Strange brake issue...

[ZooMad75]

I had a leaking master cylinder on my 75 that I changed out today. Did everything right, bench blead and then blead the rest of the sytem. Under hard stops the brake light comes on. Pedal feels hard and it's not touching the floor when the light comes on. Could do 10 light stops without the brake light on and then a hard stop (hard enough to lock them up on dirt) and the light comes on again.

It was pain to bleed. Plus I blead it again after the first test drive. Even tapped on the prop valve trying to get air from it. After the 2nd bleed job the pedal feel is consistant, solid with not an ouce of sponginess. Brakes stop well, just still turns on the light under really hard panic type stops.

So I'm thinking I got a crap master cylinder or got an air bubble in the prop valve or something else I missed. Looking for any suggestions.

 

[AZ79K5Project]

Click Here

Check the thread.

 

[mjnemmer]

check ur fluid level. if its close to low then when u stop hard all the fluid sloshes forward and sets off the level sensor

 

[83PJW]

Bad sensor? Go least expensive 1st!

 

[ZooMad75]

Thanks so far on the advise. We had thought about resetting the prop, but didn't. I'll try that today. Otherwise, the fluid is up to where it's supposed to be and it stops really good. I'll give the button a try and report back!

 

[ZooMad75]

Well, I tried pressing the button a couple of times and couldn't really feel it move. Maybe a little but not much. How far should I have to press the button? When it trips does the button get pushed out? I'm not sure I've made any difference as it still turns the light on on hard stops.

 

[AZ79K5Project]

I had air in the proportioning valve when I did some work. A lot of people have luck gravity feeding, I didn't. I built a pressure bleeder and forced a couple air bubbles out that didn't move with gravity feed.

I personally don't like the peddle method to bleed brakes. My "helper" may not keep the peddle down and pull air back in before I can get the bleeder screw closed.

Also, if the master cylinder was not level during the bench bleed, small bubbles could remain and may be giving you the pressure difference that is causing the light to come on. Pressure bleeding may push those out. It will also flush the fluid if it has not been done in a while.

 

[norville]

did you crank up the drum brakes at the wheels?

bob