Sticky caliper, or maybe not?
Discussion
I’ve just replaced what I thought was a sticking brake caliper, could feel it dragging and it seemed quite slow to release when the pedal pressure was released. Disc and calliper getting hot, usual stuff.
New caliper was fine for a few days and now is doing the exact same. It’s possible that the new caliper is defective, but I doubt this, especially as I’ve inspected the old one and can find nothing wrong with it. All pistons move smoothly.
Can’t figure out what else could cause this problem. Any ideas? Car is a RenaultSport Megane and the calipers are 4 piston Brembo.
New caliper was fine for a few days and now is doing the exact same. It’s possible that the new caliper is defective, but I doubt this, especially as I’ve inspected the old one and can find nothing wrong with it. All pistons move smoothly.
Can’t figure out what else could cause this problem. Any ideas? Car is a RenaultSport Megane and the calipers are 4 piston Brembo.
E-bmw said:
Also, could just be the pads are a bit too tight causing them not to release well.
I normally dress the pads lightly with a file to make sure they move freely when fitted.
Don’t think it’s the pads. I’m leaning towards internal degradation of the flexi hose. It seemed to need more pressure on the brake pedal than I’d usually expect to bleed the new caliper too. That points towards some sort of obstruction I’m thinking. Odd that it seemed OK for a week or so though. I normally dress the pads lightly with a file to make sure they move freely when fitted.
E-bmw said:
Also, could just be the pads are a bit too tight causing them not to release well.
I normally dress the pads lightly with a file to make sure they move freely when fitted.
My wife's astra has had that problem. If you get them too hot, the relative expansions mean that the pad sticks. The trick in stop start traffic in the summer is to use the parking brake when you come to a stop and take it out of drive at traffic lights, so that the pads aren't being pushed against the hot disc soaking up heat. Last time I did the pads, I was enthusiastic with a file. I normally dress the pads lightly with a file to make sure they move freely when fitted.
Is it affecting one specific caliper, or all calipers?
There's a known 'feature' of common brake master cylinders that the brake circuit is designed to be open to the reservoir when the brakes are fully off. The first bit of pedal travel closes the port between the circuit and the reservoir, turning it into a closed system. If something prevents the master cylinder from travelling back far enough to open that port, the system remains sealed even while the brakes are off. In this state, anything at all that builds up pressure in the system will cause the brakes to drag slightly. That would cause heating within the calipers, leading to fluid expansion, leading to more pressure, and so on in a vicous spiral.
This could be caused by wear or accumulated gunk inside the master cylinder, or just the pushrod to the pedal being adjusted too tight.
To see if this is the problem, try to reproduce the heat build-up problem and then crack a bleed nipple on the affacted wheel. If the circuit is under pressure, either the master cylinder is holding pressure or a brake line has failed and is holding pressure.
If it isn't caused by line pressure then you're looking at a mechanical problem in the affected caliper, or its sliders if applicable.
There's a known 'feature' of common brake master cylinders that the brake circuit is designed to be open to the reservoir when the brakes are fully off. The first bit of pedal travel closes the port between the circuit and the reservoir, turning it into a closed system. If something prevents the master cylinder from travelling back far enough to open that port, the system remains sealed even while the brakes are off. In this state, anything at all that builds up pressure in the system will cause the brakes to drag slightly. That would cause heating within the calipers, leading to fluid expansion, leading to more pressure, and so on in a vicous spiral.
This could be caused by wear or accumulated gunk inside the master cylinder, or just the pushrod to the pedal being adjusted too tight.
To see if this is the problem, try to reproduce the heat build-up problem and then crack a bleed nipple on the affacted wheel. If the circuit is under pressure, either the master cylinder is holding pressure or a brake line has failed and is holding pressure.
If it isn't caused by line pressure then you're looking at a mechanical problem in the affected caliper, or its sliders if applicable.
GreenV8S said:
Is it affecting one specific caliper, or all calipers?
There's a known 'feature' of common brake master cylinders that the brake circuit is designed to be open to the reservoir when the brakes are fully off. The first bit of pedal travel closes the port between the circuit and the reservoir, turning it into a closed system. If something prevents the master cylinder from travelling back far enough to open that port, the system remains sealed even while the brakes are off. In this state, anything at all that builds up pressure in the system will cause the brakes to drag slightly. That would cause heating within the calipers, leading to fluid expansion, leading to more pressure, and so on in a vicous spiral.
This could be caused by wear or accumulated gunk inside the master cylinder, or just the pushrod to the pedal being adjusted too tight.
To see if this is the problem, try to reproduce the heat build-up problem and then crack a bleed nipple on the affacted wheel. If the circuit is under pressure, either the master cylinder is holding pressure or a brake line has failed and is holding pressure.
If it isn't caused by line pressure then you're looking at a mechanical problem in the affected caliper, or its sliders if applicable.
It’s just the one calliper. Front OS. No sliders to stick as it’s a 4 piston Brembo There's a known 'feature' of common brake master cylinders that the brake circuit is designed to be open to the reservoir when the brakes are fully off. The first bit of pedal travel closes the port between the circuit and the reservoir, turning it into a closed system. If something prevents the master cylinder from travelling back far enough to open that port, the system remains sealed even while the brakes are off. In this state, anything at all that builds up pressure in the system will cause the brakes to drag slightly. That would cause heating within the calipers, leading to fluid expansion, leading to more pressure, and so on in a vicous spiral.
This could be caused by wear or accumulated gunk inside the master cylinder, or just the pushrod to the pedal being adjusted too tight.
To see if this is the problem, try to reproduce the heat build-up problem and then crack a bleed nipple on the affacted wheel. If the circuit is under pressure, either the master cylinder is holding pressure or a brake line has failed and is holding pressure.
If it isn't caused by line pressure then you're looking at a mechanical problem in the affected caliper, or its sliders if applicable.
Firstly, there is never any need to file a pad if the carrier/ housing is properly cleared of scale (and it's a decent quality pad).
As far as flexi-hoses developing restrictions, it's difficult to test, as it's not the hose 'collapsing internally' as suggested above, it's caused by a little bits of rubber debris that roll up and down inside the hose and eventually form a 'ball-valve' with the 'seat' being the slight constriction where the ferrule crimps the hose. Hoses aren't dear and don't last for ever, treat it to some new ones.
As far as flexi-hoses developing restrictions, it's difficult to test, as it's not the hose 'collapsing internally' as suggested above, it's caused by a little bits of rubber debris that roll up and down inside the hose and eventually form a 'ball-valve' with the 'seat' being the slight constriction where the ferrule crimps the hose. Hoses aren't dear and don't last for ever, treat it to some new ones.
TwinKam said:
Firstly, there is never any need to file a pad if the carrier/ housing is properly cleared of scale (and it's a decent quality pad).
And, as I have said before, which would you rather the pad or the caliper?Yes there SHOULD be no need to do it, but unfortunately as pads are pretty crudely stamped out, sometimes there is.
E-bmw said:
TwinKam said:
Firstly, there is never any need to file a pad if the carrier/ housing is properly cleared of scale (and it's a decent quality pad).
And, as I have said before, which would you rather the pad or the caliper?Yes there SHOULD be no need to do it, but unfortunately as pads are pretty crudely stamped out, sometimes there is.
In 44 years of professional car repair I have NEVER filed a pad. But then, neither have I ever filed a pad carrier or caliper to remove metal, I'm only talking about removing baked on scale back to bright metal. So it's not a case of which one to file to remove metal, in truth it's neither!
Edited to add:
I very much suspect that the pad filers out there are simply too lazy to go to the trouble of removing the pad carriers from the car, taking them to the bench vice and working hard for 20 minutes or so to get them prepped for the new pads...
Edited by TwinKam on Thursday 18th April 23:11
TwinKam said:
E-bmw said:
TwinKam said:
Firstly, there is never any need to file a pad if the carrier/ housing is properly cleared of scale (and it's a decent quality pad).
And, as I have said before, which would you rather the pad or the caliper?Yes there SHOULD be no need to do it, but unfortunately as pads are pretty crudely stamped out, sometimes there is.
In 44 years of professional car repair I have NEVER filed a pad. But then, neither have I ever filed a pad carrier or caliper to remove metal, I'm only talking about removing baked on scale back to bright metal. So it's not a case of which one to file to remove metal, in truth it's neither!
Edited to add:
I very much suspect that the pad filers out there are simply too lazy to go to the trouble of removing the pad carriers from the car, taking them to the bench vice and working hard for 20 minutes or so to get them prepped for the new pads...
Personally, I completely remove all parts from the car when doing discs/pads with the exception of disconnecting the actual caliper.
The carrier will be completely cleaned of any crud/rust etc, the sliders will be cleaned & greased, the pistons will be pushed part way out & greased lightly, the pads are trial fitted with everything else back in place & dressed if required.
After that everything is reassembled & the braked tried to ensure everything works properly & is free & the pads checked to see if they are fully free to move & not binding.
Then I do a bleed/fluid change at the same time.
The vast majority of the time (with disc/disc cars) I do the full lot at the same time.
Over the years, I have probably felt the need to do some dressing on maybe 10% of the pads I have fitted.
Shedding said:
How old is your brake fluid?
I had the same on an old XC90. One of the front wheels would get so hot with brake bind that the wheel bolts loosened with thermal cycles. Ultimately, fresh brake fluid fixed it. The old stuff had been in there a long time.
It’s fresh, as I’ve just replaced the calliper, thinking that was the problem. I’m going to replace the hose when a get a minute to do so and see if that helps. It would certainly align with the need for excessive pressure when bleeding if the hose is blocked. I had the same on an old XC90. One of the front wheels would get so hot with brake bind that the wheel bolts loosened with thermal cycles. Ultimately, fresh brake fluid fixed it. The old stuff had been in there a long time.
v9 said:
It’s fresh, as I’ve just replaced the calliper, thinking that was the problem. I’m going to replace the hose when a get a minute to do so and see if that helps. It would certainly align with the need for excessive pressure when bleeding if the hose is blocked.
Fresh as in the whole system flushed through, or just enough for a bit of leakage while swapping caliper?Never simple is it? Just got round to replacing the flexi pipe to see if that sorts it. Nut is seized on the hard pipe, so I guess it’ll need a new hard pipe too. That needs half the engine bay dismantled to get access unless I can get a repair on a small section at the end done. That’s probably a job for a workshop as I’ve neither the tools nor the time to sort that at the moment. Just hope I can persuade them to use the flexi pipes I’ve bought. Most places seem very reluctant (with good reason) to say yes to fitting parts they’ve not sourced.
Edited by v9 on Wednesday 24th April 21:02
v9 said:
Never simple is it?
^^^ ThisMy car put up a yellow EML light last week but seemed to still be running perfectly. Put it into the garage for a "just in case" OBD check. Oh dear, now that fluttering sound you can hear in the background is a large stack of £50 notes leaving my wallet...
Hope you get the brakes sorted.
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