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| Re: [GMCnet] Brake Problems [message #270702 is a reply to message #270631] |
Wed, 28 January 2015 22:37   |
Rick Staples
Messages: 126
Registered: May 2014
Location: Johnstown, Colorado, USA
Karma:
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Jon Darcy wrote:
" Have brake pedal when engine is off, goes down to within 1" of floor when engine starts. Hardly any rear brakes when I try them. "
Jon,
The first question is whether the pedal is spongy (air in the system), or just low but solid. I found my '75 GMC fairly easy to bleed by gravity, and it sounds like you've bled the heck out of it, so I'm wondering about other things. One thing I'd try is readjusting the rear shoes. The self-adjusters are nearly useless (Few of us back up and hit the brakes hard.), so do it the old=-fashioned way:
-Raise and support the rear, wheels off the ground but tires in place.
-Back off the parking brake cables until they are very loose. (Make SURE they aren't sticking near the brake from rust or whatever.)
-Now one at a time, tighten the brake adjusters with a brake spoon or bent screwdriver, turning the wheel back and forth every few clicks on the adjuster, until the wheel completely locks up. (Can't turn it by hand.) Note the feel of the wheel turning as you do this. You'll probably find that it drags more in some spots than others, indicating the drum is out-of-round and/or not concentric on the hub. If it is TOO uneven, you may need to resurface or replace the drum. (Even NEW drums aren't always perfect.)
-Finally, loosen the adjuster a little at a time, trying to turn the wheel back and forth (You'll have to get another tool through the hole to hold the self-adjuster away. PITA.) until the wheel can be turned with a little drag. (New shoes and new/resurfaced drums, more drag, otherwise, less drag)
NOW, try your pedal, see if it's better, and if the rear brakes work. If they do, great, if not I apologize for wasting a couple hours of your time. 
If things are better, only then readjust the e-brake cables, but not so tight they significantly increase the drag.
Remember, you'll have to repeat this whole process after a few hundred miles as the shoes wear in, but you'll get even better braking when you do. What I've found in many cases is that the E-brake cables, through misadjustment or sticking, cause the shoes to make only partial contact with the drums. This give lousy braking, and the shoes sort of bend when the cylinder pushes on them, giving a low, slightly spongy pedal.
FWIW, my '75 Eleganza, with the oversize front calipers, Jim Bounds' enhanced booster and master cylinder (which DO raise the brake pedal more than I'd like), 1/16" oversize leading rear cylinders, and Jim Kanomata drums, can lock up several rear wheels in a panic stop. (Not sure how many, there was too much tire smoke!) As we used to say, "It'll stop on a dime, and give you 9ยข change!"
HTH. YMMV.
Rick
Rick Staples, '75 Eleganza, Johnstown, CO
"Advice is a dangerous gift, even from the Wise to the Wise, and all paths may run ill." -Tolkien
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