ok so ive been having a bit of a problem with my brakes lately. identical problems in two different cars.

first car is my 91 crx si. i used to have stock brakes with just a 15/16 MC, stainless braided lines, hawk hps pads, and valvoline synpower brake fluid. now the problem i was having was primarily only seen at the racetrack (1/4 mile). after a few runs the brakes would feel like they were fading. while sitting still or moving the brake pedal would just sink to the floor. it was slow, and i still had some pressure, but i would just have to keep pushing the pedal further til it hit the floor and lost almost all pressure. im losing absolutely no fluid anywhere, ive checked and ive kept an eye on my fluid level. my 95 integra LS is having this EXACT same problem with the same symptoms, again no fluid loss.

my first instinct tells me that im just overheating the brakes and its causeing fade and the fluid to boil. so 2 days ago i upgraded the crx's brakes to 10.2" rotor with type r calipers and hawk hps pads again. it was my understanding that this would reduce the amount of heat being generated and help fade (i really should have zero fade with this setup). so i did that, bled the brakes and i thought everything was fine. but today i took a trip to the bank and sure enough after about 30 mins of driving the pedal started to sink again. i have yet to bleed the brakes on the integra cause my brother has it.

since i have no fluid loss to me this says its the fluid boiling again, but 1 i have bigger brakes now, and 2 i JUST bled the brakes and i cant see the fluid boiling this fast. im not even braking really hard or really slamming on them, just driving normal. this really only seems to happen when ive been driving for a while and when im braking frequently. if ive been driving on the highway with very little braking its fine. so do i just need better fluid? or what? the valvoline fluid has like a 500 degree boiling point and i dont think ive gotten the temps up that high since when i get out of my car i can touch the brakes without severley burning myself (it is slightly hot though, as expected). or could this be something else going wrong in the brake system?

remember im having the exact same problem with 2 different cars on 2 different brake setups. both under the same conditions, with the same symptoms. maybe the MC?

any help is greatly appreciated.

 

i have same problem they told me brake booster

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by LoCoReX &raquo;</TD></TR><TR><TD CLASS="quote">i have same problem they told me brake booster</TD></TR></TABLE>

Who is they? I had the same problem in my HF, master cylinder shot. It's not leaking fluid outside, just by the seals in the bore. My GSR is doing it now...oh well.
I bet it does it more when hot under the hood?
HTH
chris

 

probally is your master cylinder. i think mine is going bad too. the pedal is getting spongy and it isn't the brake fluid. in a crx can you replace the mc from other cars. i thought so but what cars. i want a bigger master cylinder.new from the honda dealership.

 

It's the master cylinder on both cars. Internal leak. Weird how it happened on both cars at the same time. How hard are you pushing on the brake pedal when bleeding the brakes?

A booster won't cause a sinking pedal, it would cause pedal firmness problems. If it was fluid leaking into booster, you would probably see some idle problems (low idle).

 

yeah i vouch for master cylinder also. i have the same problem in my car and i will be doing a master cylinder in it in the coming weeks.

 

it is the master cylinder. and like partially said above, what happens is when you push on the pedal, the brake fluid runs past the piston in the master cylinder BACK into the reservoir.