Fought this problem for awhile. Street tires, not heated, and the front tires roll, not skid. Replaced master cylinder, front brake hoses switched to StopFlex braided steel and bled the brakes more times than I care to count. Using the mash and hold pedal followed by pressing button, releasing pedal and mash again. Have tried pumping before mashing with the same disappointing results. Hurst unit, have the outgoing port of the unit plumbed to a tee which separates into the left and right front brakes. Car is a 67 Fairlane with a power drum set-up and pressure differential switch as original. Have considered the press/diff/ switch(PDF) to be the culprit. Thinking of bypassing the PDF completely and running the front/rear brakes independent of the PDF for testing purposes. Thoughts? Have not tested the psi of the system. Thanks, JB.
air in the lines or pads adjusted too far out? n/m
August 2 2012, 8:46 AM
1964 Galaxie 4Dr Sedan, 289, 3spd (re-installing OD soon), a Texas Sargent's Personal Car
1967 416 GT engine, BIBO Wide R TL
1968 428 'C', '69 SCJ heads, Gal Wide R TL
Oh and a Bicycle daily driver.
This message has been edited by TorinoBP88 on Aug 3, 2012 5:52 AM This message has been edited by TorinoBP88 on Aug 2, 2012 8:47 AM
Why do you mash the pedal again? My line-locs never
August 2 2012, 11:30 AM
required mashing the brake pedal after setting the button. Seems counter-productive to set the brake and then re-apply the brake after the button is pushed. Might be confusing the solenoid, or over centering it while electricity is applied. You may be causing the problem that was not a problem to start with. Just a thought. Joe-JDC.
This message has been edited by MsgtJoe on Aug 2, 2012 11:40 AM
with the button on. My understanding is the solenoid will still allow pressure to go to the brakes but not back. Never actually tested the theory though but it doesn't hurt anything.
If you've got top of the line metalic shoes (or pads) they won't hold shit until you get them hot. I fought that problem for a season until I bought some shoes that looked like they were made out of cardboard and then no problem holding in the burnout box. You can also try applying a little brake and hold the line lock while driving to staging to heat the shoes.
Make sure it has power and you can hear it cycle when you hit the button. Also, I use a tool made from a spare brake fitting and a piece of 1/8" drill rod. It fits in the safety valve and holds the piston centered in the valve. That should be your fist move before trying to bleed the brakes. Then check the plumbing. You should be able to either set the lock and push the brake, or push the brake and set the lock - either way one good pump should hold the car. ALSO - if the line lock turns out to be really working, then suspect your front pads. If you are using semi-metallic pads, they will not hold well for drag racing. Switch to organic pads for drag racing with a line lock.
The solenoid works, I found a decent incline and sat there for five minutes w/o any movement at all. Also tried it w/o the mash after depressing the button and thought the car slipped forward even more. That test included pumping first then holding down the pedal and also just tried a single mash and depressing the button. No dice. I feel like I need to address the pdf, whether centering as suggested or at least temporarily removing it. What if it is skewed to bleeding some of the pressure to the rear brakes and therefore not giving the full psi to the fronts. I don't claim to know how those switches work so I may be fishing here. The pads look to be of an organic compund but I'm not certain that they are not semi-metallic.I have included a pic of the insructions regarding the way I have it plumbed. The top half is the system w/o the roll control installed. Thanks for all suggestions, JB.
If you do not use a tool to hold the switch plunger centered in the valve, as soon as you open a brake line to bleed one end of the car that valve will move to seal that end off. It won't seal completely, but it is designed to reduce fluid loss and light the warning light on the dash to alert the driver to a brake problem. Once the plunger moves, you will have to re-center the valve by bleeding pressure from the other end of the car or the other end of the valve. If you are running disk/drum, do not bypass the valve as it controls application pressure ramp up to the rear brakes to prevent early lockup (drums self-energize, disks do not). Centering the valve can be tricky and in some cases it may have to be removed, disassembled and centered by hand. Hopefully you won't have to do that.
The normal way to fix the valve is to make sure the dash warning light works. Then crack the brake line loose - in this case, the rear line since you worked on the front - on the appropriate end of the valve. Have someone slowly push the brake pedal until the light goes out, then hold right there while you tighten the brake line to seal it up. If all lines are tight and air free, then subsequent pushes on the pedal should leave the light off.