Brake Problems - Won't bleed, leaking out of master - The 1947 - Present Chevrolet & GMC Truck Message Board Network

cedorris · 10-09-2012, 05:13 PM

The last piece of the puzzle before I can drive my truck home is the brakes. There seems to be a problem that we can't quite figure out. The lines won't bleed and they keep pumping fluid out of the rear of the master cylinder.

It's almost like there is damage inside the slave or master cylinder.

Is this something that happens when these trucks have been sitting for too long? It was working great 4 years ago - but that was 4 years ago.

Any help would be appreciated! Thanks.

1972 Chevy Super with Brake Booster

**Stocker** · 10-09-2012, 05:52 PM

When you say it's pumping fluid out of the rear of the master cylinder, are you talking about where the plunger is -- where it attaches to the vacuum booster? That's definitely not right and you'll need to replace the master cylinder.

Still seems like you should get some fluid through the lines though, unless they're blocked. A more likely problem is the bleeders are plugged, which is common. If so, just remove them & clear the blockage (probably mud) then screw 'em back in.

68gmsee · 10-09-2012, 07:20 PM

Yes, replace the master cylinder. Replace all three rubber lines if they are the original. They may look okay on the outside but the rubber will swell on the inside and prevent the fluid from passing through or restricts it. Not worth the trouble later on.

While you're at it, you may as well do a complete brake system rebuild. I spent a little over $200 but it was well worth the effort. All new shoes, springs kits, wheel brake cylinders, turned the drums and replaced all three rubber brake lines.

PanelDeland · 10-09-2012, 08:54 PM

Also,flush all the fluid.It will absorb water and can cause rust in the new parts and will affect your braking.

tim21391 · 10-09-2012, 11:19 PM

master cylinders are $15 lifetime warrenty at a parts store... they are cheap cheap cheap

BMERDOC · 10-09-2012, 11:31 PM

Leaking M/C's are bad....mmmk

cedorris · 10-09-2012, 11:35 PM

Quote:

Originally Posted by tim21391

master cylinders are $15 lifetime warrenty at a parts store... they are cheap cheap cheap

True. I bought one this evening. Hopefully it solves the issue. Will update tomorrow.
Posted via Mobile Device

cedorris · 10-10-2012, 08:52 AM

We got fluid to all four brakes, we already cleaned the bleeders. It's just when you pump them up, it emptys the front bowl into the rear bowl and forces the fluid out the top. We think the splitter valve might be bad, under pressure it fails and sends the fluid back into the rear bowl of the master cylinder.
Posted via Mobile Device

cedorris · 10-10-2012, 11:42 AM

With a new master cylinder and help from this thread: http://67-72chevytrucks.com/vboard/s...d.php?t=241722 we were able to get the brakes working perfectly.

Thanks for your help everyone!

tim21391 · 10-27-2012, 02:51 AM

right on good to hear!

10-09-2012, 05:13 PM	#1
cedorris 1972 Chevy Cheyenne Super Join Date: Feb 2009 Location: Oklahoma City, OK Posts: 302	Brake Problems - Won't bleed, leaking out of master The last piece of the puzzle before I can drive my truck home is the brakes. There seems to be a problem that we can't quite figure out. The lines won't bleed and they keep pumping fluid out of the rear of the master cylinder. It's almost like there is damage inside the slave or master cylinder. Is this something that happens when these trucks have been sitting for too long? It was working great 4 years ago - but that was 4 years ago. Any help would be appreciated! Thanks. 1972 Chevy Super with Brake Booster __________________ -Clayton 1972 Cheyenne Super LWB 350 - farm truck restore project - twitter @oldgreen

10-09-2012, 05:52 PM	#2
Stocker 20' Daredevil (Ret) Join Date: May 2003 Location: Jefferson State Posts: 13,698	Re: Brake Problems - Won't bleed, leaking out of master When you say it's pumping fluid out of the rear of the master cylinder, are you talking about where the plunger is -- where it attaches to the vacuum booster? That's definitely not right and you'll need to replace the master cylinder. Still seems like you should get some fluid through the lines though, unless they're blocked. A more likely problem is the bleeders are plugged, which is common. If so, just remove them & clear the blockage (probably mud) then screw 'em back in. __________________ - Mike - 1972 K20 LWB 350/350/205 RIP El Jay

10-09-2012, 07:20 PM	#3
68gmsee Active Member Join Date: Jul 2007 Location: Centrally located between Houston, Austin and Waco. BCS area. Posts: 7,947	Re: Brake Problems - Won't bleed, leaking out of master Yes, replace the master cylinder. Replace all three rubber lines if they are the original. They may look okay on the outside but the rubber will swell on the inside and prevent the fluid from passing through or restricts it. Not worth the trouble later on. While you're at it, you may as well do a complete brake system rebuild. I spent a little over $200 but it was well worth the effort. All new shoes, springs kits, wheel brake cylinders, turned the drums and replaced all three rubber brake lines. __________________ 68 GMC 250/3 speed Saginaw p/b p/s 69 Chevy 350/350 currently in pieces still lookin for a cab 06 Trailblazer I just want a vehicle that I can work on, that won't talk to me, leave error msgs or keep track of how I drive...

10-09-2012, 08:54 PM	#4
PanelDeland I am a Referee of life. Join Date: Jun 2000 Location: Greensboro N.C. Posts: 13,993	Re: Brake Problems - Won't bleed, leaking out of master Also,flush all the fluid.It will absorb water and can cause rust in the new parts and will affect your braking. __________________ The 47-present Chevrolet and GMC Truck Message Board Network,it's owners,moderators,members,and associates of any type should not be held responsible for my opinion. You can't fix stupid,not even with duct tape. "My appearance is due to the fact that "GOD" does punish you for having too much fun!" Barrett-Jackson has perfected alchemy,they make rust into gold! "You can lead a horse to water but you can't saddle a duck" "Cleverly disguised as a 'Responsible Adult' "Sometimes your Knight in shining armor is just a retard in tinfoil"

10-09-2012, 11:19 PM	#5
tim21391 Registered User Join Date: Jul 2007 Location: Salina, Kansas Posts: 1,998	Re: Brake Problems - Won't bleed, leaking out of master master cylinders are $15 lifetime warrenty at a parts store... they are cheap cheap cheap __________________ 1972 C-10...402/400..flowmaster 40 series 1967 Mustang 347 stroker/C-4 1966 Mustang 289/3-speed 2013 Mustang V6/6speed w/300 ponies I may be 23, but i sure do knows 67-72s are sexy! Its not MPG its smiles per gallon! build started 11/25/08 build thread: http://67-72chevytrucks.com/vboard/s....php?p=2993796

10-09-2012, 11:31 PM	#6
BMERDOC Registered User Join Date: Jun 2011 Location: Richmond,Va Posts: 2,934	Re: Brake Problems - Won't bleed, leaking out of master Leaking M/C's are bad....mmmk __________________ Nick Carter 1967 C10 Short bed Fleetside Project Cheap Thrills! 2WD C10 Modern/Performance Alignments Easiest Alignment Ever!

10-10-2012, 08:52 AM	#8
cedorris 1972 Chevy Cheyenne Super Join Date: Feb 2009 Location: Oklahoma City, OK Posts: 302	Re: Brake Problems - Won't bleed, leaking out of master We got fluid to all four brakes, we already cleaned the bleeders. It's just when you pump them up, it emptys the front bowl into the rear bowl and forces the fluid out the top. We think the splitter valve might be bad, under pressure it fails and sends the fluid back into the rear bowl of the master cylinder. Posted via Mobile Device __________________ -Clayton 1972 Cheyenne Super LWB 350 - farm truck restore project - twitter @oldgreen

10-10-2012, 11:42 AM	#9
cedorris 1972 Chevy Cheyenne Super Join Date: Feb 2009 Location: Oklahoma City, OK Posts: 302	Re: Brake Problems - Won't bleed, leaking out of master With a new master cylinder and help from this thread: http://67-72chevytrucks.com/vboard/s...d.php?t=241722 we were able to get the brakes working perfectly. Thanks for your help everyone! __________________ -Clayton 1972 Cheyenne Super LWB 350 - farm truck restore project - twitter @oldgreen

10-27-2012, 02:51 AM	#10
tim21391 Registered User Join Date: Jul 2007 Location: Salina, Kansas Posts: 1,998	Re: Brake Problems - Won't bleed, leaking out of master right on good to hear! __________________ 1972 C-10...402/400..flowmaster 40 series 1967 Mustang 347 stroker/C-4 1966 Mustang 289/3-speed 2013 Mustang V6/6speed w/300 ponies I may be 23, but i sure do knows 67-72s are sexy! Its not MPG its smiles per gallon! build started 11/25/08 build thread: http://67-72chevytrucks.com/vboard/s....php?p=2993796



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