helping a friend / brake pedal

[RBuhr69]

Thought I would reach out to you guys for some buddy help....I was over at friends house last night helping him bleed brakes after installing new master cylinder and power booster. Car is all all disc with proportioning valve, performed the bench bleed all good, bleed brakes as normal excellent flow to all calipers, no leaks what so ever...

the problem.....when you pump the brakes or apply brakes and have a good pedal, then let off for about 15-20 seconds then re-apply brakes the pedal goes to the floor........Then you can pump brakes back up, have good pedal let off then let sit 15-20 seconds then pedal goes to floor.

any thoughts what could be casuing this?

[Apogee]

Sounds like you still have air in the system. When you bench bleed the MC, what method did you use? Recirculation or plugged-port or both? Partially bleed MC's tends to be the culprit most of the time IMO.

If you apply the brakes and hold steady pressure, does the pedal drop at all over time? If so, then there may be an issue with the MC or a loose connection somewhere or a bad seal.

Tobin
KORE3

[RBuhr69]

Bench bleed the MC, what method did you use? Recirculation and performed this twice to be sure...

If you apply the brakes and hold steady pressure, does the pedal drop at all over time? No, pedal stays firm......when you release it and let sit 15-20 seconds and reapply the pedal it goes to the floor..

As mentioned no leaks all connections verified tight. I have one one of the Motive pressure bleeders (Plate on top of MC connected to the pressurized tank with brake fluid) as well and used it and still same result.

We are getting good fluid flow with no air bubbles coming out of system. This is why we dont suspect air in the lines...

I suspect an issue with the MC, but was checking if something we missed. He is going to try plugging the outlets disconnect lines from MC and see how the MC reacts if in the same manner, then we know it is downstream in the system somewhere possibly in the distribution block.

[protour73]

when bench bleeding (recirculation method) I learned a great trick of taking a dead blower hammer or rubber mallet and gently tap the side of the master with it. You'd be amazed at the amount of bubbles that rise to the top.

Good luck!!

[RBuhr69]

Did the block off at the master cylinder and all good there...process of elimination now, connected rear brakes all good, connected front brakes.....Bingo!

Sticking caliper on RF..

[RBuhr69]

Well we replaced RF caliper and still had problem...What we found out was the RF caliper bleeder valve position was too low in relation to being able to properly bleed the brakes. We disconnect the calipers from the caliper brackets rotated them up to where the bleeder valve was on top putting a piece of pipe in between the brake pads to bleed them and was able to bleed them finding the air pockets it was creating with the bleeder valve being too low.

Whola! We have brakes now...LOL

Lesson learned.....

[Apogee]

Is this an aftermarket brake kit? If so, please share which one so that if others search the same issue, they'll know.

Tobin
KORE3

[RBuhr69]

no aftermarket, stock OEM calipers and I believe it a Mustang front clip on the car.

Guess it was just one of those pesky air pocket that would not clear out...Oh well it is fixed and all that matters...