Help me bleed my brakes. - The 1947 - Present Chevrolet & GMC Truck Message Board Network

my new 72 · 08-22-2002, 10:09 PM

Just what the topic says'. My truck is a 72 with power brakes, and I am having a bit of trouble. I just put new calipers on my truck and I can't get my brakes bled. I have tried everything. I tried to gravity bleed them, I got one of those vaccum pumps, I had my wife pump the snot out of them, and still no luck. The master cylinder never ran dry, so I know that is not the issue. I get a lillte bit of air out of the system, but it never stops. I can't get it to run solid fluid. I have not bled the rears though since I thought that since the master is seperated, then I did'n have to. What am I doing wrong, and where could this air be coming from??

chevy72402 · 08-22-2002, 10:18 PM

did you have the top off the master cylinder when you where gravity feeding it? Is there anywhere that has sprung a leak since you did the calipers?? It should gravity feed if you have the top off... but as you said it isn't. I would try to have her pump it again and see if it will work one more time. I am not sure as to the process that you are using to pump it but make sure that the top is on the master cylinder and have her pump it up then open the bleed valve and have her keep pressure on it till you completely close the valve then repeat over and over. Hope this helps

my new 72 · 08-22-2002, 10:58 PM

The top was off when I tried to gravity feed them, but nothing was happening. I let them stay open for 3 or 4 hours with no change. I know how to bleed brakes I have done it many times before, this time has got me stumped though. I have never had trouble before.

chevy72402 · 08-22-2002, 11:16 PM

sorry about that.... sometimes people don't know. good luck

Zurbo · 08-22-2002, 11:42 PM

Had a similar problem bleeding my brakes. I replaced the back slave cylinders and could not get anythingg to them. The pedal was still stiff and pushing and holding the button on the proportioning valve did not help either. I had to crack open the fronts and then was able to bleed the system. I would imaggine you will need to cack open the backs and pump away on the pedal to recenter the proportioning valve in order to bleed the fronts.

JimKshortstep4x4 · 08-23-2002, 08:16 AM

Sometimes bleeding the truck brakes can be exaspirating and it
seems to take way more time than it should. I still don't have all of the air out of my latest truck and I have bled over a quart of fluid through it. Two suggestions. 1) bleed the master cylinder after the prop valve, one line at a time. With the right hose you can return the fluid to the reservoir. Bleeding this way you can know that the prop valve is open and remove any air that could have worked its way in. If you submerge the hose you can be assured of not getting air back into the master cylinder.

2) Use a hose and container to bleed the calipers submerging the
the hose in brake fluid. This allows you to pump with the bleeder open.

Not all prop valves have a way to push the slide valve back to the center, but you will need to look at yours to determine that.

If all else fails, power brake bleeders work well.

Good luck!

Jim

Protrucks · 08-23-2002, 10:00 AM

The way I always do my breaks is take a glass jar and fill it 1/2 way with break fluid run a piece of vacuum hose that fits tight on the bleeder valve to the jar and SLOWLY pump the breaks until the bubbles stop. The vacuum will suck up break fluid instead of air back up the tube then tighten the bleeder back up and the that wheel is done. I have done all four wheels at the same time but you really need someone to add the fluid to the master cylinder at the same time to do it this way.

OH keep the vacuum line off the bottom of the jar to keep from sucking up the junk that comes out. Of course if junk dose come out you should have flushed the system first.

my new 72 · 08-23-2002, 02:04 PM

I think I may have found the problem, but what do you guys think? I took the line between the master, and the P valve and plugged the master line with a clear hose with a tapered fitting on the end of it to make a seal. I then pumped the brakes as I watched the clear line. When I pressed the peddle down I could see bubbles coming out of the master, but when I hooked up the bleeber vaccum I didn't get bubbles. Has my master cylinder gone bad or what.

my new 72 · 08-23-2002, 06:49 PM

ttt

71GMC_3/4T · 08-23-2002, 07:44 PM

Sounds like your master cylinder is shot. A common thing that happens when you bleed the brakes is that you end up pushing the pedal all the way to the floor, where it hasn't been in years. This puts the cups of the piston in all the rust and crap that has built up, cutting the lips of the cup. I've read somewhere (GMCPaul's site maybe) to use a 2x4 under the pedal and bleed normally. This limits the travel.
Throw a new master cylinder on her, or rebuild your old one if the rust pits aren't too bad. Bubbles means it's getting air on the return stroke, probably past the seals. If you don't change it out now, you should wear your old shoes for a while - unless you like brake fluid stained shoes.

**MikeB** · 08-23-2002, 10:10 PM

Another good reason to use my vacuum bleeder! The original reason was not having to listen to my wife ask me when she can stop pumping the pedal and go back in the house! Best $30 I ever spent.

08-22-2002, 10:09 PM	#1
my new 72 faster, faster, faster Join Date: Dec 2001 Location: Houston ,Texas ,USA Posts: 1,354	Help me bleed my brakes. Just what the topic says'. My truck is a 72 with power brakes, and I am having a bit of trouble. I just put new calipers on my truck and I can't get my brakes bled. I have tried everything. I tried to gravity bleed them, I got one of those vaccum pumps, I had my wife pump the snot out of them, and still no luck. The master cylinder never ran dry, so I know that is not the issue. I get a lillte bit of air out of the system, but it never stops. I can't get it to run solid fluid. I have not bled the rears though since I thought that since the master is seperated, then I did'n have to. What am I doing wrong, and where could this air be coming from?? __________________ I'm going to Law School, wanna debate? It's good practice.

08-22-2002, 10:18 PM	#2
chevy72402 FARMER/RANCHER Join Date: Apr 2001 Location: SD Posts: 597	did you have the top off the master cylinder when you where gravity feeding it? Is there anywhere that has sprung a leak since you did the calipers?? It should gravity feed if you have the top off... but as you said it isn't. I would try to have her pump it again and see if it will work one more time. I am not sure as to the process that you are using to pump it but make sure that the top is on the master cylinder and have her pump it up then open the bleed valve and have her keep pressure on it till you completely close the valve then repeat over and over. Hope this helps __________________ 1972 chevy super, long box, 402 big block (2,000 miles on rebuild) 2wd tach, tilt, tool box on bedside, a/c, sliding rear window, orange and white. 1972 Chevy Blazer 2wd, tach, tilt, a/c, my first engine overhauling experience, Orange, with white top 2006 Gmc Sierra, XM, Z-71, dark blue, onstar, leather, rear entertainment (audio only) heated seats, (the wife loves that feature) upgraded tires immediately after purchase to Goodyear Wrangler AT/S (hate those rock throwers that come from the factory) BWC

08-22-2002, 10:58 PM	#3
my new 72 faster, faster, faster Join Date: Dec 2001 Location: Houston ,Texas ,USA Posts: 1,354	The top was off when I tried to gravity feed them, but nothing was happening. I let them stay open for 3 or 4 hours with no change. I know how to bleed brakes I have done it many times before, this time has got me stumped though. I have never had trouble before. __________________ I'm going to Law School, wanna debate? It's good practice.

08-22-2002, 11:16 PM	#4
chevy72402 FARMER/RANCHER Join Date: Apr 2001 Location: SD Posts: 597	sorry about that.... sometimes people don't know. good luck __________________ 1972 chevy super, long box, 402 big block (2,000 miles on rebuild) 2wd tach, tilt, tool box on bedside, a/c, sliding rear window, orange and white. 1972 Chevy Blazer 2wd, tach, tilt, a/c, my first engine overhauling experience, Orange, with white top 2006 Gmc Sierra, XM, Z-71, dark blue, onstar, leather, rear entertainment (audio only) heated seats, (the wife loves that feature) upgraded tires immediately after purchase to Goodyear Wrangler AT/S (hate those rock throwers that come from the factory) BWC

08-22-2002, 11:42 PM	#5
Zurbo Registered User Join Date: May 2001 Location: Bel Aire, Kansas, USA Posts: 186	Had a similar problem bleeding my brakes. I replaced the back slave cylinders and could not get anythingg to them. The pedal was still stiff and pushing and holding the button on the proportioning valve did not help either. I had to crack open the fronts and then was able to bleed the system. I would imaggine you will need to cack open the backs and pump away on the pedal to recenter the proportioning valve in order to bleed the fronts. __________________ Zurbo's Chevy - 1972 Black/White Cheyenne Super. 402 Big Block /THD 400, factory air and tilt. My other Chevy - 1998 Camaro SS

08-23-2002, 08:16 AM	#6
JimKshortstep4x4 Senior Member Join Date: Jul 2001 Location: Muskegon,MI,USA Posts: 6,026	Sometimes bleeding the truck brakes can be exaspirating and it seems to take way more time than it should. I still don't have all of the air out of my latest truck and I have bled over a quart of fluid through it. Two suggestions. 1) bleed the master cylinder after the prop valve, one line at a time. With the right hose you can return the fluid to the reservoir. Bleeding this way you can know that the prop valve is open and remove any air that could have worked its way in. If you submerge the hose you can be assured of not getting air back into the master cylinder. 2) Use a hose and container to bleed the calipers submerging the the hose in brake fluid. This allows you to pump with the bleeder open. Not all prop valves have a way to push the slide valve back to the center, but you will need to look at yours to determine that. If all else fails, power brake bleeders work well. Good luck! Jim

08-23-2002, 10:00 AM	#7
Protrucks Registered User Join Date: Jun 2001 Location: Kalamazoo MI USA Posts: 161	The way I always do my breaks is take a glass jar and fill it 1/2 way with break fluid run a piece of vacuum hose that fits tight on the bleeder valve to the jar and SLOWLY pump the breaks until the bubbles stop. The vacuum will suck up break fluid instead of air back up the tube then tighten the bleeder back up and the that wheel is done. I have done all four wheels at the same time but you really need someone to add the fluid to the master cylinder at the same time to do it this way. OH keep the vacuum line off the bottom of the jar to keep from sucking up the junk that comes out. Of course if junk dose come out you should have flushed the system first. __________________ 1967 Chevy 1/2 SWB (under construction) 1968 GMC (propane-under construction) 1969 GMC Flatbed (propane) 1970 3/4 LWB (propane) 1970 Stepside 402 (gasoline) 1971 GMC Burb

08-23-2002, 02:04 PM	#8
my new 72 faster, faster, faster Join Date: Dec 2001 Location: Houston ,Texas ,USA Posts: 1,354	I think I may have found the problem, but what do you guys think? I took the line between the master, and the P valve and plugged the master line with a clear hose with a tapered fitting on the end of it to make a seal. I then pumped the brakes as I watched the clear line. When I pressed the peddle down I could see bubbles coming out of the master, but when I hooked up the bleeber vaccum I didn't get bubbles. Has my master cylinder gone bad or what. __________________ I'm going to Law School, wanna debate? It's good practice.

08-23-2002, 06:49 PM	#9
my new 72 faster, faster, faster Join Date: Dec 2001 Location: Houston ,Texas ,USA Posts: 1,354	ttt __________________ I'm going to Law School, wanna debate? It's good practice.

08-23-2002, 07:44 PM	#10
71GMC_3/4T Weapons Of Construction Join Date: Apr 2000 Location: Colorado, USA Posts: 1,095	Sounds like your master cylinder is shot. A common thing that happens when you bleed the brakes is that you end up pushing the pedal all the way to the floor, where it hasn't been in years. This puts the cups of the piston in all the rust and crap that has built up, cutting the lips of the cup. I've read somewhere (GMCPaul's site maybe) to use a 2x4 under the pedal and bleed normally. This limits the travel. Throw a new master cylinder on her, or rebuild your old one if the rust pits aren't too bad. Bubbles means it's getting air on the return stroke, probably past the seals. If you don't change it out now, you should wear your old shoes for a while - unless you like brake fluid stained shoes. __________________ 1971 GMC 2500, 402/TH400 4.10 Daily Driver Lafayette, CO

08-23-2002, 10:10 PM	#11
MikeB Senior Member Join Date: Jul 2000 Location: North Texas Posts: 3,571	Another good reason to use my vacuum bleeder! The original reason was not having to listen to my wife ask me when she can stop pumping the pedal and go back in the house! Best $30 I ever spent. __________________ Mike 1969 C10 LWB -- owned for 35 years. 350/TH350, 3.08 posi, 1st Gen Vintage Air, AAW wiring harness, 5-lug conversion, 1985 spindles and brakes. 1982 C10 SWB -- sold 1981 C10 Silverado LWB -- sold, but wish I still had it! 1969 C10 (not the current one) that I bought in the early 1980s. Paid $1200; sold for $1500 a few years later. Just a hint at the appreciation that was coming. Retired as a factory automation products salesman. Worked part-time over the years for an engine builder and a classic car repair shop. Member here for 24 years! This is the very first car/truck Internet forum I joined. I still used a dial-up modem back then!



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