Brake caliper

[totty]

Hi,

The Haynes manual says that it should be possible to push the piston back in easily by hand, is this correct?
I can't budge mine by hand, but I'm more used to working on cars and generally having to use a bit of force/leverage to push the pistons back so this seems normal to me.
I've also found cracks in the hose so it'll have to be replaced.

Cheers

Allan

[matthewmosse]

I give the thing a damn good scrub with a toothbrush and then some coppa slip, then push it back in with a g cramp, often I'll push it back in and out a few times to free things off a bit (winter riding not nice to calipers) As for brake hoses I get stainless braided hoses from Custom Fastners and replace the whole lot. Having said that I now have the odds to re make the steel lower pipe with nice shiny copper so I might have a go at that next time I'm bike playing.

[totty]

I've got braided hoses on order, Earls from M&P.
Also just been out and bought a G clamp. Am I right in thinking that if it doesn't free off enough to move by hand I'll need a new piston and seal to rebuild it?

Cheers

Allan

[Bryanj]

The usual problem is a build up of special additive (SH*TE) in the seal groove behind the seal, Seal is cheap (

[totty]

In that case if it doesn't free up I'll pop the piston out and look for pitting before ordering anything.

[SteveD CB500K0]

Very rare to be the piston.

You need to strip it down and clean it.

Once done, it should be fairly easy to push the piston in by hand.

[Yoshi823]

In my SOHC owning days I used to see this situation regularly. It's not worth using a G clamp in this situation...if it won't go back in by hand, then after you've pumped it out under normal useage, the piston won't retract back into the caliper & the brakes will stick on...very dangerous. It takes so little to pop the piston out & to clean everything up...you will be pleased that you have after you see the gunge that is inside of the caliper.

[totty]

I pumped it out and forced it back in 6 or 7 times earlier tonight and it hasn't freed up, can also see what looks pitting on one side of the piston so I'll pop it out.

[K2-K6]

The ali bore before it gets to the seal groove is exposed to salt etc and usually corodes enough to go tight on the piston.

Can always push in with thumbs if operating correctly.

If you spray WD40 or similar around this and then move in / out it usaually gets easier, if so you've still got to take piston out and clean properly.

The groove and piston seal are sized (square in section) so that when you stop pulling the lever then the seal has the effect of withdrawing the piston slightly to stop the brake rubbing and building up heat when not applied.

After reasembly I put copper slip round this point to keep it cleaner in use. Cars and many later bikes have a much better crud seal on this area as I'm sure you're aware.

[florence]

I have been riding my Cb500/4 for 15 years winter and summer and I am now on my 4th piston, replaced as always due to corrosion and siezure.

Pump the old piston out and carefully scrape away any corrosion, a piece of wood is good for this as it does not damage the aluminium.  Next, clean with a rag, old towelling material is good and use brake fluid as a lubricant.  Once it looks pretty clean put in the new seal and press the piston back by hand again using brake fluid to lubricate.  The usual cause for it not going in easily is mis-alignment.  If you are putting it in correctly it will go in by hand fairly easily.  If you are forcing it with a clamp there is something wrong and you may damage the caliper.

While we are on this subject I have recently bought new brake pads from David Silver and I must say they are excellent.  I had EBC before and, althought they lasted for years, they were tough and unresponsive.  With these new pads there is a lovely feel to the brake, no squeaking, and two finger braking very usable.  Very impressed, it has transformed the machine.  I think they are made by Brembo but whatever they are they are the ones Dave Silver is stocking.

[totty]

The piston is now out and it's quite clean in there apart from some muck in the seal grove, the piston is quite pitted in a couple of areas and is tight in the calliper at those points.
I've got the parts on order from DS including new pads, bleed nipple, adjuster bolt etc. I considered the Phenolic option but went for what DS had in stock so I know I'll get it in time to fit at the weekend.

Thanks for you help guys.

Allan