Hi, I have a 1998 Acura INtegra GSR. Been running the stock front calipers for sometime. I tried a Legend caliper upgrade but had this problem with the pedal being firm with the engine off, but as soon as I start the car the pressure dissappears and the pedal starts sinking, slowly. After 2 years (with OEM calipers) I tried out some spoon calipers, and Im having the same issue. I really DONT think its the MC since I replaced it before and still have the old one which was just fine, nor do I think its my bleeding procedure. I can throw the old clappers back on, bleed, and be good with-in minutes. Its just all these damn multi piston units that are giving me a headache. Any suggestions?
(w/regards to 6spd_ek) We have properly bled the system over 100 times... seriously
the MC was bench bled as well... pedal feels very stiff & hard (like it should) when the car is NOT running. start the car & the pedal sinks to the floor. when running a couple of pumps of the pedal & pressure is there (for a second) then pedal sinks to the floor
When the car is off, you should be able to pump the brakes a couple of times, and then the brake pedal gets rock hard after that.
I had a problem where my brake pedal was hard immediately after turning off my car and all the time when off. The problem turned out to be the MC piston seal between the MC and booster, which I attributed to getting trashed because of the MC brace I used to have on the shock tower.
I replaced the MC piston seal and all has been good ever since. No need to unbolt any brake lines, just unbolt the MC from the booster and slide it off the studs (hard lines can flex a bit), replace seal, bolt MC back on.
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well the brake system isnt THAT complicated that if you are certain that there is no air and that the calipers are good, that you wouldnt be able to narrow down the problem, theres only two other parts in the system, and thats the master cylinder and the brake booster, so obviously your problem lies in either one of those areas.
The booster wouldn't cause your pedal to sink to the floor... And if you've ruled out the brake master cylinder and the bleeding, then I'm going to go on a limb...
It really sounds like you're not building pressure fast enough, and that said, I would think maybe since you're running huge calipers on the front now which require more fluid to get to them more rapidly, you might be having some sort of strange braking proportion issue... aka your prop valve doesn't give the big brakes the pressure they need when they need it, which would give you a slow pedal response and would make the pedal go down slowly...
again, doesn't seem too logical to me, but you seem to have ruled everything else out... sooo...
you have air in your lines... bleed your brakes, then bleed them again.
The reason the pedal sinks when you have the vehicle running is becasue the brake booster reduces the amout of pedal pressure you need to activate your brakes... making it far easier to compress air in the lines.
If you bleed the system properly you wont have a problem!
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