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some brake help?

Royal Sierra

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Just put in new master cylinder (tiawann unit) new wheel cylinders and shoes. Bled the brakes 4 or 5 times and the pedal goes alnost all the way to the floor before the truck starts to stop. It helps a little if I pump the brakes. Do I just need to adjust the brakes better? I adjusted them so that there was a slight drag when turning the drums by hand. Its a 70 521

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Sometimes you have to adjust them again after you get everything bled, as things center themselves, especially after you drive it.

Adjust them again, tighten them until you can't move the wheel, then back it off till it will turn.

Have you adjusted the pedal correctly, you should have about a half inch play in the pedal.

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How can I adjust the brakes without taking drums off


You dont take drums off to adjust... you wouldnt get them back on...


There is a cover on the backside with a star nut inside, turn the star with a screw driver. Note, you might need a bent screwdriver...

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Before bleeding the brakes, you want to have the shoes adjusted at each wheel first. It's a bit of a pain, but if you can have all 4 wheels off the ground and adjust each wheel until they barely turn, it will make the bleeding go easier. The reason for this is that you're trying to move the push the air in the line to the wheel cylinder and out of the system. You want the fluid to move in one direction....toward the wheel cylinder. If you have a loose adjustment on the shoes, the wheel cylinder will expand and contract as the pedal is pumped. When it expands, it will allow more air into the cylinder. If the pedal is providing more force or you don't leave the bleeder valve open long enough for the shoes to return, it can leave air in the cylinder. By adjusting the shoes out so that the cylinder doesn't move much, all the fluid movement will be from the pedal pushing. So...if the shoes are too loose and there was air in the line just outside the w/c(wheel cylinder), the pedal gets pushed, the air goes into the w/c, then the pedal is held down....the w/c is expanded at this time with fluid and some air...you open the bleeder valve, the m/c pushes fluid out because it's pushing harder than the return springs are pushing on the w/c. You tighten the bleeder before the return springs compress the w/c. Now, when the pedal is let up, the return springs compress the w/c and that air is pushed back into the brake line. The scenario I just outlined is NOT what you want. You can tighten the shoe adjustment to limit the w/c movement and you'll get pedal pressure faster and easier......or you can make sure that you hold the bleeder valve open long enough to let the return springs compress the w/c. If the shoe adjustment is too loose, it will take more than one stroke of the pedal to pump it up to engage the shoes and get resistance. If all 4 wheels are loose, it will take a lot of fluid to do this......makes bleeding the w/c's nearly impossible. If you're Ebrake is working, you can set it, then you only have to adjust the front w/c's to snug.


The point of the bench bleed is to remove any air from the m/c because it sits at an angle on the firewall on most vehicles. Also, the pedal will not bottom out the piston, so air can get left behind in the bore of the m/c. Bleach posted info years ago that finally got the point across to me. You can bench bleed the m/c in the vehicle, but you'll need a second person, which you're going to need/want anyway.


Jack the rear(typically) or the front of the vehicle up until the m/c is sitting level. Which end will depend on the slope of the ground where it's parked. Disconnect the linkage from the pedal. One person will need to be under the dash to push the linkage in and another under the hood to open/close the brake line. On a 521 single reservoir m/c, the line exits the top of the bore and I don't think they have a bleeder valve anyway. So, crack the line open about a 1/4-1/2 turn and have the assistant push the linkage in until it bottoms out in the m/c. You do not have to pump the m/c first, just a nice smooth stroke until it quits moving. Tighten the brake line. As a note, you'll want some rags under the m/c since the brake fluid that leaks out will eat your paint. Once you tighten up the brake line, then the assist can let the linkage back out. If they let it out while the line is open, it will suck air back into the system. If they get it fully bottomed out each time, you should only have to repeat this 2-3 times. Hook the linkage back up to the pedal.


To bleed the rest of the system, you want to start at the wheel that has the longest brake line and work your way to the shortest brake line. On a 521, the rear brake line runs down the driver's side, so you'd want to start with the rear passenger wheel and end at the driver's front. On a disc 620, the line goes down the pass side, so you'd start with the D side first(plus they typically have a load regulated proportioning valve which I won't go into). The assistant will pump the pedal...not too fast or it will create bubbles(air) in the system. If it's too slow, it will allow the brake fluid to move back into the m/c and you won't build up any pressure. I'm sure you've noticed this with the pedal. If you leave the pedal up for too long, you have to pump it up again. The timing isn't critical, just something to pay attention to. If it's pumped 5 times in about 3-4 seconds, ending up being pushed in and held, that should be fast enough. It may not feel like it has pumped up. For the first time or two, it can get pumped 10 times, but 3-5 should be enough. Have them hold the pedal to the floor and open the bleeder valve at the wheel cylinder for 2-3 seconds and close it. Have them pump it again. Repeat this 3x's at each wheel. You will probably have to go around the truck a time or two before you start to get good pedal feel. Don't forget to check the brake fluid level in the m/c after each wheel. Once you start getting pressure at the pedal when pumping, you can pay attention to air bubbles escaping from the bleeder valve. They pump and hold, you crack open the bleeder valve, you get a couple of spurts of air, then tighten the bleeder....repeat. When you go around the truck and get no air, you're done with the bleeding.


Now you can go around the vehicle(in no particular order) and adjust the shoes. As mentioned...from the backside with a bent screwdriver or a brake adjustment tool. Most parts stores should have a cheap one for less than $10 and if you keep drums on your vehicle...you're gonna need it! On the backing plate, there's an oval hole...typically plugged with a rubber plug. Remove the plug. You should have access to the star wheel on the adjuster. Off hand, I can't tell you if you turn it up or down to tighten and it's not uncommon for these to have been switched or replaces with the wrong one sometime in the past. Look inside the hole with a flashlight and note where the adjustment is at. Turn the wheel in one direction a couple of times and then look again to see if it moved in or out. The wheel must be off the ground and you want to have the tire mounted up and lug nuts torqued correctly. Having the wheel on gives you more leverage to turn the brake drum and tightening the lug nuts makes sure that the brake drum is seated evenly. The factory manual tells how to do this too and gives an exact number of clicks to release the shoes. I'm going to explain it slightly differently because the book was written for brand new brakes and they don't quite give some of the finer details. You'll tighten the adjuster until you can't hardly turn the wheel. They say until you can't turn the drum. Then they say how many clicks to back it off. You want it tight, preferably to where you can't turn the wheel since this will make sure that you've centered the shoes in the drum. Now, back off the adjuster until the wheel starts to turn. Most likely, you'll get an intermittent scrubbing unless you just had the drums turned. Press the brake pedal firmly to recenter the shoes. Spin the wheel. If you get the intermittent scrubbing, you'll want to keep just a bit of the scrub. Not enough to stop the wheel from rotating, but I wouldn't remove all the scrubbing. If you had the drums turned, it should go from firm scrubbing to almost no scrubbing in just a couple of clicks. Always press the pedal again to center the shoes before you decide if you like the adjustment or not. Try to get all 4 wheels about the same.....especially the front two. You don't want a hard dragging on the wheel or your brakes will get really hot and fade. You don't want to remove all the scrubbing because the w/c's will have to travel farther and your pedal travel will be too much.


Let's see....what else?


The pedal pumping up means the adjustment is too loose. If you push the pedal 3x's and it pumps up....meaning the pedal travel is less on each stroke....then the adjustment isn't close enough and the w/c's are traveling too far. With new shoes, you may notice this happening after a day or two of driving since the shoes will "seat" into the drum and you'll have to readjust the shoes.


A squishy pedal....excessively squishy....is air in the line and the system needs to be bled. For guys with some leg muscles, you'll notice some squish compared to a modern disc brake system. There's a lot of places to move and flex in the drum brakes, so a bit of squish when pressing hard is okay. We're talking about a 1/2-1" on the pedal is okay....not 2-3"....that's bad.


If the pedal is firm, but as you hold it down, it drops, you have a leak in the system. Keep in mind that fluid can leak past the m/c piston and come out under the dash. If you have carpet, you may not notice the leak, so just be aware that not all leaks will show up under the vehicle.


I should put this on my site since I've typed all this out before :) I've been at this for better than a half hour....sure wish I could type faster :) At least I have a keyboard for the ipad or I wouldn't have even started! lol


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ya...sorry....most cars have a nice rubber plug.....I forgot about the sliding adjuster. I think it gets tapped forward so that the slot gets bigger....then you can get the adjustment tool in there and spin the star wheel. A cheap flat blade screwdriver with a 30deg bend it it should work fine.


I'll add that to the list of videos to do. :)

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