Brake bleeding blues

[stevec108]

I'm 3 days into replacing the brakes on my son's '89 Cherokee and having a horrible time successfully bleeding the system. I've replaced the master cylinder, successfully bench bled the unit then, upon installing it and proceeding through the right-rear, left-rear (successfully bled), I run into chronic air bubbles in the right front disc. I've run 2 quarts of brake fluid through this thing and still can't get the system to effectively purge! Moreover, I'm noticing air back in the master cylinder again! Any ideas would be most helpful. I've done brakes a number of times in the past but have never run into this problem. I'm wondering if I've obtained an incorrect master cylinder even though it visuall appears the same as the original one? HELP!

[Ironic]

Had a simular problem, bled the dam thing like 4 times all the way around, to no avail. turns out I had a crushed brake line that was seeping in the rear, follow the line from the master cylinder to the wheel.

[stevec108]

Originally Posted by stevec108

I'm 3 days into replacing the brakes on my son's '89 Cherokee and having a horrible time successfully bleeding the system. I've replaced the master cylinder, successfully bench bled the unit then, upon installing it and proceeding through the right-rear, left-rear (successfully bled), I run into chronic air bubbles in the right front disc. I've run 2 quarts of brake fluid through this thing and still can't get the system to effectively purge! Moreover, I'm noticing air back in the master cylinder again! Any ideas would be most helpful. I've done brakes a number of times in the past but have never run into this problem. I'm wondering if I've obtained an incorrect master cylinder even though it visuall appears the same as the original one? HELP!

Thanks for the input and I'll trace all of the lines from the master cylinder watching for damage. Up till now, I've not noticed any wet areas from leaking brake fluid though. . . Stand by. . .

[89ltd]

i have the same problem on 89, just installed new rear brakes and lines, master, and when i have somebody push on the brakes and open the line on the left rear, it seems to hesitate then fly out. I blew out the bleeder screw. Still not quite right, kind of spongy. Maybe a bad wheel cylinder, I cant' figure it out

[Cam7]

Does the system have ABS? They can be tricky to bleed.Start with the passenger rear and like the other post said look for pin holes in the lines and leaking wheel cylinders. Also the front brake hoses can cause problems when worn.

[stevec108]

Originally Posted by 89ltd

i have the same problem on 89, just installed new rear brakes and lines, master, and when i have somebody push on the brakes and open the line on the left rear, it seems to hesitate then fly out. I blew out the bleeder screw. Still not quite right, kind of spongy. Maybe a bad wheel cylinder, I cant' figure it out

Thanks for the reply! This system is a non-ABS type. I have a new theory that I'm going to try out today: I've been successful in bleeding the rears but not the fronts. The two chambers of the master cylinder are dedicated to the front and rear brakes. The front, smaller chamber is for the rears and it works fine. The rear, much larger chamber is for the front discs. I noticed in unsuccessfully bleeding the discs, that the master cylinder chamber became very dirty with what appeared to be old fluid in the system. Furthermore, I noticed that the pedal, after one or two tries of bleeding/pumping, became very slow in returning to the full stroke. Lastly, when refilling the master cylinder chamber, removing the lid, I noticed a strong sucking sound, like when one removes a bottle top from a soda. Also, the rubber seal comes off distorted. I'm thinking that, with all the air in the front discs, that I'm stressing the master cylinder chamber from excessive bleeding and actually causing a vacuum in the upper system that is preventing the bleeding and, in fact, drawing the old fluid (and air) right back into the master cylinder. I'm now going to try to bleed it with the lid loose/off, taking care not to splash that nasty fluid all over the engine compartment when pumping those brakes. Stand by. . .

[JDPascal]

Originally Posted by stevec108

Thanks for the reply! This system is a non-ABS type. I have a new theory that I'm going to try out today: I've been successful in bleeding the rears but not the fronts. The two chambers of the master cylinder are dedicated to the front and rear brakes. The front, smaller chamber is for the rears and it works fine.

The rear, much larger chamber is for the front discs. I noticed in unsuccessfully bleeding the discs, that the master cylinder chamber became very dirty with what appeared to be old fluid in the system..

If you have run 2 qts of fluid thru the lines and out the calipers, you should have no old fluid left anywhere.

Have you bleed both left and right calipers????

Is the fluid "dirty" in both reservoir chambers???? or just one???? Which one???

Furthermore, I noticed that the pedal, after one or two tries of bleeding/pumping, became very slow in returning to the full stroke. .

.

Is the pedal always slow in returning now???

Lastly, when refilling the master cylinder chamber, removing the lid, I noticed a strong sucking sound, like when one removes a bottle top from a soda..

Are you sure ther is a sucking sound or is it the sound of the seal separating from the top of the master cylinder???

Also, the rubber seal comes off distorted.

The rubber seal should come off distorted!!!!!. There is a vent in the cover above the seal that allows atmospheric pressure to act on the top of the seal and pushes it down into the reservoir chamber as the fluid is moved to the calipers/wheel cylinders. If the sound you describe is actually a sucking sound, check to make sure that the vent in the steel cover is not blocked.

I'm thinking that, with all the air in the front discs, that I'm stressing the master cylinder chamber from excessive bleeding and actually causing a vacuum in the upper system that is preventing the bleeding and, in fact, drawing the old fluid (and air) right back into the master cylinder.

The only way that fluid could be drawn back into the master cylinder from the lines is if the vent is plugged in the m/cyl cover. That would set up a vacuum on top of the fluid in the reservoir.

I'm now going to try to bleed it with the lid loose/off, taking care not to splash that nasty fluid all over the engine compartment when pumping those brakes. Stand by. . .

Are you bleeding with the engine running or shut off??

Are you using a "one man bleeder tool" or do you have a helper???


JD

[stevec108]

Originally Posted by JDPascal

If you have run 2 qts of fluid thru the lines and out the calipers, you should have no old fluid left anywhere.

Have you bleed both left and right calipers????

Is the fluid "dirty" in both reservoir chambers???? or just one???? Which one???


.

Is the pedal always slow in returning now???




Are you sure ther is a sucking sound or is it the sound of the seal separating from the top of the master cylinder???



The rubber seal should come off distorted!!!!!. There is a vent in the cover above the seal that allows atmospheric pressure to act on the top of the seal and pushes it down into the reservoir chamber as the fluid is moved to the calipers/wheel cylinders. If the sound you describe is actually a sucking sound, check to make sure that the vent in the steel cover is not blocked.




The only way that fluid could be drawn back into the master cylinder from the lines is if the vent is plugged in the m/cyl cover. That would set up a vacuum on top of the fluid in the reservoir.




Are you bleeding with the engine running or shut off??

Are you using a "one man bleeder tool" or do you have a helper???


JD

Wow! Thanks for the time and trouble of providing all of this input and helpful questions! I have a helper pumping the pedal and do not run the car while doing so. I'll check the master cylinder cover to see if there is a vent hole but I'm pretty sure it doesn't exist. Stand by for any results, if any!

[stevec108]

Originally Posted by JDPascal

If you have run 2 qts of fluid thru the lines and out the calipers, you should have no old fluid left anywhere.

Have you bleed both left and right calipers????

Is the fluid "dirty" in both reservoir chambers???? or just one???? Which one???


.

Is the pedal always slow in returning now???




Are you sure ther is a sucking sound or is it the sound of the seal separating from the top of the master cylinder???



The rubber seal should come off distorted!!!!!. There is a vent in the cover above the seal that allows atmospheric pressure to act on the top of the seal and pushes it down into the reservoir chamber as the fluid is moved to the calipers/wheel cylinders. If the sound you describe is actually a sucking sound, check to make sure that the vent in the steel cover is not blocked.




The only way that fluid could be drawn back into the master cylinder from the lines is if the vent is plugged in the m/cyl cover. That would set up a vacuum on top of the fluid in the reservoir.




Are you bleeding with the engine running or shut off??

Are you using a "one man bleeder tool" or do you have a helper???


JD

Problem solved!!!!! As it turns out, the "brand new" master cylinders (I tried TWO of them) that I purchased from NAPA, were either faulty or incorrect units. Out of desperation and one last attempt, I re-installed the original, sporadically faulty master cylinder and immediately had pedal and have successfully bled the entire system. I have now called Jeep and ordered a factory master cylinder, about three times the cost of the NAPA unit and will install that when it comes in. It goes to show me once again that once gets what one pays for! Caveat emptor!!!
Thanks for all the advice that propelled me forward to try different things.

[89ltd]

i'm wondering if my master is faulty as well, only with my brakes its the rears i'm having the same problem with. I converted from abs to standard and put a new master on , now the pedal is spungy with a lot of travel. I already handed in the core, i just figured since i had it all apart i may as well change it. I also ran 1 liter through the rear wheel cylinders (new) as well! I'm not sure how the pedal should feel on these vehicles since the brakes did not work when i bought it. Can anybody desribe how they should be?

[stevec108]

Originally Posted by stevec108

Problem solved!!!!! As it turns out, the "brand new" master cylinders (I tried TWO of them) that I purchased from NAPA, were either faulty or incorrect units. Out of desperation and one last attempt, I re-installed the original, sporadically faulty master cylinder and immediately had pedal and have successfully bled the entire system. I have now called Jeep and ordered a factory master cylinder, about three times the cost of the NAPA unit and will install that when it comes in. It goes to show me once again that once gets what one pays for! Caveat emptor!!!
Thanks for all the advice that propelled me forward to try different things.

Since I'm the guy that originated this particular threaded discussion, I may not be the best person to express my opinion here. However, in my opinion, "good pedal" is that in which one feels solid resistance at least 1/2 way through the full travel/sweep of the brake. If there is any sponge-like quality to the pedal, then it is likely caused by a faulty master cylinder and/or slave/wheel cylinders OR air in the brake system. I returned my incorrect/faulty master cylinders today to NAPA and with appreciated apologies, the parts guy suggested that the next time I bring in the original master cylinder from which they could take the servial numbers for a better match. Again, my original master cylinder was visually identical to the new one I bought, but the thing did not work. The parts guy also thought that the activation rod may have been too short or too long for the system. I have no idea about retrofitting from ABS to conventional so you're on your own with this. However, brakes are brakes and they all basically work the same in my opinion. I'd be suspicious of the master cylinder connecting rod, of its length, in particular.
Good luck!

[89ltd]

thanks for the info, I removed the abs system from my 89 and replaced it with a booster and master and combination valve from an 88. Everything fell into place nicely. I confirmed with a few parts stores and online that everything else is the same, all wheel cylindrers, callipers etc. I guess i have either bad wheel cylinders or the master, I think I will start with the master as my pedal travels about 1.5 " from the floor.