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OT: brake calipers


JST
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sorry for the OT put i guess it will improve general mechanical knowledge (assuming someone knows!!)

i need to change the brake discs on an A3. i haven't taken the wheels off yet but going on what the MOT man said

fronts are pretty straight fwd, remove caliper and undo the screws holding the disc on.

but rears he said something about winding the caliper back in(???) said he thought it had a normal thread so that issue is covered, but what does he mean by wind then in? they are std sliding calipers single pot in the rear (i think)

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From memory, when I did my Mk4 golf (and assuming your A3 is an 8L chassis - ie the old shape) the rear pistons did indeed screw back into the caliper body. I used a caliper wind back tool from halfrauds to achieve it. I will have to go and look at the tool to remember how to use it though...

Essentially, you cannot just push the piston back into the caliper though...

Mark

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alot of calipers are made that way if they have the handbrake mech in them, its the adjuster inside the caliper which needs winding back in, just rotate the piston (normally clockwise) to return the piston to home.

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Guest diesel_jim

Some i've seen (and IIRC my ex bro-in-law's mazda 323 was the same) there was a large slot across the head of the piston, enough to fit a big screwdriver or spanner (on its edge) into, then just turn & push.

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JST, you should be able to cobble up a tool or sometimes pliers "points forward".

You may find you have to push quite hard (I had blisters from doing a Volvo) as well as turn.

Can't remember what holds the discs but it won't be too weird, spline drive IIRC.

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Some rear brake calipers also incorporate the handbrake mechanism, which is a worm drive inside the caliper body. When you replace the brake pads you can't just press the piston(s) back in in a straight line, but rather turn them and push at the same time. You can twist and push the piston with a big screwdriver, or snipe-nosed pliers/mole grips to achieve the same result. Sometimes the pads have a raised 'lug' that has to engage in the slots in the piston, so it's important that the piston ends up in the right position in order to fit the pads correctly. There is a special tool for doing this, but I have never bothered with one - pressure and a screwdriver is what I usually do. This is what the proper tool looks like:-

http://www.lasertools.co.uk/item.aspx?item=3183&cat=518

Les.

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Guys thank you all for the advice, job completed this morning 2hrs to do all four discs/pads etc. yes 7mm allen needed for front calipers and 8mm for rear.

ref the wind in rear calipers, i didnt have a special tool and the screwdriver approach with leverage and turning did nothing so in the end i resorted to a G clamp, which work a treat, used it across the caliper and as it wound in clockwise the swivel G clamp turned the piston as the force was applied. just glad it wasnt an opposite thread wind in!

again than you for all the advice.

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