Brake Bleeding.......101

[mbryson]

OK....I've been trying to 'bleed' my brakes for a few hours this morning. The fronts seem to work out OK........ Still lots of air, but I think I've got something I can work with there.

The rear....different story. I've taken the hardline off at the master cylinder and got a 'squirt' all over my engine after pushing the brake pedal, so I think the master cylinder is working. I'm using a YJ mc, and am not familiar at all with them (they look suspiciously GM, though) specifically. Does it just take a rediculously long time to 'pump' enough fluid into the empty lines to get to the rear to hold fluid or is there a shortcut I don't know about (or is my mc kinda lacking?).

 

[rkillpack]

Try gravity Bleeding.

I had a similar problem with bleeding the calipers on the rear of my suburban after a MC swap and rear disk conversion. Just open the bleeders and see if gravity will pull your fluid down. Let it sit and check on it every so often till they leak. When they leak then close them and start bleeding them like normal.
If yours turns out like mine, this will only get you so far though, I ended up having to go to a shop and have them power bled. It costs too much though to make a habit of it.

 

[Greg]

Gravity bleeding will help you get started, but if the fluid needs to be flushed out of the lines, I'd go buy one of those big containers of brake fluid and begin pumpin'! (BTW... if you don't know, leave the cover off the reservoir while gravity bleeding.)

I'd connect all brakelines and open each rear bleeder, one at a time. Pump the brakes & empty each line until you see the new, clear fluid coming out. Once you're getting new fluid, gravity bleed it by leave the bleeder all the way opened and let it drip. After you're getting a nice steady flow, close that bleeder and do the same for the otherside. Then bleed the brakes again, like normal.

Also, there's a pattern to bleeding brakes, something like driver front, pass front, driver rear, pass rear.

Hope that helps!

 

[bobdog]

A motive presure bleeder works well. I love mine.

 

[way2nosty]

Gravity bleeding will help you get started, but if the fluid needs to be flushed out of the lines, I'd go buy one of those big containers of brake fluid and begin pumpin'! (BTW... if you don't know, leave the cover off the reservoir while gravity bleeding.)

I'd connect all brakelines and open each rear bleeder, one at a time. Pump the brakes & empty each line until you see the new, clear fluid coming out. Once you're getting new fluid, gravity bleed it by leave the bleeder all the way opened and let it drip. After you're getting a nice steady flow, close that bleeder and do the same for the otherside. Then bleed the brakes again, like normal.

Also, there's a pattern to bleeding brakes, something like driver front, pass front, driver rear, pass rear.

Hope that helps!

that depends on the pairing of the brakes, generally you start with the longest line and move to the shortest. if you have a newer GM, or an abs system you will need to power or pressure bleed the system.

 

[Greg]

that depends on the pairing of the brakes, generally you start with the longest line and move to the shortest. if you have a newer GM, or an abs system you will need to power or pressure bleed the system.

Yeah, I may have been bass-ackwards... it's been a long time since I did this stuff for a living. Bleed the furthest from the MC and work your way to the closest.

And it's not a newer GM with ABS, it's a YJ with a SBC.

 

[Milner]

Yeah, I may have been bass-ackwards... it's been a long time since I did this stuff for a living. Bleed the furthest from the MC and work your way to the closest.

And it's not a newer GM with ABS, it's a YJ with a SBC.

Thats how I have always done it.
You can pick up oe of the squeeze pumps that suck the fluid thru....I thik they are about $30. I never liked the ones I have used that used compressed air to power the vacum pump....

 

[waynehartwig]

Also, if you are replacing a faulty master cylinder or component, the proportioning valve may have cut off the supply to the rears. If that's the case, you need to push hard on the brakes to allow the flow to the rear to start up again. Of course, the rear lines need to have either fluid in them or a lot of air to make the valve think there is nothing wrong with the brakes. Even then, sometimes that valve will stay stuck and require disasembly.

If it were me, I would take a vacuum pump and hook it up to the bleader screw on the rear passenger and start pumping. It will take a little while for the valve to let fluid by. Just keep the reservoir full of fluid and leave the cap off. After you start getting fluid and no more air, then close the screw and move to the other side and do the same thing. After you get fluid and no more air, close the screw and pump the breaks to a hard peddle. After it gets hard, push on the brake peddle HARD! Then you should be able to open a bleader screw on the rear passenger and have it drip on it's own - gravity bleed. Once you have all the air out, move to the driver rear then the passenger front and driver front. No more bleeding is necessary and make sure you do all of this with the engine off and keep the reservoir full. To open a bleeder screw, it only requires one or two turns.

 

[mbryson]

OK.....maybe 101 was a little bit of a stretch. They finally 'gravity' bled (with a little pursuasion from the pedal---OK, a LOT).........about 15 min. after I posted this. They don't have the right 'feel' yet, but I'll worry about it after I've got something to sit on.

 

[Tacoma]

Also start at the rear, it helps. I was always taught to do the one farthest from the master cylinder and work forward from there. I've also got a driveway that slants and that helps as well LOL ....

Wayne's got a perty good plan there.

 

[JoeT]

What about brakes that feel good until you start the motor? Just bleed mine, started the motor brake light went off, pumped it a couple of times, light came on and brakes went weak.

 

[waynehartwig]

What about brakes that feel good until you start the motor? Just bleed mine, started the motor brake light went off, pumped it a couple of times, light came on and brakes went weak.

Sounds like a power booster gone bad....

I'd shut the motor off, and try bleeding them again. If you have air in the lines, then you have a bad master cylinder. But if there is no air, then it's the power booster.

 

[mbryson]

What about brakes that feel good until you start the motor? Just bleed mine, started the motor brake light went off, pumped it a couple of times, light came on and brakes went weak.

I'd bet it's the brake booster.

 

[way2nosty]

I'd bet it's the brake booster.

there's a rubber boot between the master cylender and the booster, Check it and make sure it isn't cracked etc.

 

[Shawn]

If the booster has gone bad, when you depress on the brakes there should be a change in engine RPM's. The booster runs off of vac so you will create a leak in the system when the brakes are pressed.

 

[Shawn]

I have had great results with opening the bleeder screw and slipping a rubber hose over it and running the other end of the hose in a jar of brake fluid. Then pump the sheet out of it. That way the fluid comes in and out. Once I get most of the air out on the lines, I gravity bleed the system while I am tapping on the calipers.

 

[waynehartwig]

If the booster has gone bad, when you depress on the brakes there should be a change in engine RPM's. The booster runs off of vac so you will create a leak in the system when the brakes are pressed.

Not always.... Sometimes they will constantly leak and won't hold a vacuum at all. And with todays computer controlled engines, a vacuum leak is compensated by the computer, so you may never see a change.

 

[JoeT]

My rpms are changing when the pedal is pushed, but not much.

 

[waynehartwig]

My rpms are changing when the pedal is pushed, but not much.

Like Shawn said, check your booster... An easy way to isolate it from the motor is to unhook the vacuum line and plug it. But if you have a hard pedal with the motor off, but not when it's on, you have a bad booster (or air in the lines)... As that is the only thing that changes when the motor is running.

 

[JoeT]

Like Shawn said, check your booster... An easy way to isolate it from the motor is to unhook the vacuum line and plug it. But if you have a hard pedal with the motor off, but not when it's on, you have a bad booster (or air in the lines)... As that is the only thing that changes when the motor is running.

I'm going to try bleeding my lines out some more. But first I really need to take care of some that are leaking at the connections.