Sorry by slide the tires, I ment lock them up. And also when I switched the lines at the mc the result was the same, great up front and nothing at the rear. I'll print up a diagram for the shoes and dubble check, I've made mistakes many a times. But if that checks out what next? If my mc is shot anyone know what year vette is for disc/drum and power ? I'll grab one tom and try that. Thanks to everyone , got quite a few good leads.
If you switched lines at the master cylinder, and the problem stayed in the rear, that should tell you quite a bit. There's obviously fluid coming out of the rear port, are you getting fluid the rear cylinders? Check to see how far to fluid is traveling down the line. Could be a m***ive air pocket, malfunctioned cylinders, ect.
pull your drums and take a couple of pics to post, also, you havent really said that your getting a good blast of fluid out of your rear cylinders when you bleed them, when you bleed your rear brakes someone pumps them up, you crack the bleeder and then yell, OK, before they let them off, right?
FYI the proportioning valve and the residual valves perform 2 entirely different functions, and make a complete system when installed properly. The proportioning valve slows or meters the pressure to the rear brakes to allow the fronts to load with the weight of the car where approx. 60% of the braking should take place to keep the rears from locking and sliding. The residual valves hold a prescribed pressure in the system to keep your pads or shoes from retracting to far and needing more fluid than really necessary to operate and maintain a good strong pedal. I'm not being a wise *** ....just thought I'd let you know.
residual pressure valves, 10lb, for drum brakes do not keep the shoes from returning, they are there to keep the cylinder cups in contact with the bores, return springs are good for about 25lbs at 1/4"
how far does your brake pedal move before the master cylinder piston does? (you may have to look thru small fluid ports in bottom of master cylinder reservoir) if more than an inch or so you may have a pedal problem, not a hydraulic problem. I have seen where pedal was half way to floor before piston moved fluid. Also if a GM master the front brakes are activated by the port closest to the pedal and Ford and Chrysler the opposite. Residuals are necessary as check valves or hydraulic diodes to keep pressure in lines but the prop may not be needed or only an adj prop for rear brakes. Are your rear drums adjusted tight enough? (slight equal drag or "cage" them at .025").
Rear drum brake adjustment is what gives correct pedal height. Initial adjustment is; Tighten the shoes tightly against the drum(s)... Releasing the self adjuster arm, back off shoes until you can get a 1/2 wheel turn with a hard push... Press brake pedal down (this will center the shoes on the backing plates)... Re-check adj to get 1/2 turn on hard push... This will get you correct initial adjustment. You most likely will have to manually re-adjust in two weeks or so as the shoes seat (contour) to the drums. The self adjusting feature should take over after this. Now, a disc-drum setup has to have a front metering valve. This valve delays front application until the rear brakes are energized. The drums have to have a 10# residual valave as this keeps the WC pistons from slapping one another on brake release upsetting the cups. A proportioning valve distributes hydraulic pressure between the front and rear of the system on hard braking. It limits total flow to the rear wheel cylinders as weight ransfer of the vehicle causes weight transfer from back to front causing the rear brakes to lock. A combination valve will have a metering valve, a transfer valve and a pre-set (for vehicle) proportioning valve. Usually, the 10# residual will be in (included) the outlet port of the drum side in the MC. The larger of the two MC reservoirs supplies the front disc and the smaller reservoir of the MC supplies the rear drum. 2# residual valves are needed for under floor MC installation.
Worked on the truck last night, this what we found. First in between the mc and vac***e booster was an adjustmentrod and jam nut, anfter setting this properly on to the mc itself. The bore was too big, and needed to be replaced. Still no good, next was the 10# valve the seak in it was no good and needs replaced. Should have the new one tom. If this works, I'll be a happy camper!!! Thanks everyone for all the help! I'll post the results tom. hard to believe all those new parts would be bad. Again thanks !! Spike
How could you tell the 10 # residual valve was bad, I'm having the same problem you are but don't know how to tell if the valve is bad or not. thanks
Thanks for the reply, I was hoping there is a way to check the residual valve visually but I'll see if I can rig something from my brake bleeder pump.
you need the check valves. the only time you need an adj valve is when you have 4 wheel disc brakes. take it out. crack all your bleeders and let it set a day or so dont touch the pedal the air will work its way out. make sure you have enough stroke on the pedal IE from your pedal mt pin to the M.C. push rod should be around 2 1/2 in bill www.billsrodandcustomshop.com
My valve was easy to tell that it needed replaced, I blew air through it with my mouth and it held no pressure. Not a good test, but it worked, I then looked at the internals and the rubber was bad. It had a small tear.
That won't work in his rig as the master cylinder is even with or well below the calipers and wheel cylinders.
Thanks, I thought that might be my problem too and after tearing out what little hair I have left after trying many good suggestions from several people on the hamb with no better results I finally decided I must have a kink in the brake line so I proceeded to start taking the brake lines dowm by pulling the flex line to the rear axle first and discovered that this really "fancy" flex line that really looked good when I bought it at a swap meet had less than a 1/16th inch opening in it. I don't know why I missed that when I bought it and installed it but have replaced it with an ordinary plain jane line and now have great brakes. After all the advice to get rid of the proportioning valve I find that the rear brakes are now locking up too fast so I will be re-intalling the valve. I do feel like a complete idiot! Hope you find your problem sooner than I found mine!
Spike , this may sound real stupid, but I just read a post on another column and a guy was saying that he thought turning the valve closed was applying more pressure when it was actually the oppisite. He had the same complaints and when he turned the valve the direct oppisite of what he expected it all started to grab in the rear - it started to finally lock down. Just an idea. Maybe it's not righty tighty - know whatta' mean? Pork
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