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Slightly binding front calliper

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Old Aug 26th, 2019, 15:42   #1
dan 244
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Default Slightly binding front calliper

So now the next problem!!

So one of my front callipers seems to not completely release the pads completely. It feels free, the slide pins are new, I have worked the piston in and out a few times with a bit of brake fluid around it. The pins are well lubricated. It comes on and grips ok, recently passed mot, but when you release the brake it doesn’t seem to retract quite as much as the other side. So when you spin the wheel by hand it only spins about 1 turn once you let go, where the same on the other side it is about 3 or 4 turns. Also comparing the temperature after a run that wheel always is slightly hotter, but not silly hot if that makes sense. It also squeakes slightly like a chirping canary.

So is there anything that affects the retraction of the callipers like in the servo or master cylinder or will I simply need to replace the calliper?
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Old Aug 26th, 2019, 15:51   #2
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I would try the Flexi first then the caliper
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Old Aug 26th, 2019, 16:08   #3
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Originally Posted by classicswede View Post
I would try the Flexi first then the caliper
Ok thanks, done Flexi hoses both sides, that’s when I noticed the slight binding, while the car was in the air. Had complete brake fluid change too.
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Old Aug 26th, 2019, 17:49   #4
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If the flexi has been changed and the pins are well lubed with silicone grease or High temp grease then it can only be the piston sticking slightly. I say slightly because its obviously retracting when you release the pedal otherwise you would not be able to turn the wheel.
If I get one like this, I normally remove pads and calliper, then with a can of WD40 with the straw attached, get the straw just inside the piston boot, a small blunt screwdriver or similar will get the boot away from the piston without damage to allow you to get the straw in. A squirt of WD40 then remove the straw. Push the piston firmly home with a "G" clamp. Unwind the "G" clamp a few turns but leave in place, apply the brake pedal gently, you will have to do this a few times until the piston is stopped by the "G" clamp. Repeat this a few times, you will feel it gets easier until you get to a point where it gets no easier. That's the point you are after as it is now as free as its going to be. The WD 40 will dry out and leave protection where needed.
I have done this procedure countless times over the years and it has never failed for me.
Just last week I had the exact same symptom on the rear N/S of our XC70 and carried out this to good effect.

Last edited by lynns hubby; Aug 26th, 2019 at 17:51. Reason: Added info
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Old Aug 26th, 2019, 18:45   #5
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As lynns hubby says. Same method but I used silicone spray when mine did it. It leaves a slight lubrication in place.
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Old Aug 26th, 2019, 21:12   #6
Laird Scooby
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If you try retracting the piston as described above to lube it, open the bleed nipple and attach a one-way bleed valve so the fluid doesn't go back up the hoses/pipes etc to the ABS modulator and/or the master cylinder - it can easily carry dirt with it that will compromise either of those.
May also be worth rebledding that leg of the system, if you have a small air bubble in there that will compress under braking and then expand when released, keeping the piston closer to the disc.

Also worth checking the clearance between the pedal and servo pushrod, there needs to be some clearance there for the servo to completely shut - also check the servo non-return valve and the air intake valve, either of those can cause unexpected brake action.

Something else that can cause the problem is if the pads have burrs on the edges where they sit in the calipers. A few minutes with a file taking them off and a wire brush cleaning the caliper where the pads slide with a smear of copper grease after can work wonders.
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Old Aug 27th, 2019, 00:00   #7
dan 244
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Ok thanks for all that guys. A few things to try tomorrow and good tip with the opening the bread nipple while compressing the piston. And then another bleed.

I did wire brush the seating points in the callipers and cleaned up the edges of the pads and applied copper slip when I last looked at them.

The clearance between servo rod and peddle is that inside the car in the pedal area?
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Old Aug 27th, 2019, 08:57   #8
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Quote:
Originally Posted by dan 244 View Post
The clearance between servo rod and peddle is that inside the car in the pedal area?
Yes, you should be able to feel it by pushing on the pedal by hand, as it starts moving down it should go with minimal pressure then as the clearance is taken up, go hard. Only needs to be a short distance of travel before the clearance is taken up but it needs to exist.
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