Sinking brake pedal with SPOON clappers
 

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?

Heres what I have

1" OEM GSR -MC (new and replaced after this issue)
https://honda-tech.com/forums/acura-integra-6/problem-legend-caliper-retrofit-spongey-pedal-still-1477259/

Russell stainless brake lines.
98 ABS Moduator
ITR/ Prelude rotors redrilled to 4x100 (fastbrakes)
Used SPOON twinblock calipers.
SuperBlue brake fluid (dot4) just swapped in.

again brakes seam fine with engine off. Its just once I fire up the car the pedal begins to sink slowly to the floor.

Thanks!
Mike

Re: Sinking brake pedal with SPOON clappers
 

sounds like theres some kinda of vac. leak
but sell me you spoones haha

did you chk you lines? could be the calapers need to be reworked and or your porportion valve needs to be upgraded?

Re: Sinking brake pedal with SPOON clappers
 

Could be the brake booster. I had a similar problem w/ a toyota truck and that was the issue.

Re: Sinking brake pedal with SPOON clappers
 

I had this problem a couple weeks ago on my DA I replaced the booster and problem solved.

Re: Sinking brake pedal with SPOON clappers
 

I have the same problem - when the car is off there is a good pedal feel but when the car is running the pedal sinks to the floor.

I thought this shows the booster IS working because of the vacuum assist - how could the booster being bad cause this?

Re: Sinking brake pedal with SPOON clappers
 

yeah just sounds like you have air in the lines, did you bench bleed the master cylinder?

Re: Sinking brake pedal with SPOON clappers
 

sinking brake pedal is usually a good sign of air

Re: Sinking brake pedal with SPOON clappers
 

(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

Re: Sinking brake pedal with SPOON clappers
 

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.

Re: Sinking brake pedal with SPOON clappers
 

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.

Re: Sinking brake pedal with SPOON clappers
 

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...

Re: Sinking brake pedal with SPOON clappers
 

spoon calipers shouldnt be too big for the cars master cylinder at all, if he isnt building pressure fast enough, i would still attribute it to a master cylinder or brake booster

Re: Sinking brake pedal with SPOON clappers
 

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!

Re: Sinking brake pedal with SPOON clappers
 

6spd_ek has since replaced the MC with a new OEM ITR one. I then pressure bled the system running 4qt thru each corner. the problem remains :(

Re: Sinking brake pedal with SPOON clappers
 

how are the rear brakes? Pull the calipers off and check the seals and make sure they are all good. Also i hate to ask but i have seen it before. Do you have the calipers on the right sides?