Sticky piston

[Santa-2512]

So following on from my rough running,

I noticed that the bike would occasionally slow as though it was pulling shit through the injectors,
keeping a WOT it would cleqr and normal running was resumed

Then a couple of days ago, i though I had a flat , the bike was very hard to push, but once rolling , normal service was resumed

I'd run some fule stabiliser into the tank, so i was confident it wasnt that

Anyway comming home tonight at about 50mph, i tapped the brakes to bleed off some speed for slowing traffic

And it kept slowing and slowing, i needed more throttle to stop the bike from stalling, going down through the gears

and as fast as it started it stopped, and i carried on as normal

Brakes was my first thought, and when i got home i went checking

Rear disc, cool as a cucumber , so not that

Front right disc again cool

Front Left disc , hot .. Stoppie hot !!!!!!

and there is a slight hue to the disc , not blued, but it has a slight colour

So the strip down commenced

The pads pin , was sticky and is showing early signs of wear, so I'll replace them both

The pads came out with a bit of wiggling , lots of caked brake dust but in reasonable condition

The wear bars are still evident on the pads, so there not worn out, but the LH pad has a strange mark on the contact face , might be nothing, bot worth noting

The two inboard pistons went back in very easily, the two outboard pistons are hard to get back in

I used the old pads as spacers and pumped the inboard pistons back and forth , there free and I'm happy with those

The outboard pistons are what is troubling me , I've managed to free the lower piston, Leverage & brake cleaner , and it goes back in with a lot of pressure

The upper piston needs a lot of pressure to get it moving back in from extended, but after a certain point moves a bit easier,

They don't look scored or stuck they just don't like to move

I turned the pads round and dropped the mounting face onto the piston, and pumped it, to simulate a metal to metal contact and then sprayed the piston with brake cleaner


Again its a pita to get moving and back in

Any ideas, or is it new calliper time ?

 

[Gee-]

Might be the inner seals have gone, and muck has gotten in between the piston and caliper wall.
Buy yourself a used caliper to swop over so you can strip the sticky one and rebuild it, after deep cleaning
and new pads
Motorworks have used calipers, for £100.00 handy spares.
I have done this a few times on different bikes over the years, so I can keep riding. Good luck.

 

[Pukmeister]

I would get it rebuilt professionally by a specialists, I think “powerhouse” was a company name.

FWIW a mate just came off his Speed Triple on the A3 at high speed last week and he thinks it was due to a jammed piston. He was lucky not to have hit the Armco at speed or get run over.

Edit: trading under a new name…..

https://brake-masters.com/motorcycle-brake-caliper-refurbishment-service/

In my experience it’s the expansion of corroded bare alloy in the piston outer dust seal groove that grips the pistons and causes sticking, requiring a full calipers strip and rebuild with fresh seals.

 

[seahorse]

If you rebuild the calipers yourself, I believe the recommendation is to not split the caliper halves. Doing so is likely lead to leaks after reassembly. Seal kits don't even include the little o ring that goes between the caliper halves.

 

[Santa-2512]

So i popped the pistons back and worked them a few times , seems ok

Fitted new pads, and all seems good on a the test ride,

Ill keep and eye on it , if not its £300 for a new caliper , and then the mad scramble for someone to fit it before i go away lol

 

[Santa-2512]

Dont think its all good at mill

When i got to work this morning , LH disc hot , Rh disc cold

Summat is not right

rather than faff around with refurb kits , i may just bite the bullet and order a set of calipers , at least i know ill get another 15 years out of them

 

[seahorse]

I did the same although mine were only beginning to get a bit sticky. Bought a pair off here for 90 quid and will refurb the originals so will have them ready for the future.

 

[botus]

its corrosion behind the dust seal and the brake piston seal - clean it up with a dremel
the dealer's stock (or should), new pistons and seals in a rebuild kit (4 pistons and 8 seals per kit)

if the pistons are not stone chipped or corroded - you can pull it apart without fitting anything new - but its a little naughty - but remember the mess you are riding with now - is the very same stuff - just stuck with rotting seal grooves !

 

[Santa-2512]

So i rang my mechanic today,

he said unless i can get the callipers for virtually FOC, don't bother, he will strip flush and clean / grease everything up

so booked in for week after next

 

[Slipperyeel]

Only just seen your post. After you mentioned the LH disc was hot, I was thinking seals. Maybe new pistons if they've been scored. But it's a relatively straightforward job, especially if they're still moving in and out!!
Maybe fit new pistons as well?

 

[Santa-2512]

Only just seen your post. After you mentioned the LH disc was hot, I was thinking seals. Maybe new pistons if they've been scored. But it's a relatively straightforward job, especially if they're still moving in and out!!
Maybe fit new pistons as well?

I'll let you know. What the menders say

It's booked in for next week