Front Brakes

Technical Forum for the Porsche Macan
TheTraveller
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Post by TheTraveller »

Just a bit of info'.
This weekend I replaced the front pads, not the discs. Although replacing them is only an extra screw to undo. Any one contemplating having a go at DIY, I can say they are a doddle to do. For ease, a tool to compress the 6 pistons back into the callipers is needed. Just saves fighting with bars and levers. For a heads up, you may wish to include the pad wear cables, as no matter how careful I was removing them from the pad, they both broke. They are only carbon, like the brushes in early drills, etc. And are very small where they affix to the pad.
And they are £50 a pair, ouch.
The pads were only approx' 30% worn. Original from new, with just under 40K on the clock. Not driving it hard enough, I know. :lol:
Only replaced them because of the dislike of the pedal travel needed, for the brakes to start to begin to bite.

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Nuclear Nick
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Post by Nuclear Nick »

Interesting reason for changing. Pad thickness should make no difference to pedal travel as the hydraulic system compensates for wear by 'replacing' the pad material with brake fluid. If you have long pedal travel it's for another reason that should be investigated further. Reasons could be warped discs and/or sticking pistons.
Nick

Defender 90 V8

991.2 C2 GTS

Macan Turbo - sold

BMW K1300S, BMW R1250 GSA
gasgas1
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Post by gasgas1 »

very carful driving with 2 tonnes and 40k, well done The Traveller, just considering changing mine shortly second set and 46k
CamGTS
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Post by CamGTS »

did you check your rears ? On mine the rears were worn more than the fronts. I've posted on here how to do the rears - again it's a doddle if you do it the right way.
TheTraveller
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Post by TheTraveller »

Good point Nick, but it's just how brake systems work. The pedal is now at the top, and feels good. Re the pistons sticking, as soon as the calliper is wobbled from side to side, to free it from the very slight outer lip on the disc, which is caused by surface rust, the pistons moved freely, and then very little effort needed to retract them fully back home. The more the disc wears the more clearance is needed, to remove the calliper away from it, due to that lip. There was very little if any at all, wear of the disc. Any run out of the disc would have been noticed by judder to some extent, coming through the pedal, or the car, when applying the brakes. But there was none there.
The rears were checked, and they were good.
The tool I used to retract the pistons, fitted fully into the calliper, when the pads were removed. And then with a ratchet, forced two plates apart. Worked perfectly.
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Nuclear Nick
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Post by Nuclear Nick »

TheTraveller wrote: Tue Apr 27, 2021 10:49 am Good point Nick, but it's just how brake systems work. The pedal is now at the top, and feels good. Re the pistons sticking, as soon as the calliper is wobbled from side to side, to free it from the very slight outer lip on the disc, which is caused by surface rust, the pistons moved freely, and then very little effort needed to retract them fully back home. The more the disc wears the more clearance is needed, to remove the calliper away from it, due to that lip. There was very little if any at all, wear of the disc. Any run out of the disc would have been noticed by judder to some extent, coming through the pedal, or the car, when applying the brakes. But there was none there.
The rears were checked, and they were good.
The tool I used to retract the pistons, fitted fully into the calliper, when the pads were removed. And then with a ratchet, forced two plates apart. Worked perfectly.
Good that the pedal feels better now.

Not sure what you mean by 'it's just how brake systems work.'

Renewing the pads has not brought this improvement about. Much more likely is exercising the pistons has cleaned them and freed them up somewhat thus allowing them to maintain closer tracking of the disc surface. I make the point again here as I wouldn't want others to be needlessly changing perfectly good pads in an attempt to reduce pedal travel.
Nick

Defender 90 V8

991.2 C2 GTS

Macan Turbo - sold

BMW K1300S, BMW R1250 GSA
TheTraveller
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Post by TheTraveller »

Nuclear Nick wrote: Wed Apr 28, 2021 11:34 am
TheTraveller wrote: Tue Apr 27, 2021 10:49 am Good point Nick, but it's just how brake systems work. The pedal is now at the top, and feels good. Re the pistons sticking, as soon as the calliper is wobbled from side to side, to free it from the very slight outer lip on the disc, which is caused by surface rust, the pistons moved freely, and then very little effort needed to retract them fully back home. The more the disc wears the more clearance is needed, to remove the calliper away from it, due to that lip. There was very little if any at all, wear of the disc. Any run out of the disc would have been noticed by judder to some extent, coming through the pedal, or the car, when applying the brakes. But there was none there.
The rears were checked, and they were good.
The tool I used to retract the pistons, fitted fully into the calliper, when the pads were removed. And then with a ratchet, forced two plates apart. Worked perfectly.
Good that the pedal feels better now.

Not sure what you mean by 'it's just how brake systems work.'

Renewing the pads has not brought this improvement about. Much more likely is exercising the pistons has cleaned them and freed them up somewhat thus allowing them to maintain closer tracking of the disc surface. I make the point again here as I wouldn't want others to be needlessly changing perfectly good pads in an attempt to reduce pedal travel.
The pistons were definitely not sticking, they were just too free. I do have a feeling for them, as I've done hundreds of braking systems, in the past.
Without going too far into the workings of the braking system. The fluid galleries in the master cylinder, allow the fluid to flow to the pistons within it. But the reservoir, where we fill it with fluid, is not contiually open to the pressurised side of the brake lines, as when the brakes are applied, would force fluid out through that reservoir, and the brakes would fail. Also when the systems are designed, they have to ensure that hydraulic lock does not occur. Whereby fluid keeps entering the system but has no way of being released, thereby locking the brakes contiually on.
As the brakes wear down on all cars, mainly with discs (because there is usually more material to wear away over ones with drum brakes), you will notice that the brake pedal has further to travel before the brakes begin to bite.
If you think of your senario, where the fluid fills the space of the missing pad material due to wear, keeping the pedal in effect at the top, Then it would not matter where the piston, if it is sticking, has stuck, for the fluid to fill that gap.
The pistons on my callipers were fully extended, all in the same plain. And only a micro bit of movement of the calliper was needed to free it from the disc, as there was hardly any disc wear, and virtually no lip due to hardly any surface rust on the edges of the discs. And if they had been sticking in that fully extended ( as far as the pads would allow) position, and if fluid was replacing the worn discs, then the pedal in your senario, would have been at the top. In fact if the pistons had been sticking in any position, in what you are saying, then the fluid would have still replaced the worn brakes, and the pedal would have still operated from the top. But in my case it didn't.
I noitce it more than most as I sometimes drive in bare feet, and then become hypersensitive to the feel of the pedals.
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Nuclear Nick
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Post by Nuclear Nick »

TheTraveller wrote: Wed Apr 28, 2021 1:59 pm
Nuclear Nick wrote: Wed Apr 28, 2021 11:34 am
TheTraveller wrote: Tue Apr 27, 2021 10:49 am Good point Nick, but it's just how brake systems work. The pedal is now at the top, and feels good. Re the pistons sticking, as soon as the calliper is wobbled from side to side, to free it from the very slight outer lip on the disc, which is caused by surface rust, the pistons moved freely, and then very little effort needed to retract them fully back home. The more the disc wears the more clearance is needed, to remove the calliper away from it, due to that lip. There was very little if any at all, wear of the disc. Any run out of the disc would have been noticed by judder to some extent, coming through the pedal, or the car, when applying the brakes. But there was none there.
The rears were checked, and they were good.
The tool I used to retract the pistons, fitted fully into the calliper, when the pads were removed. And then with a ratchet, forced two plates apart. Worked perfectly.
Good that the pedal feels better now.

Not sure what you mean by 'it's just how brake systems work.'

Renewing the pads has not brought this improvement about. Much more likely is exercising the pistons has cleaned them and freed them up somewhat thus allowing them to maintain closer tracking of the disc surface. I make the point again here as I wouldn't want others to be needlessly changing perfectly good pads in an attempt to reduce pedal travel.
The pistons were definitely not sticking, they were just too free. I do have a feeling for them, as I've done hundreds of braking systems, in the past.
Without going too far into the workings of the braking system. The fluid galleries in the master cylinder, allow the fluid to flow to the pistons within it. But the reservoir, where we fill it with fluid, is not contiually open to the pressurised side of the brake lines, as when the brakes are applied, would force fluid out through that reservoir, and the brakes would fail. Also when the systems are designed, they have to ensure that hydraulic lock does not occur. Whereby fluid keeps entering the system but has no way of being released, thereby locking the brakes contiually on.
As the brakes wear down on all cars, mainly with discs (because there is usually more material to wear away over ones with drum brakes), you will notice that the brake pedal has further to travel before the brakes begin to bite.
If you think of your senario, where the fluid fills the space of the missing pad material due to wear, keeping the pedal in effect at the top, Then it would not matter where the piston, if it is sticking, has stuck, for the fluid to fill that gap.
The pistons on my callipers were fully extended, all in the same plain. And only a micro bit of movement of the calliper was needed to free it from the disc, as there was hardly any disc wear, and virtually no lip due to hardly any surface rust on the edges of the discs. And if they had been sticking in that fully extended ( as far as the pads would allow) position, and if fluid was replacing the worn discs, then the pedal in your senario, would have been at the top. In fact if the pistons had been sticking in any position, in what you are saying, then the fluid would have still replaced the worn brakes, and the pedal would have still operated from the top. But in my case it didn't.
I noitce it more than most as I sometimes drive in bare feet, and then become hypersensitive to the feel of the pedals.
I don’t need your Noddy guide to brakes thanks. I’m afraid you don’t understand how basic hydraulic brakes work, particularly your belief that as the pads and discs wear the pedal has to travel further. But I think we’ll have to leave it there, as I said my comments were intended to avoid misinformation being picked up by others.
Nick

Defender 90 V8

991.2 C2 GTS

Macan Turbo - sold

BMW K1300S, BMW R1250 GSA
TheTraveller
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Post by TheTraveller »

As I said it's how they operate. It's a ballance, some it is taken up by the fluid in the res', but it also affects the travel of the pedal. Mine wasn't a lot, but enough to bug me to replace the pads. And thats the only thing that I remedid. Anybody who has the brakes replaced, anywhere on the car will find that the point of bite, will be nearly at the top, if not at the top. Historically this would have been the only warning that the brakes were getting near to replacing, before any warning devices were fitted, or in fact thought of (for cars).
Alfanut
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Post by Alfanut »

Bottom line is if the pads were only 30% worn they did not need to be changed. You may have solved your pedal position issue by the work you did but it was not caused by the pads.
2022 Macan GTS & 718 GT4.
Past: Macan S, Audi S4 B8 Avant / Alfa 147 Q2 Diesel / Alfa 147 2.0 Selespeed
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