Tricks for centering brake calliper pistons?

[Skylark]

I prefer using old destroyed pads and the spreader lever - so the pistons don't get marked - but someone should really make a proper pad spreader tool - should be easy enough with a set of old pads and a bolt - and a tig torch applied with some skill...

This is the baus of pad spreaders, its safe to use even without pads in,(granted at least one pad needs to be in or something that thick for the spreader to lever against and completely retract the pistons) the key is in that angled edge, what a joy to use, no screwdriver or in the moment DIY lever comes close.

http://www.partsgiant.com/p343470-park-tool-hydraulic-brake-caliper-spreader-tool

Park Tool Hydraulic Brake Caliper Spreader Tool

http://www.partsgiant.com/images/8UPRCE56EI36WS7V-product-large.jpg

A plastic tyre lever won't damage the piston. Use it to hold the working piston back and operate the lever to get the stuck one out. Repeat a few times until they work more or less evenly - it may take a few cycles.

 

Thanks that an excellent option, the issue I'm talking about is once the calliper is centered over the rotor and the pads are in, its that last 1-2mm to get the pistons perfectly balanced/even clearance on either side of the rotor. I would expect it to even itself out after a good ride but it tends not to, have experienced this on Hopes & latest gen Shimanos. Once you get them centered then it seems to be fine and they don't get uncentered again over time.

 

I've noticed often its this last little bit of fine tuning that is the only way to get your brakes into that perfect zero rubbing zone of bliss!

[Skylark]

Which brakes are you talking about?

 

Because if it is like a double piston issue and it keeps on recurring after pushing them back all and using the brakes again, then you have to clean the pistons thoroughly (my Hopes gave me this issue a lot, so I bought Guides  )

 

But otherwise I do what V12 also mentioned, (with double pistons) old brake pads in and gently pushing them back with a flat tool a bit at a time both sides so it kinda goes back equally and not one (or one side) fully with the other still out completely. 

 

Mmmmmm interesting, was thinking of going from single piston to dbl piston Hopes, did you have those issues with the Tech M4's?

 

The problem I've experienced with pushing the piston back in(its allways the one difficult bastard) is the same one just pops out again when you let go, to do it properly you have to hold the one piston back and then squeeze the brake lever which allows the opposite piston to come out some more and then that seems to equalize the fluid balance behind each piston. It is a bit of a fiddle!

[NotSoBigBen]

Don't do this. 

 

Can you be a bit more specific why not, just so I know? As an aside the brakes I did it on are on my training bike (did it before Xmas) and still work perfect;y ....

[GrahamS2]

Can you be a bit more specific why not, just so I know? As an aside the brakes I did it on are on my training bike (did it before Xmas) and still work perfect;y ....

Q20 and rubber piston seals don't mix well...

[hayleyearth]

Can you be a bit more specific why not, just so I know? As an aside the brakes I did it on are on my training bike (did it before Xmas) and still work perfect;y ....

 

As just mentioned the rubbers in a hydraulic brake assembly is very finicky, hence all the drama about which manufacturers recommend which break fluid etc etc.

 

Also even though there is a rubber 'protecting the brake fluid from coming past the piston' it can not 100% guarantee that non of your Q20 will go and contaminate the brake fluid - and that liquid, well that is even more finicky. 

[mikkelz]

I've noticed often its this last little bit of fine tuning that is the only way to get your brakes into that perfect zero rubbing zone of bliss!

 

And what a wonderful zone that is! 

[droo]

Thanks that an excellent option, the issue I'm talking about is once the calliper is centered over the rotor and the pads are in, its that last 1-2mm to get the pistons perfectly balanced/even clearance on either side of the rotor. I would expect it to even itself out after a good ride but it tends not to, have experienced this on Hopes & latest gen Shimanos. Once you get them centered then it seems to be fine and they don't get uncentered again over time.

 

The bit about holding the free piston back and cycling the stuck one in and out a few times is what gets them working evenly again - it shifts the gunk out of the bore and frees up the lazy piston. If this still doesn't work, bleed. If that doesn't work you'll need to replace pistons.