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05-25-2004, 09:55 AM
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Brakes Have Me Stumped
Ok, I have installed the following:
11" disks/ calipers in front "new" (MII) Brand new MPBrakes Under-floor booster/M.C. Proprtioning Valve 2lb/10lb residual valves 10" x 2.5" drums in rear with all new hardware. All new lines through-out. The problem is this. I have bled the system as required, no leaks but have a very soft pedal. GREAT grabbing preassure on front disks but very very low preassure on rear drums. My thinking is the proportioning valve may be the problem, or "call me dumb" but is it redundant to have a 10lb residual going to the rear drums and would this possibly cause my problem? Thanks in Advance, K D 
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05-25-2004, 10:48 AM
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Depending on the front/rear weight proportioning of your car, you probably need an adjustable proportioning valve.
__________________
Ontario Rodders
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05-25-2004, 03:43 PM
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Poncho, I was wondering about that.
Thanks, something I'll need to research further me thinks.
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05-26-2004, 05:55 PM
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Also, you may have the lines hooked up wrong at the MC. What MC and proportioning block are you using and how is it presently hooked up? Front discs to big chamber or small chamber?
Trees
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05-26-2004, 06:53 PM
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Kinda sounds like the rear drums have not been adjusted correctly or enough...check that out before buying more parts...
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05-27-2004, 04:19 AM
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Try pinching off the rubber hose at all wheels, this should give you a nice hard pedal, then remove them one at a time until the soft pedal returns, that will tell which wheel is the culprit, if no hard pedal w/lines blocked?, look between m/c and valves.
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05-27-2004, 12:16 PM
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Update.....
Checked preassure frome M/C....good. Checked preassure from Combination Valve.......also great Checked preassure from Residual Valve ("out" end) great...BUT, noticed a little "suction when the pedal was released. Seems the fitting I had used was a tad to long, this inturn kept the "plunger-like" white valve inside open all the time. Changed fitting.....re-bled lines, "better pedal but still not great. The rear drums grab but only enough to "slow the hubs.....not stop them completely. I'm hoping we're down to a further bleeding and adjusting problem now. "I Hope"! Somebody suggested that the "switch valve" on my combo valve may be in the "shut down mode" I'm headed to MP brakes to find the remedy...or part of it. I have rubber lines to my front brakes but only a center line (rubber) splitting off to hardlines to both back wheels. Shall I attempt to "pinch" of the center hose? Still won't let me know which rear corner may be the culprit.
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05-27-2004, 12:31 PM
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If your rear brakes aren't 'locking' the drums when pressure is applied, it's likely that the shoes aren't adjusting up enough. Try manually adjusting them tighter. If the shoes are too far away from the drums, the master cylinder has to pump much more fluid which will make the pedal spongy.
Tim
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05-28-2004, 04:19 AM
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You replaced hardware, does this include rear wheel cylinders?Usually, spongy pedal is air in lines, low pedal which comes up after 2 applications, is rear shoe adjustment, are you getting good flow when bleeding rear?
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05-28-2004, 09:21 AM
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Wrencher, Replaced wheel cylinders along with everything else in system. The flow in the rear is "better since changing out my residual valve fitting but still not what it should be. Could the trouble be the amount of volume getting to the rear? I'm running a 1 1/8 M/C, with 3/16 lines all around, is it possible the wheel cylinders are just not getting enough volume?
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05-28-2004, 10:09 AM
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I would double check the shoes and hardware,and adjustment, short shoe to the frt, have a buddy apply the pedal and check the shoe travel, and bleed starting LF,RF,LR,RR, shoes should have a light drag when adjusted on the rear. The low amount of pressure is probably caused by the shoes not hitting the drum or air!
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05-28-2004, 10:12 AM
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That will be tonights project, let you know how it turns out, and thanks!
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05-28-2004, 12:47 PM
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I had a similar problem with a brake system I installed - was pulling my hair out! Finally I just decided I had done everything right and that was just as good as the system was going to operate and quit fooling with it.
But as I drove the car more and more the brakes got better and better! I now have a hard high pedal with good stopping power at all wheels. The shoes/pads needed to be run in on the rotors/drums. Give them a chance to wear in a little. Good luck.
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05-29-2004, 06:15 AM
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The proper sequence for bleeding the entire system , is RR__LR__RF__LF, always start with the bleeder the furthest from the master cylinder.
Troy __________________ If you don't make mistakes. your not doing anything. 69 ss rs full custom camaro 98 ISCA grandchampion 69 ss rs bb camaro wifes driver 66 Elcamino 350/all dz parts,ac,windows,loaded,my driver 69 ss chevelle bb conv.fresh frame off 26 T sedan street rod
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05-31-2004, 09:03 AM
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UPDATE.
After spending 21/2 hrs bleeding system FINALLY got all the air out of her. Good pedal height and stops all 4 corners as it should. Thanks for all the help folks! K
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