Constant air in line while bleeding

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  #1  
Old 03-23-10, 06:50 PM
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Constant air in line while bleeding

So I am trying to bleed the brakes on a 1992 Chevy Corsica for a friend. Constantly while I try to bleed the air out, there is a swoosh of lots of small bubbles, and some large bubbles following it/between the smaller bubbles. It doesn't go away or change.

I have a friend push the brake pedal, and while it is pushed, I momentarily open the bleed screw with clear line, and let it drain, then shut the bleed screw while he lets the pedal back up.

This is also a brand new master cylinder has been installed. I did my best to bench bleed it, but they didn't provide every fitting that was required to do so, and so while I felt I did an OK job, I believe there were still small bubbles remaining.

I also tried bleeding the two upper bleeder screws on the master cylinder, and managed to get just one tiny bubble after many pumps.

I just don't know what to do. I wonder if I should get another master cylinder? What else could be wrong?
 
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  #2  
Old 03-25-10, 04:01 AM
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Don't let off the pedal til the bleeder is completely closed,
check all the line connections ,be sure they are tight.

Good luck and have a great day
 
  #3  
Old 03-25-10, 05:16 AM
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As liljman said, you have to be sure the bleeder is closed before you release the pedal, as that would pull air into the line. I use a check valve and a hose on the bleeder. I can run the hose back to the master and continuously pump the breaks. By watching the line and of course being sure the master does not go low, I can see when the bubbles stop, and it is a one man job.

If there is a leak, it would be more apparent on the push than the release, as brake fluid would be showing somewhere. Pulling in air is a relatively low pressure, so is most likely associated with the bleeder you are opening and closing.

Bud
 
  #4  
Old 03-25-10, 10:23 AM
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It is best to use a pressure bleeder applied to the brake fluid reservoir.

Brake pumping can damage the internal seals of an older master cylinder because you are pushing the plunger beyond the normal point that you reach when braking. A little ridge can build up at the end of normal plunger travel. Pushing the plunger and its seals past the ridge can damage the seals.

While you have a new master cylinder so there is little chance of seal damage as per above, it is better to pressure bleed the system rather than brake pedal pumping. You'll get the results you seek faster.
 
  #5  
Old 03-26-10, 07:33 PM
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Originally Posted by Bud9051 View Post
As liljman said, you have to be sure the bleeder is closed before you release the pedal, as that would pull air into the line. I use a check valve and a hose on the bleeder. I can run the hose back to the master and continuously pump the breaks. By watching the line and of course being sure the master does not go low, I can see when the bubbles stop, and it is a one man job.

If there is a leak, it would be more apparent on the push than the release, as brake fluid would be showing somewhere. Pulling in air is a relatively low pressure, so is most likely associated with the bleeder you are opening and closing.

Bud

Thank you all for your help. Isn't there an air gap in any opened bleeder nipple, though? I mean, as soon as it can allow fluid to exit, it can allow air to enter through the threaded portion?
 
  #6  
Old 03-26-10, 09:38 PM
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I would assume that would be a relatively tight fit and yes it is possible, but very slow. For example, when the bleeder is open, you don't see a lot of fluid leaking out around the thread area.

Bud
 
  #7  
Old 03-26-10, 10:31 PM
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Don't know what happened posted this for you a couple days ago but could only find it in my posts in my account.
Here is GM procedure for that one Wolf. I included only the manual methods along with the manual bleeding. You must have the master bled out before starting this.Good Luck
Notes

Before bleeding the rear brakes, the rear displacement cylinder pistons must be returned to their top most position. Using a TECH 1 scan tool or suitable equivalent, enter the manual control function and ``APPLY'' the rear motor. Ensure the enable relay is ``ON.'' If a scan tool is not available, bleed the front brakes to ensure that a firm brake pedal exists, then carefully drive vehicle over 4 mph to cause the ABS to initialize itself. This will return the rear displacement cylinder to the top position. The entire brake system should now be rebled.

Manual Bleeding

1. Remove master cylinder reservoir cover, then fill reservoir as necessary.
2. Attach one end of a clear plastic hose to rear bleeder valve of the brake control assembly, then put opposite end of the hose into a clean container of brake fluid.
3. While depressing brake pedal, slowly open bleeder valve, until fluid begins to flow.
4. Close valve and release brake pedal, then repeat procedure for front bleeder valve.
5. Ensure master cylinder is full, then raise and support vehicle.
6. Bleed wheel cylinders and calipers using the following sequence:

1. Right rear.
2. Left rear.
3. Right front.
4. Left front.

7. Lower vehicle and check fluid level in reservoir, fill as necessary.
8. Turn on ignition and note pedal travel and feel as follows:

1. If pedal feels firm and constant, start the engine and recheck pedal travel, if pedal still feels firm and constant, proceed to step 9.
2. If pedal feels soft or has excessive travel either initially or after engine is started, repeat bleeding procedure.

9. Road test vehicle, make several normal stops from a moderate speed, then make one or two ABS stops at approximately 50 mph.
10. Ensure pedal is still firm and constant.
Make sure your dealing with a 92 also the 93 has a different set of steps
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  #8  
Old 04-06-10, 05:14 PM
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Originally Posted by Maniac Mechanic View Post
Don't know what happened posted this for you a couple days ago but could only find it in my posts in my account.
Here is GM procedure for that one Wolf. I included only the manual methods along with the manual bleeding. You must have the master bled out before starting this.Good Luck
Notes

Before bleeding the rear brakes, the rear displacement cylinder pistons must be returned to their top most position. Using a TECH 1 scan tool or suitable equivalent, enter the manual control function and ``APPLY'' the rear motor. Ensure the enable relay is ``ON.'' If a scan tool is not available, bleed the front brakes to ensure that a firm brake pedal exists, then carefully drive vehicle over 4 mph to cause the ABS to initialize itself. This will return the rear displacement cylinder to the top position. The entire brake system should now be rebled.

Manual Bleeding

1. Remove master cylinder reservoir cover, then fill reservoir as necessary.
2. Attach one end of a clear plastic hose to rear bleeder valve of the brake control assembly, then put opposite end of the hose into a clean container of brake fluid.
3. While depressing brake pedal, slowly open bleeder valve, until fluid begins to flow.
4. Close valve and release brake pedal, then repeat procedure for front bleeder valve.
5. Ensure master cylinder is full, then raise and support vehicle.
6. Bleed wheel cylinders and calipers using the following sequence:

1. Right rear.
2. Left rear.
3. Right front.
4. Left front.

7. Lower vehicle and check fluid level in reservoir, fill as necessary.
8. Turn on ignition and note pedal travel and feel as follows:

1. If pedal feels firm and constant, start the engine and recheck pedal travel, if pedal still feels firm and constant, proceed to step 9.
2. If pedal feels soft or has excessive travel either initially or after engine is started, repeat bleeding procedure.

9. Road test vehicle, make several normal stops from a moderate speed, then make one or two ABS stops at approximately 50 mph.
10. Ensure pedal is still firm and constant.
Make sure your dealing with a 92 also the 93 has a different set of steps
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Maniac Mechanic you are a lifesaver! The weather has been awful (Rain, 120 MPH winds) here so I have gotten to it today. Worked perfectly!! Zero air! Brakes are perfect! You did it!
 
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