Brake Problems, Help

[ron_toolman]

Hi ....... had a busted line, replaced that and also a new caliper . I blead all lines and master cylinder, also lines going to ABS module no air at all ..... full pedal. Then when started the pedal drops to the floor as if it's full of air. replaced master cylinder, good uded one, same thing. Now they tell me it's the booster, but I tool the two lines off the master and made short 3" crimped ends and re-started vehicle, pedal now does not go to floor. So that would tell me the booster is ok ? ........ Haynes book says if the master ever gets are in it, it has to be hooked to a scanner to bleed all lines properly ..... called ford dealer and they say nope ... bleed as you usual. Any ideas ? ........ Appreciate any help.

 

[NHale623]

What year truck is this?

 

[ron_toolman]

What year truck is this?

93 Explorer Ltd.

 

[gijoecam]

Of course the pedal won't go to the floor with the lines crimped off!! The fluid in the master cylinder has no place to go, so the pedal can't go down. Doesn't mean the booster isn't bad.

The only things that can force the pedal to the floor with the engine running are your foot and the booster, and your foot can't do it without the booster anyways.

It's possible that the clearance between the push-rod and the booster needs to be adjusted. I forget what the spec is for the clearance, but they should not be touching IIRC.

-Joe

 

[NHale623]

Regarding the special bleed procedure, that's for '96 and earlier 4WABS systems. That procedure is only required if air enters the hydraulic control unit, not the master cylinder.

If your truck as RABS (Rear ABS), it does not apply and your Ford dealer is correct.

 

[NHale623]

This thread may also help.

http://www.explorerforum.com/forums/showthread.php?t=169401

There are a couple of threads that discuss the rod length that gijoecam mentioned, you might want to do a search and see if you can find them.

 

[ron_toolman]

Regarding the special bleed procedure, that's for '96 and earlier 4WABS systems. That procedure is only required if air enters the hydraulic control unit, not the master cylinder.

If your truck as RABS (Rear ABS), it does not apply and your Ford dealer is correct.

Still not working ...... this is a 93 with rear ABS, tok master off again today and bled. Opened lines at Module and allowed to flow out. I blocked off lines to front and have a full pedal when started, so I try blocking each of the two lines coming from the module, when I do this and start it I loose my brakes ..... straight to the floor ....... So would that be the Booster ? ..... I removed the vacuum line from booster when not running and it sucks air in, the check vave is ok....... no leaks for sure. Where is the bug in my system. Thanks .

 

[CDW6212R]

Curious, I am also thinking that those didn't take specail procedures for having air in the ABS. I have my old 93 master cylinder, and I think that the booster is out back also. How far away are you?

 

[ron_toolman]

Curious, I am also thinking that those didn't take specail procedures for having air in the ABS. I have my old 93 master cylinder, and I think that the booster is out back also. How far away are you?

I'm from N.S. Canada ..... probably too far from where your at. I give up for the weekend. I called another repair shop and he seems to think that the 93 doesn't need the scanner tool .... I guess I'll just have to take it somewhere and let them play with it. I think it's all in that module unit, why would the booster decide to go at the same time I had a busted line. Ohwell, see what happens .... thanks to all who replied.

 

[gijoecam]

The booster has nothing whatsoever to do with the ABS, and the ABS can absolutely not move the brake pedal to the floor. It's just not possible.

Just thinking about my previous statment WRT the push-rod length, that can't be the problem either. If the push-rod was too long, it would simply either cause the brakes to drag, or result in excessive pedal travel before it actuated the brakes. It would not cause the pedal to instantly shoot to the floor upon applying vacuum to the booster.

I'm 100% sure you got a bad booster. Call the auto parts store where you got that one and tell them what it's doing. I'm sure they will concur.

edit: Just saw that it was the original booster.... to answer your question, yes, it's mere coincidence. It's possible that while bleeding the brakes, the valve in the booster was somehow damaged and is stuck. Replace the booster and your problem will be solved.

-Joe

 

[ron_toolman]

The booster has nothing whatsoever to do with the ABS, and the ABS can absolutely not move the brake pedal to the floor. It's just not possible.

Just thinking about my previous statment WRT the push-rod length, that can't be the problem either. If the push-rod was too long, it would simply either cause the brakes to drag, or result in excessive pedal travel before it actuated the brakes. It would not cause the pedal to instantly shoot to the floor upon applying vacuum to the booster.

I'm 100% sure you got a bad booster. Call the auto parts store where you got that one and tell them what it's doing. I'm sure they will concur.

edit: Just saw that it was the original booster.... to answer your question, yes, it's mere coincidence. It's possible that while bleeding the brakes, the valve in the booster was somehow damaged and is stuck. Replace the booster and your problem will be solved.

-Joe

Thanks for your reply ....... you say the valve may be damaged in the booster ? .... What valve.... I really don't know how they work except that it is vacuumed to make it easier to apply brakes. While I had the Master off I pushed the pedal while my buddy was holding a stick against it, then started the engine and tried the same thing, no way could he hold it back. Just something we thought we'd try ..... so you think it's the booster eh ... please explain a little what is happening inside that booster. Thanks again.

Just thinking of what you said in one of your replies .... didn't you say the that ABS module only need to be scanned if it were a 96 or earlier model ? ..... I'm confused now .... the book keeps saying if the master goes dry the HVC has to be scanned to get all air out .....

 

[gijoecam]

Thanks for your reply ....... you say the valve may be damaged in the booster ? .... What valve.... I really don't know how they work except that it is vacuumed to make it easier to apply brakes. While I had the Master off I pushed the pedal while my buddy was holding a stick against it, then started the engine and tried the same thing, no way could he hold it back. Just something we thought we'd try ..... so you think it's the booster eh ... please explain a little what is happening inside that booster. Thanks again.

Just thinking of what you said in one of your replies .... didn't you say the that ABS module only need to be scanned if it were a 96 or earlier model ? ..... I'm confused now .... the book keeps saying if the master goes dry the HVC has to be scanned to get all air out .....

From Wikipedia:

Many modern hydraulic brake systems have a "Vacuum-assist" module which is attached between the master cylinder and the brake pedal and multiplies the braking force applied. Typically described as a vacuum booster, these units consist of a hollow housing with a moveable rubber diaphragm across the center, creating two chambers. When attached to the low-pressure portion of the throttle body or intake manifold of the engine, the pressure in both chambers of the unit is lowered. The equilibrium created by the low pressure in both chambers keeps the diaphragm from moving until the brake pedal is depressed. A return spring keeps the diaphragm in the starting position until the brake pedal is applied. When the brake pedal is applied, the movement opens an air valve which lets in atmospheric pressure air to one chamber of the booster. Since the pressure becomes higher in one chamber, the diaphragm moves toward the lower pressure chamber with a force created by the area of the diaphragm and the differential pressure. This force, in addition to the driver's foot force, pushes on the master cylinder piston. The diaphragm will stop moving when the forces on both sides of the chamber reach equilibrium. This can be caused by either the air valve closing (due to the pedal apply stopping) or if "runout" is reached. Runout occurs when the pressure in one chamber reaches atomospheric pressure and no additional force can be generated by the now stagnant differential pressure. After the runout point is reached, only the driver's foot force can be used to further apply the master cylinder piston.

There's more info here:

http://auto.howstuffworks.com/power-brake.htm

At one point in time, I saw a good cutaway... I wish I could find it again.... Bingo!

I suspect it's the internal valve in the booster that controls the vacuum. It's stuck in the open position, causing the engine vacuum to pull the pedal down and apply the brakes. It's a simple unit.

As for the bleeding issue, I can't say for sure on a 93. I honestly don't know. (It wasn't me that posted about it) Best bet would be a factory shop manual.

Your latest test just reinforced the fact that you have a bad booster. Replace it and all your problems will disappear. You don't even need to bleed the brakes again.

 

[NHale623]

Just thinking of what you said in one of your replies .... didn't you say the that ABS module only need to be scanned if it were a 96 or earlier model ? ..... I'm confused now .... the book keeps saying if the master goes dry the HVC has to be scanned to get all air out .....

That isn't what the book says. Like I posted earlier

Regarding the special bleed procedure, that's for '96 and earlier 4WABS systems. That procedure is only required if air enters the hydraulic control unit, not the master cylinder.

If your truck as RABS (Rear ABS), it does not apply and your Ford dealer is correct.

You said you had RABS.

 

[ron_toolman]

That isn't what the book says. Like I posted earlier



You said you had RABS.

Hi ...... My Haynes book (# 2021 - 91 thru 95 Explorer, Chapter 9, section 10 ) it explains if air gets into the master or Hydraulic unit you need a special scan tool. So lets assume air did get into the master and (HUC) What I don't understand is when started and the pedal goes to the floor, where is the rod from the pedal going, it's a solid rod is it not ? through the booster into master cylinder .... it must be still pushing on the master cylinder which tells me there's still air trapped somewhere. It's a 3 line ABS system Front L and R .and One line to rear. If I plug front line from Master the rear works while started, if I block rear line then I have no front brakes. Maybe I'm explaining it all wrong , but i don't wanna buy a booster to find out that that's not the trouble. Just double checking ..... thanks.

 

[gijoecam]

Hi ...... My Haynes book (# 2021 - 91 thru 95 Explorer, Chapter 9, section 10 ) it explains if air gets into the master or Hydraulic unit you need a special scan tool. So lets assume air did get into the master and (HUC)

I've blen mine successfully without the tool for years and never had a problem. The tool gets all the air out of the HCU. However, teh HCU is not causing your pedal to drop to the floor when you start the engine. I don't know how many other ways I can say it.

What I don't understand is when started and the pedal goes to the floor, where is the rod from the pedal going, it's a solid rod is it not ?

No.

through the booster into master cylinder .... it must be still pushing on the master cylinder which tells me there's still air trapped somewhere. It's a 3 line ABS system Front L and R .and One line to rear. If I plug front line from Master the rear works while started, if I block rear line then I have no front brakes. Maybe I'm explaining it all wrong , but i don't wanna buy a booster to find out that that's not the trouble. Just double checking ..... thanks.

THe booster is tremendously strong. When the valve sticks like it has in your case, the force applied is far, far greater than you or I could ever apply directly to the master cylinder with our feet. The booster is about 10" in diameter, which gives you a piston roughly 12" in diameter, with an are of about 110 square inches. Just two PSI of vacuum against it, and you're going to get 220 lbs of force on the master cylinder push-rod. The engine will provide between 7 and 14 psi of vacuum at idle. You do the math: The booster is hella-strong.

You verified it is the booster when you disconnected the vacuum line going to it. With no vacuum applied to the booster, the brake pedal is firm, right? Plug the vacuum line back in and the pedal falls to the floor, right? By testing that, you've isolated it to the booster and nothing else. No amount of air in the lines will cause the pedal to fall to the floor when you start the engine. In fact, you could drain every bit of fluid out of the entire brake system, and the pedal should stay right where it's at when you start the vehicle.

I don't know how many other ways I can explain it. You're dealing with two completely isolated and unrelated systems. (The booster and the ABS) No amount of air in the ABS system will cause the booster to do what it's doing. You have a bad booster, plain and simple.

 

[ron_toolman]

I've blen mine successfully without the tool for years and never had a problem. The tool gets all the air out of the HCU. However, teh HCU is not causing your pedal to drop to the floor when you start the engine. I don't know how many other ways I can say it.


No.



THe booster is tremendously strong. When the valve sticks like it has in your case, the force applied is far, far greater than you or I could ever apply directly to the master cylinder with our feet. The booster is about 10" in diameter, which gives you a piston roughly 12" in diameter, with an are of about 110 square inches. Just two PSI of vacuum against it, and you're going to get 220 lbs of force on the master cylinder push-rod. The engine will provide between 7 and 14 psi of vacuum at idle. You do the math: The booster is hella-strong.

You verified it is the booster when you disconnected the vacuum line going to it. With no vacuum applied to the booster, the brake pedal is firm, right? Plug the vacuum line back in and the pedal falls to the floor, right? By testing that, you've isolated it to the booster and nothing else. No amount of air in the lines will cause the pedal to fall to the floor when you start the engine. In fact, you could drain every bit of fluid out of the entire brake system, and the pedal should stay right where it's at when you start the vehicle.

I don't know how many other ways I can explain it. You're dealing with two completely isolated and unrelated systems. (The booster and the ABS) No amount of air in the ABS system will cause the booster to do what it's doing. You have a bad booster, plain and simple.

Well hate say but it's not the Booster, just finished re-placing it and same thing .... start engine apply brakes and pedal to the metal. So I guess it is all in the ABS module, that's the only thing I haven't changed or had checked, no good replacing it if you need a scanner to bleed the system. Well I have to quit for the day ... too hard on the head. ...

 

[gijoecam]

Well hate say but it's not the Booster, just finished re-placing it and same thing .... start engine apply brakes and pedal to the metal. So I guess it is all in the ABS module, that's the only thing I haven't changed or had checked, no good replacing it if you need a scanner to bleed the system. Well I have to quit for the day ... too hard on the head. ...

I don't understand how it's possible.... [shakes head] It just doesn't add up....

Where's the fluid going??? that doesn't make any sense... if it was the ABS, it would happen just by turning the key on. The engine would not have to be running. To isolate it, yank the connector off the ABS module and try it. If it's truly the ABS causing it, that will isolate it and the brakes should work normally.

OK, let's look at it from another perspective. Let's say for argument's sake that that ABS is somehow drawing the pedal down. Where's the fluid going? Why isn't it sucking the fluid out of the reservoir to start with? when the brakes aren't actuated, the fluid in the lines is open to the reservoir via the compensating ports. (that's where the fluid flows through when you compress the calipers when changing brake pads) That would also mean that when the ABS doing whatever it's doing, it's trying to suck the fluid out of the brake lines. When it tries to suck the fluid out of the brake lines, if the pedal is depressed past the compensating ports, it forms a vacuum and sucks the push-rod down. So, why isn't it sucking the reservoir dry when the brake pedal isn't depressed?

There is definately still a problem there, but I'm still confident it's not with the ABS. I asked earlier and never recieved a response: Did you ever adjust the push-rod to booster clearance as I mentioned above? I realize I initially steered you away from it, but maybe it's still a possibility?

Also, if you disconnect and cap the vacuum line to the booster, does the problem still occur? If not, again, it points to the booster, not the ABS.

-Joe

 

[Mike_27]

I'm wondering if the master cylinder was bled correctly. This sounds more like the front section of the master cylinder has air in it.

Mike

 

[ron_toolman]

I don't understand how it's possible.... [shakes head] It just doesn't add up....

Where's the fluid going??? that doesn't make any sense... if it was the ABS, it would happen just by turning the key on. The engine would not have to be running. To isolate it, yank the connector off the ABS module and try it. If it's truly the ABS causing it, that will isolate it and the brakes should work normally.

OK, let's look at it from another perspective. Let's say for argument's sake that that ABS is somehow drawing the pedal down. Where's the fluid going? Why isn't it sucking the fluid out of the reservoir to start with? when the brakes aren't actuated, the fluid in the lines is open to the reservoir via the compensating ports. (that's where the fluid flows through when you compress the calipers when changing brake pads) That would also mean that when the ABS doing whatever it's doing, it's trying to suck the fluid out of the brake lines. When it tries to suck the fluid out of the brake lines, if the pedal is depressed past the compensating ports, it forms a vacuum and sucks the push-rod down. So, why isn't it sucking the reservoir dry when the brake pedal isn't depressed?

There is definately still a problem there, but I'm still confident it's not with the ABS. I asked earlier and never recieved a response: Did you ever adjust the push-rod to booster clearance as I mentioned above? I realize I initially steered you away from it, but maybe it's still a possibility?

Also, if you disconnect and cap the vacuum line to the booster, does the problem still occur? If not, again, it points to the booster, not the ABS.

-Joe

Back at it again ..... Yes I checked the rod from booster clearence and it's correct. I plugged the vacuum line and the problem goes away, good pedal but no more power brakes. Since changing the Booster the pedal does seem a little different, like spongy .... so I re- bled all the lines again and have full pedal when not running, but before the engine even starts with your foot on the brake it will go to the floor, pump a few times and I have a little brake. So where the fluid is going I don't know. If there's air still in the system shouldn't I still have some kind of brakes. Oh ... also disconnected the module so when starting it wouldn't have power. Anymore Ideas ?

Something Else I tried today ...

pinched all flex lines (3), started engine and removed clamp from rear line, still full pedal .... when I un-clamp either front line the pedal will go to the floor. also jacked up one front wheel at a time .... spin wheel and touch pedal slight and stops, press hard and goes to floor .... does this help .... it's like the calipers are leaking, but they're not. Now it's like the master is working on the rear, but bypassing and no pressure to the front. ?

 

[Ostereo]

It's been a month: how'd this wind up?
I'm having a similar problem.

Thanks,
Andy