Brake questions

[Dbow20]

Removing the master cylinder and bench bleeding it accomplishes two things only: it assures the mechanic that there will be a ***minimum*** of air in the system when the master cylinder is installed and that the brake fluid in that cylinder will allow the bleeding process to start without reintroducing air into the system. In other words, the master cylinder has to be filled with brake fluid in order for the brake pedal to have any effect. Thus removing the master cylinder at this point accomplishes nothing. It's important to realize that any air anywhere in the brake system is a problem and you get rid of it by bleeding in the proper sequence and making sure at the same time that you never deplete the fluid in the master cylinder. If the master cylinder is removed, you will introduce air in the brake line when you re-install the cylinder. That air has to move the full length of the tubing and exit through a bleeder. There are no shortcuts.

I understand I will have to bleed each caliper after removing the master cylinder.
If air was introduced to the master cylinder will I be able to remove that air without removing it and bleeding it on the bench? It’s my understanding that it can become trapped in the master cylinder because of the angle the MC sits at allowing the air to rise and not be flushed out.

 

[hotrod45]

I'd like to see something in a manual regarding the possibility of a closed hydraulic system having a flaw of that magnitude. I have been away from brake work for a long time, so I'm not "up" on all the details. However, I have looked at a few things and have noticed that some ABS devices also have a bleeder screw in addition to the bleeder on the caliper. You really need to get your hands on a proper manual. Rumors that somebody heard from somebody who did a brake job once involving "trapped air" aren't the right way to go. ***If*** you don't bleed the brakes in the proper sequence (and bleed sufficiently to get the air out), you will run the risk of leaving air in the system, not because it's trapped, but because you did not let it out by following the proper procedure. It's mechanics, not mystery.

 

[hotrod45]

Here is an excerpt from popularmechanics.com. Note the last part, starting with "By the way":
Your ABS light is on. Now what? First, be sure it really is the ABS light and not the light that indicates an issue with your normal service brakes. If you do have a conventional brake issue, like low pedal or grinding noises, this is the wrong Saturday Mechanic for you. Be sure your brakes have adequate lining life, aren't frozen up and are completely free of air. By the way, if you ever need to replace your brake fluid, try as hard as you can to avoid getting air into the ABS controller. It's difficult to bleed, and many require the use of a scan tool to bleed at all. (The scan tool has a function that cycles the pump and valves to move air out of internal passages that can't be bled properly otherwise.)////end quote///

Different systems have different procedures. I don't know how detailed Haynes Manuals might be, but it might be worth checking. I'd get some dependable info on your specific year/model. BTW, the first rule of mechanics is "Don't touch anything you don't have to touch." Hence, I recommend not fooling with the master cylinder until you know that it is required.

 

[Dbow20]

Here is an excerpt from popularmechanics.com. Note the last part, starting with "By the way":
Your ABS light is on. Now what? First, be sure it really is the ABS light and not the light that indicates an issue with your normal service brakes. If you do have a conventional brake issue, like low pedal or grinding noises, this is the wrong Saturday Mechanic for you. Be sure your brakes have adequate lining life, aren't frozen up and are completely free of air. By the way, if you ever need to replace your brake fluid, try as hard as you can to avoid getting air into the ABS controller. It's difficult to bleed, and many require the use of a scan tool to bleed at all. (The scan tool has a function that cycles the pump and valves to move air out of internal passages that can't be bled properly otherwise.)////end quote///

Different systems have different procedures. I don't know how detailed Haynes Manuals might be, but it might be worth checking. I'd get some dependable info on your specific year/model. BTW, the first rule of mechanics is "Don't touch anything you don't have to touch." Hence, I recommend not fooling with the master cylinder until you know that it is required.

Thanks for the help. The part you say to pay attention to says “try as hard you can to avoid getting air into the ABS controller.” During a normal flush how would air enter the ABS controller? It’s possible I have air in the ABS but I do not know how this would have happened.

Up to this point I have been convinced it’s air in the system based on everyone’s recommendations and opinions but I am starting to think it may be something else. I was careful during the fluid flush and I followed the correct bleeding procedure. And after several bleeds with no air bubbles at all I think the air is out of the system.
I am going to inspect all calipers and slide pins for a stuck component. New brake pads are in the mail so I will check everything when I change the pads out.

 

[madtrucker2016]

Thanks for all the replies.
I guess it is possible that the speed bleeder screws I have are the wrong part but I don’t think so. I checked the size of the stock screw and ordered the speed bleeder in the same size.
I am going to pull the MC and bench bleed it to see if that is where the air is. Maybe during the fluid flush I let it get to low. If that doesn’t solve the issue I will go back to the old bleeder screw to see if that is where the problem is.

If I was you what is the common thing to do is remove those dumb bleeders and put back the OEM ones on the truck and hope you didn't mess the tread up on the parts they go into.

 

[hotrod45]

Thanks for the help. The part you say to pay attention to says “try as hard you can to avoid getting air into the ABS controller.” During a normal flush how would air enter the ABS controller? QUOTE]
The short answer is "I don't know." Another thing I don't know is whether there is a block that distributes pressure front/rear in a divided system and whether there is a piston that needs to be centered. If you have a proper manual, all of that would be laid out for you, along with the step-by-step procedure for either preventing a problem or for correcting it.

 

[Dbow20]

If I was you what is the common thing to do is remove those dumb bleeders and put back the OEM ones on the truck and hope you didn't mess the tread up on the parts they go into.

Using a screw with the correct thread pitch will not screw up the threads on the caliper. If it comes down to it I will go back to the OEM bleeder screws and see if that’s what’s causing the issue.

 

[Dodge 1500 4X4]

Having worn brake pads will cause a partial low pedal, what condition are your sliders in, I assume you have disc brakes on all 4 wheels, and what condition are your brake hoses in if you have a weak hose your brakes wont release, have you tried gravity bleeding thats opening up all the bleeders and let the master cyl supply fluid to the wheels. hope it all works out for you.

 

[Dbow20]

Having worn brake pads will cause a partial low pedal, what condition are your sliders in, I assume you have disc brakes on all 4 wheels, and what condition are your brake hoses in if you have a weak hose your brakes wont release, have you tried gravity bleeding thats opening up all the bleeders and let the master cyl supply fluid to the wheels. hope it all works out for you.

Thanks for the advice. I haven’t tried gravity bleeding yet. I did use alfaobd to bleed the abs unit and that removed air form the system. However, I still have the same problem when the truck is off. No brake pedal.
The pads are worn on the rear but not close to end of life for them. I have replacements in the mail though so I’ll change them to see if that’s the issue.

 

[hotrod45]

At what point does the brake pedal recover? If you put the ignition in the "run" position, does the pedal recover? If not, is it immediate on starting the engine?

 

[Dbow20]

At what point does the brake pedal recover? If you put the ignition in the "run" position, does the pedal recover? If not, is it immediate on starting the engine?

It does not recover when set to run. It recovers immediately on engine start.

 

[hotrod45]

Are all the vacuum lines in place?

 

[Jebb]

Thanks for the help. The part you say to pay attention to says “try as hard you can to avoid getting air into the ABS controller.” During a normal flush how would air enter the ABS controller? It’s possible I have air in the ABS but I do not know how this would have happened.

Up to this point I have been convinced it’s air in the system based on everyone’s recommendations and opinions but I am starting to think it may be something else. I was careful during the fluid flush and I followed the correct bleeding procedure. And after several bleeds with no air bubbles at all I think the air is out of the system.
I am going to inspect all calipers and slide pins for a stuck component. New brake pads are in the mail so I will check everything when I change the pads out.

My truck only has 7000 miles on it, has never been messed with, and has this same problem you have. I have a long post about it here: https://www.ramforum.com/threads/wh...rakes-not-stopping.128905/page-6#post-2148965

The dealer had it for a WEEK - flushed the fluid and bled it with their fancy automatic machine - still no good. Going to a different dealer on Wednesday to try again.

IMO, any brake system that is this hard to bleed is a BAD DESIGN. My father-in-law's 2015 Jeep Grand Cherokee also feels like this. I'm wondering how many people are driving around with air in their brakes and won't know it until they need to do a panic stop and the pedal goes to the floor. In my case it seems to have come from the factory this way.

 

[DodgeDude99]

The ABS module tends to be a PITA to bleed and needs a scan tool of such that can trigger the motor in it.

If you were just flushing the system to get new fluid in it, it doesn’t matter where you start, the only time it does if you replace the MC, ABS, or run something dry.

If you replace a caliper, you wouldn’t bleed the other 3 calipers.

 

[Yukonbill]

Ok, I went ahead and tried bleeding them again and it is slightly better but still more pedal travel than I think there should be. There is no fluid leaking so I know it must be air in the system just stuck somewhere or maybe a bad master cylinder? How do I diagnose If it’s a bad master cylinder?

I have new pads on the way so I will also install those When they arrive and see if there is any change.

With ABS, the hydraulic brake unit needs to pulsate while bleeding in order to get the air out. Most require ability to hook up to shop computer. There are aftermarket tools, but cheaper to just have a dealer bleed the system. Keep us updated.

 

[patmanz28]

Did you replace any brakes? I had a bolt I either didn't tighten correctly or the thread locker didn't take, and it backed partially out and it made the pedal spongy as all heck. I could not figure it out, and so I just started all over. I started to pull all the bolts I messed with, and voila the third bolt I checked was partially loose. Tightened it, and hard pedal again.

 

[Dbow20]

Been busy the last few days but had time today to do more work on the brakes. I replaced all rotors and pads. One caliper slide pin was seized so I removed it and replaced with a new pin. Greased everything and bolted all back together to torque specs. Bled the system yet again. That’s about three quarts through the system bleeding. I even went back to the old bleeder screws just to eliminate those as the problem as some thought.

Braking performance is greatly improved in the short test drive I took but... upon engine shut down brake pedal went spongy to the floor again. Bummer.

I know that the ABS requires a scan tool. I used AlfaOBD and bled the ABS. So I have that box checked.

I have a motive power bleeder that should be here tomorrow so I will try that as well as using AlfaOBD again to bled the abs again. I just don’t think it’s air.

It could be a vacuum issue but all vacuum lines are in place and I need to read more about troubleshooting that.

Thanks for all the replies and please let me know if you have any ideas for me to try.

 

[Dbow20]

My truck only has 7000 miles on it, has never been messed with, and has this same problem you have. I have a long post about it here: https://www.ramforum.com/threads/wh...rakes-not-stopping.128905/page-6#post-2148965

The dealer had it for a WEEK - flushed the fluid and bled it with their fancy automatic machine - still no good. Going to a different dealer on Wednesday to try again.

IMO, any brake system that is this hard to bleed is a BAD DESIGN. My father-in-law's 2015 Jeep Grand Cherokee also feels like this. I'm wondering how many people are driving around with air in their brakes and won't know it until they need to do a panic stop and the pedal goes to the floor. In my case it seems to have come from the factory this way.

thanks for the input but I don’t think we have the same issue. Mine has never had a problem stopping and pedal is firm with the engine on. Only problem I have is soft pedal when the engine is shut off.

 

[hotrod45]

I am not up to speed on what sort of split system your truck has, but that would be something I would want to check. Do you have any warnings showing up on the dash that involve the brakes?

 

[Dbow20]

I am not up to speed on what sort of split system your truck has, but that would be something I would want to check. Do you have any warnings showing up on the dash that involve the brakes?

No warnings, lights, or codes.