1G Brakes: The Epic PITA version

[nlzn]

My Epic PITA brake storyline all started a few months ago. The pedal starts to get squishy and suffers severe braking performance. Eventually it goes to the point after my repeat bleedings the pedal won't even return. Master Cylinder right? Easy fix. Replace the cylinder, get pressure back (well, somewhat). Still mushy after draining two 16oz containers of dot3.

Then my ABS starts flipping out. Even at slow roll stops (below 10mph). I hear it click and I can feel it clicking the pedal. Good time to just get rid of the system and save some weight in the process.

To jump forward in my Brake Oddesy I used non-abs 1g lines in the front with a non abs prop valve (that happened to be bad, so I went to a junkyard and pulled 3 of em just in case). I got one in there that worked but then I realized I cut the wrong line for the rear. Oops Yes folks, even our storyline heros can make mistakes!

So I take the better part of a weekend and re-run both rear lines. My shining flare tool broke on the 2nd line but luckily I had a spare, like any good soldier facing enormous odds would. I was prepared. I conquered the beast, and did a damn good job running the rear lines from scratch. I had one leak that was a quick fix via a flare re-torque.

After myself and a buddy rebled the system using another 16oz container plus 1/2 of another in my driveway I finally had my awaited dream: a STIFF pedal. We're talking 1.5 MAYBE 2" of play in that sucker. ROCK HARD

With my euphoric sense of accomplishment I proceed with heavy, heavy hopes to the much anticipated test drive. My driveway is kinda long so I give it som roll stops. Holy hell, pedal never felt that great! I'm riding the waves of confidence as I pull out the driveway.

Then, tradegy strikes. My hopes and dreams are sucked out the window faster than my -30hg vacuum pump could ever pull them out. It does stop better.. but I'm still in the same boat.. it's not right. I can get the sucker to lock up but I have to use both feet and really get on it. I can leg press 1k lbs, needless to say I really have to get on that pedal.

I know there's more to those brakes. While removing the ABS and replacing the master cyl definitely helped the issue it's still not right. The only thing left is the brake booster, it's all I can think of that could cause my problems.

 

[nuclearr]

Wich master did you use? I think abs and standard brakes use diffent masters. Also is your break boster hooked up to your intake manifold?

 

[nlzn]

Yes..

 

[cbrfrenzie]

What brake master are you using? Maybe the 3000GT master with the bigger bore will help you out.

It sounds almost like you are compressing the fluid, as in some small amount of air is lurking somewhere. What order did you bleed the brakes? I usually start with the corner with the longest line and work to the one with the shortest.

 

[nlzn]

Trust me they are bled to perfection, Pass Rear, Driver Rear, Pass front, Driver front.

And a 3000gt MC is not the answer. That's a possible bandaid fix.. but I don't 1/2 ass problems

 

[cbrfrenzie]

I'm not questioning your abilities, these are just things I've ran into in the past. Here are some thoughts that come to mind....

Have you compared the brake master cylinder from an ABS model to a non-ABS model? If in fact they are different then a new brake master would be the solution, and not a bandaid.

Other things to check is the grease on your caliper bolts. If its dry and binding that could hinder brake performance.

Have you checked the thickness of your brake rotors? How much life is left on the pads?
Maybe they are worn out therefore you're needing that extra travel to lock the brakes up.

Also I've experienced people having the cap on the brake fluid reservoir leaking air VERY slightly, but in your case where the pedal pressure is HARD I doubt that's the case.

Is there any way the front and rear lines coming out of the proportioning valve are swapped? That would give more bias to the rears instead of the fronts.

It would be interesting to put a gauge on the input line, as well as the 4 output lines of the prop valve to see what your actual brake distribution is. Maybe one line will show significantly less pressure and un-cover your problem.

Also, do you still have the factory rubber lines from the hard line to the caliper? They could be rotten and "ballooning" when you step on it. Stick a zip tie snugly on the line and have someone depress the brake pedal. You should be able to see the line swell around the zip tie if this is the case.

Thats all I've got, good luck man!

 

[nlzn]

I actually disassembled the calipers to paint them.

I had checked them previously to make sure they would move and could slide, and they did work well, both front and back.

Pads are New (less than 100miles on them) same with the rotors.

I did this with two different prop valves (3 if you consider the bad one too)

The lines aren't swapped, Fronts go into the bottom 2ports , rear into the back 2 ports. I would have had to bend them like crazy to change that positioning.

Lines from the master to the prop valve flow fluid well, same with the the caliper bleeders all around. We aren't talking a dribble, under full pedal pressure my backs cleared 2 feet.

 

[cbrfrenzie]

I actually disassembled the calipers to paint them.
Lines from the master to the prop valve flow fluid well, same with the the caliper bleeders all around. We aren't talking a dribble, under full pedal pressure my backs cleared 2 feet.

Then I'd say pressure loss and/or binding is not your problem

What about the rubber lines that connect the calipers to the hard lines in the wheel wells? Are they still factory, could they be ballooning up on you, absorbing pressure and distorting the line? It deff sounds like your internal volume is expanding more then normal under pressure.

 

[sbiggi]

Sounds like the booster is bad, or the check valve in the line, not the master cylinder.

 

[nlzn]

How do you test a brake booster?

Can I hook it up to the tester expecting it to hold vacuum if good?

 

[tkelly27]

Yes. If it leaked under vacuum that would be an unmetered air leak and cause problems, so it really shouldn't leak.

I'm also not questioning your bleeding skills, just ruling this out. You used a clear tube dunked in fluid or a vacuum system to view the air bubbles coming out, right? I only ask because I had someone tell me they had been bleeding brakes for 10 years professionally and had never heard of doing that.

I know you don't want a different master cylinder, but for people wondering, smaller master cylinders should increase pressure but require more throw, and bigger master cylinders will decrease pressure and have a shorter throw. P=F/A For a given force a higher area will make less pressure, which is what is ultimately transmitted to the caliper pistons. I went with a smaller master cylinder out of a NT and I really like it.

 

[nlzn]

I actually did it 3 ways for the bleed.

For the initial bleed after I replaced the lines I used old fashioned, have a friend press the pedal, open and close the bleeder screw.

After we did that twice to all 4 calipers (in the order stated above) I took my vacuum bleeder to them with some grease around the bottom of the bleeder, just like I'd use in a one man bleed.

Last I did the method you're thinking of I believe, where i just hook some hose to the bleeder (greased at the bottom), running the hose into my little jar of clean brake fluid (actually I made mine with a jar top and a little peice of 3/16" hard brake line)

I'm dodging questions about the master cylinder because i doubt it's bad. Fluid pressure seems good, it's almost brand new and the problem I'm having started before the MC went south to begin with.

 

[fhudsonjr]

Trust me they are bled to perfection, Pass Rear, Driver Rear, Pass front, Driver front.
QUOTE]

I don't know if this will make a difference, but my '93 Chrysler Corp. Laser/Talon service manual show a diagram that you bleed the Pass Rear, then Driver Front, Driver Rear, and lastly Pass Front... page 5-51.

Good luck.

 

[nlzn]

Pretty much has to be the brake booster.

It won't hold vacuum on my tester and going in reverse down my driveway (it's kinda steep and long) my pedal goes 100% stiff and if I don't ebrake I won't stop.

Hopefully I'll get one in there next weekend.