Drilled hole in brake piston .... Why?

[ConcreteMike]

Hi, I found a brake fluid leak on the rear brakes for my iveco daily, and when I took the caliper off I found a small hole (approx 1mm) drilled into the dust boot recess on the piston during manufacture.

Can anyone shed light on what this is for? I'm guessing that it shouldn't have brake fluid coming out of it, and given that it has, I guess I need a new piston . The caliper and the piston are in great condition so I think it's only a couple of years old. Even the dust seal looks really good, but it's lost all my brake fluid after standing for a few days.

I also can't seem to get the piston out. I assume it needs to wind out anticlockwise but I must have twisted it around 50 times and it still won't come out. Do I need to stop the mechanism inside from twisting somehow?

Thanks, Mike.

 

[Kram]

Usually pistons are hollow open ended shapes, so the open end where your groove and hole is, should have no fluid inside. This keeps fluid well away from the brake pads and stops it getting excessively hot and boiling too easily.

Have you a pic looking up the end of the piston?

*Maybe not on the newer stuff..

 

[Ruffian]

That ridge should only be for the dust seal,

Fluid o ring should be in the bore further down and not reach that position.

 

[Ross365]

That ridge should only be for the dust seal, Fluid o ring should be in the bore further down and not reach that position.

Yes. The pistons are chrome plated steel; wonder if the hole is something to do with suspension in the plating solution? Never seen one like that.

 

[zzr1200]

As the pads wear, air will enter the dust seal to stop suction pull back, when you fit new pads as you squeeze the pistons back, the air will escape through the hole without popping the dust seal out of its seating groove, also any fluid by-passing the seal will end up in the piston cavity and then run down the back of the pad to below the fiction material.

You need new calliper seals and probably new pistons, but I'd price up pattern part brake callipers first, you might be very surprised.....

 

[Ross365]

As the pads wear, air will enter the dust seal to stop suction pull back, when you fit new pads as you squeeze the pistons back, the air will escape through the hole without popping the dust seal out of its seating groove, also any fluid by-passing the seal will end up in the piston cavity and then run down the back of the pad to below the fiction material.

You need new calliper seals and probably new pistons, but I'd price up pattern part brake callipers first, you might be very surprised.....

Wow, never knew that, but makes sense. Re-building callipers is one of those jobs where sometimes everything falls in to place, but other times, can become a real pain in the Rs

 

[Kram]

The pistons dont look damaged in any way. Seen much worse on motorcycles that work fine.
Id suggest popping the pistons out and thouroughly cleaning the seals and seal grooves.

On cars, pistons are pushed back in all the time. On bikes, with a less adequate dust seal design, crap gets in to the piston seals when they are pushed back. Cleaning can remove it, but new seals are best.

Note that pattern seals are often shiet, its worth getting either genuine seals or ensure they are equal quality. I have had bad new seals.

 

[colnerov]

That piston looks a long way out, enough that it's come past the seal and is allowing the fluid to leak out.

Colin

 

[graffian]

That piston looks a long way out, enough that it's come past the seal and is allowing the fluid to leak out.

Colin

I would guess hes trying to take it out.

 

[bricol]

If you want a way to get them out that I have never repeated . . .

Wrap the fingers of one hand around the reaction frame opposite the piston.
Use the other hand to hold an airline.
Use the air line to blow crap off the outside of the caliper, making sure to accidentally blast full shop pressure down the hose inlet . . .

Instantly drop air line and grasp the main caliper body and try to extract fingers from around the reaction frame, now pinned by the partially ejected piston.
Realize piston has cockled over and there no way you are pushing back . . .
Use the nearest large vice to grip the caliper and piston, winding the vice closed, thus forcing the piston, whether it wants to or not, back into bore, cockled or not . . .

Inspect fingers . . .

 

[Robert Weaver]

Is there a handbrake mechanism on the back of the caliper, not in the photo? If so, could the piston be stuck on that, so not coming out?

 

[ConcreteMike]

Thanks for all the replies, and yes pattern calipers look like they may be the most sensible option.

The piston is a long way out because I was trying to remove it. A little help with an airline saw it past the inner seal but it still won't come out. Yes there is a handbrake mechanism on the back and I guess this is what's stopping it from coming out, but I can't see what I need to do with it to remove the piston. I'll keep persevering :-)