Brake bleed issue

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Ont240

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2007 lt 5.3
for almost a year i've had intermittent service stabili-track light . Brakes still were working fine as i understand the system just shuts that function off. Lately i had a front caliper (r) not backing off and generating a hot rotor. Determined the one piston was quite sticky so replaced both front calipers with rebuilt. Now after several attempts to bleed all four wheels , the fronts are continually pushing air bubbles and the brake pedal has next to no resistance. even with the engine running the pedal goes nearly to the floor and the front rotors can be turned by hand. No braking effect on the front. The back brakes have resistance at the bottom of the pedal travel. is there something special to bleeding these brakes. I'M doing
LF,RF,RR,LR
IT's like the master cylinder is letting air past the front position. Yet everthing was working well before the caliper change.

Help please on this one!
 

wjburken

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2007 lt 5.3
for almost a year i've had intermittent service stabili-track light . Brakes still were working fine as i understand the system just shuts that function off. Lately i had a front caliper (r) not backing off and generating a hot rotor. Determined the one piston was quite sticky so replaced both front calipers with rebuilt. Now after several attempts to bleed all four wheels , the fronts are continually pushing air bubbles and the brake pedal has next to no resistance. even with the engine running the pedal goes nearly to the floor and the front rotors can be turned by hand. No braking effect on the front. The back brakes have resistance at the bottom of the pedal travel. is there something special to bleeding these brakes. I'M doing
LF,RF,RR,LR
IT's like the master cylinder is letting air past the front position. Yet everthing was working well before the caliper change.

Help please on this one!
You should start your bleeding sequence with the caliper that is furthest from the master cylinder and work your way closer so RR, LR, RF, LF. You also need to make sure you are not letting the reservoir go empty as your bleeding it. Some folks use vacuum systems to pull the fluid out, some pressurize the reservoir to force fluid along, other, like me, use someones foot on the brake pedal and have them pump it slowly. Make sure you don't go too far with the brake pedal or you can cause some damage. Might put a short piece of 2x4 behind the brake pedal to limit the travel of the pedal while you are doing this. You also want to make sure the brake line going to your caliper is in good shape and doesn't show signs of swelling as this can hinder things.

If you have air in your ABS module, there are a few ways that I have heard of people dealing with this. I have never done this but have read many posts on here from folks who have. One is with a Tech2 or similar tool that puts the ABS module through bleeding sequence. The other is to take your vehicle to a grassy field or a gravel area and drive the vehicle and then slam on the brakes so the ABS kicks in, repeating this a 1/2 dozen times.
 
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Ont240

Ont240

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How can pushing he pedal to the floor damage the B Master?
The sequence i used was what a tech video was showing on an auto bleed after the abs module was replaced.

I'll try your suggestion again.
 
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Ont240

Ont240

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no luck. on RR LR RF LF sequence after almost 2 litres of brake fluid
PEDAL IS SOFT AS A SPONGE.
no braking effect on the front.
Anyone else have an idea?
does the ignition key need to be turned on while bleeding?
 

swathdiver

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2007 lt 5.3
for almost a year i've had intermittent service stabili-track light . Brakes still were working fine as i understand the system just shuts that function off. Lately i had a front caliper (r) not backing off and generating a hot rotor. Determined the one piston was quite sticky so replaced both front calipers with rebuilt. Now after several attempts to bleed all four wheels , the fronts are continually pushing air bubbles and the brake pedal has next to no resistance. even with the engine running the pedal goes nearly to the floor and the front rotors can be turned by hand. No braking effect on the front. The back brakes have resistance at the bottom of the pedal travel. is there something special to bleeding these brakes. I'M doing
LF,RF,RR,LR
IT's like the master cylinder is letting air past the front position. Yet everthing was working well before the caliper change.

Help please on this one!

Something is wrong with a brake line and or the master cylinder gave up the ghost. I think the latter. One problem might have been masking another.

If there is air on the ABS side, that needs to be bled with a Tech-2 scan tool.
 
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Ont240

Ont240

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bench test OEM Bosch unit:
With the master purged of fluid:
Finger held over furthermost line port and depressing the plunger then releasing the finger one hears that plunger move ahead by the spring pressure as if the rear was getting pedal pressure.
Holding finger over front closest to firewall and depressing there is no pressure on the finger.
Now with fluid in the reservoir, the rear will squirt fluid on each pump.
the front (firewall side ) fluid just runs out all the time. and there is next to no pressure if one holds their finger over that port.
To me I say the front seal must be ???

tried taking apart. After removing the internal c-clip , depressing the plunger and quickly releasing did not let the plunger come out . There is no position screw any where. How does it come apart?
 
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