? about brakes

[714x4lover]

lets see, everything worked fine before the hose broke, i blew out a front brake hose, i bought the set of three to repair them.i took the front lines off at the same time and put them back on ok. i took off the rear hose , i started to put it back on and come to find out the two places where the ridged lines go into didnt fit, sooo i put the old one back on, then i tightened everything back up. i proceded to bleed the lines to get all the air out. well i've bled and bled and put a quart of brake fluid through the system. it still seems spongy and air still comes out,the passenger side only,the other side is only oil, i dont have any leaks anywhere in the lines that i've seen. i've changed the two calipers up front and pads.shoes are new in rear, whats funny is when i push brake peddel after the engine is off its real hard to push and when i release it it seems to shoot out like its under pressure. i pump the peddel with the engine stoped and alot of air comes out also. im stumped anyone out there in chevy land have any idea of what i can do now? it seems like i've changed the booster last year i think the only thing i have not changed is the perportioning valve, any help would be appreciated very much.

[JimKshortstep4x4]

It sounds like you still have air in the system. Sometimes it it can be real difficult to get it all out. I would suggest bleeding after the prop valve, rebleeding the front and then finish up with the rear. Rear brakes take a lot of bleeding. Make sure that rears are adjusted if you have not done that already. (The self adjusters may not be functioning).

Good luck!

Jim

[Rooster's 67]

start by bleeding the master cylinder, then start with the wheel furthest from the Master ie: right rear,left rear, right front, left front.

[714x4lover]

how do u bled the master cylinder?

[JimKshortstep4x4]

With the master cylinder in the truck, I bleed the MC and prop valve at the same time. This also gives you assurance that the prop valve is not closed in one direction. Remove front and rear line from prop valve, screw in adapters for 1/4" hose on both ends. Attach hoses and route them to open master cylinder (after flushing, by pumping a couple of times). Retain hoses by clipping to MC with ends of hoses submerged. Then it is just a matter of pumping the brakes until the air is bled out.

If the fluid is dirty, (usually I am working on new components), change out the fluid and clean the reservoirs out so that you are not pushing dirt into your system.

Jim

[southern parts]

I had the same problem on a 3/4 ton truck. One of the drums was turned out past max. diameter. This allowed air to get in at the wheel cylinder. When you say your getting air from one side are you talking about the back brakes ? Did you have your drums turned ? Hope this helps.

[elk hunter]

try not to let the pedal go down to the floor. sometimes a master cylinder can suck air through the rear seal if it is over extended. also i have had experienced wheel cylinders suck air when disrupted.you can also try to pump fluid through the lines when disconnected from the master with a pump from your local parts store. mine is for pumping out of a gallon jug but you get the picture.

[714x4lover]

i got them semi stiff yesterday, but as soon as i was on the road they started up again, i have the rear shoes adjusted , would the wheel cylinders leak oil if they are sucking air? what can i do to fix the problem, i pump the brakes when im comming to a stop, they dont grab at all.how much is the min thickness of the drum wall? i am pumping the brake peddle 10x then holding it then my son would open the valve and the peddle goes to the floor, so your saying try not to push the peddle to the floor when my son opens the valve, right!! yes only one wheel the passenger side is the only one still giving up air. is there a possibility that the gasket on the master cylinder lid could be sucking air?

[PR454SS]

I think there is air in the MC. It can sometimes be a real pain in the a$$ to get it out. one thing that I had to do was make sure the MC was perfectly level last time I had this kind of problems.
Also the gasket on the lid just seals the fluid inside, it doesn't hold any pressure.

[southern parts]

If the master cylinder was getting air into it , wouldn`t the air go to whatever the wheel being bled and not just the passenger rear. I think the problem is at that wheel. When i had the same problem the wheel cylinder never leaked a drop. I bought a new cylinder but still got air when i bled it . When i saw how thin the drum was i replaced it and was able to get all air from the system. The max. diameter should be stamped on the drum somewhere.

[southern parts]

If the master cylinder was getting air into it , wouldn`t the air go to whatever the wheel being bled and not just the passenger rear. I think the problem is at that wheel. When i had the same problem the wheel cylinder never leaked a drop. I bought a new cylinder but still got air when i bled it . When i saw how thin the drum was i replaced it and was able to get all air from the system. The max. diameter should be stamped on the drum somewhere.

[elk hunter]

it is possible that the master cylinder still has air in it, and yes you should have the master as level as possible air rises to the highest point which would be the nose of the master cylinder. the wheel cylinder may not leak fluid because the fluid is pushing on the inside of a conical shaped plunger which expands the sealwhen pressurized. when the fluid returns the seal is relaxed so it is possible that that one wheel cylinder is sucking air. i would recomend replacing wheel cylinders in pairs. the normal measurment on a brake drum for the maximum size is .060 over the measurment from new. this would be something like a 12" drum would be good to a maximum of 12.060", and should be cast on the drum on the outside face around the rim. the master always has air above the fluid so no the cap seal is not the problem. you also should not pump the pedal too quickly because that causes the fluid to foam which puts air in the system. nice and slow. you can diagnose where the air is at by clamping the rubber lines (all of them) and push on the pedal. this will tell you if the air is in the master. if pedal is solid, release each clamp one at a time to reveal where the air is. if you cant get the air out most shops have either a pressure bleeder or a vacuum bleeder.

[Rooster's 67]

careful clamping down on old rubber lines, the inside liner can become brittle and will crack and break with a clamping force. It will cause all kinds of weird problem so clamp at your own risk.

Personally I would look closely at the cup seals on all four corners of the truck. they could be weak or the bore of the cylinder could be coroded allowing air to be sucked back in.