Brake pedal to the floor! (1 Viewer)

[r71]

Anyone seen this? I've bled the brakes several times now and it works great. I can lock the 35s up with (some) effort.... but a weird thing started happening. If I depress the pedal, it will engage about 25% down, then if I lift up the pedal just enough to release pressure, then press it again, it will go all the way to the floor(almost 90%). But it still engages at the bottom. It scares the s*** out of you cause it seem like you lost the brakes.

Now, if I lift up the pedal all the way up(like take my foot off the pedal), it goes back to normal.(engage at 25%). Brakes are not spongy. When I engages, it's stiff.

The problem only occurs only after the initial engagement. It's like when you are slowing down and riding the brakes a bit, then you wanna coast a little further so you slightly let off then press further to stop, this is when pedal just goes all the way to the floor, like you lost it. But it still engages at the bottom.


Any thoughts where to start?

PS, this is a 88 with 5.3 Vortech.

 

[cruisermatt]

what sort of work did you do before you started having issues?

 

[OSS]

My guess:
Master Cylinder malfunction.

Remedy:
Replace

 

[r71]

what sort of work did you do before you started having issues?

None.really, was working then not.

 

[Freewheel]

If you did full long presses to the floor when bleeding the brakes, you can get past the normal cylinder travel into the rusty crappy area at the end of the brake cylinder. This can tear the rubber gasket on the piston. It's a common issue on an older master cylinder. Its working fine, and you change the fluid and bleed it and suddenly it's messed up.

When you bleed an older cylinder you have to do it using a pressure bleeder, or use half length brake pedal strokes, so you don't push the piston too far.

Easiest fix at this point is a new cylinder, and since it's new, you can use whatever length pedal stroke you want when you bleed it...

 

[r71]

If you did full long presses to the floor when bleeding the brakes, you can get past the normal cylinder travel into the rusty crappy area at the end of the brake cylinder. This can tear the rubber gasket on the piston. It's a common issue on an older master cylinder. Its working fine, and you change the fluid and bleed it and suddenly it's messed up.

When you bleed an older cylinder you have to do it using a pressure bleeder, or use half length brake pedal strokes, so you don't push the piston too far.

Easiest fix at this point is a new cylinder, and since it's new, you can use whatever length pedal stroke you want when you bleed it...

Ordered a new MC. Let's see what happens. Thanks all for now.

 

[Seth S]

Sounds like air in system or master failure.

 

[r71]

Sounds like air in system or master failure.

Yeah, I'm confident it's not air. Went through like 2 qts. Fluid is coming oit nicely without any bubbles. Let's see what the new MC does....

 

[60Works]

Yeah, I'm confident it's not air. Went through like 2 qts. Fluid is coming oit nicely without any bubbles. Let's see what the new MC does....

Make sure to bench bleed the master before installing it. When using the pedal it doesn't push the piston all the way to the stop. This can leave a tiny bit of air in the piston that can't be bled.

If there is a bubble in the master, sometimes it will work itself out after a few days/weeks.

 

[Seth S]

Yeah, I'm confident it's not air. Went through like 2 qts. Fluid is coming oit nicely without any bubbles. Let's see what the new MC does....

Did you account for the proportioning valve?