bypassing RABS
Cargo Master
Joined: Mar 2002
Posts: 3,132
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From: W (BY GOD) V
Did you bleed the MC after running it dry (either bench or on truck isolated from system) before bleeding the entire system?
Let me correct myself. Bleed preferably on bench to ensure MC is level and stays level. On vehicle only if on level floor.
Let me correct myself. Bleed preferably on bench to ensure MC is level and stays level. On vehicle only if on level floor.
Cargo Master
Joined: Mar 2002
Posts: 3,132
Likes: 217
From: W (BY GOD) V
OK, these are dueling piston calipers, right? The cheapest thing you could buy?
Is the bleeder screw(s) pointing up @ install? If not totally pointed up air can be trapped in the caliper reservoir. A piston(s) may also be sticking in the caliper bore or there is still air in the system either in the caliper itself or the MC. Remember, if the MC is not completely bled, it will shoot trapped air into the entire system.
Of course the rear shoes have to be adjusted properly also. Most pedal height comes from rear shoe adjustment.
It's all I can think of just simply servicing the front brakes as you did.
Is the bleeder screw(s) pointing up @ install? If not totally pointed up air can be trapped in the caliper reservoir. A piston(s) may also be sticking in the caliper bore or there is still air in the system either in the caliper itself or the MC. Remember, if the MC is not completely bled, it will shoot trapped air into the entire system.
Of course the rear shoes have to be adjusted properly also. Most pedal height comes from rear shoe adjustment.
It's all I can think of just simply servicing the front brakes as you did.
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Senior User
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after running the system dry i bled,and bled and bled.decided to go ahead and just buy another MC thinking maybe i smashed something in it during it going dry.bench bled the new unit until solid .installed it and then did a on truck bleed with the MC isolated and rear jacked up to level it out.bled the entire system i can remember how many times with no air present in the system.adjusted the rear and they lock up for a split second on hard pedal and then the ABS seems to kick in which is telling me that is fine at this point....i am losing my mind with this thing...
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Senior User
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lmao...nope... did that once before never will again
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ok...worked most of he morning from back to front to back again.looked at thr rear cylinders...no leaks,adjusted the rear brake...again,bledthe rear lines,bled the rear abs module,bled the fronts and see no leaks or air any where.went back to isolating....i have a soft pedal when i cut off the rear brake lines.i already bypassed the RABS this morning and it made no difference.crimped off the line to the RF calipers and BAM now i got a hard pedal!!WTH?so is it in that caliper as i actually hear a drag coming from that side a little?how could the caliper be bad when i didnt smash it back to install the pads and this is the second pair of front calipers!!
Cargo Master
Joined: Mar 2002
Posts: 3,132
Likes: 217
From: W (BY GOD) V
ok...worked most of he morning from back to front to back again.looked at thr rear cylinders...no leaks,adjusted the rear brake...again,bled the rear lines,bled the rear abs module,bled the fronts and see no leaks or air any where.went back to isolating....i have a soft pedal when i cut off the rear brake lines
...i already bypassed the RABS this morning and it made no difference. crimped off the line to the RF calipers and BAM now i got a hard pedal!! WTH? so is it in that caliper as i actually hear a drag coming from that side a little?how could the caliper be bad when i didnt smash it back to install the pads and this is the second pair of front calipers!!
New hoses? If old hose one could be swelling.
If you had front brake dragging noise @ or after install, it may have a seized piston(s) or less likely frozen sliding pins. When you installed the calipers, did you happen to notice if the pistons themselves were phenolic or stainless steel?
Also, when you bleed the rear circuit, shouldn't you bleed the RABS valve and then the rear cylinders?
I am really hoping you find the solution (actually you will) as it has my curiosity up. Also, those valves are not cheap.
OH! Where are you getting the calipers?
Cargo Master
Joined: Mar 2002
Posts: 3,132
Likes: 217
From: W (BY GOD) V
(I am adding stuff to this post as I go. Hope it is not confusing)
If all else fails (after caliper diag)-
TSB Article 96-25-19 - Shown Below
It seems the aftermarket is aware of this problem also-
CARDONE- http://my.cardone.com/techdocs/PT%2010-0008.pdf
I also found a reference to a ZERO LOSS BOOSTER for the 94-97 model years. I will try and find that info also.
Here- https://www.ford-trucks.com/forums/8...ake-pedal.html
EDIT! - Note- Diesel-powered trucks P/N F5TZ-2005-CA (Motorcraft BRB 22) is not a service
replacement, it must be ordered by the part number specifically, not the vehicle application.
Source- PowerStroke bulletins and parts
TECH ARTICLE HERE- https://www.oilburners.net/articles/...dalproblem.pdf
If all else fails (after caliper diag)-
TSB Article 96-25-19 - Shown Below
It seems the aftermarket is aware of this problem also-
CARDONE- http://my.cardone.com/techdocs/PT%2010-0008.pdf
I also found a reference to a ZERO LOSS BOOSTER for the 94-97 model years. I will try and find that info also.
Here- https://www.ford-trucks.com/forums/8...ake-pedal.html
1997 and earlier diesel trucks equiped with vacuum power brakes--Low/creeping pedal:
Many owners have complained of a low or creeping brake pedal on their trucks, often mistaken for a bad master cylinder or Rear ABS valve. If the condition occurs after the vehicle has come to a stop, and no other brake concerns are found, (worn or out-of-adjusted brakes, cocked pads, or hydraulic problems) the condition is normal and the result of the vacuum pump replenishing the vacuum inside the power booster. Ford has developed a Zero-Loss Travel brake booster to correct this condition if the customer finds it unacceptable. This part is only for use on diesel-equiped trucks--P/N F5TZ-2005-CA--and is not a service replacement; it must be ordered by the part number, not vehicle application.
This condition is similar to the low brake pedal concern on all 1995 F-series that required a larger-diameter master cylinder
Many owners have complained of a low or creeping brake pedal on their trucks, often mistaken for a bad master cylinder or Rear ABS valve. If the condition occurs after the vehicle has come to a stop, and no other brake concerns are found, (worn or out-of-adjusted brakes, cocked pads, or hydraulic problems) the condition is normal and the result of the vacuum pump replenishing the vacuum inside the power booster. Ford has developed a Zero-Loss Travel brake booster to correct this condition if the customer finds it unacceptable. This part is only for use on diesel-equiped trucks--P/N F5TZ-2005-CA--and is not a service replacement; it must be ordered by the part number, not vehicle application.
This condition is similar to the low brake pedal concern on all 1995 F-series that required a larger-diameter master cylinder
replacement, it must be ordered by the part number specifically, not the vehicle application.
Source- PowerStroke bulletins and parts
TECH ARTICLE HERE- https://www.oilburners.net/articles/...dalproblem.pdf
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Senior User
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When you say you crimped off the line to the RF calipers do you mean you crimped off both calipers (the front brake hoses) at one time or did you do either separately? If you do them separately, it will ID the bad side/caliper.
YES CRIMPED WITH FLAT VISE GRIPS.I JUST CRIMPED THE rf CALIPER
New hoses? If old hose one could be swelling.
checked for swelling at all soft lines.i saw no swelling.
If you had front brake dragging noise @ or after install, it may have a seized piston(s) or less likely frozen sliding pins. When you installed the calipers, did you happen to notice if the pistons themselves were phenolic or stainless steel?
i did not look sorry.
Also, when you bleed the rear circuit, shouldn't you bleed the RABS valve and then the rear cylinders?
i thought i was doing it the right way by what i have read up on??
I am really hoping you find the solution (actually you will) as it has my curiosity up. Also, those valves are not cheap.
OH! Where are you getting the calipers?
YES CRIMPED WITH FLAT VISE GRIPS.I JUST CRIMPED THE rf CALIPER
New hoses? If old hose one could be swelling.
checked for swelling at all soft lines.i saw no swelling.
If you had front brake dragging noise @ or after install, it may have a seized piston(s) or less likely frozen sliding pins. When you installed the calipers, did you happen to notice if the pistons themselves were phenolic or stainless steel?
i did not look sorry.
Also, when you bleed the rear circuit, shouldn't you bleed the RABS valve and then the rear cylinders?
i thought i was doing it the right way by what i have read up on??
I am really hoping you find the solution (actually you will) as it has my curiosity up. Also, those valves are not cheap.
OH! Where are you getting the calipers?
Cargo Master
Joined: Mar 2002
Posts: 3,132
Likes: 217
From: W (BY GOD) V
You have a bad caliper or possibly brake hose IMO...
The pad(s) is dragging as you have experienced noise.
Phenolic pistons will distort/fail/disintegrate due to brake heat and stick in the bore. This heat is also transferred to the caliper body and into the fluid reservoir causing the rubber hose to fail over time. The hose may be swelling not allowing full pressure to the piston(s) OR/AND the rubber has failed inside and not allowing full fluid pressure release to the MC.
This was a common problem back in the late seventies. I had no idea that plastic pistons were still being used (learn something everyday).
When you get a properly operating caliper(s) and you still have the low pedal, refer to the TSB's.
The pad(s) is dragging as you have experienced noise.
Phenolic pistons will distort/fail/disintegrate due to brake heat and stick in the bore. This heat is also transferred to the caliper body and into the fluid reservoir causing the rubber hose to fail over time. The hose may be swelling not allowing full pressure to the piston(s) OR/AND the rubber has failed inside and not allowing full fluid pressure release to the MC.
This was a common problem back in the late seventies. I had no idea that plastic pistons were still being used (learn something everyday).
When you get a properly operating caliper(s) and you still have the low pedal, refer to the TSB's.
Thread Starter
|
Senior User
Joined: Sep 2012
Posts: 193
Likes: 0
You have a bad caliper or possibly brake hose IMO...
The pad(s) is dragging as you have experienced noise.
Phenolic pistons will distort/fail/disintegrate due to brake heat and stick in the bore. This heat is also transferred to the caliper body and into the fluid reservoir causing the rubber hose to fail over time. The hose may be swelling not allowing full pressure to the piston(s) OR/AND the rubber has failed inside and not allowing full fluid pressure release to the MC.
This was a common problem back in the late seventies. I had no idea that plastic pistons were still being used (learn something everyday).
When you get a properly operating caliper(s) and you still have the low pedal, refer to the TSB's.
The pad(s) is dragging as you have experienced noise.
Phenolic pistons will distort/fail/disintegrate due to brake heat and stick in the bore. This heat is also transferred to the caliper body and into the fluid reservoir causing the rubber hose to fail over time. The hose may be swelling not allowing full pressure to the piston(s) OR/AND the rubber has failed inside and not allowing full fluid pressure release to the MC.
This was a common problem back in the late seventies. I had no idea that plastic pistons were still being used (learn something everyday).
When you get a properly operating caliper(s) and you still have the low pedal, refer to the TSB's.