650 Twin front brake issue

[Buz]

I have a 2008 650 twin, covered about 8K5 miles.
Intermittantly when braking the front lever feels stiff as if there is something between the brake pads and disc (there isnt, just trying to explain) The only thing i can liken it to is when you pump a cars brake pedal without the engine running, its hard to push and feels like there is a lot of resistance there.
The front disc has been changed along with the brake pads due to a warped disc, it also happened a few times before this was changed.
As said, it happens very intermittantly.

Anyone any ideas?
If it was the servo would it affect the rear brake as well? (rear one seems ok)

 

[Schtum]

Your bike doesn't have a servo. It sounds as if it's a problem with either the master cylinder or your front brake caliper. Have you ridden the bike through the winter? If so, the brake caliper(s) may need to be overhauled.

 

[Buz]

Your bike doesn't have a servo.

shows how much i know about bikes

Have you ridden the bike through the winter? If so, the brake caliper(s) may need to be overhauled.

No, i didnt ride it through the winter, it was stored in a centrally heated garage, well, the central heating boiler is in the garage.......
I'd have thought the dealer would have checked the caliper when they serviced it and changed the Disc, there agin

 

[v8legend]

Have you got ABS?

When the ABS activates, the 'brake feel' does change. You're most likely to feel this if braking on a bumpy surface.

 

[Blind Lemon Ade]

Did they identify the cause of the warped disc?

Could it be that the brake caliper pistons are siezed, as Schtum said, causing either the pads to remain in contact with the disc, thus warping it, or the lever to feel "solid" ?

I've never noticed the front ABS cut in on my 650 twin, even when sliding over a diesel spill the other day...

 

[Greger]

Are the calipers floating on this model? - other bikes have had calipers that have stuck so may be worth a look.

 

[bobbsy]

I have exactly the same happen on my 800. Its definitely something to do with the ABS - it happens after te front wheel goes over a sharp bump, the front brake lever feels like it is "frozen" for a second or two, then normal action returns. Have had it checked out twice - both times they say they cannot replicate it...

 

[Smythson]

Same here - to replicate try braking over speed humps. ABS every time

 

[Buz]

I have exactly the same happen on my 800. Its definitely something to do with the ABS - it happens after te front wheel goes over a sharp bump, the front brake lever feels like it is "frozen" for a second or two, then normal action returns. Have had it checked out twice - both times they say they cannot replicate it...

I dont think it is the normal feel when ABS cuts in, to me that feels like grit between pads and discs. Now you mention the going over bumps bit that rings a bell, the road in to work is a bit potholed and bumpy just before it happened.

 

[chas820]

For me BMW got it wrong with the abs on the F800gs it`s far to sensitive.A bit of road which i use every day has a small sunken trench across it a few yards from the traffic lights and the abs activates every time,it`s nearly caught me out a couple of times.My old 1100rt abs would hardly ever activate even under severe braking.

 

[bobbsy]

I agree, I think the abs is very sensitive. When mine goes over the bumps, it doesnt activate as if the abs was working, it does something however and the front brake lever goes hard (you can't pull it in). After a few seconds this has gone and normal action returns. Very off-putting. I dropped the bike in a slow corner last minute as that happened just as was approaching corner, and couldnt lose the speed.

 

[Magnet]

Do you have handguards? Can be an issue with guard changing position slightly and the lever catching on it.

 

[kokni]

It happens also to me (2008 F650GS), even with the ABS disabled, and this weekend I am searching the internet for other guys facing this problem after the explanation I got offered by BMW service (see below).

My experience it that it happens quite often when going over several bumps or over a single pothole and less often when going over a single bump. Another interesting thing is that you have to press the brake level gently in order to reproduce this behavior. If you brake "decisevely" so to say, it does not happen as easily or the ABS kicks in and obviously you get the ABS feeling on the brake lever.

The combination of the right bump/pothole, speed, and braking force was a nightmare to explain at BMW service. When finally we managed to reproduce this behaviour, I got the explanation that:

(quoting) "floating calipers get slightly out of alignement and enough brake fluid pressure is required to put them back in alignement, thus, don't be afraid and brake more heavily+sharply when going over bumps/potholes. The ABS will take care of the excessive braking force"

Obviously this does not apply on the dirt with ABS disabled, which does not make me very happy. And of course I am not happy to brake sharply and rely on the ABS keeping the front wheel on track.

What do you think about this?