Subaru Forester Owners Forum banner

1 - 5 of 5 Posts

·
Registered
2005 FSTI 'The Limo' Manual
Joined
·
420 Posts
Discussion Starter #1
When referbing the calipers to go on my foz I noticed that there were 3 little knobbles on the base of the piston.

Does anyone know what these are actually for?

My guess is that they are there to retain some fluid behind the piston when you push them all the way in (ie when changing pads) thus making it easier for them to come out when you first push the brake pedal.

Im now refurbing my impreza 4 pots and have seen stainless pistons but they are flat on the bottom with no knobles, yet the original 4 pot pistons have a small recess and 3 knobbles (see pic)



If the stainless piston manufacturer has left them off are the knobbles that important?

Any help/suggestions greatfully received!
 

·
Registered
1997 T/tb
Joined
·
511 Posts
you could be right,

also it creates a larger surface area.

do these pistons need screwing in to retract them? there might be 3 locating holes in the bottom of the caliper so you know that it is fully home.
 

·
Registered
2005 FSTI 'The Limo' Manual
Joined
·
420 Posts
Discussion Starter #3
No locating holes and they are not screw retraction.

The reason Im asking is my father-in-law is in the metal fabrication business and can get me some stainless pistons made. The pistons can be made on a lathe but if the knobbles have to be added then they will have to go on another machine too so costs will go up. As other stainless piston manufacturers are making them without the knobbles I think I will have them made without and try them out.

Once made and tested Im looking at getting some more sets made up if anyone is interested?
 

·
Registered
99 UK S-turbo
Joined
·
8,566 Posts
I would imagine as you suggested its to prevent them 'sealing' back inside the housing, where in theory (if unlikely) you could create a scenario where if no fluid can get behind it it won't come out under hydraulic pressure, it would only need a small groove across the rear face for the same effect, or just make it plain and rely on a little luck!

Simon
 

·
Registered
2005 FSTI 'The Limo' Manual
Joined
·
420 Posts
Discussion Starter #5
I know someone who bought a set from godspeed and they make them flat on the bottom so thats what I have gone with. Should be completed by the weekend and with me by the middle of next week.
 
1 - 5 of 5 Posts
Top