Brake pedal feel

I replaced the master cylinder and did my normal (engine off) brake bleed, then I did my ABS scan tool bleed, then bled again. Still needed the annoying one quick pump to raise the pedal to proper feel.

Next I bled again with engine running (vacuum assist) and did the bleed again. Still need the one quick pump but BETTER THAN BEFORE.

Bottom line I replaced a 16 y.o. master cylinder and it does feel a bit better. But I’m still suspicious there is air someplace in the system.

In ABS ??? Maybe I’ll invest in a manual power brake bleed system for $60 or so.

FOLLOW UP : )

Could never get a proper pedal unless I pumped once or twice.

  1. Bled many times, the normal cup and hose method.
  2. Replaced Master cylinder with a new one.
  3. Bought a power bleeder and adapter for my master cylinder. Power bled 2-3 times.

Still needed one or two pumps.

  1. Finally replaced the two front calipers with new ( the rears were replaced last year)

  2. Bled the normal cup and hose method.

  3. The brakes are now like new. No pumping and excellent stopping.

Apparently it was the front calipers. A new one on me after working on brakes for 50++ years.

P.S forgot to add I also bought an ABS activating scanner and ran it through the abs bled cycle 4-5 times. No luck.

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One more follow up.

After recuperating from the 91* heat and sun in driveway. I went out and looked at calipers. One had a tear and the piston was not frozen but definitely tough to move.

That must be why it needed the quick pump or two to get the pedal up.

Interesting. Thanks for the update. I wouldn’t have guessed replacing the calipers would be the solution. Not that a caliper can’t be bad, but seems unlikely related to a system bleeding problem. Usually if there’s a problem with the caliper hydraulics they’ll have a visible external brake fluid leak or there’s a problematic brake bleeder valve. Occasionally someone will inadvertently install a caliper upside down, so the bleeder is at the bottom pointing down. That configuration is never going to be bleed-able.

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George. I’m with you. I’ve been doing brakes on cars since working in the local gas station in the late 1960’s. I’m stumped.

Trying to second guess my work I still can’t figure out why immediately after changing the front calipers and doing a (front brakes only) normal cup and tube bleed the brakes continue to be 100% perfect today.

( the partially frozen caliper did always bleed properly, if it didn’t bleed normally that would have been a clue to something was wrong with it but it bled fine)

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My theory, the pistons on the old calipers were retracting too much when you removed your foot from the brake pedal. Air in the fluid wasn’t why you had to pump the brake a couple times to return it to the normal position. There was no air in the fluid in the first place. The pedal pumping was necessary to move the piston back out enough the pad was starting to contact the disc. IIRC the elasticity of the rubber boots is what supplies the force to retract the caliper pistons, so it’s possible all you needed to do was replace those boots.

I think it was on my Kia Forum site that I did put that thought out about, “dried out shrinking outer seals pulling the piston back in” making the quick pump necessary to push the piston out again. I never got any positive comments about the possibility so I let it go.

But I do believe you are correct it never was air in the system. Live and learn : )

I agree with the no air in system but one thing I’ll disagree with.
The boots aren’t designed to pull the piston back ( I believe mine were since they were dried out and shrinking ??? ) but it’s the almost imperceptible wobble in the rotor that knocks the piston back ever so slightly.

Maybe I’m wrong and I know I’ll hear why from more knowledgeable than me.