Brake help! Pedal goes to the floor…at first

[vlad_d]

* If you have the dual line system, then your front and rear brakes are separate hydraulic systems. You won't see any benefit from rotating around while bleeding. Focus on each: front or rear.

* Bleeding the Shuttle valve(PDWL) can be a pain. I found the best way was to unscrew the switch mechanism out of the valve and center the valve manually with a flathead screw driver. You can have someone buddy press the brake pedal down while you hold the valve centered, ensuring that both front and rear circuits are open(keeping the Shuttle valve from closing off the side with the air pocket/pressure drop). Make sure to use a hose attached to the bleeder screw into a jar with fresh brake fluid. I had to leave the bleeder screw open while holding the Shuttle valve...so you want to make sure it doesn't suck back air at the bottom of the pedal stroke. The jar of brake fluid and hose make sure it can't.

* Do that for each side: rear. then front...about 3-4 times until no bubbles come put. Push through clean brake fluid until you can confirm the fluid you put in the MC is what's coming out the bleeder screws.

* The Shuttle valve can do its job and block off one side(the leaky/air bubble side). If that happens, you can either get a soft pedal as the valve moving just eats up any hydraulic pressure. Or, it can be stuck shut, and no amount of pressing of the brake pedal will push fluid to that closed circuit. It's doing its job...blocking off a compromised circuit. So, hold it open and push fluid through both circuits until it's centered by the fluid in both lines.

* I messed around for weeks going from wheel to wheel, bleeding. Nothing improved. As soon as I centered the Shuttle valve and pushed out the bubbles, and didn't let the system suck in any air...the pedal went rock hard and I had great brakes.

* 109 Series III should have 11" brakes with two wheel cylinders on the front. It will look different than the diagram below. But the springs will still need to be on a peg of the backing plate and then one the shoe. Never attached to both shoes. The rear brakes on a 109 look like the diagram, though.

* Braking power is 80% front brakes. FYI. If you have bad brakes, it's probably air in the lines, or worn pads. Rarely just the back brakes. You might not even notice bad rear brakes.FYI.

Good luck!

[bigblue79]

Just wanted to give a quick update on what I have been able to do so far. I was able to clamp off all flexible hoses and got good pressure. Then released clamps one by one and checked, isolated, and bled each one (rear, left front, right front). I got good pressure and pedal. The isolated front vs rear and got good pedal on just front and just rear. Then when the whole system was free I had a soft pedal again. Going to try to bleed the shuttle valve next. Wanted to update just in case this helps anyone to narrow the issue down and help me figure this out. Thanks for all the advice!

[jimrr]

If you're confident you've removed all air and the pedal WILL stay positioned with your foot on it then i'd suspect something going on with one of the brake shoes but it can be hard to get all the air out sometimes. maybe try advancing the adjuster till the shoes are up tight and see where the pedal is?

[73series3]

Just got this issue yesterday on the way home from work lost all break pressure barley stopped after pumping the brakes a few times it would build pressure for that one press then the vacuum booster would pull the remaining brake fluid right into the intake manifold and let out a huge poof of white smoke from the exhaust pretty sure the master cylinder is bad going to just change both all my lines and servos are new waiting for the delivery after the holidays