Servo Brakes - odd behaviour or character?

[ferg]

Hello folks,

I have a 2003 with the servo brakes. It had been on and off the road over the last few years due to a young family and playing about on smaller bikes on smaller trips. However I've been putting some energy back into getting it sorted.
I've replaced the brake lines and bled through the system. The brakes are their usual incredibly strong selves but when coming to a stop and still trailling the brakes I get an 'off on off on' from the front brakes. Just using the rear is fine. At speed or with a bigger input the front brakes are fine and operate as you'd expect them to. It's just at that last part with a very light pressure on the lever. I've re-bled the servo and wheel side of the system a couple of times and that all seems good. What should I be looking at next? I understand the sensors have a bigger operating range than the earlier systems but could that be the next thing to look at? Or is this servo character that I've forgotten about over the last few years?
Any experienced thoughts welcome! There are other issues too which I'll be looking for some guidance on too!

 

[Ian J Hartley]

You have a 2003 what ?

 

[ferg]

You have a 2003 what ?

R1150GS....

 

[Ian J Hartley]

Assuming you have no fault indications showing.

Try this

If you apply the front brake only, the front servo brake motor/pump should run continuosly. The pitch of the motor should vary depending on the pressure applied at the lever.

If you apply the rear brake only, the rear servo brake motor/pump should run and then stop. During the brief period the motor/pump is running, the pitch of the motor should vary with pedal pressure.

Ian

 

[ferg]

Assuming you have no fault indications showing.

Try this

If you apply the front brake only, the front servo brake motor/pump should run continuosly. The pitch of the motor should vary depending on the pressure applied at the lever.

If you apply the rear brake only, the rear servo brake motor/pump should run and then stop. During the brief period the motor/pump is running, the pitch of the motor should vary with pedal pressure.

Ian

Cheers Ian, I'll give that a shot. There are no warning lights etc and otherwise the brakes are working very well.

 

[Fireflyer]

I take it that you are not confusing the feeling that is experienced with a warped disc!

You mention that the front brakes feel strong in their stopping power from faster speeds and you only get the on off pulse at slow speed with light pressure on the brake lever.

This is a typical symptom/feel that warped discs can give with the pulsing feeding back when the discs push the brake pads back into the callipers pistons which in turn force brake fluid back up to the master cylinder and brake lever.

Worth a check

 

[ferg]

Yeah you're right it's definitely worth a check to rule it out. It doesn't feel like a warped disc from past experience and feels like the brakes are squeezing and then letting off in a reasonably quick pattern. I thought I would have felt something at speed too if a disc was out?

 

[ELIMINATOR]

Hello folks,

I have a 2003 with the servo brakes. It had been on and off the road over the last few years due to a young family and playing about on smaller bikes on smaller trips. However I've been putting some energy back into getting it sorted.
I've replaced the brake lines and bled through the system. The brakes are their usual incredibly strong selves but when coming to a stop and still trailling the brakes I get an 'off on off on' from the front brakes. Just using the rear is fine. At speed or with a bigger input the front brakes are fine and operate as you'd expect them to. It's just at that last part with a very light pressure on the lever. I've re-bled the servo and wheel side of the system a couple of times and that all seems good. What should I be looking at next? I understand the sensors have a bigger operating range than the earlier systems but could that be the next thing to look at? Or is this servo character that I've forgotten about over the last few years?
Any experienced thoughts welcome! There are other issues too which I'll be looking for some guidance on too!

After I retired, the 2003 bike was no.longer used in winter. Brakes didnt feel right when first using the bike again, no warning lights, but lever seemed to come back further than it used to. Seemed to rectify itself.
Next year it didnt get better. No warning lights, lever came back a long way, rear brake alone was OK.
After 114,000 miles and knowing the failure rate of the electric servo ABS, I removed it.
I dont miss it.

 

[Steptoe]

Yeah you're right it's definitely worth a check to rule it out. It doesn't feel like a warped disc from past experience and feels like the brakes are squeezing and then letting off in a reasonably quick pattern. I thought I would have felt something at speed too if a disc was out?

Check the abs ring on the wheel hasn’t any missing teeth or damage. It can cause the symptoms you describe.

 

[Fireflyer]

I thought I would have felt something at speed too if a disc was out?

If it’s quite out of true yes you will feel it at pretty much all speeds and again will get progressively more obvious as things slow down. At faster speeds (high rpm of the disc) the warped section obviously comes around a lot quicker and if it’s only slightly warped the frequency of the pulses can be so close together that it’s less noticeable, only becoming obvious at slower speeds as the frequency becomes less frenetic.

As it’s such an easy thing to rule out it’s worth a couple of minutes checking before launching into a more costly servo fix.
Don’t forget to have a squint for any high spots on the disc due to irregularities in the disc metal, a lot less likely but not unheard of

 

[Fireflyer]

Check the abs ring on the wheel hasn’t any missing teeth or damage.

Just curious- you might know the answer
As the bikes been laid up for a couple of years would a badly rusted abs ring cause any issues even if no teeth were missing?

Never allowed any of my bikes to get that rusty so haven’t got a barking whether it is a thing or not.

 

[DrFarkoff]

Just curious- you might know the answer
As the bikes been laid up for a couple of years would a badly rusted abs ring cause any issues even if no teeth were missing?

Never allowed any of my bikes to get that rusty so haven’t got a barking whether it is a thing or not.

Yes with a coating of rust on it the clearly defined signal is lost and the data to the control module is out of spec

This is an ABS 2 one that had been lying up for quite a few years and that "cleanup" was all it took to reinstate the ABS

Before


After