but it's pretty much getting that lucky noise description that matches someone elses.

[black roadster]

Regarding #2 It could be your parking brake cable has stretched. There is adjustment built-in but I've never done it. Other causes might be missing or improperly installed brake pad springs (they need to be installed after caliper is in place, not under the caliper), sticky brake shims or dried out brake slider pins.

Drive the car for a while while you recreate the noise, use brakes sparingly and stop and see if caliper or rotor is hot. If they're dragging the will generate heat which means the pads for some reason are not completely releasing. It also could be the dust shield is touching the rotor. Confirm this by looking to see if it is touching any where.

[Jiggerachi]

Finally had time tonight to jack the car up and check it out. With the wheel off the rear pass brake is missing a spring. I forgot I had sent it into orbit during the last brake change. Anyway replaced that with a spare but here's the question...

When I rotate the disk with the handbrake off the pad has very light but constant contact with the rotor. I've heard a little is normal but I can almost recreate the noise exactly by spinning the rotor.

Aren't the calipers (not handbrake) self adjusting? Is this one possibly seized? For the record I re lube the slider pins each brake change...maybe 6 months ago, and the pins are nice & shiny with good boots.

[sammm]

Rears are not self-adjusting. There's an allen-head screw in there under a plastic cap. Tighten the screw until it touches the rotor, then back it off 1/2 turn.

EDIT...nevermind, I was thinking about the parking brake.

[Jiggerachi]

Hmm... after I posted that I worked the brakes a bit and took the car for a spin. The noise is noticeably much less. Wierd, because I remember hearing this noise back when I had all the springs. I'll have to do more listening Monday on the way to work, but that may been it...

Now I have to track down the weak handbrake.
Edit: wonder if this has anything to do with the handbrake issue
http://www.dfwmiata.com/showthread.php?12580-broken-e-brake-cable&highlight=

Edit: Nevermind, i'll pull the wheels tomorrow and re-adjust the hex screws before asking anymore stupid questions. I could have botched it the first time.