Brake advise needed. Master cylinder empty. - JeepForum.com
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post #1 of 22 Old 08-21-2017, 04:36 PM Thread Starter
JOHNWON454
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Brake advise needed. Master cylinder empty.

Hi;
1993 JGC 5.2
I'm not sure how much brake fluid ran out when I had driver's side caliper hose disconnected..?? But when I checked the master cylinder rear most reservoir, it was empty. I hear you should not let this happen. What should now be done to correctly fix this situation? Thank You.
PS: I did not pump the brake pedal any at all.

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post #2 of 22 Old 08-21-2017, 06:24 PM
wingless
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The two potential issues w/ running the master cylinder dry are:
  1. The master cylinder may require a bench bleed. (Probably required) The reservoirs are filled w/ fluid and the brake hose fittings are connected to short loop that dumps into the reservoir. The piston is pumped until all the air bubbles are out of the piston.
  2. The ABS may require a DRB bleed. This requires the DRB tool. This is required if the ABS was activated while the fluid was gone. (Probably not required)

The brake lines also require a conventional bleed.




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post #3 of 22 Old 08-21-2017, 06:54 PM Thread Starter
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Originally Posted by wingless View Post
The two potential issues w/ running the master cylinder dry are:
  1. The master cylinder may require a bench bleed. (Probably required) The reservoirs are filled w/ fluid and the brake hose fittings are connected to short loop that dumps into the reservoir. The piston is pumped until all the air bubbles are out of the piston.
  2. The ABS may require a DRB bleed. This requires the DRB tool. This is required if the ABS was activated while the fluid was gone. (Probably not required)

The brake lines also require a conventional bleed.


DRB II ABS Bleed
I was hoping that if I did not press the brake pedal I'd not have to do the bench bleed procedure. Is it pretty easy to remove the master cylinder that has been on there since 1993 without damaging any seals? Or is it a situation where a new master cylinder should replace the original? Thanks for the detailed answer above.
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post #4 of 22 Old 08-21-2017, 08:24 PM
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You are welcome.

Go the "easy" route first.

Do a conventional bleed and see if a firm pedal is attained.

My very strong recommendation is to use the Motive Products Power Bleeder for one-man bleeding.


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post #5 of 22 Old 08-21-2017, 08:50 PM Thread Starter
JOHNWON454
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Originally Posted by wingless View Post
You are welcome.

Go the "easy" route first.

Do a conventional bleed and see if a firm pedal is attained.

My very strong recommendation is to use the Motive Products Power Bleeder for one-man bleeding.
Well, if there is nothing to loose or further negative consequences from going ahead with conventional bleeding, I may as well give it a shot first. I would like to use the Motive Products devise, except I need to get this back together by Wednesday. I have an appointment with a garage to fix a different issue that I don't want to take on.
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post #6 of 22 Old 08-21-2017, 09:38 PM
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Quote:
Originally Posted by JOHNWON454 View Post
I was hoping that if I did not press the brake pedal I'd not have to do the bench bleed procedure. Is it pretty easy to remove the master cylinder that has been on there since 1993 without damaging any seals? Or is it a situation where a new master cylinder should replace the original? Thanks for the detailed answer above.
Brakesystems work the other way, if you wanted to prevent the brakefluid from leaking out you should have used a piece of 2x4 between the seat and brakepedal to press down the pedal. That way the mastercylinder will be closed from the rest of the system and the only fluid leaking out is the fluid that is in the brakeline and hose for that wheel.

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post #7 of 22 Old 08-21-2017, 11:27 PM
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Quote:
Originally Posted by Pierre_r View Post
Brakesystems work the other way, if you wanted to prevent the brakefluid from leaking out you should have used a piece of 2x4 between the seat and brakepedal to press down the pedal. That way the mastercylinder will be closed from the rest of the system and the only fluid leaking out is the fluid that is in the brakeline and hose for that wheel.
Real good tip Pierre I haven't heard before, thanks.

I've told others to put a double layer of kitchen plastic wrap under the reservoir cap, screw cap on tight, and it will create a vacuum effect. Much like putting your thumb on a straw full of liquid. While this seemed to work on my 96 with just one cap on the reservoir it didn't work worth a crap on my 93 XJ with 2 caps. Not sure why but but this was in replacing both my front calipers last week. I shoved a small piece of vacuum line through the square block on the hose end which plugged up the hole.

On my 93 XJ I've run at least one section of the reservoir dry a couple times. Not my fault when bushy-tailed rats chew on brake lines/hoses. Luckily have never had to bench bleed the master cylinder. Believe those older MC's are less finicky than the later year ones and good luck.

96 4.0 ZJ Laredo, 2004 4.7L WJ Limited, 96 4.0 XJ (son's)


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post #8 of 22 Old 08-22-2017, 06:30 AM Thread Starter
JOHNWON454
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Quote:
Originally Posted by Pierre_r View Post
Brakesystems work the other way, if you wanted to prevent the brakefluid from leaking out you should have used a piece of 2x4 between the seat and brakepedal to press down the pedal. That way the mastercylinder will be closed from the rest of the system and the only fluid leaking out is the fluid that is in the brakeline and hose for that wheel.
That's a new one on me. Makes sense when you think about it though.. Thanks for helping me learn some useful tips in this over site of mine.
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post #9 of 22 Old 08-22-2017, 08:25 AM
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Quote:
Originally Posted by JOHNWON454 View Post
I was hoping that if I did not press the brake pedal I'd not have to do the bench bleed procedure. Is it pretty easy to remove the master cylinder that has been on there since 1993 without damaging any seals? Or is it a situation where a new master cylinder should replace the original? Thanks for the detailed answer above.
You don't have to take it off to bench bleed it unless you're being very literal. Just buy a bench bleed kit and use it with the master cylinder bolted to the booster. With the engine off you can just have someone pump the brake pedal slowly until all the bubbles go away. I just replaced my master cylinder on my 93 and I bled it on my bench vise for a bit then finished with it installed on the car. Credit I think goes to Uni for suggesting this in other threads.

FWIW general consensus is that if the ABS doesn't activate while the master cylinder is dry you can't get air in the ABS. Also that air in the ABS doesn't affect normal braking. Which makes sense since if there was hydraulic communication between the ABS and normal brakes all the time you wouldn't need the DRB to bleed them.
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post #10 of 22 Old 08-22-2017, 03:51 PM Thread Starter
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Originally Posted by zjosh93 View Post
You don't have to take it off to bench bleed it unless you're being very literal. Just buy a bench bleed kit and use it with the master cylinder bolted to the booster. With the engine off you can just have someone pump the brake pedal slowly until all the bubbles go away. I just replaced my master cylinder on my 93 and I bled it on my bench vise for a bit then finished with it installed on the car. Credit I think goes to Uni for suggesting this in other threads.

FWIW general consensus is that if the ABS doesn't activate while the master cylinder is dry you can't get air in the ABS. Also that air in the ABS doesn't affect normal braking. Which makes sense since if there was hydraulic communication between the ABS and normal brakes all the time you wouldn't need the DRB to bleed them.
I have been reading some about that "leaving it on the vehicle" I've even seen a video on youtube where a guy just runs a line from the closest caliper up to the reservoir rather than crack open the lines exiting the master cylinder.
Is there any good reasoning that would warrant jacking up the rear end of the vehicle in order to level the master cylinder, to closer duplicate it being clamped in a bench vise?
Also along those lines... Other than wasting brake fluid, wouldn't just hooking a tube to the bleeder valve on the closest caliper and submerge the end in a bottle of brake fluid and pump away suffice rather than back in the reservoir...??
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post #11 of 22 Old 08-22-2017, 07:54 PM
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I guess you could try to do that but the bubbles that come out are pretty small and the fluid tends to flow out as you push the pedal and then reverse and head back in a little as you release the pedal. That's using the short ~1 ft hoses that come with a master cylinder bleeding kit. I don't know how long it would take to bleed if your hoses ran all the way to the calipers, if they bled at all. You'd also have to run a hose to the front and rear brakes if you wanted to bleed both circuits. I know you only drained the rear one. Seems like a hassle to me.

When you bleed a new dry master cylinder it should be relatively level. Otherwise you might get an air bubble trapped at the end of the bore that won't bleed out. See here: http://my.cardone.com/techdocs/PT%2010-0003.pdf

I bled my new one mostly on the bench and then finished it mounted on the ZJ. I've got a much better pedal than before. If you want to do it all on the vehicle you would need to jack up the back to get it level. In your situation though since you only drained the rear circuit I'd probably try bleeding it installed and if the pedal wasn't great after I'd take it off and bench bleed it. Either way when you're done bleeding the master you have to bleed the rest of the brakes too.

Taking the master off is a bit of a pain but not too bad. There is a seal between the master and booster but I reused it once and it was fine.
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post #12 of 22 Old 08-22-2017, 09:52 PM
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Quote:
Originally Posted by zjosh93 View Post
You don't have to take it off to bench bleed it unless you're being very literal. Just buy a bench bleed kit and use it with the master cylinder bolted to the booster. With the engine off you can just have someone pump the brake pedal slowly until all the bubbles go away. I just replaced my master cylinder on my 93 and I bled it on my bench vise for a bit then finished with it installed on the car. Credit I think goes to Uni for suggesting this in other threads.
Thanks for remembering where that came from Josh. Actually I was going nuts a few years ago trying to get the air out of my ZJ or WJ master cylinder by bench bleeding it locked in a workmate. I was in a parts store and telling them all the problems I was having. Some 'good ole boy' kid who worked there said, "bench bleed it with it still attached to the booster". Everybody stared at him in disbelief. Smart kid!

Quote:
Originally Posted by JOHNWON454 View Post
I have been reading some about that "leaving it on the vehicle" I've even seen a video on youtube where a guy just runs a line from the closest caliper up to the reservoir rather than crack open the lines exiting the master cylinder.
Is there any good reasoning that would warrant jacking up the rear end of the vehicle in order to level the master cylinder, to closer duplicate it being clamped in a bench vise?
Also along those lines... Other than wasting brake fluid, wouldn't just hooking a tube to the bleeder valve on the closest caliper and submerge the end in a bottle of brake fluid and pump away suffice rather than back in the reservoir...??
For now I'd just fill up your master cylinder reservoir and bleed all 4 bleeder screws to see what you end up with. In mentioning the above MC bleeding with it attached to the booster I didn't have the rear higher and it still bled the air from the MC.

I know that link Josh posted makes sense to have it level but my brakes became tight as can be w/o jacking anything up.

Sounds like a real bad idea to connect a hose from a caliper and run it into the top MC reservoir. You probably have enough residue/debris in your reservoir already and don't need to be pumping water, dirt, other grime from your lines/calipers into your reservoir.

On any new/reman caliper I get I remove the bleeder screw and coat the threads with anti-seize stick-type. Have done the same with rear wheel cylinders and don't need screws breaking off. Have done the same with any old bleeder screws and as you probably know you best be hosing them down with rust cutter ahead of time before loosening.

I have not had much success with connecting a hose to a bleeder screw then putting the end of the hose in a jar of new brake fluid. The thread tolerances of new bleeder screws are so bad you will suck air right back into the caliper when you let off the pedal. One of the reasons I used the stick-type anti-seize to try to fill up the thread voids but it still didn't work very well. Just my experiences.

96 4.0 ZJ Laredo, 2004 4.7L WJ Limited, 96 4.0 XJ (son's)


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post #13 of 22 Old 08-23-2017, 05:26 AM Thread Starter
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Originally Posted by zjosh93 View Post
I guess you could try to do that but the bubbles that come out are pretty small and the fluid tends to flow out as you push the pedal and then reverse and head back in a little as you release the pedal. That's using the short ~1 ft hoses that come with a master cylinder bleeding kit. I don't know how long it would take to bleed if your hoses ran all the way to the calipers, if they bled at all. You'd also have to run a hose to the front and rear brakes if you wanted to bleed both circuits. I know you only drained the rear one. Seems like a hassle to me.

When you bleed a new dry master cylinder it should be relatively level. Otherwise you might get an air bubble trapped at the end of the bore that won't bleed out. See here: http://my.cardone.com/techdocs/PT%2010-0003.pdf

I bled my new one mostly on the bench and then finished it mounted on the ZJ. I've got a much better pedal than before. If you want to do it all on the vehicle you would need to jack up the back to get it level. In your situation though since you only drained the rear circuit I'd probably try bleeding it installed and if the pedal wasn't great after I'd take it off and bench bleed it. Either way when you're done bleeding the master you have to bleed the rest of the brakes too.

Taking the master off is a bit of a pain but not too bad. There is a seal between the master and booster but I reused it once and it was fine.
Those instructions are what I was thinking as for trying to simulate bench bleeding while still mounted on vehicle..
It apparently must not be too much of a problem with the air gap that will be left in the lines leading up to the proportioning valve that will result after removing them from the master cylinder..?? Being the proportioning valve has a line leading to the ABS pump, this looks like it will in turn lead to the need of the DRB devise..??
Am I just looking at it wrong to think this thought? But rather, a normal bleed at all four calipers/wheel cylinders will be all that is necessary after the bench bleed process? I apologize for being overly cautious prior to preforming this procedure. Just want to understand clearly. I do value and thank you for your time you have spent sharing your knowledge on this subject.
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post #14 of 22 Old 08-23-2017, 05:43 AM Thread Starter
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Originally Posted by Uniblurb View Post
Thanks for remembering where that came from Josh. Actually I was going nuts a few years ago trying to get the air out of my ZJ or WJ master cylinder by bench bleeding it locked in a workmate. I was in a parts store and telling them all the problems I was having. Some 'good ole boy' kid who worked there said, "bench bleed it with it still attached to the booster". Everybody stared at him in disbelief. Smart kid!



For now I'd just fill up your master cylinder reservoir and bleed all 4 bleeder screws to see what you end up with. In mentioning the above MC bleeding with it attached to the booster I didn't have the rear higher and it still bled the air from the MC.

I know that link Josh posted makes sense to have it level but my brakes became tight as can be w/o jacking anything up.

Sounds like a real bad idea to connect a hose from a caliper and run it into the top MC reservoir. You probably have enough residue/debris in your reservoir already and don't need to be pumping water, dirt, other grime from your lines/calipers into your reservoir.

On any new/reman caliper I get I remove the bleeder screw and coat the threads with anti-seize stick-type. Have done the same with rear wheel cylinders and don't need screws breaking off. Have done the same with any old bleeder screws and as you probably know you best be hosing them down with rust cutter ahead of time before loosening.

I have not had much success with connecting a hose to a bleeder screw then putting the end of the hose in a jar of new brake fluid. The thread tolerances of new bleeder screws are so bad you will suck air right back into the caliper when you let off the pedal. One of the reasons I used the stick-type anti-seize to try to fill up the thread voids but it still didn't work very well. Just my experiences.
I often thought about the air leak between the threads too.. I never was totally convinced that was a real solution to bleeding brakes properly. Thank you for sharing your time and knowledge on this subject matter.
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post #15 of 22 Old 08-23-2017, 07:42 AM
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Quote:
Originally Posted by JOHNWON454 View Post
Those instructions are what I was thinking as for trying to simulate bench bleeding while still mounted on vehicle..
It apparently must not be too much of a problem with the air gap that will be left in the lines leading up to the proportioning valve that will result after removing them from the master cylinder..?? Being the proportioning valve has a line leading to the ABS pump, this looks like it will in turn lead to the need of the DRB devise..??
Am I just looking at it wrong to think this thought? But rather, a normal bleed at all four calipers/wheel cylinders will be all that is necessary after the bench bleed process? I apologize for being overly cautious prior to preforming this procedure. Just want to understand clearly. I do value and thank you for your time you have spent sharing your knowledge on this subject.
The air bubble you get while you are reconnecting the lines to the master cylinder after bench bleeding gets bled out when you bleed the brakes at the wheels. The fluid normally just passes through the ABS control unit. As long as the ABS doesn't activate while there is air in the lines the valves won't open and it won't pull in any air. Like I mentioned before, I just put a new master cylinder on my ZJ and it bled fine. Brake pedal is great. ABS works fine. No need for the DRB.
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