650GS rear brake locking up

[Deleted account 190419001]

Posted for a friend of mine who has a 650 with a recurring issue with the rear brake. Its OK on gentle braking then goes from gentle slowing to locking with only a little more pressure on the brake pedal.

If the ABS is on it invokes the antilock, if the ABS is off it locks up. Pads and pins have been changed, everything moves freely, the disc is running true, anyone got any ideas as I'm out of theories....

Any help much appreciated.

 

[harry]

My guess would be the master cylinder seals.

 

[Dansin]

As above. The rear master cylinder corrodes on the inside which causes the piston to stick. Repair kits are available or new rear master cylinder.

Also worth checking the calliper pistons aren't sticking.

 

[Deleted account 190419001]

Thanks Chaps, seems sensible!

 

[Deleted account 190419001]

Back to the drawing board....

New piston and seal kit was installed at the weekend. Still doing the sticking thing....

Here's his thread from another forum, add to the list new piston and seal kit.... Anyone got and other ideas?

F650 GS 2005

Have a problem with the ABS kicking in when i use the rear brake - medium to hard braking. If i turn the ABS off the wheel locks up far to easily - seems to get worse the more i use it / the warmer it gets.

This only started after i had the wheel out to change tyres (new pair of Anakee 3's) so im guessing ive done something wrong as the back brake was excellent before i did this.

1) had the wheel off and on again, no difference

2) Changed pads (and new pin kit) - no difference (Old pads were thin but had worn evenly)

3) Double checked wheel alignment.

4) No binding when i spin the wheel.

5) Wheel bearings seem fine.

6) Adjusted the ABS sensor clearance - no change but ruled that out as the wheel locks up far too easily with ABS off.

7) Placed a pencil against the disc as i spun it and as far as i can see it isnt warped.

8) Caliper bracket is seated correctly & slides smoothly when using the chainadjusters.

9) Done plenty of miles on the tyre so its not slippy new tyre syndrome + front is excellent

10) Caliper piston and slider moves freely


Running out of ideas now so any help / suggestions appreciated !

Thanks

Andrew