CV antilock brakes
rlauzze
08-14-2005, 09:45 AM
After about 100 miles of trying, 93 Crown Vic started vibrating severely again. (See thread about 6 down.) Car vibrates severely after warmed up, worse when brakes applied (like tire out of balance bad or loose lug nuts). Immediately pulled antilock brake fuze (mechanic thinks hydralulic control unit pulsing without a command). No change. Immediately drove home (feeling like brakes dragging). Upon jacking up car, front wheel brakes locked, rears spin freely. Again pulled antilock fuze in dash, then antilock control fuze and antilock pump fuze in power distribution under hood. No change. Could not spin either front wheel - and very hot (from dragging?). Working on drivers side, opening bleeder valve DID NOT release wheel (engine on, engine off, fuzes in or out). Was careful not to let air enter system, but could not get brake to release. Finally used 'C' clamp to release caliper - then seemed to work normally. This doesn't make sense to me - Lots of questions - (1) What caused brakes to apply in the first place? Vibration started on straight and level, while cruising. (2) Can antilock pump pressurize front brakes? Thought control valve only released pressure to prevent lock up? (Traction Assist can apply to rears?) (3) If antilock, pressurized the front brakes, why did they remain applied after fuzes removed? (4) If brake hose as suggested earlier - makes sense - but why BOTH front brakes at same time? Makes sense to change them, but they don't seem to be the problem. (4) Why didn't brakes release after bleeder opened? (New master cylinder last year, when this all started.) Other reader with apparently same problem (dcolemanslaw) replaced his calipers and turned rotors with no improvement! To me - it doesn't sound like the brake hose, doesn't sound like the ABS, doesn't sound like the master cylinder, doesn't sound like the calipers - so what gives. Could the heat of the dragging brakes cause the caliper pistion to temorarily lock? My mechanic thinks the problem is in the Hydraulic Control Unit, and has warned me that it may need replacement for a mere $1000! So I will have spent nearly $2400 on this. I just love new technology (and now the 'antilock' light on the Bronco has started coming on too!).
peppermrj
08-14-2005, 07:56 PM
Boy, it seems like you are just having all sorts of fun with that panther. Let me put my 2 cent in.
1 ABS systems can apply the brakes even if you don't.
2 Depending on the system some ABS units have pumps to apply the brakes and and most have a high pressure resevior that when activated apply the brakes.
3 If the ABS is not functioning properly pulling the fuse may not work. Resevior is possibly sticking open.
4 Brake hoses will fail and cause the brakes to drag. Both at the same time would take a lot of luck tho and would not apply the brakes.
5 If the brakes were dragging due to fluid under pressure opening the bleeder should release the brakes.
6 Heat from the dragging brakes could have done a fair amount of damage. Distorting both the rotor and the caliper.
Did you have the same results on the passenger side when you opened the bleeder? Did fluid come out under pressure when you opened the bleeder? Did this all start after something was changed (mastercylinder)?
My thoughts on what is going on. If this started on its own and not as a result of a replaced part my first thought is that the ABS is indeed applying the brakes. Releasing the brake fluid pressure should release the brakes unless the caliper is bad or overheated and binding. I would pull the abs fuses and see if the problem will recreate itself. If not then its a safe bet it is the ABS.
The ABS stuff is very expensive and not something you want to throw parts at. I recommend talking with Harold at the power brake x-change. 800-580-5729 Small family owned shop, they are factory authorized rebuilders and distributors for most major ABS systems. Best brake guy I ever met. The car dealers go to him.
Good luck and let us know.
1 ABS systems can apply the brakes even if you don't.
2 Depending on the system some ABS units have pumps to apply the brakes and and most have a high pressure resevior that when activated apply the brakes.
3 If the ABS is not functioning properly pulling the fuse may not work. Resevior is possibly sticking open.
4 Brake hoses will fail and cause the brakes to drag. Both at the same time would take a lot of luck tho and would not apply the brakes.
5 If the brakes were dragging due to fluid under pressure opening the bleeder should release the brakes.
6 Heat from the dragging brakes could have done a fair amount of damage. Distorting both the rotor and the caliper.
Did you have the same results on the passenger side when you opened the bleeder? Did fluid come out under pressure when you opened the bleeder? Did this all start after something was changed (mastercylinder)?
My thoughts on what is going on. If this started on its own and not as a result of a replaced part my first thought is that the ABS is indeed applying the brakes. Releasing the brake fluid pressure should release the brakes unless the caliper is bad or overheated and binding. I would pull the abs fuses and see if the problem will recreate itself. If not then its a safe bet it is the ABS.
The ABS stuff is very expensive and not something you want to throw parts at. I recommend talking with Harold at the power brake x-change. 800-580-5729 Small family owned shop, they are factory authorized rebuilders and distributors for most major ABS systems. Best brake guy I ever met. The car dealers go to him.
Good luck and let us know.
rlauzze
08-15-2005, 07:57 AM
Boy, it seems like you are just having all sorts of fun with that panther. Let me put my 2 cent in.
1 ABS systems can apply the brakes even if you don't.
2 Depending on the system some ABS units have pumps to apply the brakes and and most have a high pressure resevior that when activated apply the brakes.
3 If the ABS is not functioning properly pulling the fuse may not work. Resevior is possibly sticking open.
4 Brake hoses will fail and cause the brakes to drag. Both at the same time would take a lot of luck tho and would not apply the brakes.
5 If the brakes were dragging due to fluid under pressure opening the bleeder should release the brakes.
6 Heat from the dragging brakes could have done a fair amount of damage. Distorting both the rotor and the caliper.
Did you have the same results on the passenger side when you opened the bleeder? Did fluid come out under pressure when you opened the bleeder? Did this all start after something was changed (mastercylinder)?
My thoughts on what is going on. If this started on its own and not as a result of a replaced part my first thought is that the ABS is indeed applying the brakes. Releasing the brake fluid pressure should release the brakes unless the caliper is bad or overheated and binding. I would pull the abs fuses and see if the problem will recreate itself. If not then its a safe bet it is the ABS.
The ABS stuff is very expensive and not something you want to throw parts at. I recommend talking with Harold at the power brake x-change. 800-580-5729 Small family owned shop, they are factory authorized rebuilders and distributors for most major ABS systems. Best brake guy I ever met. The car dealers go to him.
Good luck and let us know.
Hey thanks, you've been helpful. Sounding more and more like the HCU (or the electronic controller?). Unfortunately, front brake lockup and subsequent severe vibration is very intermittent. Drove the car about 60 miles last nite with absolutely no problems. Funny there is no vibration like a warped rotor after an episode. Like you said, why didn't brake release when bleeder opened. I'm guessing possibly that the caliper was so hot, it was sticking and wouldn't release.
Unfortunately when I released the bleeder on the driver's side caliper, I was in a time crunch and didn't check the bleeder on the passenger side - although the brake was stuck on (I could force the wheel to turn a little on the passanger side - but not at all on the driver's side). Fluid came out under pressure on the driver's side - but not as forcefully as I expected. Had buddy press pedal, and bled the caliper (carefully to let no air in) - but it never released until I 'C' clamped it.
My mechanic wants to 'back flush' the HCU, before we talk about replacing it. I think that makes sense. (That may also help with the somewhat mushy feel to the pedal. That's the main reason I had the master cylinder changed, and the system flushed previously. My mechanic thinks the mushy feel and vibration problems are connected). I'll also pull the underhood ABS electronic controller fuze, as you suggest, to see it I can duplicate the problem - the only problem there is it's so darn intermittent.
I also read where some people put a switch on the power line to the electronic controller so they can turn off the traction assist - Ford should have done that! But the switch also turns off the ABS, so the car acts 'normally', but without ABS (my guess is the ABS lite stays on in the dash, like the fuze was pulled). Since I've got a 93, I'm not anxious to invest several thousand dollars to get the ABS working perfectly - I just want dependable brakes. - Thanks again, I'll keep you posted.
1 ABS systems can apply the brakes even if you don't.
2 Depending on the system some ABS units have pumps to apply the brakes and and most have a high pressure resevior that when activated apply the brakes.
3 If the ABS is not functioning properly pulling the fuse may not work. Resevior is possibly sticking open.
4 Brake hoses will fail and cause the brakes to drag. Both at the same time would take a lot of luck tho and would not apply the brakes.
5 If the brakes were dragging due to fluid under pressure opening the bleeder should release the brakes.
6 Heat from the dragging brakes could have done a fair amount of damage. Distorting both the rotor and the caliper.
Did you have the same results on the passenger side when you opened the bleeder? Did fluid come out under pressure when you opened the bleeder? Did this all start after something was changed (mastercylinder)?
My thoughts on what is going on. If this started on its own and not as a result of a replaced part my first thought is that the ABS is indeed applying the brakes. Releasing the brake fluid pressure should release the brakes unless the caliper is bad or overheated and binding. I would pull the abs fuses and see if the problem will recreate itself. If not then its a safe bet it is the ABS.
The ABS stuff is very expensive and not something you want to throw parts at. I recommend talking with Harold at the power brake x-change. 800-580-5729 Small family owned shop, they are factory authorized rebuilders and distributors for most major ABS systems. Best brake guy I ever met. The car dealers go to him.
Good luck and let us know.
Hey thanks, you've been helpful. Sounding more and more like the HCU (or the electronic controller?). Unfortunately, front brake lockup and subsequent severe vibration is very intermittent. Drove the car about 60 miles last nite with absolutely no problems. Funny there is no vibration like a warped rotor after an episode. Like you said, why didn't brake release when bleeder opened. I'm guessing possibly that the caliper was so hot, it was sticking and wouldn't release.
Unfortunately when I released the bleeder on the driver's side caliper, I was in a time crunch and didn't check the bleeder on the passenger side - although the brake was stuck on (I could force the wheel to turn a little on the passanger side - but not at all on the driver's side). Fluid came out under pressure on the driver's side - but not as forcefully as I expected. Had buddy press pedal, and bled the caliper (carefully to let no air in) - but it never released until I 'C' clamped it.
My mechanic wants to 'back flush' the HCU, before we talk about replacing it. I think that makes sense. (That may also help with the somewhat mushy feel to the pedal. That's the main reason I had the master cylinder changed, and the system flushed previously. My mechanic thinks the mushy feel and vibration problems are connected). I'll also pull the underhood ABS electronic controller fuze, as you suggest, to see it I can duplicate the problem - the only problem there is it's so darn intermittent.
I also read where some people put a switch on the power line to the electronic controller so they can turn off the traction assist - Ford should have done that! But the switch also turns off the ABS, so the car acts 'normally', but without ABS (my guess is the ABS lite stays on in the dash, like the fuze was pulled). Since I've got a 93, I'm not anxious to invest several thousand dollars to get the ABS working perfectly - I just want dependable brakes. - Thanks again, I'll keep you posted.
gbic1
11-18-2005, 08:09 PM
If it happens again try loosening the brake lines at the master cylinder. A bad MC wil cause this also. Loosening the lines will bleed off pressure and allow the brakes to release.
iponnet
11-26-2005, 10:09 AM
I agree with gbic this kind of problem is usually caused by a bad master cylinder, abs problems usually dont cause lock up,,gl
Gandolf
11-26-2005, 01:57 PM
You may need to completely remove the bleeder to release pressure, they sometimes become clogged with time.
When changing the master cyl. the distance between the booster and m. cyl. needs to be checked, this insures no free play and that it does not keep the cyl. from returning to it's stop which would block the return hole which allows the fluid to return to the reservoir.
Brake fluid is Hygroscopic (gathers moisture) and over a period of time becomes saturated. This moisture will turn to steam when heated and apply the brakes if the return hole in the master cyl. or a rubber flex line is defective.
Those rubber lines can deteriorate from the inside and restrict the fluid, pressure can get through but the passive return is too great for the fluid to pass.
Note; Once brake fluid has been overheated it is TOAST!! So change your fluid and look hard at the items listed above.
Hope this helps, good luck
When changing the master cyl. the distance between the booster and m. cyl. needs to be checked, this insures no free play and that it does not keep the cyl. from returning to it's stop which would block the return hole which allows the fluid to return to the reservoir.
Brake fluid is Hygroscopic (gathers moisture) and over a period of time becomes saturated. This moisture will turn to steam when heated and apply the brakes if the return hole in the master cyl. or a rubber flex line is defective.
Those rubber lines can deteriorate from the inside and restrict the fluid, pressure can get through but the passive return is too great for the fluid to pass.
Note; Once brake fluid has been overheated it is TOAST!! So change your fluid and look hard at the items listed above.
Hope this helps, good luck
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