I just finished doing the rear brakes on my 40 Chevy pickup. New shoes, drums, wheel cylinders, spring kit and rear brake hose. The brakes are gm A body and dual master cylinder with booster. It stopped fine before I started and the pedal felt great, but now the pedal goes all the way to the floor when I go to back out of the garage. Bled the rear at both sides, didn’t touch the fronts. No leaks. Any ideas what could be causing this?
Sometimes, I've read, if one half of the system goes limp the prop valve will slide the divider to the other side and make sure the other half remains operational. Just wondered if you having the rear half with no pressure made it do that.
Maybe I’ll try bleeding again. There seemed to be quite a bit of air in the lines. Bled the rears for a good hour or so. Didn’t bleed the fronts, shouldn’t have to right if it’s a split MC the fronts and tears are totally isolated right? If you get air in the rear circuit that wouldn’t effect the front circuit, right? Also, if the rear shoes aren’t adjusted properly, that wouldn’t cause this issue, would it? The backing plates don’t have the adjuster slots, but the new drums had punch outs i guess so you can reach the adjusters from the front of the drum, but they wouldn’t budge no matter how hard I wacked them, and I was too lazy to get the drill out, so I just figured I would adjust them out as much as I could to where I could just barely slide the drum on, and then let the self adjusters do their job the rest of the way. So the rears are kinda adjusted, but not adjusted well or properly. That wouldn’t cause the pedal to go to the floor though, would it? I have discs on the front that I didn’t even mess with.
Bleed all 4 wheels . re adjust the rears as they may have seated after your test drive . I let off the parking brake adjustment when I replace shoes on drum brakes , as sometimes over the years the parking brake gets adjusted out to far and throws off the initial brake adjustment. Not saying this is your issue , but something to look at .
If you're using a factory style proportioning block, you need one of these for bleeding. Remove the switch and install this goodie. It keeps the slide in the valve from moving. Good luck!
here's a you tube to watch , yes , you have go bleed the fronts . sometimes if you stomp the. Brake pedal sharply it will automatically reset the valve .
But that would stop all the misinformation ,supposition , wives tales ," my buddy saids" , " that reminds me's" , " we gotta know the size of your lug nuts " , "who'd you buy your parts from" , long drawn out engineering theory , & just plain bullshit that makes up every new tech question that's posted LOL
You did adjust the rear shoes when you replaced the brakes? Back in the early 70's when I was doing several brake jobs a week I often had to straighten out someone's weekend brake job on Monday because they didn't adjust the brakes right. I agree with Vandenplas in that you also have to back the park brake adjustment off and then adjust it after you get the brakes adjusted right. Tighten the adjuster up until you can't turn the tire with one hand and then back it off 11 clicks. You have to have a certain degree of drag for the brakes to work right.
The pedal height is affected by both proper adjustment and what is in the line. What felt like contact may have been from an unseated, off center shoe. You may well have gotten the air out. The pedal won't be good 'til the shoes are seated properly. Get out the BFH and sharpen that old chisel. Set the drums flat on the ground. After a cup of coffee, Make that chisel sing. Now, when the drum is put back on, you can use your brake spoon to run the adjustment tight. Once full contact is made, the adjuster actuator plate needs to be pulled out away from the adj. star wheel. ( You can either find a hook, tool at the store, or fashion a hook from a sturdy coat hanger. ) You can then back the now, centered and seated, shoes off enough to turn the drum by hand, and still hear and feel some drag. Time to test. Perhaps bleed, maybe not. Have fun. As a young buck I would do this shit all day long. But gimme coffee. They won't let me have it now.
While holding the self adjuster out of the way & turning the star wheel with the adjustment tool , how do you measure / produce " clicks" ?
In order to open the adjuster hole we need to remove the plug. The drum is stamped with an oval shape, to make the slot. Removing the plug for one thing takes some force. Uncontrolled force can bend the drum face. Should that happen it can be corrected with hammer blows. Better plan though, is to strike the slot plug at its edge line with a sharp chisel to cut into the stamped impression. Once you break the plug from its position you can finish removal with a pliers. Thanks for asking.
Good point With Mr48chev's permission,, lets say we just loosen the adjuster 'til the drum turns free. Then notch by notch we tighten er up til we feel drag. Once the shoes are making contact then we can hang the tire/wheel and use the reverse gear, back up procedure to finish the job.
Im a little confused on the prop valve. I got one of those things to thread into the top to keep the needle centered, but I can’t figure out how to get it in. When I remove the fitting in the top there is this plastic shaft that’s still stuck in there. I didn’t mess with it too much because I don’t want to break anything, but this doesn’t look like any other prop valve. What am I looking at here?
I don't think that's a proportioning valve. I think it is simply a brake pressure differential valve, used simply to turn the light on and possibly restrict fluid flow to the side with low pressure. It looks a lot like the valve used on American Motors cars so many years ago, when I worked at the local dealership. You might be able to release the jammed plastic pin by opening up the side that has always had pressure and try and center the valve that has moved because of loss of pressure.
The only issue with that is some times the shoes are a tad off kilter and you have to tighten them up so you seat them in the drum and square them up. Doing it right really isn't that hard and it isn't rocket science. I've popped probably 300 of those metal plugs out of the front of drums an never had a problem with screwing up a drum. If you don't have the spring against the adjuster to feel the click you just go by feel. It isn't that hard to figure out you are moving the wheel about 3/16 of an inch at a time.
Right you are. So I been thinkin' And thought of a good tip to share. One step I've always taken is before placing the drum on, I'll grab both shoes at the bottom, pull them away from the plate, yank them fore and aft, as much as the holddowns will allow, then center to the plate, set them against the plate. You are correct that they need to be square. I guess my issue with hittin the mark on the drum comes from living my life with one eye ( no depth perception ) and 10 years a drunkard. Swinging a hammer for me is a crap shoot. Enjoy this day.
Too complex an item for the application, IMO. I buy distribution blocks from places like Summit for around $70. https://www.summitracing.com/parts/clp-apv-db
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