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Brake Pedal gradually goes to the floor!

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Old 02-16-2017, 09:39 PM
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Default Brake Pedal gradually goes to the floor!

Recently had a complete brake job do by my local Indy Shop.
New rotors, pads and a new Master cylinder. The system was completely flushed.
After the work was done and driving the vehicle home, I noticed as I kept my foot on the brake pedal fairly hard it gradually crept closer to the floor.
I returned to the mechanic and complained and he assured me that was normal. I was just pressing to hard on the brake pedal and the power assist was continuing to apply more pressure to the system. He said there is no need to apply that much pressure. He said all the Jaguar XJ (2006) would do the same thing. I had never noticed this before the brake job, but maybe I did not apply the same amount of pressure. Your comments or observations would be appreciated.
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Old 02-17-2017, 07:38 AM
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If the brake pedal gradually goes to the floor when pressing on the pedal, then you definitely have a problem. Get the car to a more qualified shop before you find you have no brakes.
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Old 02-17-2017, 09:43 AM
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Yep, that is very definitely not right; the pedal shouldn't get anywhere near the floor. It sounds like there's air in the system somewhere ie they didn't bleed the system properly when they finished fitting all the new kit.
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Old 02-17-2017, 09:58 AM
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After refurbishing my front calipers last year I had a similar problem.It was air still in the system.You have to bleed the master cylinder.Its a pain to do because you have to remove the plastic surround that fits around the master cylinder to get good access to the bleed nipple.Once this was done no problems ever since.

Cheers Steve.
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Old 02-17-2017, 12:44 PM
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Quote:
Originally Posted by R1doode View Post
After refurbishing my front calipers last year I had a similar problem.It was air still in the system.You have to bleed the master cylinder.Its a pain to do because you have to remove the plastic surround that fits around the master cylinder to get good access to the bleed nipple.Once this was done no problems ever since.

Cheers Steve.
Is bleeding the master cylinder a one pump of the pedal process?
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Old 02-17-2017, 01:40 PM
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If you can pump the brake pedal a few times and it pumps up hard then hold the pedal down hard and it creeps to the floor then you have a bypassing master cylender ,

If however you pump frantically and it never firms up then you have air in the system and requires bleeding ,
Any profeshonal mechanic who tells you that a spongy brake pedal that goes to the floor is normal should be avoided , he is most probably avoiding rework and either stupid or lying or both .
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Old 02-18-2017, 02:27 PM
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Datsports could you please explain what you mean by a bypassing master cylinder.
The brake pedal feels firm a first and it's only when you maintain a constant firm, or hard pressure that the pedal slowly sinks down. One quick release and the pedal returns to normal (no pumping is necessary). The mechanic said that as long as you maintain pressure on the system, the power boost continues to build pressure on the brake system. He told me not to apply so much pressure as the system was working the way it was designed.
Apply just enough pressure to hold the car at a stop.
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Old 02-18-2017, 03:28 PM
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Your mechanic is wrong , you can stand on the brake all day if you want it should not do that !
Bypassing at the cylender means the high pressure side of one of your cup seals are bypassing fluid back to the resivuar port on the non pressured side of the seal wilst pressurised .

See here

Brake Master Cylinder Sinking Pedal and Pedal Fade
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Old 02-21-2017, 07:16 PM
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I agree. Your indy is dead wrong. My SV8 has the best peddle feel out of any of my past Jags.
Have you had it pressure bleed? I just had a rear caliper replaced. After replacement my mech pressure bleed them. They really aren't bleed with pressure, they bleed them with a vacuum unit hooked up to an air supply. This sucks everything out, and bleeds the line thru the master too. They just keep an eye on the fluid level in the master cylinder thru out the process. Takes about 30 seconds.
The vacuum unit they use is not to be confused with a hand unit like a "mityvac". Hand units do create enough vacuum to pull all the air out. I found out the hard way, 2 qts later, still air in the lines.
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Old 02-21-2017, 09:22 PM
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I use a Schwaben power bleeder. The cap fits on the master cylinder reservoir.
Holds three liters of brake fluid. Pour in a half gallon of DOT4, pressure up to 20 psi and start power flushing.
It is a 20 minute, one person job. Draining the catch bottle at the bleeders is the hardest part.
I think I talked Don into buying one.
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Old 02-22-2017, 07:59 AM
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It seems to me that the real issue here is a professional mechanic who tells you that a sinking brake pedal is normal.

Given the knowledge/education/IQ required of modern auto Techs, ya gotta ask yourself, "How did this idiot/crook slip through the cracks?" Under certain circumstances this could be legally actionable or perhaps a visit from the local "equalizer" is a more effective solution.
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Old 02-22-2017, 08:42 AM
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At the risk of being lamblasted, it depends. Some sink is normal if you keep hard pressure on pedal when stopped . But it is a educated feel to know what is normal drop and what is too much from a master cylinder bypassing internally.
Remember they probobly uses a "rebuilt" not new . And rebuild only means new seals. Depending on the units previous life may have a little too much bore wear for optimum performance and sealing leaving too much internal pressure bypass
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Old 02-22-2017, 01:25 PM
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Hay Brutal. Glad to see you are still around.
Re the pedal sink issue I still gotta ask --- sink to da floor?
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