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Front disc brake dragging
- Thread starter lbuch40
- Start date
Interesting..... I think I would replace the booster. Just make sure the rod is the correct length for whatever master cylinder you have.
The booster check valve, where the vacuum hose connects, keeps vacuum in the booster. That allows you to stop if the engine dies, however, as you release the pedal, the internal valve should equalize pressure inside the booster so that the rod retracts with the pedal.
The booster check valve, where the vacuum hose connects, keeps vacuum in the booster. That allows you to stop if the engine dies, however, as you release the pedal, the internal valve should equalize pressure inside the booster so that the rod retracts with the pedal.
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When you removed the hose, did you pull the check valve with it?
If not then likely you wobbled the check-valve enough while removing the hose that you released the vacuum inside the chamber.
Otherwise nothing should have changed by just removing the hose since there is no vacuum held on that side of the check-valve.
Either your booster is bad (release valve leaking slightly, or spring too weak), or as has been said (and you should be testing/fixing at this point), the pedal is adjusted wrong or is otherwise somehow holding the same release-valve open slightly.
If releasing the vacuum hose results in the booster retracting, I would suspect that the release valve on the back of the booster (what opens when the pedal is pushed) is partially failed and allowing an imbalance between the two chambers.
If that's what actually is happening then only testing on your part will determine if it's the pedal or the booster at fault.
Unless someone knows that the pedal can't do that, and only a failed booster will act this way?
Paul
If not then likely you wobbled the check-valve enough while removing the hose that you released the vacuum inside the chamber.
Otherwise nothing should have changed by just removing the hose since there is no vacuum held on that side of the check-valve.
Either your booster is bad (release valve leaking slightly, or spring too weak), or as has been said (and you should be testing/fixing at this point), the pedal is adjusted wrong or is otherwise somehow holding the same release-valve open slightly.
If releasing the vacuum hose results in the booster retracting, I would suspect that the release valve on the back of the booster (what opens when the pedal is pushed) is partially failed and allowing an imbalance between the two chambers.
If that's what actually is happening then only testing on your part will determine if it's the pedal or the booster at fault.
Unless someone knows that the pedal can't do that, and only a failed booster will act this way?
Paul
I’m thinking that if the pedal rod was too long, and was holding the booster valve open, that the booster rod would extend even if the pedal was not pressed. That’s not the way it was described. A good test would be to shorten the pedal rod.....
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Agree. Didn't read through his last comments carefully and completely missed that it it not pull forward when vacuum was applied. But once applied, does pull back when vacuum is released.
Seems like a bad booster then. Just like some of the others have experienced.
But as you say, a quick test would be to shorten the rod. But if he can still pull up on the pedal even after it's back in it's neutral position, then theoretically it's not the rod. Unless that movement is just excess play in the linkages and pivot points.
Still, can't hurt to test that theory. Besides, what's one more test!
Here's a compilation of recent comments that pertain:
Did you ever try this when you were driving and the brakes were dragging, to see if it relieved the pressure? Or at least once you were parked with a wheel in the air to see if it was easier to turn by hand once you pulled up on the pedal?
Or did you only get a chance to do this while things were apart and you were watching the rod?
Can you tell if there is much play in the cantilever setup inside the booster mounting bracket?
Did you remember to grind the other knuckle for clearance? Last you reported you'd only done one and gone out for a test drive before you'd done the other one.
Paul
Seems like a bad booster then. Just like some of the others have experienced.
But as you say, a quick test would be to shorten the rod. But if he can still pull up on the pedal even after it's back in it's neutral position, then theoretically it's not the rod. Unless that movement is just excess play in the linkages and pivot points.
Still, can't hurt to test that theory. Besides, what's one more test!
Here's a compilation of recent comments that pertain:
Did you ever try this when you were driving and the brakes were dragging, to see if it relieved the pressure? Or at least once you were parked with a wheel in the air to see if it was easier to turn by hand once you pulled up on the pedal?
Or did you only get a chance to do this while things were apart and you were watching the rod?
Can you tell if there is much play in the cantilever setup inside the booster mounting bracket?
Did you remember to grind the other knuckle for clearance? Last you reported you'd only done one and gone out for a test drive before you'd done the other one.
Paul
Thanks all for thoughts and Paul for the compilation of symptoms.
I did try shortening the pedal rod and all it did was drop my pedal closer to the floor. Still had the same issue with the booster rod not going all the way back in when vacuum is active. But only was able to watch this while parked and no warm up.
When I pulled the vacuum hose off, it included the check valve so there was no residual in the booster. Thats when the rod would then retract that last 1/8" or so - when no vacuum was present.
I just got done grinding the passenger side knuckle, although there appeared to be about 1/8" clearance to the knuckle already. These are basically new pads. Now I have plenty of clearance. there is some slight drag on the rotor even in the brake "neutral" position. I assume that is normal? I can still easily turn it by hand.
The driver's side is a little more "sticky" than passenger side.
I have moved my pedal rod back to the length it was originally and going for a test drive now. Its nice and warm today so hopefully it will be a good test run.
Stay tuned!
I did try shortening the pedal rod and all it did was drop my pedal closer to the floor. Still had the same issue with the booster rod not going all the way back in when vacuum is active. But only was able to watch this while parked and no warm up.
When I pulled the vacuum hose off, it included the check valve so there was no residual in the booster. Thats when the rod would then retract that last 1/8" or so - when no vacuum was present.
I just got done grinding the passenger side knuckle, although there appeared to be about 1/8" clearance to the knuckle already. These are basically new pads. Now I have plenty of clearance. there is some slight drag on the rotor even in the brake "neutral" position. I assume that is normal? I can still easily turn it by hand.
The driver's side is a little more "sticky" than passenger side.
I have moved my pedal rod back to the length it was originally and going for a test drive now. Its nice and warm today so hopefully it will be a good test run.
Stay tuned!
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I don't know if these will help, and don't even know for sure if it's the same stuff as ours, but here are links to the instructions for both our disc brake kit install, and the power booster install:
Wild Horses Disc Brake Installation Instructions
Wild Horses Vacuum Booster Installation Instructions
Just in case there is anything in either of them to help along as things progress.
Not unusual to have a very slight drag you can feel. But it does sound odd that one is more than the other. Anytime that happens with brakes you have to start thinking about what might be at fault.
But if it's just slight, then I would not hesitate to at least drive it for testing and see if anything changes.
I think your 1/8" should be enough. At least for now.
The way things work with the brakes, as the pads wear down the caliper actually gets closer to the knuckle as the piston extends and the body moves inward.
But 1/8" is generally considered workable, albeit kind of the minimum. The setups that have the most trouble probably had less than that 1/8" to begin with. Like yours did initially.
Good luck. Crossing fingers that with all the stuff you've done so far you will have a working system.
But from the sounds of it, based on your most recent testing and comments, I'd have to lay my bets on a bad booster.
Paul
Wild Horses Disc Brake Installation Instructions
Wild Horses Vacuum Booster Installation Instructions
Just in case there is anything in either of them to help along as things progress.
Not unusual to have a very slight drag you can feel. But it does sound odd that one is more than the other. Anytime that happens with brakes you have to start thinking about what might be at fault.
But if it's just slight, then I would not hesitate to at least drive it for testing and see if anything changes.
I think your 1/8" should be enough. At least for now.
The way things work with the brakes, as the pads wear down the caliper actually gets closer to the knuckle as the piston extends and the body moves inward.
But 1/8" is generally considered workable, albeit kind of the minimum. The setups that have the most trouble probably had less than that 1/8" to begin with. Like yours did initially.
Good luck. Crossing fingers that with all the stuff you've done so far you will have a working system.
But from the sounds of it, based on your most recent testing and comments, I'd have to lay my bets on a bad booster.
Paul
Thanks again. Just back from a test drive. No dragging this time! It was only a 10 mile trip to town, a few stops and back home again. But it was a good initial test. I am also focusing in on the power booster as the culprit. Maybe the problem with it is intermittent. But I am carrying wrenches and a bottle jack now so if it happens again I can try to check it on the spot!
After more test driving I will give a follow up report. Hope this thread has been helpful for other folks as well.
After more test driving I will give a follow up report. Hope this thread has been helpful for other folks as well.
Last edited:
REPORT: Front brakes started dragging yesterday. Loosened the Master cylinder from the power booster when I got home and they released. More and more pointing to a power booster problem. I could not make them lock again by just engaging the brake pedal. But if they drag again and they release when I pull the vacuum line off the power booster I think that will be the clincher.
Suffering a very similar issue as Ibuch but have been following the thread closely and made some changes and have a new possibility..
-Acts fine for a while and then, over time starts to drag, but to the point to where I can pull the pedal back up just slightly with my foot to get the brakes to free up. I can slow to a stop and they are dragging, but pull the pedal back just a hair to the stop and you can feel them free up
-Plenty of room around the calipers and have checked them hot as well
-Went back and adjusted all the linkage from the pedal to the booster to ensure it's tight and as per directions
-Booster passes all advised tests, such as builds and hold pressure with engine off and pedal falls when engine starts
-Pulled the master from the booster (purchased as a complete kit) and found that the master would not sit flush with the booster due to the pushrod. I ended up removing the locknut from behind the threaded pushrod end which got the master flush. Retracted the pushrod end to about 1/16" gap and bolted the master back up and re-set brake pedal to the stop
-Re-tested system and while brakes felt more responsive initially, over a stop and go drive the problem started again, to where I could simply pull the pedal back ever so slightly with my foot to free the brakes
-After cussing and staring, I have a new question to the pros
-PO has chrome full length headers installed. I added the power brakes, including a new prop valve and pre bent hard line from the prop valve to frame mounted block. It was very close to the headers so I wrapped the pipes with exhaust wrap above and below areas where the brake lines seemed close.
Since the problem surfaces only after driving for a while, I am thinking that the lines are getting to hot from the headers and causing the fluid to expand. The line from the prop valve going down to the block gets hot, but you can still hold your hand against it for a second, but the prop valve gets overly hot to the touch.
Also after the last drive when I got back and popped the hood, the master was pushing fluid out to the point there were a couple of drips on the fenderwell. (Always great to find)
So I'm wondering if, in spite of the wrap, as the problem surfaces the longer I drive (heat builds) if the fluid isn't getting too hot in the line and starting to force the caliper.
-So, as brake fluid is rated at high temps, is this a possibility? And if so, for those who have headers, are there any other mods like shields you've added?
-If the heat shouldn't be a factor then what next?? Could it still be the booster?
Thanks much for the help
-Acts fine for a while and then, over time starts to drag, but to the point to where I can pull the pedal back up just slightly with my foot to get the brakes to free up. I can slow to a stop and they are dragging, but pull the pedal back just a hair to the stop and you can feel them free up
-Plenty of room around the calipers and have checked them hot as well
-Went back and adjusted all the linkage from the pedal to the booster to ensure it's tight and as per directions
-Booster passes all advised tests, such as builds and hold pressure with engine off and pedal falls when engine starts
-Pulled the master from the booster (purchased as a complete kit) and found that the master would not sit flush with the booster due to the pushrod. I ended up removing the locknut from behind the threaded pushrod end which got the master flush. Retracted the pushrod end to about 1/16" gap and bolted the master back up and re-set brake pedal to the stop
-Re-tested system and while brakes felt more responsive initially, over a stop and go drive the problem started again, to where I could simply pull the pedal back ever so slightly with my foot to free the brakes
-After cussing and staring, I have a new question to the pros
-PO has chrome full length headers installed. I added the power brakes, including a new prop valve and pre bent hard line from the prop valve to frame mounted block. It was very close to the headers so I wrapped the pipes with exhaust wrap above and below areas where the brake lines seemed close.
Since the problem surfaces only after driving for a while, I am thinking that the lines are getting to hot from the headers and causing the fluid to expand. The line from the prop valve going down to the block gets hot, but you can still hold your hand against it for a second, but the prop valve gets overly hot to the touch.
Also after the last drive when I got back and popped the hood, the master was pushing fluid out to the point there were a couple of drips on the fenderwell. (Always great to find)
So I'm wondering if, in spite of the wrap, as the problem surfaces the longer I drive (heat builds) if the fluid isn't getting too hot in the line and starting to force the caliper.
-So, as brake fluid is rated at high temps, is this a possibility? And if so, for those who have headers, are there any other mods like shields you've added?
-If the heat shouldn't be a factor then what next?? Could it still be the booster?
Thanks much for the help
ntsqd
heratic car camper
Brake fluid is rated to whatever temp it is at the moment that you open the jar. From that point on it's boiling point steadily is lowering as it gains moisture out of the air. In a humid climate the rate of loosing boiling point is faster than in an arid climate.
Brake fluid is supposed to absorb moisture, and it is supposed to be flushed at minimum every 2 years. If it did not absorb moisture then you have a situation like with silicone brake fluid where the moisture eventually condenses at the low spots in the system and corrodes whatever it is in contact with. BT, DT with a vehicle that I bought that had silicone in it from the PO. The front calipers turned the rotors blue!
I don't have a lot of faith in header wrap, and it can hold oil in it if not sealed. MISF danged near lost a car to that oil in the wrap catching on fire. Instead try placing a thin sheet of aluminum or Stainless Steel between the brake plumbing and the headers. Give both sides an air gap and try to shape the shield such that air is encouraged to flow on both sides of it.
Brake fluid is supposed to absorb moisture, and it is supposed to be flushed at minimum every 2 years. If it did not absorb moisture then you have a situation like with silicone brake fluid where the moisture eventually condenses at the low spots in the system and corrodes whatever it is in contact with. BT, DT with a vehicle that I bought that had silicone in it from the PO. The front calipers turned the rotors blue!
I don't have a lot of faith in header wrap, and it can hold oil in it if not sealed. MISF danged near lost a car to that oil in the wrap catching on fire. Instead try placing a thin sheet of aluminum or Stainless Steel between the brake plumbing and the headers. Give both sides an air gap and try to shape the shield such that air is encouraged to flow on both sides of it.
I'm glad someone is getting some good out of this long-term diagnosis. I've noticed my dragging brakes are also related to the heat, although I do not have headers. I am running sst braided brake lines from the MC down to the proportioning valve mounted on the top of the frame. Last summer I tried fashioning a temporary aluminum heat shield between the exhaust and the proportioning valve and part way up the brake lines leaving plenty of room for air flow. It didn't seem to help. For whatever its worth, I am running DOT 4 brake fluid which is supposedly better for high heat.
I have also removed that locknut from the booster pushrod in order to the the MC to mount to the booster without spacers. Yesterday, I noticed just some ever so slight drag after driving about 15 miles with air temps in the low 80s. Pulled the vacuum line off the booster and no more drag. You might try that test.
If the booster has just a minor flaw, I wonder if the expanding ambient air as heat increases under the hood causes the booster to malfunction??
I'm to the point where ready to try a new booster. But not sure how to make sure the booster I get will match my MC. Any thoughts on this? Mine also was purchased as a kit by the previous owner.
ntsqd
heratic car camper
If there isn't air flow one at least one side & preferably both sides of the shield it won't do a lot. The shield needs to have an air gap on both sides to work.
Any idea who the kit supplying vendor was?
Any idea who the kit supplying vendor was?
I received a book from PO with major receipts from his work. Interestingly, I have an "invoice" from BC Broncos from Jan 2012 that says "complete power brake kit, all applications" and also a "sales receipt" from Bronco Connection in March of 2012 that says "Complete power brake booster assembly w/prop valve disc drum".
If I had to guess between the two, I would say probably Bronco Connection.
If I had to guess between the two, I would say probably Bronco Connection.
Narrowed it down and ordered a replacement booster. I also discovered that I can release the brakes by pulling the pedal up with my toe. But still fairly confident that the cause is a faulty booster. Early on in this thread someone mentioned that turned out to be their problem also on their full size Bronco.
Will report after new booster is installed.
Will report after new booster is installed.
OK please do as I am actively working on looking for some heat shielding for the prop valve and steel line to the front block.
Just curious, did you run the normal tests on the booster? Builds pressure with the motor off by pumping the brakes, pedal falls when the motor starts? Mine does, but after this thread I just don't know what to think, but the issue is making me crazy.
Just curious, did you run the normal tests on the booster? Builds pressure with the motor off by pumping the brakes, pedal falls when the motor starts? Mine does, but after this thread I just don't know what to think, but the issue is making me crazy.
Wished I could tell you! I ordered the booster, but haven't received it yet. I'm trying to track it down.
In the meantime, I am always able to keep them from dragging by pulling the pedal back with my toe.
Will keep you posted. Good luck with yours! Let me know.
In the meantime, I am always able to keep them from dragging by pulling the pedal back with my toe.
Will keep you posted. Good luck with yours! Let me know.
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