Rear Brake on a R1150GSA

[roddy]

Folks,

Need a wee bit of advice, my rear pads are needing replaced so I thought I clean the calipers at the same time, they weren't too bad with crud and have cleaned up okay.

the bike is a R1150GSa servo model. with the ignition off should both piston move out at the same time when you press the pedal ?

I ask since when I press the pedal only the piston nearest the front moves, but if I hold the front piston the rear will move okay, and if I press both the pistons back in using my hands it feels like both need the same amount of pressure to push them back into the caliper which would suggest both pistons are free of excessive crud and moving freely, also the worn pads have worn evenly (IE not lob sided along there length)

Is this just a quirk of the servo system or something else ?

any pointers would be helpful, cheers

 

[Tallbloke]

no expert on this model but engineering experience tells me the fluid will take the route of least resistance, and move the first piston, until you hold the first piston, then the route is the second piston, hence it moves...???

 

[sproggy]

Both pistons should move together, with or without the ignition on. The servo makes no difference. If one doesn't move then it's tighter, but even brake pad wear each side suggests that the difference is insignificant.

Not sure what you mean by front/rear pistons, though - there's only one each side

 

[roddy]

Not sure what you mean by front/rear pistons, though - there's only one each side

The rear caliper is a sliding design so only has 2 pistons both on the same side of the caliper, so with the caliper fitted to the bike, I mean the front piston the one nearest the engine, rear piston will be the one furthest from the engine.
Hope that clears up what I meant

my experience with brakes is limited but in the past on other bike models when I've replaced pads and checked all piston where working they all moved at the same time ?

 

[sproggy]

It's been a while since I changed rear brake pads - I'd forgotten the details. Would the calliper be designed to have one piston move first to reduce/prevent squeal? Either by having different sized pistons (from memory they're the same, though?) or by restricting fluid flow slightly to one of them?

 

[Number 6]

....... if I hold the front piston the rear will move okay, and if I press both the pistons back in using my hands it feels like both need the same amount of pressure to push them back into the caliper.....

The fluid will always move the 'easiest' piston first. Don't worry about it, if you can move both pistons by hand then it's fine

 

[roddy]

cheers for the reply's folks, I did suspect it was nowt tae worry about, but thought it best to ask