Extremely soft brake pedal

[TurbochargedKid]

Hey guys, i converted my 85 T-Type to vacuum a few months ago, i swapped the pedal with the booster and everything, and the pedal is extremely soft, i have new calipers and rotors up front, new rear wheel cylinders and have bled the system repeatedly, and i still have to push the pedal pretty much to the floor to get the car to stop. What could possibly be wrong here? Proportioning valve, debris in the lines, slow leak somewhere? Any advice would be very much appreciated.

 

[Vince13]

I have an 1986 but there is a plunger that needs to be depressed on the brass proportioning valve bolted to the frame rail when you bleed the brakes. I don't know if your 1985 is the same.

Also set up your emergency brake so it is engaged after 3 clicks.

 

[chopped39]

Install line locks on brake hoses and see if pedal is hard. Then remove one at a time until pedal drops. It should drop very little but if it drops alot there is air. The valve may have triggered. Are you getting fluid from rear cylinders? If so valve should be ok. Find someone with vacuum bleeder. The vacuum bleeder wont trigger valve.

 

[zeus87gn]

Did you bench bleed the master cylinder?

 

[TurbochargedKid]

I bench bled the master cylinder, tightened all the lines, replaced my front brake hoses, new calipers, new pads, new rear wheel cylinders, brakes adjusted in the rear, yet the pedal still goes halfway to the floor with the car off, it has vacuum because there is a crazy amount of assist when its running and it goes virtually to the floor. Im gonna try bleeding it this weekend with my week off school, but i dont know what to do, i tried a hand vacuum pump but that busted within 2 minutes. Could my booster be too large for the car? Its from a 79 olds cutlass.

 

[chopped39]

The pushrod between the master and booster may be the wrong size. I would pull the master and check length of rod

 

[TexasT]

I would definately bleed them again. Do you have a helper? Anyone who can push and hold the pedal while you open and close the bleeders. Be sure to keep the master cylinder topped off as you go.

Open bleeder with hose in clear catch container. "Down" have them only press the pedal about half way. I have a 2x4 to put under the pedal to keep the helper from pushing it all the way to the floor. Then close the bleeder, and tell helper "up" then repeat until you don't get bubbles in the catch container. Top off master and move to the next corner.

 

[TurbochargedKid]

I got the master specifically for the brake booster. so it should work. ill try bleeding the hell out of them

 

[TexasT]

I got the master specifically for the brake booster. so it should work. ill try bleeding the hell out of them

Could be a bad master cylinder. Even new and rebuilt stuff is bad sometimes.

 

[TurbochargedKid]

I pushed a ton of air out of the fronts. the pedal goes down about a quarter of the way. I don't know if it shoulf be that much

 

[TexasT]

Are you starting at the pass rear getting all the air out , then moving to Dr rear, then pass front, then Dr front?
You may not have gotten all out when you bench bled the master.

I never bench bleed, as the cars I generally work on are old and need the system flushed with new fluid any way.

Be sure to be topping the master cylinder off as you go as if you run it dry you must start over as you have introduced air into the system again.

 

[TurbochargedKid]

well I push the pedal max halfway now and she locks up. I pushed maybe six pumps of aor out of the front left. I'm now concerned about flat spotting my tires haha!