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Old 06-05-2020, 10:02 AM
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Sloan66 Sloan66 is offline
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Default Bleeding Brakes?

Had to replace a wheel cylinder and was curious on the service manual procedure. I had always been under the impression when bleeding the system you started at the furthest point, i.e. the right rear and work forward.

The 66 Service manuals states the following for bleeding by operation of the pedal( paraphrase)
1. Fill Master cylinder
2. Start with left front
3. close bleeder proceed one at a time, right front, left rear, right rear
4. when complete check master cylinder


So have I been doing it wrong for all these years?

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Old 06-05-2020, 10:32 AM
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I’ve been doing this procedure just like you Kevin.

So, I guess I was taught the wrong way also.

But it’s always worked fine for me.

Chris.

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Old 06-05-2020, 10:33 AM
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Quote:
Originally Posted by Sloan66 View Post
Had to replace a wheel cylinder and was curious on the service manual procedure. I had always been under the impression when bleeding the system you started at the furthest point, i.e. the right rear and work forward.

The 66 Service manuals states the following for bleeding by operation of the pedal( paraphrase)
1. Fill Master cylinder
2. Start with left front
3. close bleeder proceed one at a time, right front, left rear, right rear
4. when complete check master cylinder


So have I been doing it wrong for all these years?
Imagine that, you did it exactly opposite of the shop manual, and it worked just fine. After 50 years working on cars for a living, I've never followed either procedure. I gravity bleed every system I've ever worked on, and no matter which sequence I do it, the air gets out of the system, and the pedal is firm.

If I was to bleed all 4 wheels I open all 4 bleeders and let them drip until there is no air coming from the bleeders, as they stop passing air I shut each one off and it's done. People make a big production out of bleeding brakes, when it's just gravity and physics.

No pressure bleeders, no vacuum bleeders, and I never have another person helping me bleed brakes.

The most important thing is to keep an eye on the level in the master cylinder to keep it from going dry. Of course if it empties you're going to be starting all over again.

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Old 06-05-2020, 11:51 AM
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Yep, agree, just found it interesting. Lots of saturdays growing up being the labor behind the pedal with my dad, always worked the way he taught me.

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Old 06-05-2020, 01:10 PM
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only replacing 1? wheel cylinder,,,, hmmmm ok

I am a gravity bleeder also ...

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Old 06-05-2020, 01:56 PM
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no scott should have been more clear, the left one was the start of the adventure,

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Old 06-05-2020, 07:12 PM
PontiacJim1959 PontiacJim1959 is offline
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Book is wrong. Start with the farthest one away from the master. Passenger rear, driver's rear, passenger front, then drivers front. This is the only way I have ever done it with a single reservoir master cyl.

I have also bled brakes using the brake bleeder/vacuum pump which works great if you do not have another body to help. Just make sure the master does not run dry.

Have done the gravity feed to bleed the lines, but only to get air out initially, and then have another person help pump the pedal as insurance that I go all the air out.

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Old 06-05-2020, 09:43 PM
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Quote:
Originally Posted by Sirrotica View Post
Imagine that, you did it exactly opposite of the shop manual, and it worked just fine. After 50 years working on cars for a living, I've never followed either procedure. I gravity bleed every system I've ever worked on, and no matter which sequence I do it, the air gets out of the system, and the pedal is firm.

If I was to bleed all 4 wheels I open all 4 bleeders and let them drip until there is no air coming from the bleeders, as they stop passing air I shut each one off and it's done. People make a big production out of bleeding brakes, when it's just gravity and physics.

No pressure bleeders, no vacuum bleeders, and I never have another person helping me bleed brakes.

The most important thing is to keep an eye on the level in the master cylinder to keep it from going dry. Of course if it empties you're going to be starting all over again.
What do you do when the master cylinder is under the floor and even with the wheel cylinders?

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Old 06-05-2020, 09:51 PM
PontiacJim1959 PontiacJim1959 is offline
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Originally Posted by fyrffytr1 View Post
What do you do when the master cylinder is under the floor and even with the wheel cylinders?
Same bleeding procedure. Under the floor is how many of your older cars from the 1950's and earlier were set-up. Hot rodders also prefer under the floor master cyl set-ups due to limited space under the hood with a big V-8.

You probably won't be using the gravity feed bleed, but having a helper pump the brake pedal or using the vacuum/brake hand held pump works great. Did this not too long ago on a 1948 International KB-5 12-foot box truck I have with the master cyl under the floor between the frame rails. Worked perfect and was a breeze doing by myself.

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Old 06-05-2020, 10:04 PM
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Quote:
Originally Posted by fyrffytr1 View Post
What do you do when the master cylinder is under the floor and even with the wheel cylinders?

Pontiac Jack had that problem, and he asked me the same question about gravity bleeding. It's pretty simple you jack one end up higher and bleed the lower axle. Then reverse the inclination of the chassis as long as you get a siphon started it, works just fine. Physics and gravity works every time.

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Old 06-05-2020, 11:49 PM
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How long do you think it would take to gravity bleed a completely empty, never used brake system?

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Old 06-06-2020, 12:04 AM
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How long do you think it would take to gravity bleed a completely empty, never used brake system?
10 minutes.

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Old 06-06-2020, 05:44 AM
Geoff Geoff is offline
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If the m/c is original or a replacement of the original, it will have a residual line pressure valve [ also called a check valve ], which will prevent gravity bleeding. The pedal needs to be pushed to overcome the check valve & force fluid through the lines.
If no check valve, gravity bleeding should work.

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Old 06-06-2020, 01:26 PM
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Quote:
Originally Posted by Geoff View Post
If the m/c is original or a replacement of the original, it will have a residual line pressure valve [ also called a check valve ], which will prevent gravity bleeding. The pedal needs to be pushed to overcome the check valve & force fluid through the lines.
If no check valve, gravity bleeding should work.
I've bled everything from 1956-2008 by gravity, with and without ABS, I have no trouble whatsoever. GM, ford, chrysler, toyota, etc. I don't own any brake bleeding assistance tools. I never have anyone helping me in the garage, so someone to pump the brake pedal while I open the bleeder can't happen. Believe whatever you'd like to.

Just believe that if you rupture a brake line on any car, it will empty the master cylinder while it sits there without anyone pumping the brake pedal. Anyone seen a broken brake line not empty the master cylinder?

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Old 06-07-2020, 05:29 AM
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It is not what I believe, it is about physics.

The check valve retains some pressure in the brake system of drum braked cars.

Bleeding brakes by gravity doesn't work because the CV stops fluid from leaving the m/c under gravity [ 14.7 psi at sea level ]. If you are able to gravity bleed the brakes, then the CV has been removed or it is faulty.
From my 1966 Motors Manual: "The piston spring will close the CV when pressure in the line is reduced to 8-12psi, maintaining a slight pressure in the lines at all the times". Nowhere does it state gravity feed will work; pressure is reqd to overcome the CV pressure, either by using a pressure bleeder or foot on the brake pedal. This pressure overcomes the CV & forces fluid into the lines.

The same info, pumping the brake pedal or use of a pressure bleeder is stated in my 67 GTO manual.

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Old 06-07-2020, 08:15 AM
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I have to agree with Geoff.

If the Residual Valves are in place and functioning properly they will not allow for gravity bleeding.

The Residual Valves will only be found in the drum brake ports

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Old 06-07-2020, 10:24 AM
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Originally Posted by dmorg1 View Post
I have to agree with Geoff.

If the Residual Valves are in place and functioning properly they will not allow for gravity bleeding.

The Residual Valves will only be found in the drum brake ports

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Dave

www.stellarmachine.com


Well Dave and Geoff, may I call your attention to the 67 GTO in my signature pictures. 4 wheel drum brakes, and I never used anything but gravity to bleed them in the 5 years I drove it on the street, and raced it for 3 years. The brake system was apart many times while the car was street driven, and even more times while I was racing it, gravity bled every time. I know, it can't happen, but it did...........LMAO

The only technical explanation possible is that Pennsylvania air must be much heavier than the rest of the world. Most all of the times I've bled brakes on the cars in question was in Erie Pa. Could either of you confirm that theory?

I assume both of you believe if I cut a brake line on a 67 drum brake car that the master cylinder will remain full? Yes?

Post all the pictures you want, and quote the shop manual too. I know better because I've actually done it. I'm not going to argue theory, when I've done what you both claim is impossible.

Forty plus years of making a living working on cars as my profession, starting out working at a Pontiac dealer in 1970, I believe I know what I'm talking about. I also owned a few examples of the cars you claim can't be gravity bled, plus worked on plenty of customer cars of the same lineage.

I never owned a pressure bleeder, and it's virtually impossible to pump the brake pedal and open a bleed screw with one person. How did I do it? Not once, but numerous times.

I guess it's good thing that no one told me back in the 70s that it was impossible to bleed these systems without a pressure bleeder, or a second person pumping the brake pedal, because the cars would have sat until I procured one of the required assets. Somehow I was able to do what was impossible, and bleed these brake systems using the same method you claim can't work, gravity.

Amazing that every time this subject comes up, there are people that claim it can't be done, yet I've done it over and over, got paid for the job and went on.

FWIW, I can't recall any shop manual ever referring to gravity bleeding in all the ones I've looked at. It's not going to show up in any current shop manuals, same as it didn't show up in any of the 60s. It doesn't have to be in print to be valid, there are lots of things that are used everyday in the world that aren't printed in a manual, doesn't make them invalid if they're not on a printed page, written by an engineer.

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Last edited by Sirrotica; 06-07-2020 at 11:21 AM.
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Old 06-07-2020, 11:44 AM
PontiacJim1959 PontiacJim1959 is offline
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Quote:
Originally Posted by Geoff View Post
It is not what I believe, it is about physics.

The check valve retains some pressure in the brake system of drum braked cars.

Bleeding brakes by gravity doesn't work because the CV stops fluid from leaving the m/c under gravity [ 14.7 psi at sea level ]. If you are able to gravity bleed the brakes, then the CV has been removed or it is faulty.
From my 1966 Motors Manual: "The piston spring will close the CV when pressure in the line is reduced to 8-12psi, maintaining a slight pressure in the lines at all the times". Nowhere does it state gravity feed will work; pressure is reqd to overcome the CV pressure, either by using a pressure bleeder or foot on the brake pedal. This pressure overcomes the CV & forces fluid into the lines.

The same info, pumping the brake pedal or use of a pressure bleeder is stated in my 67 GTO manual.
I believe you are misunderstanding the pressure/CV purpose. It maintains pressure in the line so as to keep the brake shoe/brake pad ready for foot pressure when applying the brakes. Yep, it closes when line pressure (you take your foot off the brake pedal and the high line pressure is now reduced) drops around 8-12 psi. The pressure valve closes off and maintains a slight line pressure rather than go back to 0 line pressure.

The pressure valve is a one way check valve in that brake fluid can travel to the brake cylinders or disc piston, but does not allow the brake fluid to completely return back to the master cylinder. As the fluid flows back to the master, once the check valve spring senses the pressure drop within the line at somewhere around 8-12psi, the spring pressure seals off the valve and line pressure is maintained at the 8-12psi pressure.

If the line has that 8-12psi, and the valve is functioning, when you crack open the bleeder, that line pressure will drop to zero because you have now released the line pressure on the opposite side of the pressure valve in which fluid can flow and escape. The pressure valve is still functioning and is shut off, but by cracking open the bleeder, that slight amount of pressure is now gone and there is 0 pressure in the brake line.

That said, the pressure valve is a one way valve in which the high pressure brake fluid can travel to the brakes to apply them. The valve allows the return of the high pressure fluid to return back to the master cylinder UNTIL the pressure of the brake fluid drops down to 8-12psi in which case the spring within the pressure valve closes the check valve and maintains that 8-12psi of pressure from the check valve location back to the brake cylinders/disc piston that it is designed to function with.

If you crack the bleeder on a line with the check valve, or a master cyl with a residual valve, there will be NO pressure maintained in that line to hold the check valve closed - it is a one-way check valve dependent on brake fluid pressure of 8-12psi on one side of it to keep it closed and maintain that low residual brake line pressure. Brake fluid will flow freely past the check valve, down the line, through the wheel cylinder, and out the bleeder, ie gravity bleed.

Maybe that will explain it a little better. If you go to Youtube, you will also see "modern cars" being gravity bled.

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Old 06-07-2020, 01:38 PM
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Originally Posted by PontiacJim1959 View Post
I believe you are misunderstanding the pressure/CV purpose. It maintains pressure in the line so as to keep the brake shoe/brake pad ready for foot pressure when applying the brakes. Yep, it closes when line pressure (you take your foot off the brake pedal and the high line pressure is now reduced) drops around 8-12 psi. The pressure valve closes off and maintains a slight line pressure rather than go back to 0 line pressure.

The pressure valve is a one way check valve in that brake fluid can travel to the brake cylinders or disc piston, but does not allow the brake fluid to completely return back to the master cylinder. As the fluid flows back to the master, once the check valve spring senses the pressure drop within the line at somewhere around 8-12psi, the spring pressure seals off the valve and line pressure is maintained at the 8-12psi pressure.

If the line has that 8-12psi, and the valve is functioning, when you crack open the bleeder, that line pressure will drop to zero because you have now released the line pressure on the opposite side of the pressure valve in which fluid can flow and escape. The pressure valve is still functioning and is shut off, but by cracking open the bleeder, that slight amount of pressure is now gone and there is 0 pressure in the brake line.

That said, the pressure valve is a one way valve in which the high pressure brake fluid can travel to the brakes to apply them. The valve allows the return of the high pressure fluid to return back to the master cylinder UNTIL the pressure of the brake fluid drops down to 8-12psi in which case the spring within the pressure valve closes the check valve and maintains that 8-12psi of pressure from the check valve location back to the brake cylinders/disc piston that it is designed to function with.

If you crack the bleeder on a line with the check valve, or a master cyl with a residual valve, there will be NO pressure maintained in that line to hold the check valve closed - it is a one-way check valve dependent on brake fluid pressure of 8-12psi on one side of it to keep it closed and maintain that low residual brake line pressure. Brake fluid will flow freely past the check valve, down the line, through the wheel cylinder, and out the bleeder, ie gravity bleed.

Maybe that will explain it a little better. If you go to Youtube, you will also see "modern cars" being gravity bled.
Jim, I believe you've hit upon the explanation, with zero back pressure the valve remains open. That's exactly the scenario you have when gravity bleeding a system. I'm speaking from experience, not citing a shop manual about the attributes of the residual valve.

The bias shut off valve on a front and rear system can be off center and shut off half the system rendering gravity bleeding inoperative until it is manually centered. I have run into that problem, and it's easily remedied. Never have I not been able to gravity bleed a 4 wheel drum system because of residual valves. stopping fluid flow from the master cylinder.

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Old 06-07-2020, 01:49 PM
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It doesn't matter what wheel you start with or end with, they are all dedicated hydraulic circuits..

I used to gravity bleed until I tried my brothers pump, wow what a difference! I think I got an extra inch of brake pedal..

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