RobE952

Good morning gents,

Some issues for your collective consideration:

Freshly rebuilt Turbo S transaxle. She is topped up with new Redline fluid. I took her around the block to to fill the oil cooler and then topped it up again. Sounds great. Shifting is crisp. I couldn't be happier.

Last night I am going for a spirited highway drive and suddenly a new noise appears. When on power I hear a loud whine/scraping noise. It's faint / intermittent when coasting in gear and silent when in neutral. I can't really tell if it is coming from the front (clutch) or rear (trany). I limped back home at low speed.

Another possible symptom; the clutch pedal becomes rock hard when the car gets up to temp. The factory spec free play completely disappears. I've noticed this symptom ever since my engine & clutch rebuild last year. I thought it might have been an air bubble in the clutch fluid that was expanding when it got hot, but I've since bled the clutch twice (with a motive power bleeder).

The clutch is a brand new Spec Stage 3 hybrid (6-puck carbon semi-metallic on one side and Kevlar on the other). Brand new master and slave cylinders.

Does this sound like a clutch problem? Is it possible the shop installed my clutch disc backwards (kevlar side vs. metallic side)? What symptoms would that display?

Is this a trany problem? What about the torque tube?

I'm at my wits end with this car yet again!

JohnKoaWood

Is the noise present in all gears?
Does the noise change from gear to gear?
Is the noise speed or engine RPM dependant?
If coasting in neutral at idle is the noise still present (car moving but gear selector in neutral)?

Clutch issue deffinitely could be related, and deffinitely sounds hydraulics related.. durring the engine clutch rebuild did you replace anything in the clutch hydraulic system?

RobE952

Yes, present in all gears and sounds l the same. RPM/speed dependant. It fades significantly when off power but still in gear.

Coasting in neutral (car moving, foot off the clutch, gear selector in neutral) it is silent. Does that rule out torque tube bearings?

Just spoke with Dave Lindsey, he says he is 99% sure that it is impossible to mount the clutch disk backwards.

If something in the hydraulic system is causing the clutch to disengage slightly (ie. there is pressure on the throw-out bearing) when on power could this cause the noise? I do not feel the clutch slipping, but I am also not applying much power since the noise is quite unnerving.

Thanks for your help guys!

JohnKoaWood

I will second what Dave said, but 100%.. if you mounted the clutch disk backwards, the entire stackup wouldn't mount to the car, except for the solid centered disk..

IF there is pressure being applied to the throwout bearing, the noise you are hearing COULD be the bearing eating itself when foot is off clutch it should be unloaded completely)..

RobE952

Can the throwout bearing be changed without removing the pressure plate? Or would it require essentially a full clutch job?

JohnKoaWood

No it cannot.... it is captive to the pressure plate being held in by a spring washer.

rlm328

Sounds like you may have air in your clutch line, did you bleed it up or down after you replaced the clutch.

RobE952

Yes, per my original post, it has been bled at least 3 times. Once in conventional manner on original instal and and twice recently with a pressure bleeder. And I even stroked the pedal a few times while flowing with the pressure bleeder to make sure no bubbles remained in the master cylinder.

I'd say, based on how stiff the pedal feels when its hot, that it acts like there's water in the system which, of course, expands significantly when it boils into steam. But how could that be the case when its been bled so thoroughly with brand new ATE super blue????

Has anyone ever experienced a clutch pedal that changes from "normal" to "super stiff" as the car reaches temp?

This is not how a poorly bled clutch should react in my experience. Normally, if there is a bubble in the system the pedal will just hit the floor. No?

RobE952

I took it for spin around the block last night and confirmed that there are no issues when cold. The clutch has the correct amount of free play and there are no unusual/alarming noises.

Unless anyone has any other suggestions or tips I suppose my only choice at this point is to buy more DOT4 and power bleed again. This time I will try raising the rear of the car only, disconnecting the slave cylinder and raising the bleeder as high as possible to try and free any bubbles that may be stuck.

Tedro951

I don't think bleeding it again will help, but it doesn't take much to try.

If it was mine, I'd inspect the master for solid mounting, and if the nuts are tight, I'd consider replacing the master.

If the master doesn't fix it, then I'd lean more towards the TO bearing, possibly binding. I'd also look at the pilot bearing while you're in there. Obviously these aren't saturday morning items, but if the hydraulics don't fix it, you'll have to dive in deeper.

My guess is that you have 2 unrelated problems.

RobE952

Thanks for the suggestions. So you think that its possible that the stiff clutch pedal and the harsh drivetrain noise are separate problems? Even though they both coincide with the car reaching temp? Can you elaborate more on this?

The master cylinder is brand new, but regardless, I just don't see a method for it to fail or come loose that would reproduce my intermittent symptoms.

I wouldn't doubt that the TO bearing is damaged at this point, but is it a casualty or the cause of the problems? If it was out of alignment or somehow installed improperly could it act up when hot to push back on the clutch fork? What about the pressure plate?

The pilot bearing is new as well, but perhaps thermal expansion is causing it some grief? That could create the noise, but doesn't explain the pedal issue.

Keep the ideas coming guys, please!

Tedro951

The stiff pedal at temp is a problem other mfrs have had on recent cars. New master fixes. Not saying it will, but it's an idea.

It also doesn't require tons of labor to try. Was the old master bad?

RobE952

No it never failed on me, I just thought it would be prudent to replace it while I had the engine out last year. I had failed the slave cylinder previously and figured the master was probably on its way out as well.

Tom M'Guinn

I've never heard of bad hydraulics causing loud noises or a stiff pedal. Sorry to say it, but sounds like you need to take a look to see what's going on in there.

Tedro951

Just food for thought...

http://www.ls1tech.com/forums/manual...ad-master.html

http://www.bimmerfest.com/forums/sho...d.php?t=389895