Bleedin' Brakes

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Oscar
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Bleedin' Brakes

Post by Oscar » Sat Jan 21, 2006 12:12 pm

Hello

Changed the brake pads the other day. The near side pads were much more worn than the off side - they were down to the metal, when the off side pads had 1.5 mm left.


The near side piston went in very quickly and easily, but the offside barely moved. After realising that at the current rate of progress I'd be out there for another 2 hours, I undid the bleed nipple and the piston went in very quickly after that.

Is this normal? Is it related to the different rates of wear? Do I need to be concerned or to take action?

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Post by Stinkwheel » Sat Jan 21, 2006 12:22 pm

urm, at first i would say sticking piston but the more i think about it i would say maybe its time to change the flexi hoses as they may be internally restrictive to fluid flow.
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Post by ken newbold » Sat Jan 21, 2006 12:38 pm

Oscar, the usual method of getting the piston to retract is to turn the piston with a square shafted screwdriver or similar and in effect screw the piston back in.

I find by doing this you also help to lubricate and keep the piston free moving.

The other point you should have checked, was the caliper free moving on the slide bars? The whole caliper should move freely along the slide bars otherwise you will get uneven wear on the pads i.e. the pad in contact with the piston will wear down much quicker than the other one.
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Post by jeremy » Sat Jan 21, 2006 12:59 pm

We must be talking back brakes here if we're talking about 2 pistons. The pipework for the back brakes is a bit tortuous as the feed is from the rear suspension circuit and then runs to the valve on the back of the pedal and then back to the brakes.

A difference of 1.5 mm isn't anything to worry about as they have probably been in there for 150,000 miles and don't do a great deal unless the car is laden. This does however mean that the discs do corrode and loose efficiency that way.

What does concern me however is that on a well maintained car the pads would have been replaced when they reached the wear limit which is 2mm or greater. Its important to remember that this is a minimum thickness when in use wich means that if you intend to inspect again in 5000 miles time you should allow enough additional thickness so that there is still the 2mm in 5000 miles time. After all someone's life may depend on your brakes working at their optimum.

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Oscar
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Post by Oscar » Tue Jan 24, 2006 2:42 pm

Thanks for feedback guys

Ken - all correct procedures were observed, and the caliper was moving freely.

Jeremy - it was front brakes, one piston on each side. Good to know that the difference isn't significant. Your point about thickness is well taken- the brakes are often checked but obviously not frequently enough.

But I'm still at a loss as to why it was taking so much time and effort to push the piston back in.
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Post by tom » Tue Jan 24, 2006 2:46 pm

'Cos it doesn't push, it screws in. It is actually due to the ratchet action of the handbrake mech inside it. It needs to be both pushed and turned at the same time. When you set it up, there should be a 1mm gap between the pad and the disk, as per Haynes.

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Post by Oscar » Tue Jan 24, 2006 3:28 pm

To clarify

It was pushed and turned at the same time, using the same techniques as all the other times I've changed pads (twice, actually :D )

The screwing went fine. But it wasn't moving in until I undid the bleed nipple.
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Post by Vanny » Tue Jan 24, 2006 4:12 pm

i dont bother rotating the capilers any more, just use a quick g-clamp and they go straight back with no bother, then just a bit of turny turny to loosen the buggers up. Infact even when i used to use the square shaft screw driver approach they tended to just push back, so is there any actual reason to rotate the buggers?


If they weren't siezed and you had to release the fluid then there can be only one reason, no path for the fluid to return, so either the brake pipes are suspect OR they had become air locked maybe?

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Post by Stewart (oily!) » Tue Jan 24, 2006 5:08 pm

Check your handbrake cables too, Ive had a broken outer cause dragging brakes, i couldnt feel them whilst driving but the disc turned blue! fuel economy improved a bit as well.
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Oscar
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Post by Oscar » Tue Jan 24, 2006 5:10 pm

Stewart you may have hit the nail on the head - the handbrake cable snapped during the MoT and was replaced. I'll keep it in mind when checking.

O
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Post by mnde » Wed Jan 25, 2006 11:50 am

Stewart (oily!) wrote:Check your handbrake cables too, Ive had a broken outer cause dragging brakes, i couldnt feel them whilst driving but the disc turned blue! fuel economy improved a bit as well.
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My, you might just have encouraged me to check them myself. I've noticed while sitting in traffic that sometimes the car doesn't roll back like it should on a gentle slope. Or if it does roll back and I apply the brakes to stop it, then release again, the car doesn't move... it reminds me of a BX automatic! and my fuel econ is a bit pants...

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Post by ken newbold » Wed Jan 25, 2006 5:13 pm

Mark, I'd certainly check the rears if I were you, these are notorious for siezing up.
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