Girling master cylinder problem

[Mike Drew]

Hi guys,

Not in my GT40 (I haven't bought my Superformance yet, that $100K keeps failing to materialize for some reason), but rather in my 427 Cobra replica.

Both typically use the same Girling 3/4 inch bore clutch master cylinder:

My old one was tired and sprung a leak, past the seal and into the cabin, so I bought a new one from Pegasus. Swapping it out wasn't quite straightforward, but I got the job done. Now I can't get it to bleed at ALL.

The inlet and outline lines are both hooked up properly, the remote reservoir is full. With somebody pumping the pedal and me under the car operating the bleeder for the internal hydraulic throwout bearing, I get nothing but air getting pumped through the system. It doesn't appear to be drawing any fluid from the reservoir into the master.

I have even tried hooking up a pressure bleeder, pressurizing the reservoir to 10 psi, makes no difference?

What could possibly explain this, and what do I do about it? :huh:

 

[Phil]

Mike:
I had a master once that was defective, thats the obvious choice and I am sure you have considered that, also if the master cyl is mounted at an angle there may be an air bubble thats just impossible to bleed out.
I know it would be a task as you are installed already, but removing the master and pre-bleeding it may solve the problem.
Running a short piece of brake line from the pressure side into the reservoir and operating the pushrod while keeping the whole thing level may solve the problem.
Good luck
Phil

 

[Mike Drew]

Thanks--bench-bleeding is worth I try I suppose.

Installation of this thing is a nightmare. You almost have to remove the brake master cylinder in order to get the clutch master in and out. Fortunately my girlfriend has tiny hands (and I've got tiny girly-man hands too) so we were able to get it done, with some effort.

Removing it to futz with it will be negative fun. Removing it to futz with it, then re-installing it and finding it's still not working will be beyond negative fun! :furious:

 

[Seymour Snerd]

I can't come up with any explanation either; it seems like on return the M/C is drawing air from somewhere rather than pure fluid from the remote reservoir. All I can think of is a leak and/or blockage between the M/C and the reservoir. Can you pull the supply line right at the M/C and verify that fluid comes pouring out? If so, then if you can temporarily extend the supply line from the reservoir above the level of the reservoir you should be able to apply suction to that and verify still that no air comes out. Furthermore, if you block the reservoir's breather hole, you should be able to apply suction and get nothing out (thus proving no leaks on the supply side). Then it seems it has no choice but to pull fluid or pull nothing.

Maybe if one of the seals in the M/C is backwards or really damaged it's not "sucking" it's just "pushing". I don't know if that would produce the symptom you have though.

The only other black magic I can think of is try to suction bleed, and bang like hell on the M/C to try to knock any bubbles loose. But you already know that and besides this isn't a single bubble problem it's a "large quantity of air" problem.

Thinking about "I have even tried hooking up a pressure bleeder, pressurizing the reservoir to 10 psi, makes no difference" the only explanation I can think of is a blocked or pinched supply hose or blocked reservoir output. Makes me want to do the "disconnect at the M/C and see if I get doused in fluid" test.

 

[Mike Drew]

HAH!

I just found the problem. I'm a bonehead. :laugh:

I didn't remove the master cylinder originally; a friend was helping me and he yanked it out while I was under the dash. I therefore failed to note the routing for the feed hose (just a thick rubber hose) from the remote reservoir to the master.

Turns out there's a big-time kink in that hose now, because when I put everything back together I routed it incorrectly. DOH!

Due to the way the builder plumbed the car, the only way to install the line on the master is to hold the line stationary, and spin the master around in circles. So in order to fix the problem, I have to completely remove the master, swing it around in circles until the line comes free, re-route the line, spin the master around again and then reinstall.

Sigh....