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Old 09-11-2009, 12:13 AM
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Is my Brake Master Cylinder Toast?

Hey guys, I picked up my '75 280z in late June 2009 as a non-runner. It has been sitting for the previous 3+ years. When going through my engine bay prior to my LSx swap in early July I removed the master cylinder to avoid getting paint on it. On Monday earlier this week I re-installed the master cylinder and added new fluid and began the bleeding process starting with the master cylinder itself, then the pass rear bleeder, driver rear bleeder, pass front bleeder, and finally driver front bleeder.

After getting all the air out of the system I am still having issues with getting the brakes to work. The pedal gives me some resistance vs when I first started bleeding the system, but still goes to the floor, even if I pump the pedal repeatedly with all the bleeders closed.

I have since re-bled the system 4 times since, including the master cylinder, and I even tried using a vacuum pump and gravity bleeding, and installed Russell Speed Bleeders on all 4 corners. No changes. I haven't driven the car yet but I have inspected the pads and shoes and they look great. The rear drums are adjusted correctly as well.

So this leaves me thinking that the master cylinder could be bad. I figure it might be bypassing internally since it doesn't leak a drop, thoughts on this?

Thanks guys!!

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Old 09-12-2009, 08:06 AM
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very possible, I would replace it just to be safe.
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Old 09-16-2009, 11:48 AM
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Confirmed the master cylinder was my problem. Replaced it, re-bled everything and now everything is good to go.

Too bad I am still a long way from driving it.
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Old 09-16-2009, 12:21 PM
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Not to hijack the thread, but it looks like my master cyl in my 67 Impala is leaking. 4 corner drums, non-power brakes, and it happened right after I installed all new wheel cylinders and bled the brakes (flushed out all old dirty fluid). the two brake lines coming from the cyl are tight, so it looks like it's coming from the top cover, so i took the cover off, cleaned up the rubber mating surface and sanded/scraped the mating surface on the cyl. After driving for about 30 min or so, I'll pop the hood and it'll emit maybe a drop or two, and after 2 to 3 weeks of driving like this I checked the levels, and the front reservoir had 2/3rds of fluyid in it, and the rear had 1/2. What could be causing this and how would I fix it?
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Old 09-16-2009, 12:23 PM
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Quote:
Originally Posted by BowTiePride
Not to hijack the thread, but it looks like my master cyl in my 67 Impala is leaking. 4 corner drums, non-power brakes, and it happened right after I installed all new wheel cylinders and bled the brakes (flushed out all old dirty fluid). the two brake lines coming from the cyl are tight, so it looks like it's coming from the top cover, so i took the cover off, cleaned up the rubber mating surface and sanded/scraped the mating surface on the cyl. After driving for about 30 min or so, I'll pop the hood and it'll emit maybe a drop or two, and after 2 to 3 weeks of driving like this I checked the levels, and the front reservoir had 2/3rds of fluyid in it, and the rear had 1/2. What could be causing this and how would I fix it?
You might have some trash between the flares on your fittings. Just a thought.
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Old 09-16-2009, 12:24 PM
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Good point, but I never took the lines off. Just dumped new fluid in and flushed it out and bled like normal
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Old 09-16-2009, 12:35 PM
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Gotcha.

Could you of overfilled the master cylinder? The fluid level will raise when you apply the brakes and could be pushing past the cover seal.
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Old 09-16-2009, 12:41 PM
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You're gonna laugh at me for this one, (but I'm a small block guy, not a brakes guy that's my Dad's thing) but what should the fluid levels be? And thank you for your help btw
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Old 09-16-2009, 12:50 PM
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I usually keep my fluid level 3/4" below the rim. I am sure there is an official measurement, but I have no idea what it is.
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