Changing Brake Discs

You disconnect the motor from the calliper, just two bolts. You can then, with the aid of a socket, wind the mechanism back, away from the rear of the calliper piston. Once this is done you can then push the piston back like any other calliper piston. You need to do this because the new pads will be thicker than the old ones. Here's a picture of my calliper and piston which should show what I mean.
View attachment 246813

Excellent! Thanks! Presumably, when you put it all back together, the car just adjusts automatically to the new pd thickness and takes up whatever slack it needs to? (I think they just tend to run the motors unti lthey stall, but I'm not sure. Sometimes on the company car, I manually apply the EPB and can year the motors running for a second or so, but when I turn the ignition on, they run again, very briefly. I therefore wonder if they only artially apply themselves most of the time the car is on reasonably level ground, and then just run until they stall when you turn the ignition off, or pull and hold the switch?
 
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I'm sure that Mottie knows this, but for other people's benefit you need to be really careful that you put the car in a mode that it won't automatically apply the EPB part way through the job. If it does apply the epb whilst you've got the caliper off, it'll push the piston out of the caliper.
I don't understand that. If the motor has been removed, how can it push the piston out?
 
They're normally a fine-pitched thread. (Plus, I'd be worried about using M8 as I think there's a pretty good chance the OE ones would be higher tensile and shearing a pair of 8.8 bolts in an emergency stop would definitely ruin your whole day...)!


The Service manual states that is removed they should be replaced - so I bought 4 new ones in readiness.
 
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I don't understand that. If the motor has been removed, how can it push the piston out?
You are correct, if the motor is removed it can't push the piston out.

The point i was making was that if you remove the caliper in order to remove the motor or to change the pads, you need to be aware that the car can apply the EPB for a multitude of reasons, and if it does apply the epb whilst the caliper is removed without a blocking tool of some sort in place, it will push the piston out of the caliper.
 
Perhaps a simple expedient approach would beto unplug the electrical wire that feeds the motor at the start of the job .... then it can't operate
 
Perhaps a simple expedient approach would beto unplug the electrical wire that feeds the motor at the start of the job .... then it can't operate
Which throws a fault code on some cars...
 
Perhaps a simple expedient approach would beto unplug the electrical wire that feeds the motor at the start of the job .... then it can't operate
That's what mottie suggested in #85, but there's the fault code as mentioned in #86, though that may not apply to your car. If it does, I would hope the code would clear itself when everything put back together, but I don't know.
Why do they have to make cars so bloody complicated?
 
You are correct, if the motor is removed it can't push the piston out.

The point i was making was that if you remove the caliper in order to remove the motor or to change the pads, you need to be aware that the car can apply the EPB for a multitude of reasons, and if it does apply the epb whilst the caliper is removed without a blocking tool of some sort in place, it will push the piston out of the caliper.
OK thanks, but wouldn't you remove the motor before removing the caliper?
 
The Service manual states that is removed they should be replaced - so I bought 4 new ones in readiness.
That's pretty standard practice because when you remove them, you disturb the thread locking compound on them. In practice, by the time they need to be removed, the thin layer of rust is plenty to hold them securely anyway. I've never replaced one and never had one come loose, but what you're doing is correct and "best practice".
 
As a cautionary note, if people don't know what they are getting into there are some jobs best left to professionals or at least those who do know what they are doing.

At least one more page to go :D
 
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