Front brake intermittently disapearing

[nigmar]

Help needed 07 1200 GS

Just fitted new discs and pads test rode all well for 15 miles then had to pump brake lever to get brakes to bite. Happened a few times now, not sure what I've done. Any help much appreciated as I'm off to Wales on it Sunday.

Thanks in advance
Nigel

 

[duckspeed]

Are you sure that the disc is mounted correctly? as it sounds like it's running out of true effectively pushing the pads back

 

[nigmar]

They look like there running true and it's not happening all the time.

 

[duckspeed]

Maybe you have air in there has it got ABS?

 

[nigmar]

Yes it has ABS, could it get in without opening the system?

 

[nigmar]

I'm going to check they are running true as I had the wheel powder coated whilst it was off, maybe there is a build up on the fixing surface.

 

[duckspeed]

I think that's most likely to be honest a dial gauge will be the best measure of run out

 

[nigmar]

Checked the run out today only 0.2 mm. A lot of movement on the near side disc against the spring washers so have shimmed it so it's closer to the movement of the off side (0.5 mm ) this seems to have improved the problem but not totally eradicated it.

 

[duckspeed]

Sounds like you are on the right track

 

[nigmar]

Wishful thinking I feel, seems to be getting worse!

 

[JJH]

Check for vapor lock. It happens when the brake fluid gets contaminated and its boiling point lowers. When the brakes get hot trough use or slight binding the fluid boils and you loose the brakes. It's known as the silent killer as when the brakes are checked afterwards they are working as they have cooled and the brake fluid is again fluid.