Brake Pressure

[xupkid2]

I posted on this a little while ago but now I have tried a few things with no luck. My issue is that my brake pedal is soft. I have blead the brakes with a power bleeder and Super Blue. I have replaced the master cylinder. I have checked for vaccum leaks and still I can't figure it out. I'm hoping I don't have to mess with the brake booster but who knows. Any ideas?

Thanks
Brian

[924RACR]

How old/what type are your hoses??

[phoenix_iii]

I don't know anything so don't listen to me.

If you use say a Motive power bleeder... it gives you a gauge, pump it up to 15PSI, and see if you have any leaks (loss of pressure) over say 10 minutes. If so, find it. Of course, the connection of the motive between the resevoir and the adapter are prone to leak, so do those right... but otherwise, if you get a good seal, you can determine if you have a leak somewhere else, or if it is an internal leak.

Internal = brake cylinder (you replaced this), or brake booster (I suppose). How else/what else is there to test?

[xupkid2]

Sorry I should have probably added some more info. The brake lines have been replaced with stainless braided lines and I have checked for leaks all around.

The car is race prepped as I run it in PCA stock class. I have Hawk HT-10 pads all around. When on track it seems to build up pressure as the brakes heat up but when it's cold they are spongy.

[Techno Duck]

That sort of sounds like you are just not in the ideal operating temperature range of the brake pads. Im not familiar with the HT-10 compound, but if they are more aggresive than the Hawk Blues its probably the reason. The pedal really shouldnt feel spongy, there just wont be that initial 'bite' on a cold track compound pad.

[xupkid2]

It's not so much the initial bite as it is a soft pedal. It feels like there is air in the lines but I am 100% positive there isn't. I've sent a couple bottles of superblue through there to make sure along with bleeding the clutch but have had no success. I was thinking the booster may be bad but I don't fully understand what the booster does. It just makes me a little uneasy driving the hard at its full potential on a track knowing that there may be some issue with the brakes.

[greg bradbury]

hi,

To test the booster do this- With the engine off apply the brakes two or three times. this will deplete the stored vacuum in the booster. The pedal should become hard to push. Hold the pedal down and start the engine, The pedal will go down slightly as the booster helps out. If the booster was faulty then your braking would be terrible (scary)/

Have you rebuilt the calipers lately? If so you might try putting the old pads back in and drive it around like that for a few 100 miles to let the calipers come out. Once the sponginess goes push the calipers back just enough for the new pads the go in.

[944 boy]

I wonder if you might have a vacuum leak in the line to the booster. My '88 has stainless lines and race pads. The brakes are as hard as a brick. I also use a Motive Power-Bleeder and Blue fluid. I am now running a Turbo booster so the vac. lines are different. +1 for making sure the calipers move smoothly. They may be binding when hot and loose when moving, vise/versa?