Changing brake pads

not really, but it is good practise to let the fluid out of the caliper rather than push it back into the system.

I didn't know that. Whyzat? Just to avoid spillages or...?

Si

Releasing the fluid in the caliper is good for several reasons on any vehicle: you get the caliper fluid out, which tends to have picked up the most moisture and gives you a certain amount of fluid change and the bleed nipples get moved and so have less chance of seizing. Also pushing the fluid back may over fill the master and cause spillage. I have also heard that some abs systems do not like having fluid pushed back, quite why I don't know. Either way, releasing fluid at the wheel is the modern recommended way and seems to work well and logically. I do the following: remove any fluid I can from the master cylinder and refill with fresh, clamp the brake hose, remove the bleed nipple completely and clean the threads on a power wire brush, grease the threads and replace, put a hose on the nipple and push the pistons back and tighten the nipple, do all the pad change palaver, replace the caliper, remove the hose clamp and using small stabs on the pedal push the pistons back out to regain a firm pedal, then repeat for the other side but you don't need to remove the fluid from the master as a first step. Finally re-check fluid level and test the brakes.

Sounds good to me, ta.

Si

I don't top up the master cylinder ever. So changing pads will not cause it to overflow. But I do change the fluid at the maker's recommendation - about every two years.

I've had three cars with ABS and never opened a bleed nipple when changing pads.

I am talking about many hundreds of cars, and best practise, particularly if you do not know the entire and exact history of the car.

Thanks Mr C

Yehbut, have you actually known for certain of damage being caused by resetting the pistons in the usual way? My guess it's yet another urban myth. As regards the master cylinder overflowing, if it has been topped up with the pads worn, use one of those household pump sprays to remove some. Avoids the possibility of introducing air to the system by opening a bleed valve - unless you intend changing the fluid at the same time. No bad idea on a vehicle with unknown history.

no air will get in IF you take care, greasing the nipple threads will stop air being sucked along the threads, clamping the pipe stops dirty, damp containing fluid going back up into the system, the tube on the bleed nipple will fill with fluid and prevent air going back in that way, once the piston is back the nipple is tightened and there is no chance of air getting in again. The other benefit of letting the fluid out is that if there is any air (left over from previous work) in the caliper then that gets expelled too, often leading to a better brake pedal afterwards. There are many sites on the internet that say not to push fluid back on ABS systems, one I noted was :