Gravity Bleeding Brakes - The 1947 - Present Chevrolet & GMC Truck Message Board Network

skokie · 01-19-2008, 02:17 PM

When you gravuty bleed you brakes do you open up all 4 bleeders and come back in 15 mins or do you do them one at a time?

Thanks

JimKshortstep4x4 · 01-19-2008, 07:47 PM

I do all four at once if the whole system needs bleeding. If I only worked on one end than I just open the two on that end. The fluid can start out pretty fast, so be prepared!

Jim

Longhorn Man · 01-19-2008, 07:56 PM

if you are gonna walk away, then I'd only do one end at a time.

Old Chevy Mech · 01-19-2008, 08:44 PM

I havent done it as late, but last time the front seemed to drain out faster. I wouldnt leave it, I'd watch the level in the master cyl.

Frank

**truckdude239** · 01-19-2008, 09:19 PM

when i replaced my rear frame line i just opened both rear bleeders about 3 mins i had fluid pouring out. after that i did a manual bleed to be sure i got all the air out( i let it drian till i got clear fluid out )

skokie · 01-20-2008, 01:03 AM

Thanks guys I will give that a try. Will let everyone know how it goes.

ChevLoRay · 01-20-2008, 01:45 AM

If I remember my old school brake bleeding course, you start at the wheel fartherest away from the master cylinder......

Are you sure you can't get anybody to help you by pumping the pedal????? Sure would make it easier to do it right.

Mordachai · 01-20-2008, 03:21 AM

Quote:

Originally Posted by ChevLoRay

If I remember my old school brake bleeding course, you start at the wheel fartherest away from the master cylinder......

That's what I was taught too...pass rear, driver rear, pass front, drivers front.

But then again, I've always had someone around to pump the pedal, or enticed someone over with some beers...

ChevLoRay · 01-20-2008, 04:34 AM

Beer and Brakes....Brakes and Beer....don't matter which order you put them in, does it? Pump the pedal.....pour a beer.

Mordachai · 01-20-2008, 05:46 AM

Yep, as long as both are being emptied out of their respective containers everything should work out.

That is until you fill the Master with beer!

old_blew_72 · 01-20-2008, 06:12 AM

i've heard that pumping the pedal just moves the air back and forth in the lines and doesn't really build any pressure or for that matter do you any good at all. the best way is to gravity bleed... furthest to closest, but if you want to use the pedal dont pump it just hold it down while someone else opens the valve then close the valve while the pedal is still down so air doesn't suck back in the lines. then lift the pedal and repeat.

Longhorn Man · 01-20-2008, 06:37 AM

the start at the furthest wheel thing is way old school. That was from the days of single reivour master cylinders.
The rear go to one side now, and the front go to the other side of the master cylinder. It doesn't matter if you go left rear or right rear, there is only ONE line going from the front, to the rear axle.
Gravity bleeding is perfectly fine, and if you are starting from empty (talking aobut the lines, not the whole system) then it is prefered. Pumping takes a large bubble of air, and turns it into many many little bubbles.
Once you have clear clean fluid dribbling out, you can do the old pump and bleed if the pedal doesn't feel good, but most of the times I've gavity bled, it wasn't needed.

Mordachai · 01-20-2008, 07:45 AM

heh, I didn't even think about the way the lines run. Makes alot of sense with the more modern master.....so just don't listen to me!

skokie · 01-20-2008, 11:46 AM

Ok its done. I opened them up with a clear tube going to a water bottle. The right rear was ok, left rear was loaded with bubbles. Layed under the truck for 10 mins listening to the planes coming in for a landing, the right front was ok, left front was loaded with bubbles. Sat under there for 15 mins looking at my frame and thinking how much fun I could have on that frame with my grinder and some sanding discs if I had a place to put my cab.

**53burb** · 01-20-2008, 05:38 PM

did it work good??

LONGHAIR · 01-21-2008, 12:05 AM

Andy is absolutely right.....the more air there is in the lines, the better it is to gravity bleed. It does exactly what you need, gets the air out, plus flushes out the old fluid. The old fluid has absorbed water from the air and has caused at least some internal rusting. So it needs replacing anyway.
Pumping just foams up the old stuff. I learned to do it years ago to get a proportioning valve recentered and have prefered it since.
The gravity way is a solo thing too, no helper needed. Not every helper is so helpful.....

ChevLoRay · 01-21-2008, 12:37 AM

I have a pressure bleeder that I "recovered" from our local dump, back in '75. It still has fluid in it and it still had pressure. Only thing missing is the plate that goes on top of the master cylinder. A man who ran a DX station in our town had died, and his daughter/son-in-law cleaned it out and took what they didn't want to the dump. I think they call it scavenging, but I was saving our environment by taking the scrap out of the ecological food chain.

If you have one of these, it would take gravity bleeding to a little higher plane. LonghornMan brought up a good point, one that I hadn't considered.

But the comments about pumping the pedal just moving the air around.....The principle of hydraulics is that you cannot compress a liquid. It's what makes brakes work....that is the pressure in the master cylinder is directed to a wheel, or several of them, to actuate the wheel cylinder or caliper piston. If there is any air in the system, and it doesn't compress, you have reduced pressure at the wheel that is affected.

Glad you got it done. Lots of good discussion show up here, and that should be good for those who are new to the hobby and/or are learning about mechanical things. It's good for all of us.

LONGHAIR · 01-21-2008, 12:58 AM

As ChevLoRay said, there are alternatives....but they co$t. Pressure systems force the fluid down the lines. There are also vacuum systems that suck the fluid from the bleeder valve end too. Gravity is free....

nac593 · 01-01-2009, 07:19 PM

How do you gravity bleed? Truck level or front wheels higher than the back wheels? I've had my 2 back bleeders open for a while and nothing is coming out. The master cylinder is full.

68gmsee · 01-01-2009, 08:01 PM

It may be possible that your rubber hoses are swelled on the inside and preventing the fluid from passing through without the pressure of the pedal. That happened to me long time ago and had to replace all my hoses.

Anyway, these days I do the bleeding with someone depressing the pedal while release the valve. A lot faster and easier -for me anyway.

LONGHAIR · 01-01-2009, 08:02 PM

If nothing is coming out, your brake light is probably on?
This is indicating that the proportioning valve is "popped"...meaning that it is in "safety mode" which has "cut off" the flow of fluid to the rear brakes. This happens do to a loss of pressure on that side of the valve. It needs to be re-centered (balanced) by reducing the pressure on the "good" side.
Open the bleeders on the front brakes, pump them a few times going to the floor, you should feel a "click" (the light will go off too)

At that point, be sure that the master cylinder is full and allow all of the bleeders to flow....Don't touch the pedal. Let it run a while, being sure that it doesn't run dry, refill as necessary. Close all of the bleeders before you touch the pedal again. You should be good to go.

rerun of a year old thread, for those who didn't notice....LOL

nac593 · 01-01-2009, 08:23 PM

I just switched to disc brakes in the rear. The brake lines in the rear are new and empty. The prop valve is centered. I went thru that when I switched the front brakes a few months ago. Still no fluid coming out. Should I have 1 rear open or both? Should I just try to push the pedal to push fluid thru?

LONGHAIR · 01-01-2009, 08:32 PM

That little "detail" would have been nice in the first post....

First you should have had to replace the master cylinder too, along with proportioning valve. It is not as simple as just bolting calipers/rotors on the rear axle...

Open both, no need to touch the pedal, it will flow on its own.

nac593 · 01-01-2009, 08:51 PM

I bought the front and rear disc kits from ECE with a new brake booster, master cylinder, and prop valve. They told me it would be fine to do the front discs first and then at a later time do the rear. They said it was the same master cylinder and prop valve for the drums or discs in the rear. I did the fronts a couple months ago. When I went to bleed the fronts the prop valve got off centered. I took it to a brake shop and they fixed it. Now I just did the rear and still no fluid.

LONGHAIR · 01-02-2009, 03:08 PM

Quote:

Originally Posted by nac593

I bought the front and rear disc kits from ECE with a new brake booster, master cylinder, and prop valve. They told me it would be fine to do the front discs first and then at a later time do the rear. They said it was the same master cylinder and prop valve for the drums or discs in the rear. I did the fronts a couple months ago. When I went to bleed the fronts the prop valve got off centered. I took it to a brake shop and they fixed it. Now I just did the rear and still no fluid.

First of all, I'm not buying it that they are the same. The residual valve is different at very least. A drum brake system holds more pressure in the lines when you are not pressing the pedal, this would cause a drag on the discs if it were run like that.

In any case, you have the same problem again

01-19-2008, 02:17 PM	#1
skokie Registered User Join Date: Oct 2003 Location: San Jose Ca. Posts: 3,354	Gravity Bleeding Brakes When you gravuty bleed you brakes do you open up all 4 bleeders and come back in 15 mins or do you do them one at a time? Thanks __________________ RIP to my son Dylan. 5/17/2002 - 8/18/2018 If you want to know more about rare forms of pediatric cancer or if you want to help fund pediatric cancer research, please check out the website for the non-profit I started. https://slothforpedcancer.org 68 build thread http://67-72chevytrucks.com/vboard/s...d.php?t=223234

01-19-2008, 07:47 PM	#2
JimKshortstep4x4 Senior Member Join Date: Jul 2001 Location: Muskegon,MI,USA Posts: 6,026	Re: Gravity Bleeding Brakes I do all four at once if the whole system needs bleeding. If I only worked on one end than I just open the two on that end. The fluid can start out pretty fast, so be prepared! Jim __________________ 1971 Shortbox step side 4x4, 350 sbc, 3:07 rear end 1965 Impala SS 400 sbc, Muncie rock crusher 1966 Impala SS 396 bbc, TH 400 1969 El Camino, 350 sbc, TH 350 1971 Snowplow built on a Blazer frame 1972 GMC Short bed, stepside, TH 400, 427 BBC

01-19-2008, 07:56 PM	#3
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	Re: Gravity Bleeding Brakes if you are gonna walk away, then I'd only do one end at a time.

01-19-2008, 08:44 PM	#4
Old Chevy Mech Keepin it runnin! Join Date: Oct 2007 Location: Deep River, CT Posts: 1,036	Re: Gravity Bleeding Brakes I havent done it as late, but last time the front seemed to drain out faster. I wouldnt leave it, I'd watch the level in the master cyl. Frank __________________ 1970 K-5 4X4 Blazer 1970 K-20 4X4 Long Bed "Liberty Means Responsibility, that is why most men dread it"

01-19-2008, 09:19 PM	#5
truckdude239 Senior Member Join Date: Sep 2005 Location: Lewisville, Nc Posts: 10,238	Re: Gravity Bleeding Brakes when i replaced my rear frame line i just opened both rear bleeders about 3 mins i had fluid pouring out. after that i did a manual bleed to be sure i got all the air out( i let it drian till i got clear fluid out ) __________________ David fuller Ase Certified Mechanic Click here to help support our board!! 1971 Chevy c-10 under going a 4.8l LSx swap Build Thread http://67-72chevytrucks.com/vboard/s...d.php?t=421305 2007 Honda Accord my daily 145kmiles 2002 Honda Accord 4 door With 330k(sisters car) 2005 toyota Avalon 228k( brothers car) 2002 Sububran 5.3 245k 2000 Tahoe 5.3l 378 General manager for Marco's Carwash & lube Last edited by truckdude239; 01-19-2008 at 09:20 PM.

01-20-2008, 01:03 AM	#6
skokie Registered User Join Date: Oct 2003 Location: San Jose Ca. Posts: 3,354	Re: Gravity Bleeding Brakes Thanks guys I will give that a try. Will let everyone know how it goes. __________________ RIP to my son Dylan. 5/17/2002 - 8/18/2018 If you want to know more about rare forms of pediatric cancer or if you want to help fund pediatric cancer research, please check out the website for the non-profit I started. https://slothforpedcancer.org 68 build thread http://67-72chevytrucks.com/vboard/s...d.php?t=223234

01-20-2008, 01:45 AM	#7
ChevLoRay Old Skool Club Join Date: Jun 2001 Location: Benton, AR "The Heart of Arkansas" Posts: 10,880	Re: Gravity Bleeding Brakes If I remember my old school brake bleeding course, you start at the wheel fartherest away from the master cylinder...... Are you sure you can't get anybody to help you by pumping the pedal????? Sure would make it easier to do it right. __________________ Member Nr. 2770 '96 GMC Sportside; 4.3/SLT - Daily driven....constantly needs washed. '69 C-10 SWB; 350/TH400 - in limbo The older I get, the better I was.

01-20-2008, 04:34 AM	#9
ChevLoRay Old Skool Club Join Date: Jun 2001 Location: Benton, AR "The Heart of Arkansas" Posts: 10,880	Re: Gravity Bleeding Brakes Beer and Brakes....Brakes and Beer....don't matter which order you put them in, does it? Pump the pedal.....pour a beer. __________________ Member Nr. 2770 '96 GMC Sportside; 4.3/SLT - Daily driven....constantly needs washed. '69 C-10 SWB; 350/TH400 - in limbo The older I get, the better I was. Last edited by ChevLoRay; 01-20-2008 at 04:35 AM.

01-20-2008, 05:46 AM	#10
Mordachai Fat Fendered Fleetside Join Date: Nov 2004 Location: WPB, S. FL, USA, Earth Posts: 718	Re: Gravity Bleeding Brakes Yep, as long as both are being emptied out of their respective containers everything should work out. That is until you fill the Master with beer! __________________ 71 GMC lwb 56 Big window swb 93 GMC Sonoma (dd) radiused fiberglass fender project for 67-72

01-20-2008, 06:12 AM	#11
old_blew_72 Registered User Join Date: Feb 2006 Location: Oskaloosa, IA Posts: 19	Re: Gravity Bleeding Brakes i've heard that pumping the pedal just moves the air back and forth in the lines and doesn't really build any pressure or for that matter do you any good at all. the best way is to gravity bleed... furthest to closest, but if you want to use the pedal dont pump it just hold it down while someone else opens the valve then close the valve while the pedal is still down so air doesn't suck back in the lines. then lift the pedal and repeat.

01-20-2008, 06:37 AM	#12
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	Re: Gravity Bleeding Brakes the start at the furthest wheel thing is way old school. That was from the days of single reivour master cylinders. The rear go to one side now, and the front go to the other side of the master cylinder. It doesn't matter if you go left rear or right rear, there is only ONE line going from the front, to the rear axle. Gravity bleeding is perfectly fine, and if you are starting from empty (talking aobut the lines, not the whole system) then it is prefered. Pumping takes a large bubble of air, and turns it into many many little bubbles. Once you have clear clean fluid dribbling out, you can do the old pump and bleed if the pedal doesn't feel good, but most of the times I've gavity bled, it wasn't needed.

01-20-2008, 07:45 AM	#13
Mordachai Fat Fendered Fleetside Join Date: Nov 2004 Location: WPB, S. FL, USA, Earth Posts: 718	Re: Gravity Bleeding Brakes heh, I didn't even think about the way the lines run. Makes alot of sense with the more modern master.....so just don't listen to me! __________________ 71 GMC lwb 56 Big window swb 93 GMC Sonoma (dd) radiused fiberglass fender project for 67-72

01-20-2008, 11:46 AM	#14
skokie Registered User Join Date: Oct 2003 Location: San Jose Ca. Posts: 3,354	Re: Gravity Bleeding Brakes Ok its done. I opened them up with a clear tube going to a water bottle. The right rear was ok, left rear was loaded with bubbles. Layed under the truck for 10 mins listening to the planes coming in for a landing, the right front was ok, left front was loaded with bubbles. Sat under there for 15 mins looking at my frame and thinking how much fun I could have on that frame with my grinder and some sanding discs if I had a place to put my cab. __________________ RIP to my son Dylan. 5/17/2002 - 8/18/2018 If you want to know more about rare forms of pediatric cancer or if you want to help fund pediatric cancer research, please check out the website for the non-profit I started. https://slothforpedcancer.org 68 build thread http://67-72chevytrucks.com/vboard/s...d.php?t=223234

01-20-2008, 05:38 PM	#15
53burb Senior Member Join Date: May 2004 Location: Queen Creek, AZ Posts: 1,010	Re: Gravity Bleeding Brakes did it work good??

01-21-2008, 12:05 AM	#16
LONGHAIR just can't cover up my redneck Join Date: May 2004 Location: Columbus OH Posts: 11,414	Re: Gravity Bleeding Brakes Andy is absolutely right.....the more air there is in the lines, the better it is to gravity bleed. It does exactly what you need, gets the air out, plus flushes out the old fluid. The old fluid has absorbed water from the air and has caused at least some internal rusting. So it needs replacing anyway. Pumping just foams up the old stuff. I learned to do it years ago to get a proportioning valve recentered and have prefered it since. The gravity way is a solo thing too, no helper needed. Not every helper is so helpful..... Last edited by LONGHAIR; 01-21-2008 at 12:06 AM.



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01-21-2008, 12:37 AM	#17
ChevLoRay Old Skool Club Join Date: Jun 2001 Location: Benton, AR "The Heart of Arkansas" Posts: 10,880	Re: Gravity Bleeding Brakes I have a pressure bleeder that I "recovered" from our local dump, back in '75. It still has fluid in it and it still had pressure. Only thing missing is the plate that goes on top of the master cylinder. A man who ran a DX station in our town had died, and his daughter/son-in-law cleaned it out and took what they didn't want to the dump. I think they call it scavenging, but I was saving our environment by taking the scrap out of the ecological food chain. If you have one of these, it would take gravity bleeding to a little higher plane. LonghornMan brought up a good point, one that I hadn't considered. But the comments about pumping the pedal just moving the air around.....The principle of hydraulics is that you cannot compress a liquid. It's what makes brakes work....that is the pressure in the master cylinder is directed to a wheel, or several of them, to actuate the wheel cylinder or caliper piston. If there is any air in the system, and it doesn't compress, you have reduced pressure at the wheel that is affected. Glad you got it done. Lots of good discussion show up here, and that should be good for those who are new to the hobby and/or are learning about mechanical things. It's good for all of us. __________________ Member Nr. 2770 '96 GMC Sportside; 4.3/SLT - Daily driven....constantly needs washed. '69 C-10 SWB; 350/TH400 - in limbo The older I get, the better I was.

01-21-2008, 12:58 AM	#18
LONGHAIR just can't cover up my redneck Join Date: May 2004 Location: Columbus OH Posts: 11,414	Re: Gravity Bleeding Brakes As ChevLoRay said, there are alternatives....but they co$t. Pressure systems force the fluid down the lines. There are also vacuum systems that suck the fluid from the bleeder valve end too. Gravity is free....

01-01-2009, 07:19 PM	#19
nac593 Registered User Join Date: Sep 2007 Location: san diego,ca Posts: 125	Re: Gravity Bleeding Brakes How do you gravity bleed? Truck level or front wheels higher than the back wheels? I've had my 2 back bleeders open for a while and nothing is coming out. The master cylinder is full.

01-01-2009, 08:01 PM	#20
68gmsee Active Member Join Date: Jul 2007 Location: Centrally located between Houston, Austin and Waco. BCS area. Posts: 7,947	Re: Gravity Bleeding Brakes It may be possible that your rubber hoses are swelled on the inside and preventing the fluid from passing through without the pressure of the pedal. That happened to me long time ago and had to replace all my hoses. Anyway, these days I do the bleeding with someone depressing the pedal while release the valve. A lot faster and easier -for me anyway.

01-01-2009, 08:02 PM	#21
LONGHAIR just can't cover up my redneck Join Date: May 2004 Location: Columbus OH Posts: 11,414	Re: Gravity Bleeding Brakes If nothing is coming out, your brake light is probably on? This is indicating that the proportioning valve is "popped"...meaning that it is in "safety mode" which has "cut off" the flow of fluid to the rear brakes. This happens do to a loss of pressure on that side of the valve. It needs to be re-centered (balanced) by reducing the pressure on the "good" side. Open the bleeders on the front brakes, pump them a few times going to the floor, you should feel a "click" (the light will go off too) At that point, be sure that the master cylinder is full and allow all of the bleeders to flow....Don't touch the pedal. Let it run a while, being sure that it doesn't run dry, refill as necessary. Close all of the bleeders before you touch the pedal again. You should be good to go. rerun of a year old thread, for those who didn't notice....LOL

01-01-2009, 08:23 PM	#22
nac593 Registered User Join Date: Sep 2007 Location: san diego,ca Posts: 125	Re: Gravity Bleeding Brakes I just switched to disc brakes in the rear. The brake lines in the rear are new and empty. The prop valve is centered. I went thru that when I switched the front brakes a few months ago. Still no fluid coming out. Should I have 1 rear open or both? Should I just try to push the pedal to push fluid thru?

01-01-2009, 08:32 PM	#23
LONGHAIR just can't cover up my redneck Join Date: May 2004 Location: Columbus OH Posts: 11,414	Re: Gravity Bleeding Brakes That little "detail" would have been nice in the first post.... First you should have had to replace the master cylinder too, along with proportioning valve. It is not as simple as just bolting calipers/rotors on the rear axle... Open both, no need to touch the pedal, it will flow on its own.

01-01-2009, 08:51 PM	#24
nac593 Registered User Join Date: Sep 2007 Location: san diego,ca Posts: 125	Re: Gravity Bleeding Brakes I bought the front and rear disc kits from ECE with a new brake booster, master cylinder, and prop valve. They told me it would be fine to do the front discs first and then at a later time do the rear. They said it was the same master cylinder and prop valve for the drums or discs in the rear. I did the fronts a couple months ago. When I went to bleed the fronts the prop valve got off centered. I took it to a brake shop and they fixed it. Now I just did the rear and still no fluid.

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