1250GS front brake calliper question

[Mart75]

Just cleaning the front brake callipers on my 2018 1250 - when squeezing brake lever only one piston moves - the AI summary on Google suggests that pistons may move at different rates - wondered if any of you know whether this is the case or whether I should be replacing the piston seals.

Thanks

 

[kevmax]

Unsure of the 1250 might be some type of progressive braking system, but can’t see how uneven pressure on the pad can be useful. Could be a jamming of that piston due to salt or road crud. Strip out the pads. Prevent the ok piston from moving, and squeezing the brake leaver until the stationary piston moves out a little( but not out completely) give it a decent clean with plenty of hot water and soap. Ensure it’s spotless before pushing it back in. Refit the pads. This maybe all it needs. Fingers crossed

 

[Hann]

It`s not unusual to see that.
Due to the small differences in the resistance/friction of the piston and seals the one with least resistance will always move before the other.
As long as the `stuck` one moves out easily once you hold the already pushed out one it shouldn`t be a problem. Just be careful not to push one piston out so far it comes out of the caliper body and leaks fluid, place something suitable like a wedge on that side of the caliper/piston to stop that happening.
A better test on how free they are is to measure how much force it takes to push them back in the caliper body - can you push them back easily enough by just hand pressure ?
Are the pads worn down evenly or have they gone wedge-shaped?

 

[Mart75]

Thanks
Pads are completely even - so not typical of stuck piston - will carry on and clean and see what happens

 

[the woodster]

I hade the same issue a couple of weeks ago and didn't resolve it at the time as I needed the bike back together for a trip the next day. I also pressed on the rear brake to see if that would move the 'stuck' piston, as I believe the GS has linked brakes? I then read that the front lever operates both front and back brakes and the back foot pedal only operates the rear. I await your findings as I do need to return to it!!

 

[siddo]

Hold each of them in place in turn until you have checked them all.
There's a lube you can buy for them and I used it when service/cleaning them. https://www.ebay.co.uk/itm/261534699479
They all moved in with finger pressure.

 

[seahorse]

Rubber grease is the way. Don't use silicone grease it's too slippy.

 

[Mart75]

Thanks - I've managed to see that they all work - though two on one side come out before the two on the other side (on each of the callipers - as Hann says probably to do with friction of individual pistons and the way in which the hydraulic fluid moves to apply pressure. So they all move out and I can push them all back in individually with finger pressure - so alongside the fact that brake pads are evenly warn - think everything is OK - they are now much cleaner too!

 

[Nick dj]

With sensible mechanical knowledge you can improve it with the callipers still on.
Warning push only one piston back at a time as there is not enough room in the Master cylinder for too much brake fluid!
Work one sides single piston back into the calliper, using the exposed tabs on the top of the pads, once started you can use a wide blade screwdriver between the pad and disc to do it gently you do not want marked or chipped pads. I also brush the newly exposd part of the retaining with a soft wire brush (brass) to clean it.
Then pump out again with the brake lever- repeat.
Now do the other piston, then the other side.
You will notice a big improvement in the brakes action.
If its really badly sticking you may need to remove the calibers and pads, but this needs step by step guides and spacers or you could pump your pistons fully out and brake fluid is highly corrosive.

 

[longdog]

My mate’s R1250GS which he has had from new in 2023, has had issues with brakes binding for ages. He took it back to the main dealers who pretty much dismissed it as “normal”. Long story short, after just about 14 months of trying to get the main dealer to sort it, the dealership lost the BMW dealership, meaning no more BMW dealers in Wales. He had to take it to a dealership in England and they got in touch with BMW Motorrad UK. The dealership said the callipers needed changing but BMW Motorrdsaid “no, there are no manufacturing faults with the callipers”. They had his bike for almost 2 months and charged him £1100 to replace the callipers and after lots of arguments, Motorrad finally offered my mate £250 as compensation. My mate said the dealership in England were brilliant but Motorrad no so much.

 

[the woodster]

My mate’s R1250GS which he has had from new in 2023, has had issues with brakes binding for ages. He took it back to the main dealers who pretty much dismissed it as “normal”. Long story short, after just about 14 months of trying to get the main dealer to sort it, the dealership lost the BMW dealership, meaning no more BMW dealers in Wales. He had to take it to a dealership in England and they got in touch with BMW Motorrad UK. The dealership said the callipers needed changing but BMW Motorrdsaid “no, there are no manufacturing faults with the callipers”. They had his bike for almost 2 months and charged him £1100 to replace the callipers and after lots of arguments, Motorrad finally offered my mate £250 as compensation. My mate said the dealership in England were brilliant but Motorrad no so much.

Bollocks to that. The Consumer Law Act 2015 would cover this if they refused to honour the warranty. I'd at least get a solicitors letter off to them, especially with the dealers support.

 

[Pukmeister]

FWIW a quick brake tip.

Years ago as a young rider my lever came almost back to the bars. Couldn't seem to solve it, took it to a local Indy. He showed me how the disk was flexing sideways under lever action as one pair of pads came out first before the others (possibly due to less friction as all pistons were clean), resulting in massive lever travel before they all eventually clamped the disk.

His solution was to put a large flat screwdriver between pad and disk on the closer side, then pull the lever to reduce the travel on the other (furthest away) pads until both pads touched down and clamped the disk at the same time. No more excessive lever travel, massive increase in stopping bite/power/feel.

Another tip, when cleaning brake pistons put a piece of scrap wood in the caliper and then fully pump out the pistons so you can clean the piston skirts using an old toothbrush and a can of brake cleaner without fear of popping a piston out and losing hydraulic fluid.