I bought a 1993 civic cx with rear discs and a integra brake booster. However with engine off it has pressure in the pedal and when running it will have pressure for about a second and then bleed off and the pedal goes to the floor. It is not leaking any fluid ive bleed the brakes three times now and bled the master cylinder. Also the check valve is good and my buddy said he put a new gasket in the booster when he put it on, however the prop valve is still the cx. Im thinking either putting the cx booster back in, unless anyone here has any ideas?

 

If the booster was bad, your pedal would be VERY hard to push just like the engine is turned off.

If the pedal is sinking to the floor after building initial pressure (with no visible leaks), it's most like an internal leak within the master cylinder. As your holding pressure with the added power of the brake booster, fluid is leaking past the master cylinder piston and back up into the reservoir. This is a common way master cylinders fail. If you have someone pump the pedal to the floor and let it out over and over, you can actually watch the fluid level go up and down in the reservoir.

PS: With rear discs, you don't need the larger booster and master cylinder of the integra. You only need the larger master cylinder if you install Integra front brakes. The booster isn't even necessary at all unless you want a softer pedal. If you still have the CX 13/16 master cylinder and matching booster, simply swap them back in to solve your problem.

I'm running rear discs with stock master cylinder and booster in my 94 CX w/ B18C swap. Stops great and has tons of pressure. The prop valve you mentioned won't effect foot pressure at all either so that's not your problem. It only effects pressure distribution between front and rear further up the line. This effects how your wheels lock up at the threshold of traction when braking. If your not locking the rear tires first when you jam on the brakes, then you don't need to worry about changing it.

 

Also, how are you bleeding the hydraulic system? Are you bleeding the wheels in the correct order?

 

i was told right rear, left front, then left rear right front. thats how i bled them with car running. however i was also told you need to bleed furthest away to closest. it doesnt make sense if it had air in the line why it would hold pressure then instantly go to the floor im going to put the cx booster back in as the integra one is from a junk yard and very possibly it could be bad

 

That's correct. If you have thoroughly bled the system and there's no fluid loss, then the master cylinder is the prime suspect, as was mentioned by 94eg!.

 

ok now this is a dumb question but can i just put my cx master cyl on my teg booster i just went and picked it up, also got a hardening silicone im goin to put it around the master before i put it to the booster

 

ok got the cx booster in bench bled the mc and put it all back together and gravity bled the calipers, all is good now thanks alot guys!

 

Cool. Glad to hear it's working.

PS: No need to use silicone between the booster and master. There is no fluid or air seal directly between the two units. It's all internal for either device.

And yes your bleed sequence was right. Honda is never farthest to closest for whatever reason...