2002zo6joe

I just replace my master cylinder, new rear calipers, new Hawk Blue Pads (Track use), bleed the system 3 times and my brake pedal goes from hard to soft at will. Help!

bikeriderga

Air in the lines, caliper leaking, caliper not holding pressure, seal around master cylinder not sealing properly, leaking or pinched brake lines.

2002zo6joe

Thanks for the info, any way to test if the calipers are holding pressure?

bikeriderga

Will probably take two people and a very good jack or a fill car lift floor jack.

Jack up the rear of the car. Get someone inside to apply the brakes (better if car running and in gear,or if you have a old fashion wheel balancer that will spin the wheels when applied to the tire, even better. If that is not possible, follow advise for front wheels).

Apply the brakes with the rear wheels spinning, Grab the tire and try to move the wheel with the brakes applied. Can you move it and how easily? Look for leaks, check for spongy brake pedal and listen to any signs of air (may make a squishing sound).

For the front, jack up the front of the car. Spin the wheel as fast as possible. Get partner to apply the brakes Can you move the wheel with the brakes applied?

Look for any leakage or sponginess in the brake pedal as well.

P.S. If you have a portable wheel balance machine that can spin each wheel manually, so much the better.

Alternate way to check is with a very fine feeler gauge. Insert the gauge at a setting where you can measure brakes fully applied of distance between rotor and pad. If there is any distance, then definitely your calipers are not fully extending and pushing pads against rotors. Check both sides.

I would eliminate the other things I suggested first. Good luck!

Robby04

This is probably not your problem as you did your work. But I once bought a car with the exact same problem. The seller claimed the brakes were just done and he couldn't figure it out at all. My roomate is a mechanic and instantly realized the rear calipers were put on upside down. We flipped them and bleed them and problem was solved.

2002zo6joe

Thank you.

555ss

I have had a this im my car and the air was in the ABS unit so when it cycled it could mess up the pedal then get sucked back in, the tech 2 bleed fixed it but I have done others at the track the trick is to bleed just after the pedal goes soft and push a bunch of fluid thru.

bikeriderga

That would do it !

bikeriderga

Did not think about this!!
The problem does sound like it is pressure related. I would check this first.

2002zo6joe

Is the brake booster suppose to make a sound like air is been pump out when I press the brake pedal with the engine off? It sounds like a leak somewhere near it in the engine compartment.

bikeriderga

No, that pretty much means that you have air in the lines.
Bleed the brake and ABS system again!

2002zo6joe

Thanks for getting back to me again, I appreciated.

How do I bleed the ABS system other than going thru each wheel again?

insertclevername

I would look deeper into the booster. Test the booster

With the engine off, pump the brakes several times, about five or six times is sufficient. This depletes the stores vacuum. Turn the engine on while pushing down lightly on the brake pedal. If your brake booster is working normally, the pedal will fall away a little bit but then become firm. If your brake booster is not working correctly, then nothing will happen, or the brake pedal will push back against your foot, once the engine starts. This could be a sign of a brake booster problem or an issue with the vacuum hose.

If you did get air into the abs during the master cyl install, then taking it to the dealer might be the next best option. They will find the issue and resolve it, at a cost of course.

Having your brakes diagnosed over the internet is not good for anyone.

555ss

if air gets in to the abs unit there are only 2 ways ot get it out.
1 take to dealer have them do a tech 2 abs bleed costs money pain to deal with.
2 drive car make abs come on if pedal feels soft afterwards bleed ASAP this will keep the air where you can get it out this can take 2 or 3 trys but it can be done. Bench bleed of a new master and bleeding the lines at the abs unit from the master when replacing a master can help this not to happen also, when bleeding never let the master go dry.
#1 is a never fail option.
#2 has worked for me at the track several times with several different cars.