After sitting still for 2 months awaiting head porting, the brakes on my car decided to crap out. On the first drive down the street, I nearly went through the stop sign and had to push the brakes all the way to the floor to get any braking action. I took it back home and noticed the fluid was low so I filled it up and bled the brakes - no luck. Next I figured the master cylinder might have kicked the bucket, so I replaced it and rebled the brakes - no luck. I then took it to a mechanic to check it out and they said it looked like my power booster was the cause since it apparently had a vacuum leak and gave it back to me no charge. This brings us up to now.

I replaced the power booster and reconnected the master cylinder and brake lines. Since I was working on the brakes I decided to convert to DOT 4 fluid. When I bled each of the brake lines, I just bled them until I got the new clean fluid out of the bleeder. I bled the back brakes just fine although they didn't seem to flow alot of fluid. However, the front brakes seemed very odd. After bleeding alot of fluid, I would start to get occaisional air bubbles out of the line (and yes I continually topped off the master cylinder). It seemed ever 3-4 bleed cylcles, I would get another series of bubbles, then the brakes would harden up. After another couple bleed cycles the brakes would soften, then the process would repeat itself. I was able to get each side bled just to the point to where the pedal was the stiffest and then I'd cap it off. Currently, the pedal is about an inch off the ground which seems OK.

Any ideas on what's causing this strange behavior though? I would think once the bubbles were out, I could bleed all day long and not see another bubble.

Thanks for any input!

 

Any ideas?

 

Yes you have a bad caliper. One of the calipers is sucking air back into the system after a few pumps.... :smash: :smash:

 

Is there a way to determine which caliper it is?

 

I just went for a ride tonight to test the brakes. The brakes do work better now than they did before, but I still couldn't lock them up if I wanted to. If I'm going about 30 and hit the brakes, the car slows down pretty quickly to about 5-10 MPH, but then takes along time to come to a complete stop. Also, the pedal will go all the way to the floor with the car running whereas it would only go down about an inch from the floor with the motor off.

Does this definitely sound like a caliper problem?

Thanks

 

I had a similiar problem. Started out replacing the master cylinder. Then I replace all the calipers with brand new ones and I could not get them to bleed out to save my life. I had the same problem that you described with bleeding your front calipers. I ran it by my mechanic and he suggested replacing he m/c again. Sure enough - that was the problem. But it didn't end there. The second master cylinder had the opposite problem. After a bit of driving - the pressure would build to the point that the brake pads would grab the discs. It wouldn't release the pressure. So I had to replace the m/c with a 3rd time. I haven't had a problem since then and my wife loves to test the brakes by locking them up on occasion with a big grin on her face.

 

I hate to bleed brakes.I purchased a mighty vac brake bleeder and use that istead of pumping.I also alway start at the furthest away and then come foward.Also open the furthest and put on a hose to the bleeder and let is seep on its own keep filling and let it leak into a jar and then send it back into the system.On a midyear there is a slight cross over in the calipers and I whacket the caliper with a rubber mallet to encourage the air to get out.

 

Is there something in the master cylinder that would be more prone to break if it just sat still? It just seems weird to me that the brakes worked great but then 2 months later hardly work at all.

Also, what exactly am I measuring when I look for runout? Anyone have pictures of this?

Thanks

 

Did you bench bleed the master cylinder before replacing it? I went through a similar situation and used 2 rebuild MCs before buying a new one. Problem solved. The rebuilt ones had a small propensity to draw air when the pedal was completely depressed.

I also needed a new power booster, lines and calipers. I am still fighting a brake pedal return spring that needs replacing, but at least it stops.

:)

 

Well I bench bled it when I mounted in the car (I don't have a vise). I filled it up and pushed two rubber hoses in the brakeline ports and routed them into the resevoir. Then I had a helper press the brakes until no bubbles came out. Is this the correct method?

 

Did you bang on the MC while bleeding it? I had to hit it gently with a wrench while bench bleeding it for about 20 minutes. The bubbles were stuck inside the MC ports and needed a little "persuasion" to come out.

You certainly could have a problem if there is still air in the MC.

FWIW... after bench bleeding it once and still had a problem, I removed it and bench bled again while hitting it and was surprised by the amount of air that was trapped.

 

Can a master cylinder go bad just by sitting?

Brett :thumbs: