Mechanics

I CHANGED FRONT BRAKES ON A . BRAKES GET HARD WITH ENGINE OFF AND SOON AS I START IT I LOSE THE BRAKES.

2001 Pontiac Bonneville • 120,000 miles

I changed rotors and pads on front. When I changed the left front and gravity bled the brakes were tight. (But I didn't start the car) when I changed the left front the bleeder broke off. Couldn't get it out. Lost my brake pedal. Then I bled out all wheels except right front. I get brakes when car is turned off but soon as I start the car I lose the brakes.
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Eagle54
October 15, 2011.



Why did you bleed the brakes? Did you replace the calipers? Have you checked since to see if fluid will flow from both front calipers? Does your master cylinder angle upward toward the front or does it sit level? Did it run empty while you were bleeding?

Caradiodoc
Oct 16, 2011.
You are getting power assist and that is causing the pedal to drop. Did you replace the caliper with a new bleeder?

No I didn't replace the calipers. I kept an eye on the brake fluid and it never ran out. My master cylinder sets level. What do you mean getting power assist. I haven't changed the broken bleeder yet. Having trouble getting it out. Yes there is fluid coming from all the calipers, but not sure on the one with the broken bleeder. There is fluid coming from the brake line at the caliper thou.
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Tiny
Eagle54
Oct 16, 2011.
If you need to bleed the caliper with the broken bleeder screw, unbolt it and hold it so the banjo bolt is at the high spot, then crack that bolt open to expel any air. If you think there might be a little air in the line yet, squeeze the piston back in. That will push the fluid back up to the reservoir and wash any air bubbles with it into thee reservoir.

One real important note. Never press the brake pedal more than half way to the floor. Crud and corrosion build up in the lower halves of the bores in the master cylinder where the pistons don't normally travel. Running the pedal to the floor runs the lip seals over that crud and can rip them.

A second problem that only pertains to GM front-wheel-drive cars is a valve will trip in the master cylinder that blocks fluid from flowing to one front wheel and the opposite rear wheel. Due to changes made in the alignment and the suspension geometry, you will very likely not notice a brake pull, but only one front brake will apply. The pedal will feel normal too. Most people don't even realize there's a problem until they've replaced the front pads two or three times and they're always worn out on one side and look like new on the other side. The other symptom is you can't get that one caliper to flow any fluid. The ONLY fix I've ever found that works to reseat that valve is to use compressed air to give a short fast squirt of air into one of the opened bleeder screws on a wheel that isn't flowing, then let it gravity bleed. If you press the brake pedal too far when just working the caliper pistons out after installing new pads, one will contact the rotor first and start to build up pressure before the other side. That can be enough to trip that valve. That's why I asked if the fluid is flowing freely. There could be air in the line yet to a wheel with a blocked port.

Caradiodoc
Oct 16, 2011.
Thank you so much. I will give that a try tomorrow.

Tiny
Eagle54
Oct 16, 2011.

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