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Front pad replacement
#1
Hi Guys,

What's your opinion, when replacing front pads and pushing the piston back should I release the pressure by cracking off the bleed nipple or not bother, I've never done a car/ bike with abs before.
The Haynes manual says I should yet I've yet to see a YouTube video where they do it including brake manufacturers training videos.

What do you think / do ?

Thanks

Mark

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#2
I think its up to you as your choice, I've never made a habit of doing it but I have done it. If not done right there's a chance of introducing air into the system

  A lot of people think you should do it to avoid damaging the ABS system/ master cylinder.  

  In operation there is fluid moving back and forward as the brakes are applied and released and that doesn't damage the system.
 
   Doing it will introduce a little fresher brake fluid into the piston cylinder but that's about all.
2001 1.9d DW8B  Berlingo
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#3
If there's muck in your brake system, chances are that it's in your calipers. I think best practice is probably to bleed the excess fluid you get from pushing the pistons back in, rather than pushing the old fluid back through the system and into the reservoir. I did mine without bleeding, the pads were low but still within limits and quite a bit of fluid was displaced out of the top.
The new MOT rules have some mention of brake fluid contamination, so probably best to top up, rather than have old fluid pushed back up.
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#4
Ok ,I'll give it a go then.

Thanks for your input.

Mark

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#5
When you depress the brake pedal, a small amount of fluid moves down the brake pipes as the brake caliper piston expands. When you release the pedal, the fluid returns to its previous position.

When you force the piston back in the caliper while changing pads, you push much more fluid further up the pipe than normal. Doing this without opening the bleed valve is effectively moving far more fluid back into the master cylinder. If you have abs, the same applies.

That's why it is good practice to open the bleed valve while forcing the caliper piston in. Excess fluid is expelled via the bleed valve, and the fluid in the pipework above this valve does not move, so there is zero possibility of dirty fluid contaminating either the pipework, the abs unit or the master cylinder reservoir.

Remember that 'dirty fluid' does not just mean an accumulation of solid particles. Brake fluid nearest to the disc goes through greater heating and cooling cycles than any other part of the hydraulic system, so this fluid gets most tired and contaminated. Expelling it through the bleed valve gets rid of this tired fluid. Remember to check the master cylinder level afterwards.
Gravity
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#6
Thanks Gravity.


Mark

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