Brake pedal went away while driving - thoughts?

[Richio1]

Was out driving around with some buddies yesterday, while sitting in some stop and go traffic the brake peddle pressure started to fade. It got progressively worse as we were heading home. I pulled over to check fluid level and look for leaks. No leaks and fluid level hadn't changed. Fortunately made it home with no incidents but pretty damn scary.

Symptoms - The 1st push is close to normal but feels "sharp", hits harder than normal. 2nd pump goes half way to floor and 3rd pump goes almost all the way to the floor. If I wait a bit I get close to full peddle again.

Seems like air in the system but I have over 1500 miles on the car so it seems odd that it would come up now. I searched the forum for ideas and came accross a response from Ron Suttons saying air could enter the system through a loose fitting but show no leaks so I will check all fittings today.

I also thought that since I was idling in traffic that maybe it was a vacuum issue but didn't seem to change once we got out of traffic and the pressure continued to get worse.

Now my thoughts are the master/booster. I am running the DSE set up which has been great. Seems like it may be the master check valve not seating and hanging up allowing fluid to seap by.

Thought, ideas, suggestions?

[Vegas69]

Likely one place the fluid is going. Out the back of the master cylinder.

Put pressure on the pedal for a few minutes with the car off and then double check all your connections for leaks. Then move to your caliper pistons. If nothing is found, unbolt your master cylinder and see if it's moist. It looks like you may have a little residue already underneath the cylinder on the booster.

[dale68z]

Fluid level remains the same. So there is no fluid loss. Possibly could be sucking air into system, but unlikely.

Most likely a bad master. Remove both lines on the master and plug the ports on the master off. Then see if you have the same pedal feel where it sinks to the floor. If it does, the master is internally bypassing.

[Che70velle]

Bad master, I'd say. What fluid are you running?

[Richio1]

Thanks for the feedback and suggestions guys.

I talked with DSE today and they seemed to think it is a vacuum issue. In their opinion, if their was leak down the peddle would go to the floor on the first pump not progressively get worse with each pump then recover after a few seconds.

They suggested checking for vacuum leaks first which I will. Would be the easiest fix too. The car is running fine and it still happens regardless of speed plus I never had the problem before so I wouldn't think that is it but I'll still check.

Second is the same thing Dale suggested which is plug the lines and see if the same thing occurs. I bought plugs today so I will give that a shot. Then if that doesn't give us a clear indication, to pull the booster and, as Todd mentioned, look to see if there is fluid in the booster or in the fork boot and if so send it back so they can bench test it and repair it.

I'll have time to give the above a shot in the next couple of days.

Chev70velle - I'm running Willwood

[Richio1]

Well I found the problem tonight.



Kind of hard to see but when I push the brake you can see all the bubbles. Not a leak anywhere in the system so it has to be the master.

[dale68z]

It is normal for the fluid to bubble up when the brake pedal is pumped.

[Vince@Meanstreets]

might have blown the seal but bench bleed it again and go from there...and double check them lines at the master. IMHO too many fittings on the brake lines.

[Richio1]

Thanks guys. Yeah I knew it would bubble some but I didn't expect it to bubble that much. I talked wth DSE yesterday and sent them the video. They agree it must be a seal so a new master is on its way. Should be here Wed. Will get it in next week and hope that is the fix.

[Vegas69]

I agree with Vince, now would be a good time to get rid of those braided lines. My opinion is that hard lines should be used everywhere possible with the least number of connections. Soft lines and more connections lead to more chances of failure. You engine compartment looks nice, my first thought looking at it would be short cut on those hoses. Not looking to beat you up...