Quick brakes question

[IFFY100]

I just wanted to check the operation of the caliper pistons so was wondering the safest way to extend the pistons out of the caliper but WITHOUT them popping out? I was doing a brake change and thinking I push the brake pedal will piston come flying out? Capiler in question is the front 4 piston caliper

 

[fifermerc]

If your brake pads are wearing evenly and normally then that would point to the pistons working normally. Unless you're looking to overhaul the calipers there shouldn't be any need to bring the pistons further out of the caliper. If you're changing pads you will need to push or wind the pistons back to make room for the new pads. Also worth cleaning the slide pins.

 

[BigJase88]

Hydraulic pump however requires caliper on bench not on the car.

I dont think it would be a good idea to attempt while on the car

 

[Spider10]

I think he's asking if he pressed the brake peddle will it pop out and the answer is no it shouldn't pop the piston all the way out

 

[190]

The piston will come out but only in small increments for each push of the brake pedal. I think your desire to check the piston is free to move is a good idea. If the piston gets stiff then the hysteresis in the piston seal will not withdraw the piston slightly when the brake is released which will result in brake drag. If you are concerned, insert a piece of wood a little thinner than the brake disc and pads combined to limit the amount of piston movement. What I will usually do is push the piston back in and then out again several times to exercise the caliper. Frankly, single piston sliding calipers need all the help they can get to remain free of brake drag.

 

[ALFAitalia]

No....not unless you pump it several times. Pump it once or twice and get out and see how much its moved. Every time I remove my pads i push the pistons out a fair.way.....pull back the rubber boot, clean the piston and apply a thin coat of red rubber grease. All helps keeping things moving freely!

 

[OneForTheRoad]

Put something in between if it's 4 piston caliper. Like old pads etc. But only 2 may move ??? Here's the size of the pistons. Each full pedal push will get you about 10mm . Some are steel some are aluminium.

Steel 55mm long

Alu 48 mm long

 

[Petrol Pete]

Be aware that if you have 2 pistons ( either opposed or side by side) one might pop out easily - brake fluid/compressed air will take the path of least resistance - leaving the other piston stuck in the caliper. I got lucky on the last one I did as I was able to get a punch through the brake fluid feed hole and was able to knock the stuck piston out.

Not the end of the world when it happens but just something to be aware of when you have more than one brake piston.

 

[IFFY100]

No....not unless you pump it several times. Pump it once or twice and get out and see how much its moved. Every time I remove my pads i push the pistons out a fair.way.....pull back the rubber boot, clean the piston and apply a thin coat of red rubber grease. All helps keeping things moving freely!

Thank you everyone for the help and advice. I'll be servicing the brakes tonight and will do as directed. One last question - as obvious as it may seem - after pulling back the rubber dust boot, I take it you put a thin smear of red rubber grease around the circumference of the piston? I know this is a totally extra step of good practice?

 

[colinallcars]

Thank you everyone for the help and advice. I'll be servicing the brakes tonight and will do as directed. One last question - as obvious as it may seem - after pulling back the rubber dust boot, I take it you put a thin smear of red rubber grease around the circumference of the piston? I know this is a totally extra step of good practice?

High risk of tearing the boot, if you do it be careful.

 

[OneForTheRoad]

Thank you everyone for the help and advice. I'll be servicing the brakes tonight and will do as directed. One last question - as obvious as it may seem - after pulling back the rubber dust boot, I take it you put a thin smear of red rubber grease around the circumference of the piston? I know this is a totally extra step of good practice?

It's a bit pointless,given you push the piston back in fully . But it's a preventive measure I suppose when the pads get down and the piston does protrude somewhat.