[bend]

I can't get my brakes bled.

Here is what I have done thus far:

I had a hole in my rear hard line - the long one that goes from the front to the back of the Jeep. I replaced it, and also replaced the master cylinder, since (a) many reports of bad master cylinders after the brake pedal is pressed all the way to the floor, (b) I would need to bench bleed the old master cylinder since it had run dry, meaning it would be off the car, and (c) it was 11 years old.

I have replaced calipers and wheel cylinders many times, and bled my brakes many times without any problem. This was my first time replacing hard lines or a master cylinder.

I bench bled the new master cylinder. I'll describe just what I did, in case I did something stupid. I filled the reservoir, and waited until the fluid flowed from the front port, then plugged the front port with an adapter that allows clear tubing to loop back into the fluid in the reservoir. When fluid started dribbling from the rear port, I placed another adapter into it, with the clear tubing looped up and into the reservoir.

Using a dowel, (and keeping the master cylinder horizontal), I pressed in the piston repeatedly, starting with small strokes and progressing to the full depth.
Eventually, no more bubbles were flowing through the tubing.

I reassembled everything, and started bleeding. I got the big bubbles out of the front left caliper, then the rear left. I did this not to get those lines perfect, but just to get the proportioning valve filled on both sides, and the major air pockets out. I then went to the right rear. All the major bubble came out with no problems. But a pint of fluid later, I was till getting tiny, tiny little bubbles. Not with every press of the pedal, but with most presses. And I was out of fluid.

I bought another quart of fluid, and tried again today. I started with the front left caliper, since I was suspecting air in the proportioning valve at this point. About 10 presses of the pedal later, things were, if anything, worse. I was getting small bubbles almost every press of the brake pedal.

At this point, I was stumped, and decided that perhaps there was air in the MC. So I removed the brake lines from the MC, and re-installed the bench-bleed lines. I know you are supposed to bench bleed horizontally, but I just wanted to see if there were any bubbles.

There were a *lot* of bubbles. About 80 presses of the pedal later, I was again getting clear fluid. (All with the MC in the Jeep.) I reassembled the system. Still getting bubbles in the front left caliper, put about 8 oz through it.

I tried the right rear; I don't know exactly why. My assistant pressed the pedal, and heard a 'clunk', and the pedal hit a hard stop about 2/3 of the way down. I thought it might be the proportioning valve sensing the loss of pressure in the rear. I continued bleeding the right rear, and after about five presses of bubbles, got five in a row with no bubbles. Yeah!

I moved to the left rear. Back to more bubbles, every press two or three small bubbles in the fluid. Even after another 30 brake pedal presses, still getting bubbles.

Uggh. Nice 70 degree weather tonight, looking at 95+ tomorrow, and I only have today and two more days before I had plans to leave on vacation. (Which can be delayed, thankfully.)

Any thoughts?

Could the MC be introducing bubbles?
Could I be sucking air into the system somewhere? (no leaks, I've looked carefully.)

[bend]

Someone asked me offline what I meant by tiny and small bubbles.

I am bleeding with a clear line attached to the bleed nipples. A 'tiny' bubble, like I was getting the
first day, is as small as you might be able to see, like a small bit of foam. A 'small' bubble almost fills
the tubing. A 'bubble' fills the tube, and produces an air gap in the brake fluid.

[armmata]

try gravity bleeding them open each caliper and let it drip tell a stead stream of fluid is coming out then move to the next one

[bend]

I went for a test drive. It stops, fairly hard even, but the pedal is very soft and squishy; a hard stop doesn't happen until the pedal is about 2/3 down, as opposed to 1/4 or 1/3 of the way down before this all started.

[bend]

Originally Posted by armmata

try gravity bleeding them open each caliper and let it drip tell a stead stream of fluid is coming out then move to the next one

How long and/or how much fluid for each caliper and wheel cylinder?

[Mean Max]

Check your calipers. The bleed screw must be located above the brake line fitting. Calipers are identical left to right, except with regard to bleed screw location. They can be easily mounted on the wrong sides, and when that happens there will always be air in the caliper.

Max

[bend]

Originally Posted by Mean Max

Check your calipers. The bleed screw must be located above the brake line fitting. Calipers are identical left to right, except with regard to bleed screw location. They can be easily mounted on the wrong sides, and when that happens there will always be air in the caliper.

Good idea, but I think they are on correctly.

The bleed screws are on the top of the caliper piston, above the banjo bolt fitting.

(Plus, I did not change them this time, and they bled fine six months ago when I installed them.)

[TimV]

Is your assistant pressing the pedal while you have the bleeder open? If so, that's your problem. Have him press the pedal 5-10 times until it firms up. Have him hold the pedal while you open the bleeder, then close the bleeder. Do that repeatedly, until you get no more air. Then go to the next wheel. This is the order you want to bleed them in: RR, LR, RF, LF. Make sure the master cylinder stays full of fluid during the process.

[Rob K]

Sounds like a leak somewhere. I had the same problem. Couldn't get rid of the tiny air bubbles. Luckily for me it was just on the front passenger side. Turned out air was leaking passed the piston on the brand new caliper. If you've bled them the right way and still getting air bubbles, look upstream for the leak.

[bend]

Originally Posted by Rob K

Sounds like a leak somewhere. I had the same problem. Couldn't get rid of the tiny air bubbles. Luckily for me it was just on the front passenger side. Turned out air was leaking passed the piston on the brand new caliper. If you've bled them the right way and still getting air bubbles, look upstream for the leak.

Thank you for chiming in, that is very interesting. The only thing that is upstream of both a front caliper and a rear wheel cylinder is the master cylinder, if I understand the braking system correctly. Can a master cylinder be introducing bubbles? I would not have thought so, but I'm not sure.

[sAe23]

I've seen (but never USED) Pressurized brake bleeding kits advertised on TV (and just Googled it for reference).
Maybe having the system under constant pressure might reveal where the air is getting in (by virtue of fluid leaking OUT)?

Just a thought (from an avid brake bleeding hater!).

[davsfsj3xjs]

Originally Posted by bend

I can't get my brakes bled.

Here is what I have done thus far:

I had a hole in my rear hard line - the long one that goes from the front to the back of the Jeep. I replaced it, and also replaced the master cylinder, since (a) many reports of bad master cylinders after the brake pedal is pressed all the way to the floor, (b) I would need to bench bleed the old master cylinder since it had run dry, meaning it would be off the car, and (c) it was 11 years old.

I have replaced calipers and wheel cylinders many times, and bled my brakes many times without any problem. This was my first time replacing hard lines or a master cylinder.

I bench bled the new master cylinder. I'll describe just what I did, in case I did something stupid. I filled the reservoir, and waited until the fluid flowed from the front port, then plugged the front port with an adapter that allows clear tubing to loop back into the fluid in the reservoir. When fluid started dribbling from the rear port, I placed another adapter into it, with the clear tubing looped up and into the reservoir.

Using a dowel, (and keeping the master cylinder horizontal), I pressed in the piston repeatedly, starting with small strokes and progressing to the full depth.
Eventually, no more bubbles were flowing through the tubing.

I reassembled everything, and started bleeding. I got the big bubbles out of the front left caliper, then the rear left. I did this not to get those lines perfect, but just to get the proportioning valve filled on both sides, and the major air pockets out. I then went to the right rear. All the major bubble came out with no problems. But a pint of fluid later, I was till getting tiny, tiny little bubbles. Not with every press of the pedal, but with most presses. And I was out of fluid.

I bought another quart of fluid, and tried again today. I started with the front left caliper, since I was suspecting air in the proportioning valve at this point. About 10 presses of the pedal later, things were, if anything, worse. I was getting small bubbles almost every press of the brake pedal.

At this point, I was stumped, and decided that perhaps there was air in the MC. So I removed the brake lines from the MC, and re-installed the bench-bleed lines. I know you are supposed to bench bleed horizontally, but I just wanted to see if there were any bubbles.

There were a *lot* of bubbles. About 80 presses of the pedal later, I was again getting clear fluid. (All with the MC in the Jeep.) I reassembled the system. Still getting bubbles in the front left caliper, put about 8 oz through it.

I tried the right rear; I don't know exactly why. My assistant pressed the pedal, and heard a 'clunk', and the pedal hit a hard stop about 2/3 of the way down. I thought it might be the proportioning valve sensing the loss of pressure in the rear. I continued bleeding the right rear, and after about five presses of bubbles, got five in a row with no bubbles. Yeah!

I moved to the left rear. Back to more bubbles, every press two or three small bubbles in the fluid. Even after another 30 brake pedal presses, still getting bubbles.

Uggh. Nice 70 degree weather tonight, looking at 95+ tomorrow, and I only have today and two more days before I had plans to leave on vacation. (Which can be delayed, thankfully.)

Any thoughts?

Could the MC be introducing bubbles?
Could I be sucking air into the system somewhere? (no leaks, I've looked carefully.)

You need to start at the farthest brake cylinder from the Master cylinder. Passenger rear, then drivers rear, passenger front, then drivers front, in order to get all the air out. Adding brake fluid as you go, of coarse.

[bend]

Originally Posted by davsfsj3xjs

You need to start at the farthest brake cylinder from the Master cylinder. Passenger rear, then drivers rear, passenger front, then drivers front, in order to get all the air out. Adding brake fluid as you go, of coarse.

I have tried them in that order. I have also concentrated on the left front at times as it is the most convenient, and the closest to the MC / proportioning valve. I know that if/when I get a good bleed on the front left, I would need to then do all four corners in order.

Last night before the test drive I bled all four corners, in the standard order (as you rightly suggested). I got no bubbles for three pedal presses on the passenger rear. I moved to the driver's rear, and could not get more than two presses in a row without any bubbles. I got two and a half presses on the front right without air. The front left was giving me several small bubbles every press.

[bend]

Two things that have always confused me is how fast to press down the
pedal when bleeding, and whether to pre-pump.

I have used a 2-3 second press of the pedal in the past. armmata said:

Originally Posted by armmata

try gravity bleeding them open each caliper and let it drip tell a stead stream of fluid is coming out then move to the next one

which is a sort of *slow* press. And Mr. Blaine (seems to really know brakes on these Jeeps, advocates a 1 second press:
http://www.jeepforum.com/forum/f9/br...ml#post5219553

I would have thought the faster the press the better the chance of dislodging air, but also the higher the chance of breaking one, easy to move, bubble into many tiny bubbles.

Which brings me to the whole 'pump or not' thing, TimV has suggested:

Originally Posted by TimV

Is your assistant pressing the pedal while you have the bleeder open? If so, that's your problem. Have him press the pedal 5-10 times until it firms up. Have him hold the pedal while you open the bleeder, then close the bleeder.<snip>

I used to do it this way, until I read a few places that this led to making the bubbles really, really, tiny and hard to bleed out.

I've always thought that there was probably one or two 'best' ways, but that almost any variation would work, which is why so many people advocate different techniques. But I wish there was a definitive source for understanding the pro and cons of the different methods.

I'm hoping Mr. Blaine might swing by this thread; he seems to have researched a lot of this sort of thing.

[Rob K]

Originally Posted by bend

Thank you for chiming in, that is very interesting. The only thing that is upstream of both a front caliper and a rear wheel cylinder is the master cylinder, if I understand the braking system correctly. Can a master cylinder be introducing bubbles? I would not have thought so, but I'm not sure.

I don't know what to tell you about master cylinders. Never had to deal with one. I've replaced lines, hoses, calipers, cylinders and they all bled out with no problems. Didn't do them in any particular order either. I do however plug the lines when removing parts to keep the remaining system from draining and taking on air. Maybe that's why I haven't had a problem.