Brake Help

[65 Fastback]

Is anyone available to help me sort out a problem with my brake system Saturday, after the Vienna Inn gathering?  I swapped my brake MC out and have not been able to pressurize the brake system since.
 
I haven't had my car on the road all year.  I did an engine swap this Spring and I'm finally getting it sorted out, but I don't have any brakes.

Tim

[Bob Lennon]

 I can't help in person but, did you "bench bleed" it?

[65 Fastback]

Yea, I bench bled it level, tilted up, tilted down, over and over until the lines ran bubbleless.  I've now pumped a liter of fluid through the system and still cannot get a hard pedal.  I must have a small air leak or something, but I can't figure it out and it's driving me nuts!

Tim

[Hot Rod]

Hey, brakes are over rated! 

[Scott Harrison]

Tell us more about the brake system and what changed with the new MC.

Any chance the new MC is undersized or leaking internally around the pistons?

[65 Fastback]

Well it's a 15/16" bore MC from a '93 Mustang Cobra mounted in a '65 fastback Mustang.  The calipers are 4 pot Wilwood SuperLites on front and a smaller 4 pot Wilwood out back.  I have had this set up for a couple of years and it has perfomed well.

The last time I was bleeding the brakes using the 2 man system, I think we over extended the MC push rod and blew a seal in the MC.  The MC would not push any fluid at all, it just recirculated inside the MC.

So I replaced the MC with the same unit and bench bled it properly - I bench bled it level, tilted up, tilted down, over and over until the lines ran bubbleless.  This time I got a MityVac and tried to bleed out the system with vacume, but could not get a hard pedal.  So then I convinced my wife to pump the brake pedal... well that didn't last very long - still no firm pedal.  So I ordered a set of SpeedBleeders and have pumped a Liter of brake fluid through the system - standard bleeding procedure, RR, LR, RF, LF.  I have two bleeder valves on the top of each caliper and bleed both on each caliper, but I still cannot get a hard pedal.  The MC is pushing fluid and I cannot find any noticable leaks.

Tim

[Ed Hunter]

Just a suggestion, but maybe cap both ports on the MC and see if you get a hard pedal.... maybe the new MC is leaking internally?  Sound's like you've pretty much covered everything else...

[tim-in-oakton]

X 2 - or is it possible that the throw is misadjusted and you aren't over/under driving the master piston? 

[Phil Cataldi]

One other thing to try, on some of my BMWs, you have to manually pump the pedal about 100 times after pressure bleeding to firm it up.  Get in there and pump it about 100 times by hand and see if it helps.

[jk]

..............  Get in there and pump it about 100 times by hand and see if it helps.

It usually does !

[Wade Chamberlain]

I've never gotten to 100

[Ben Lambiotte]

Clearly you're not doing it often enough.  The more often you do it, the more pumps it takes!  How many years have you been married?

[PINKY]

Mannnn the advice I would like to give
Pinky

[Scott Harrison]

Well it's a 15/16" bore MC from a '93 Mustang Cobra...So I replaced the MC with the same unit...

Is there any possibility the replacement is not the same bore?

[65 Fastback]

Is there any possibility the replacement is not the same bore?

No, I checked the part numbers on both MC's. 

I did bleed the brakes, two more times over the weekend and I still have the same result.  The Wilwood calipers I have, have two bleeder valves per piston.  So I bled each caliper on the inside and outside, standard rotation, RR, LR, RF, LF, then repeated the process again, going around the car until my neighbor threw his hands in the air and stomped off, mumbling under his breath.

I have pumped over a liter of brake fluid through the system.  The first time I hit the brake pedal, I can push it to the floor.  If I pump the brake pedal 3 - 4 times, I can get pedal pressure and if I keep pressure on the pedal it does not fade....So I seem to have a closed system with no leaks, but there seems to be air in the system that I cannot purge.

Any suggestions?

Tim