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73-87 Chevy _ GMC Trucks => Brakes, Frame, Steering & Suspension => Brakes and Braking Systems => Topic started by: jeffm5150 on March 13, 2012, 08:20:19 PM
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Hi all!
I've had my '87 V20 Chevy for about 10 years. It's always had a long soft brake pedal but it's stopped well enough so I haven't ever bothered fixing it. A few years ago I swapped in some rear disc brakes onto the semi-float 14 bolt and still had the soft pedal. About a month ago I replaced the power brake booster and master cylinder, then used my power bleeder to flush out all of the old fluid. Yet I still have a soft pedal.
Ok, so that's the history. Currently, when I apply the brakes then release and wait about 1 to 1-1/2 seconds, then reapply I have a strong firm pedal. So clearly I've got some air in the system but I can't figure out where it is and how to get rid of it. About the only brake system part I haven't touched is the height-adjusting brake proportioning valve. Could it be the culprit? I tow a 16' car hauler flat bed trailer with a race car from time to time, so now I want to get the brakes working at their best.
Any advice would be greatly appreciated.
Cheers,
Jeff
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I absolutely hate bleeding brakes.
I agree with your diagnosis, sounds like air in lines.
Many years ago a Vietnam Vet & gearhead gave me the following tip about bleeding brakes.
His recommendation was to remove the cover from the master cylinder, then starting at the furthest wheel cylinder/caliper from the master cylinder (i.e., passenger rear) attach your bleeder hose to the bleeder valve (other end in a coffee can) and crack the valve enough to allow fluid to slowly start to escape. Then he said, go drink a glass of iced tea and let gravity do the work. Check the master cylinder every so often to ensure it doesn't go dry and after you've seen all the air bubbles bleed out through the hose, close the valve. Then go to the next furthest wheel (driver rear) and repeat.
After he told me about it, I tried his recommendation and it really works. It takes more time but you don't have to pump the brakes or have a suction gun and it gets all the air out of the system.
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Gravity bleeding works good, but used correctly a power bleeder can't be beat!
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After ten years, I think I'd quit calling it a "a long soft brake pedal", and start calling it a working as intended brake pedal.
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My first guess would be the proportioning valve especially if it is the original. When you say after mashing them a secong time the feel firm like they should it could be that he valve isn't allowing enough flow for the disc setup.
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have you done any work on the front?
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Update - I re-bled the front calipers and was able to get out some air using the traditional 2-man bleeding technique. The problem of the initial soft pedal is effectively gone.
To answer an above question - no work on the front end - everything is stock equipment. I guess I should think about replacing the brake lines with braided lines .... who knows the condition of the inside of those front lines.