Bleeding master cylinder - Nova Tech
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  #1  
Old Apr 19th, 08, 01:43 PM
gpbeau gpbeau is offline
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Default Bleeding master cylinder

Replaced the master cylinder on my '72 because the pedal was slowly sinking to the floor. Got a new (not rebuilt) one from Classic Industries, bled it on the bench and installed it. Bled all 4 corners. The pedal still sinks to the floor, but at a much slower rate. The pedal seems stiff as a rock with the engine off. I don't see any fluid leaking out of the rear cylinders and nothing from the calipers. What am I missing? Is it better to bleed the m/c in the car with it pointing up at that crazy angle? Any thoughts are appreciated.
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  #2  
Old Apr 19th, 08, 01:52 PM
SHIFTY4
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Default Re: Bleeding master cylinder

just for the heck of it, what master (exactly) did you purchase ???

stiff pedal with engine off ??? sounds like you have power brakes, this is a normal condition with engine off as there's no vacuum assist with engine off.

i maybe am misunderstanding about seeing fluid from bleeders... are you actually bleeding or just cracking them loose ??? if there's no fluid coming from the bleeders they may be clogged, remove the bleeder screws and try to blow through them... are they clogged ??? if so a small paper-clip or safety pin inserted in the bleed hole (top & bottom) will generally unplug them.

bench bleeding with the hoses generally will get all air from the master... i don't see any reason to be concerned with bleeding from a "crazy" angle... std mounting location (pretty much level) should be just fine.

hope i helped,

JR
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  #3  
Old Apr 19th, 08, 05:32 PM
Big Dave Big Dave is offline
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Default Re: Bleeding master cylinder

Rod length change or get put in the wrong hole?
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  #4  
Old Apr 20th, 08, 12:55 AM
gpbeau gpbeau is offline
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Default Re: Bleeding master cylinder

Sorry for not being clear. Yes--power brakes. Front disk, rear drum; stock setup. My point about the stiff pedal with no vacuum is that there is no sinking to the floor--only when there is vacuum boost. I bled it on the bench, installed it (tried to get the stock rod located properly in the hole on the m/c) and then bled the brake lines at each wheel (all 4 corners). Those bleeders are fine. The m/c was a Raybestos PG Plus unitp/n MC36713. The bore is 1 1/8". No bleeders on the m/c, though.

The issue is that the pedal slowly works its way down to the floor with steady (not thunder-thigh) pressure. Not sure if there is a break-in period for the master-cylinders. Seems like that would be a liability nightmare.

Is this likely just some remaining air in the m/c?
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  #5  
Old Apr 20th, 08, 01:34 AM
SHIFTY4
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Default Re: Bleeding master cylinder

the master cylinder for power brakes should have a shallow hole for the pushrod, almost like a dimple and not a "hole".

just a thought here... in my experience when just a master is swapped, the system doesn't really need to be bled. there's no air IN the system, just the lines have been disconnected... ok so now the master is bench bled and the air is removed, bleeding with slow, steady depressing of the piston the actuation gets all the air out... with the bleeding tubes in the reservoir there's no air coming in, just out... once all the air is out of the master it should be good to go.

now let's say there is still some air in the master and it's installed, now that small amount of air is at the beginning of the systen, not down the line... the more the pedal is depressed the bubbles can break up and the fluid become (lack of better word) aereated... now the farthest wheel needs to be bled until all the air at the beginning of the system is forced out. it could take some time. naturally right when you crack open the line you'll see air, that's in the tubing that goes from the bleeder into the jar, once that air is out you'll see fluid, don't give up yet, there's air in that line, what, maybe 10' from the wheel cylinder ??? take your time and stay on that wheel until the air is gone and you have only fluid... then go to the right side rear. etc etc etc... i know ya know this stuff, just going through the motions

you might try cracking loose the lines again from the master and reattaching the bleeder hoses and confirm all air is out of master cylinder... but if you bled it and know it's good, i dunno if you'll really need to do this.

back to a previous thought... when the lines are full and the master is removed the lines don't really leak out any fluid, so there's no air in the lines, there was just the master that was dry, but then bled... so no air.

i've worked on many cars (brake jobs) and in my whole life i only encountered one car that gave me fits bleeding, this i blame on the master cylinder's design. you are not using that master cylinder so i don't really think the issue yer facing is attributed to the same situation.

long story short... i'd recheck the bleeding process and go from there.

(remember now, yer lookin' at it and i'm only typing so you'll know best what advice to take and what to ignore, i'm only tryin' ta help )

good luck, get back to us and let us know how it goes


JR
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  #6  
Old Apr 20th, 08, 12:43 PM
Philip Philip is offline
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Default Re: Bleeding master cylinder

Garret if the pedal is slowly sinking and you have no leaks at the wheels then the master cylinder is bypassing. Air in the lines will give you a spongy pedal, but it will not continue to sink.
For common maintenaince type parts buying locally is better, then if you have a problem it is easy to exchange the part. That master cylinder fits most 67 - 72 Novas, Chevelles and Camaros and should be available new from any parts store; buy one from some place local and if it solves your problem send this one from Classic back.

Are you going to be down towards Tucson/Casa Grande area anytime soon? If so I will give you a used good one you can install and see if the problem goes away.
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  #7  
Old Apr 20th, 08, 06:27 PM
gpbeau gpbeau is offline
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Default Re: Bleeding master cylinder

Thanks to all for the responses. I'll pick up a m/c bleeding kit and redo that effort and then gravity bleed the whole system.

Philip--we went down to Tucson for the Super Chevy show 2 weeks ago. Other than that, don't have much opportunity to be down that way. Thanks for the offer!
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  #8  
Old Apr 20th, 08, 08:18 PM
Philip Philip is offline
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Default Re: Bleeding master cylinder

I get to the Mesa area about once a month. My son's family and my parents live there. If it doesn't work out let me know and I can bring one up to you. I'll Pm my cell number to you.
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