Clutch master pulling air? (1 Viewer)

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Joined
Dec 12, 2021
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Location
Blue Mountains, Sydney
Trying to bleed a new clutch on another project so I can get back to the cruiser, never had a problem bleeding a clutch before. It's an '89 BMW 535is, standard hydraulic clutch system, RHD means it has it's own resevoir not shared with brake system, for any one who knows these cars.

New clutch disc, pressure plate and throw out bearing and slave, all fit nicely. I have bled this thing with every method you could think of and still don't get clutch disengagement. Slave bleeder is on the bottom of the slave, and the fork is internal without any access ports to even fit a boroscope through to check function, so I've reverse bled it with an old oil can bottom to top to make sure there's no air in the slave. Clutch pedal feels perfect, exactly how it should be, doesn't get stuck to the floor, engagement nice and high up in the travel.

Still nothing, only leaves the master. Ordered a new one, but I want to understand what's failed either way. No fluid leaks at any hard lines, soft hoses, slave, master or reservoir, soft lines aren't bulging at all and look fine, no rust anywhere and I've checked every hard line is nipped up nicely. If I pump the clutch pedal 100+ times after any kind of bleed I still get air bubbles popping up in the reservoir consistently. Standard top to bottom bleed will take 500mL of fluid while still shooting out bubbles and then I give up.

Is it possible that the master is somehow drawing air through the pushrod end past the o ring on the piston and into the cylinder? When returning the pedal back up I can hear the faintest 'slurp' sound in the last ~5% of travel. I guess this could be the problem, but I imagined if that was the case it would also be leaking fluid into the cab.
 
Man ,what a frustrating job for you. I got nothing to offer. Please post up what you find though. Good luck!
Replaced the master and all seems well, but still unsure how the master could have been sucking air into the cylinder. Bench testing it everything seemed perfect, no leaks and holding pressure fine, but obviously it was the problem. Real test will be when it's back on the ground, but the driveshaft spins in gear clutch down so it should work. Original 33yo part, not a bad run.
 
Trying to bleed a new clutch on another project so I can get back to the cruiser, never had a problem bleeding a clutch before. It's an '89 BMW 535is, standard hydraulic clutch system, RHD means it has it's own resevoir not shared with brake system, for any one who knows these cars.

New clutch disc, pressure plate and throw out bearing and slave, all fit nicely. I have bled this thing with every method you could think of and still don't get clutch disengagement. Slave bleeder is on the bottom of the slave, and the fork is internal without any access ports to even fit a boroscope through to check function, so I've reverse bled it with an old oil can bottom to top to make sure there's no air in the slave. Clutch pedal feels perfect, exactly how it should be, doesn't get stuck to the floor, engagement nice and high up in the travel.

Still nothing, only leaves the master. Ordered a new one, but I want to understand what's failed either way. No fluid leaks at any hard lines, soft hoses, slave, master or reservoir, soft lines aren't bulging at all and look fine, no rust anywhere and I've checked every hard line is nipped up nicely. If I pump the clutch pedal 100+ times after any kind of bleed I still get air bubbles popping up in the reservoir consistently. Standard top to bottom bleed will take 500mL of fluid while still shooting out bubbles and then I give up.

Is it possible that the master is somehow drawing air through the pushrod end past the o ring on the piston and into the cylinder? When returning the pedal back up I can hear the faintest 'slurp' sound in the last ~5% of travel. I guess this could be the problem, but I imagined if that was the case it would also be leaking fluid into the cab.



has anyone mentioned to you yet , that it is a unwritten GOLDEN TEq rule to always replace the master and the slave as a pair at the same exact time ?

- i learned this working at the dealerships for 12 years , its real and so is the TECH on why to never NOT practice this all the time ....



- so your working on a BMW here on this tech topic or a TOYOTA ?


- please clarify ,


thansks
 
has anyone mentioned to you yet , that it is a unwritten GOLDEN TEq rule to always replace the master and the slave as a pair at the same exact time ?

- i learned this working at the dealerships for 12 years , its real and so is the TECH on why to never NOT practice this all the time ....



- so your working on a BMW here on this tech topic or a TOYOTA ?


- please clarify ,


thansks
Always heard to replace slave first as masters seldom go bad first, from here on I'll probably do both at the same time and save the headaches.

Thought it might be a bit risky posting on mud. Yes it's on a BMW, but I figured it's a general tech question covering hydraulic clutch systems, I don't play on any other forums. It's a family members car sitting in front of my cruiser, need it finished and out of my sight so I can get back to the 80.
 

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