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Brake Problems

E3_UK

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Doing my annual brake service today, never had any issues before until today.

I take the outside pad out then restrain one piston with a clamp and pump the other one out with about four full pedal strokes bringing the piston about half way out. I then slowly push the piston fully back with a lever. I then repeat this for the other piston then replace the pad. I then repeat this process on the inside pad therefore ensuring all four pistons are free. Then usually I pump the pedal a couple of times to bring the pads into contact with the disc then repeat on the other side. The problem today is that I now have a very long travel in the pedal and can build it up to about half way with a few quick pumps. Having not disconnected any hydraulics I can't have introduced air into the system, so is this a master cylinder issue ?. It's a RHD car. With the pedal pumped up all four wheels are locked. Can a seal in the master have flipped because of the longer pedal stroke while pumping the pistons out ?. This is a procedure I perform every year but this is the first time I've had this problem.
 

TedS

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It sounds like the piston seals are holding the pistons too far back. That's my guess. Maybe repeat your procedure but don't push the pistons so far back? Do you clean the exposed portion of the pistons while they're sticking out?
 

E3_UK

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I see what you mean, I have seen this before on another car i had rebuilt the calipers on. The pistons were being held back by the seals and had to be pumped out. However my pistons are completely free, no pedal resistance to pump them out and very light pressure to push them back and no corrosion on the exposed surfaces. I suppose i could repeat the process again. I will try clamping each side in turn to see if i can isolate the problem to one side.
 

TedS

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The pistons are still free and you wouldn't feel any resistance- it's just the seals gripping slightly too much. They allow the pistons to contact the discs but then retract them too far back.
 

E3_UK

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If this was the case though, why would the pedal travel be so long ?. If the seals were gripping the pistons wouldn't there just be greater pedal resistance until the seal friction is overcome and the pistons move giving normal pedal stroke ?. As the fluid is incompressible it wouldn't be possible to just keep pumping the pedal without the pistons moving out ?.
 

dang

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First off, annually? You're a better man than me. :) if everything seems normal except for the soft pedal, I'd bleed them and check for air. At least that's what I would do as a next step since something has to be done ...
 

E3_UK

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I suppose that's the only course of action I can take,, however having not introduced air into the system and having had a perfect pedal before it isn't what I would expect to have to do. It's something I'm used to doing on my old cars, particularly the Minis as the rear brake cylinders often stick during winter layup so I always tear down the brakes and work the pistons a few times. It's the first time I've had this issue, but then the braking system on the E3 is far more complicated than a Mini, especially with the RHD setup. I have a pressure bleeder but have never used it yet (Sealey VS820), I'm not sure if it will fit the E3 reservoir. The specification states the cap is 45mm to suit most European makes, I don't have the bleeder at home so can't check if it fits. The reservoir thread does measure approx. 45mm so I'm assuming it will be ok. I have read several threads on the E9 forum about bleeding the system (RHD), is it the same for the E3 ?.
 
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Simufly

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I suppose that's the only course of action I can take,, however having not introduced air into the system and having had a perfect pedal before it isn't what I would expect to have to do. It's something I'm used to doing on my old cars, particularly the Minis as the rear brake cylinders often stick during winter layup so I always tear down the brakes and work the pistons a few times. It's the first time I've had this issue, but then the braking system on the E3 is far more complicated than a Mini, especially with the RHD setup. I have a pressure bleeder but have never used it yet (Sealey VS820), I'm not sure if it will fit the E3 reservoir. The specification states the cap is 45mm to suit most European makes, I don't have the bleeder at home so can't check if it fits. The reservoir thread does measure approx. 45mm so I'm assuming it will be ok. I have read several threads on the E9 forum about bleeding the system (RHD), is it the same for the E3 ?.
Yes, the bleeding procedure is the same PITA! However an e9 member who worked on them in the day in a dealership came up with a slightly different procedure which he was confident was better. Sadly I binned that post when I sold my coupe.
 

E3_UK

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I think I saw that post when I was searching, guy from NZ I think so he was familiar with the RHD setup, thanks.
 

dang

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I just pressure bled and vacuum bled my system and got it to the point of having a really soft pedal. It didn't get all the air out until I had my son pump the brakes before each time I opened a bleed valve. This was for a system that was completely dry with a new master.
 

TedS

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I'm not sure why you do this service if you're not cleaning off the exposed portion of the pistons. Before you did this the seals were holding the pistons so the pads were just barely off the discs. When you apply the brakes the seals deform slightly allowing the pistons to extend, pushing the pads against the discs. When you release the brakes the seals return to normal bringing the pistons with them. If you've pushed the pistons back into the calipers without cleaning them (or even sometimes after cleaning them) it's possible that the seals are gripping the pistons at a different point holding them too far back. The seals will still deform as you apply the brakes but will drag the pistons back to this new holding point. The pistons are starting from further back so require more pedal travel to get the pads to contact the discs. If you took before and after readings on the exact amount of fluid in the reservoir you'd find slightly more in there now after your "service". You haven't introduced any air or lost any fluid.
You need to push the pistons out past the point that they'd cause the pads to contact the discs then retract them only enough to fit the pads back in. This time clean the pistons with brake cleaner while they're extended.
 

E3_UK

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I've been doing this type of annual service on mine and customers cars for over 30 years, it's routine work to ensure pistons aren't sticking and yes I do clean the exposed areas if they need it, mine didn't. I've lost count of the number of customer cars that come in with "full dealer service history" with pads seized in calipers and pistons solid because the dealers don't want to spend the time doing proper servicing as they can't sell new calipers, pads and discs if they keep them maintained and hence don't make the profit they require. If you read the factory manual it actually tells you to push the pistons fully into the caliper when replacing pads. Anyway, I left the pedal blocked down overnight after pumping it up then cracked open the top bleeder on the caliper I had worked on first and there was one splurge of air. After this the pedal was fine, back to normal. Perhaps there was a small pocket of air in the system that I managed to "move" when stroking the pedal to pump the pistons out, never had this before on any car at all, just unlucky this time.
 

dang

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I'm not sure why you do this service if you're not cleaning off the exposed portion of the pistons. Before you did this the seals were holding the pistons so the pads were just barely off the discs. When you apply the brakes the seals deform slightly allowing the pistons to extend, pushing the pads against the discs. When you release the brakes the seals return to normal bringing the pistons with them. If you've pushed the pistons back into the calipers without cleaning them (or even sometimes after cleaning them) it's possible that the seals are gripping the pistons at a different point holding them too far back. The seals will still deform as you apply the brakes but will drag the pistons back to this new holding point. The pistons are starting from further back so require more pedal travel to get the pads to contact the discs. If you took before and after readings on the exact amount of fluid in the reservoir you'd find slightly more in there now after your "service". You haven't introduced any air or lost any fluid.
You need to push the pistons out past the point that they'd cause the pads to contact the discs then retract them only enough to fit the pads back in. This time clean the pistons with brake cleaner while they're extended.
I get what your saying, but wouldn't this be potential problem every time you replace the pads? (pushing the pistons too far in) I've never had an issue like this after pad replacement and it sounds like this is a first for @E3_UK. It seems like the seal position would find it's new location the first time the pistons move out against the pads.
 

E3_UK

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I agree. The seals don't pull the pistons clear of the disc, it's just the removal of the force applied by hydraulic pressure that results in the friction between disc and pad reducing to almost negligible magnitude. The pads are always in contact with the disc, there is always some drag. The piston will remain in in the same position when the force is removed. If this wasn't the case you would continually have to pump the pistons out on every application. I have worked on the original Dunlop calipers on the P6 Rovers and these have a pin in the centre of the cylinder that the piston is fitted to. The pin is designed to pull the piston back when pressure is released, I think using a spring mechanism. Same arrangement used on early Jaguars. I guess there was concern about the drag caused by the pads in continual contact with the discs. However this arrangement didn't last for long and was replaced by a conventional setup as we now know it.
I prefer to exercise the seals by pumping the pistons out, especially when the car is sitting idle for 6 months.
 

dang

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I always understood the piston/pad being "pushed back" by the rotor runout. Like you said, it's very negligible and the slight wobble of the disc is enough to push the piston back enough.
 

TedS

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It's a thing and I'm surprised you've never heard of it. It doesn't take much to cause excessive pedal movement. When servicing motorcycle brakes I sometimes have to strap the lever back against the bar overnight to reset the piston position and let any air float to the top into the reservoir.
Glad you got it fixed.
 

E3_UK

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It's a thing and I'm surprised you've never heard of it. It doesn't take much to cause excessive pedal movement. When servicing motorcycle brakes I sometimes have to strap the lever back against the bar overnight to reset the piston position and let any air float to the top into the reservoir.
Glad you got it fixed.
It's just not something I've encountered before. I have seen master cylinder seals being flipped if the pistons are shoved back with force, which I never do, but I was paranoid about it. Thankfully an easy fix though.
 
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