'94 Merc C220 front caliper piston retraction

[DIYspanner]

W202 / W202 2.2 petrol

I've been tasked to sort out sticking brakes which turned out to be a rusted slider pin as a result of a split rubber bellow.

The caliper has no apparent bleed nipple, not even a snapped off one and I'm very reluctant to push the fluid back in to the master for fear of flipping the seals.

Had a look on youtube video and with the aid of a caliper winder tool that's exactly what you do.
Naughty mechanic not wearing eye protection whilst using a windy gun in the demo!


Very strange pad TWI set up. A module is bolted onto the caliper which I couldn't remove cause the head chewed in the socket so its can stay put. Rubber coated wire end pushes into a hole in the pad.

 

[Burnerman]

Looks pretty conventional, apart from the pad wear sensor idea!
A G cramp is fine for pushing the pistons back in.....slowly if it spooks you!
What’s this about no bleed nipple......surely there is one
John

 

[DIYspanner]

Well I certainly looked for a nipple!

Only thing I could see was what looked like a cross head screw.

A bleed nipple is such an obvious object to see.

Anyway, I have a full piston winder kit so I'll do as the video shows. Only has to go back a couple of mill.

 

[Burnerman]

I reckon that cross head screw is a sheared off bleed nipple ?
Dont panic about flipping the seals over in the master cylinder.....you’d have to push the piston back very quick to do that.
Just watching the video....I use ceramic grease on all of the pad contact areas on its bracket, the same on the hub - and also the slider pins. He didnt degrease the new disc either, but not all makes need this.
I wish my garage looked like that!
John

 

[DIYspanner]

Thanks John!

 

[fixitflav]

I'm very reluctant to push the fluid back in to the master for fear of flipping the seals.

I wouldn't worry about flipping the seals. I have a 2004 Mondeo, and the Haynes manual says undo the bleed screw as the reverse flow of fluid into the master cylinder "has been known to" "flip" the MC rubbers leading to a total loss of braking. I think that's "flipping " nonsense for various reasons, mainly that when the pedal isn't depressed there's an open route for fluid back to the reservoir. And Haynes doesn't mention it for the front brakes, though the piston can be pushed back much faster than the rear one can be wound in. And why would the very modest brake fluid pressure due to retracting the pistons cause flipping, when the high pressure from braking doesn't? So I ignore it, never any problem.

 

[DIYspanner]

Job done!

Used a proper caliper piston retract tool and this both sides went back sweet as a nut - no leaks and no master seals flipped, a good brake pedal when finished.

Certainly no bleed nipples that I can, see only cross head screws so maybe the nipples have been replaced with screws?

 

[Burnerman]

Pleased the job is done!
That caliper is looking rather moth eaten and Id still guess the nipple has been sheared off.
The only system I have seen with no nipple is a tandem set up on a motorbike, where there are two banjo connections and pipes on one caliper, and one nipple on the other side. Cant recall which bike though!
John

 

[fixitflav]

Certainly no bleed nipples that I can, see only cross head screws so maybe the nipples have been replaced with screws?

There must be something, if only for initial fill in the factory. Is the other caliper the same? Calipers I've seen have identical tapped holes for brake hose and bleed screw, so can go on different cars, and use the top one for the bleed screw.