ausgeflippt951

First things first: I am using my Powerbleeder to bleed the clutch. I've never had this much trouble bleeding a clutch before so I'm a bit embarrassed/confused...

This weekend I installed a new master cylinder. I replaced the blue cloth line from the reservoir to the MC but did not replace any other lines (were previously replaced when I had done the slave cyl a while back). I also replaced the paper gasket between the firewall and the MC.

I'm having one hellllluva time getting the dadgum cylinder bled. Installation went smoothly, and bleeding *seems* to go well: fluid pours out, followed by a torrent of air, followed by fluid. I even had a buddy monitoring the fluid levels in (a) the reservoir, (b) the hose from the Powerbleeder, and (c) the Powerbleeder itself. Note that I did not prime the MC before installation; I've never needed to in the past (perhaps I just got lucky?).


I'm getting air from SOMEWHERE and I can't figure out where, exactly. I'm not leaking fluid anywhere and I've quadruple-checked the tightness of the bolts/lines.


I've narrowed it down to a couple options and would really appreciate peoples' thoughts:


1) Air is getting into the "clutch side" of the reservoir? Note that the side of the reservoir that feeds the clutch is VERY baffled, and fluid entering the top of the reservoir may not be getting all the way to the clutch-feeding side? At least, I've noticed that the levels do not align when I simply fill the reservoir up with fluid.

2) The nipple on top of the MC where fluid is fed via the blue cloth hose. It is held in place with a rubber grommet and looks possible it may be weeping? Seems like a wonky configuration to begin with...

3) What's the purpose of the paper gasket? It can't possibly be to seal anything -- unless I'm a total idiot. Looks like it could only be to prevent marring of the firewall surface...?



Thanks in advance.

Collin

Scott H

I have no proof for this, but I think it's the clutch hardline that is plumbed really high in the engine bay that creates all this trouble. It seems (to me, anyway) that air gets trapped in that section of the line. Two methods to try: 1) elevate the front of the car some more to get the hard line a little lower in relation to the reservoir. 2) fill from the bottom up using a small grease can. I used the second method when I replaced my master and slave and had the same issue and it worked like a treat.

User 52121

1) Air from the reservoir - VERY possible. The fluid doesn't have to drop very much for that hose to start sucking air.

2) Rubber grommet - That should be dry. Either it's leaking, or IMO more likely, fluid is leaking from the blue hose and dribbling down onto the top of the master. Either you've got a loose hose clamp on one of the ends or the blue line itself has a leak in it. I'd hit it with some brake parts cleaner and see if it stays dry - perhaps it's just some residual fluid?

3) Paper gasket - No idea.

IMO - top off the reservoir, get a 2nd body to help you, and do the old-style pedal pump method to bleed it.

JohnKoaWood

1) Pre-fill the reservoir with fluid before hooking up the power bleeder, and by pre-fill I mean almost all the way to the top! (Doing this WILL prevent the clutch side of the reservoir from sucking air!)

2nd, it IS possible to bleed the slave, on the lines, above the master... but this takes MUCH more work with the factory lines, and is more likely with the factory lines to cause a fault in the rubber section...I have aftermarket AN lines and fittings on my 951 for just this reason... bleeding ALL the air out is much easier!

2) I agree with Jim, it SHOULD be dry, especially with all new bits... and the source of the fluid is very likely the blue line NOT the fitting... but we could both be wrong... any chance the grommet got pinched by the plastic fitting?

3) most likely the paper gasket is only there to prevent maring, and to issolate the master cylinder from the firewall (whole dissimilar metals thing...) prevents the master cylinder from becoming rust fused onto the firewall??

ausgeflippt951

Awesome, thanks guys for the quick response. It sounds like I'm aligning with your thoughts: make sure the reservoir is perfect from the get-go. Out of curiosity, where is the slot in the baffle to allow the fluid to flow to the clutch side?

I could've sworn I made sure the reservoir was totally full on the clutch side before hooking up the PB, but it's always worth doing again.

Come to think of it: I once accidentally let the air out of my PB too quickly, and it caused cavitation in the brake fluid. I'll bet that also affected the total air in the clutch side of the reservoir.


Bought an oil can so that if this fails, I can use the bottom-to-top approach.


Not sure if the gasket is there to prevent galvanic corrosion...after all, isn't the firewall galvanized? That would sufficiently protect the MC from corrosion, assuming it's just cast iron. Now, if it were aluminum...oh well.

Van

I've had problems after replacing the clutch master-to-slave hose... Because the hose goes up, then down, air tends to trap at the top.

ausgeflippt951

Thought I'd reply to this, in case others find it helpful -- I noticed another clutch bleeding thread today.

Was able to get my clutch bled. The problem in my case was actually the blue cloth hose -- it had a nick in it that was causing air to leak in! I suppose it's possible I induced the nick when I was cutting the hose to fit it to length.

Additional things I noticed: because my master cyl was so leaky, I did need to adjust the new one slightly -- only by 1.5 turns of the clevis. Also, the blue cloth hose will seem like it's clamped down when it really is not. Be very careful to not overtighten, but certainly make sure it's tight enough.

Finally, and most importantly, pressurize your PB to ~17psi (but no need to go higher). The system can handle at least 20 so this added pressure isn't a big deal. The added pressure helps to ensure that it was vacating ALL air bubbles out of my MC.