Brake Caliper specialists please?!

[KevinRussell]

Hi all

While changing brake pads on a Merc A180 I damaged the brake piston so I have one on order.

I know how it goes back on but should the rear/hollow of the replacement Piston be filled with fluid first or does the piston fill up when I unclamp the brake fluid pipe?

Where does the air in the piston go?!

Cheers
Kevin

 

[Mottie]

If you lightly clamp off the hose and open the bleed nipple, that will allow most of the air to escape when fitting the piston then just give it a final bleed when it's all fitted back together.

 

[KevinRussell]

Mottie

Thanks for the quick response. That all makes sense - thanks!

Kevin

 

[Harry Bloomfield]

Every caliper includes a bleed nipple at the highest point. Once it is all back in place, you need to bleed the caliper of air....

You need to check the master cylinder has a good level of fluid to begin with and it will need two people...
press the brake pedal, hold it down, whilst undoing the bleed nipple to release air, then close it, release the pedal and repeat...

Keep repeating, until no more air comes out of the nipple, just fluid. Keep a close eye on the fluid in the master cylinder and keep it topped up throughout the operation, between pumping the pedal. Don't get the fluid in your eyes, or on the pads and disc.

 

[KevinRussell]

Thanks Harry, there are two of us doing it. The front Discs and Pads were simple but when doing the rears it turned into a bit of a challenge! Still, every problem is the opportunity to learn

 

[Tigercubrider]

At the risk of sounding like an idiot, your pistons go in with the hollow side to the calliper?

my only experience is with AP Lockheed callipers on 70’s Triumph motorbikes. They are the same as on a mini.
The hollow side points towards the disc, the flat side towards the fluid.

 

[Mottie]

Are they rear callipers with screw in pistons?

 

[KevinRussell]

the hollow side goes into the Caliper, there is a threaded shaft with a ball on the end then rests inside the piston. when the shaft is rotated by the Caliper motor it moves in and out pushing the piston against the pads.

The hollow side is inside the caliper and was full of fluid when it was removed. I woke up at 3am wondering how to refill it!!

 

[Mottie]

So it's a rear calliper with an electric parking brake? Personally, I'd just fit a new calliper.

 

[johnny2007]

Don't forget to grease the piston.
I use ceramic grease, but i know many use copper grease without any problem.