I've shortly got to undertake the above on my partners 1.2 Nissan Micra with ABS. Now whenever I've changed pads before(non ABS cars) I have just slowly pressed the Brake Piston back in to allow for the thicker pads to be inserted, never had any problems.
The haynes manual says its ok to do it that way but suggests you should clamp of the brake flexi and release the bleed screw before pushing the piston back to prevent potentially flipping the seals in the master cylinder. I've also read somewhere else that you should also follow this method to prevent contaminated fluid entering the ABS unit?
My worry is that due to the cars low mileage, this may be the first time the bleed nipple has been undone and I dont want to go and snap it off if there was no need to do it this way.
And how soon is "shortly"? If you can, get some penetrating fluid onto the threads of the bleed nipples once a day for several days before doing the job. You should be able to do this simply by putting the wheels on full lock, so no need to jack it up.
best practice on any car is to clamp the flexi and let out fluid at the bleed nipple.
The car should have already had a couple of brake fluid changes, so it should not be the first occasion that they are undone.
I have not come across a nipple that snaps off in the last twenty five years or so, before that I saw a few, mainly on bikes where they use alloy calipers with steel nipples and alloy wheel cylinders on cars.
The sequence I use is: use a sucker to remove as much fluid as possible from the master cylinder, refill with new unshaken fluid. Clamp the flexi. Using a single hex socket preferably and with a tbar first slacken the nipple, then wire brush and blow away away all the crap that is around the nipple (to stop it falling down the hole), then undo and remove the bleed nipple, clean the bleed nipple (I use a power wire brush ) grease the threads of the nipple (to stop air going along the threads as well as lubrication) and replace it without doing it up tight (leave it about half a turn loose) put a bleed tube on the nipple, undo the caliper and get it free of the pads (at this stage you see why the nipple is left loose, as some fluid will come out during caliper waggling about) press the piston(s) back in, observing the dirty fluid coming out, no air will get back in thanks to the tube full of fluid and the grease on the threads, when the pistons are back, nip up the nipple with a spanner, remove the tube and gently tighten with a socket. After pad relacement, cleaning, putting back together etc. remove the flexi clamp and pump the brake pedal a few times using short presses on the pedal (this avoids pushing the seals past areas of the master cylinder that have not been used before). Once a firm pedal is obtained, check the fluid level (should not have changed significantly) do the other side, after that check the fluid level, start the engine, press the pedal hard and check for leaks.
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