[MarcosPC]

Hello, first time here

So, I have searched around here and altough I have found similar cases, I did not find a solution

Heres the deal, my 2023 GSA 1250 did the third service (12000 mile)on May

It had 7000 miles, and at the time they changed the brake fluid

After a while, I started noticing a weird brake judder, when becoming to a stop (20 km/h or less) and applying little pressure to the front brakes. It doesnt happen if I apply a little bit more force, and it doesnt happen with the rear brakes

I know, you will say its probably the brake rotors, and so did the stealership

But both me and them have measured lateral runout and its well within spec (at 0,03mm when the limit is 0,15mm)

And, plot twist , the problem COMPLETELY DISSAPEARS when I try the same thing with the ignition turned off (TFT off) and comes right back again when I turn the bike back on

I started endless arguments with the stealership and I already threatened to sue them, but they keep saying the ABS has no issues and that since the rotors are within spec they cant do anything else

I do not know what else to do, it is extremely hateful for me when that happens

 

[Freedomrider1776]

Go take a ride on a gravel road and get the ABS to activate multiple times, then tie or zip tie your front brake lever over night to see if that purges any more potential air in the system.

 

[CallMeSnake]

That sounds a lot like what my 2012 does. Under very light front brake pressure it feels like a warped front rotor when coming to a very gentle stop. I believe the cause is related to the linked brake system, which is supposedly controlled by the ABS module.

If bleeding it changes it for you, please post it here 'cause I'd love to get rid of this as well. Very annoying when trying to come to a precise stop.

I'll have to see if turning the bike off changes it for me.

 

[MarcosPC]

That sounds a lot like what my 2012 does. Under very light front brake pressure it feels like a warped front rotor when coming to a very gentle stop. I believe the cause is related to the linked brake system, which is supposedly controlled by the ABS module.

If bleeding it changes it for you, please post it here 'cause I'd love to get rid of this as well. Very annoying when trying to come to a precise stop.

I'll have to see if turning the bike off changes it for me.

Im sorry to hear you have the same problem

I wasnt going to say this to not have biased opnions, but yes, Im also thinking its the linked system

Because it doesnt feel to me that the problem is on the front brakes, but something seems to be pulling and releasing the bike from behind

I feel it “floating” its weight front and back instead of a “diving” sensation from the front

Did you check if there is any error codes on your bike?

 

[CallMeSnake]

No error codes. I always figured it's just due to the design of the system, but there's so little actual information on how it's implemented I wasn't willing to try and track it down further. I'd guess there is some sort of proportioning valve in the ABS module and that has enough stiction that at low pressure it toggles on/off vs giving a nice linear output. Assumed it was 100% mechanical, but there might be some electronic valve that engages it. I'll give it a try tomorrow morning and let you know what happens as well as if I feel it with the ABS disabled.

 

[CallMeSnake]

Found this little bit, dated 2006 in a BMW media release.

To provide the desired integral function, brake pressure for the rear-wheel
circuit is generated and built up by an electronically controlled hydraulic pump.
This offers the advantage of pressure management and control completely
independent of the front wheel circuit – which is the prerequisite for dynamic,
adaptive and, ultimately, consistently ideal brake force distribution to
the rear wheel as well as fully independent brake management and control.

Wonder if that circuit is turning on and off due to the very light brake pressure.

I also recall being told by a factory BMW rider last year that applying the rear brake pedal when you start braking will disable the linked system for as long as you continue to hold some front brake pressure. Once you release pressure it will re-enable itself. I'll try that tomorrow too.

 

[MarcosPC]

Go take a ride on a gravel road and get the ABS to activate multiple times, then tie or zip tie your front brake lever over night to see if that purges any more potential air in the system.

Will do

I tried only activating the abs, but didn't leave the brake pressed overnight

 

[CallMeSnake]

So, results of my experiments yielded no change. Bike off, ABS disabled, starting braking with rear brake on all still had a tight spot notable during each revolution when coasting to a very light stop. Only noticeable on the last few revolutions before stopping. Used one finger to make sure I wasn't effecting the brake somehow. Doubt that since my Tuareg 660 which has a similar front brake setup, with button rotors and floating calipers and my KLR which has a floating front rotor don't display this behavior. No bike I've ever owned previously has.

Need to double check the runout on the rotors, but they checked OK last time. Wonder if a loose front bearing could be causing some slight wobble. I have an indicator that has a remote readout, so I might just attach it and watch what is happening to runout as I brake to a stop.

 

[MarcosPC]

So, results of my experiments yielded no change. Bike off, ABS disabled, starting braking with rear brake on all still had a tight spot notable during each revolution when coasting to a very light stop. Only noticeable on the last few revolutions before stopping. Used one finger to make sure I wasn't effecting the brake somehow. Doubt that since my Tuareg 660 which has a similar front brake setup, with button rotors and floating calipers and my KLR which has a floating front rotor don't display this behavior. No bike I've ever owned previously has.

Need to double check the runout on the rotors, but they checked OK last time. Wonder if a loose front bearing could be causing some slight wobble. I have an indicator that has a remote readout, so I might just attach it and watch what is happening to runout as I brake to a stop.

If the bike is 100% off (not even ignition turned on) try using only the front lever

The way you tried might have indicated that the problem is on your rear rotor

If you dont feel anything only using front brakes the problem will either be the linked brake system behaving erratically or the rear brake rotor

 

[MarcosPC]

By the way, in my case, I dont feel that the “tight spots” are regular

They are unpredictable and random, which gives me more reason to think its electronic instead of mechanical

 

[CallMeSnake]

I tried all possible combinations of the above, including front brake only. Only way I can think of to definitely see what is the cause is monitoring runout in real time and adding a double banjo bolt to the front and rear calipers with a pressure transducer to see what is happening inside the fluid lines.

Gentle braking on the rear brings the bike to a smooth stop in my case.

I suppose one of the rotors could be partially glazed or have some other surface issue that is changing the coefficient of friction slightly. I'll be fitting my other set of wheels to the bike in the next two weeks and I'll post if that makes the problem go away since they have brand new rotors on them.

When I do that, I'll post the results here.

 

[garethedwardbird]

This sounds a daft question but what tyres are you running and what’s the state of wear?
I have Dunlop Trailmax Missions which, for the large part, are awesome tyres, but when they wear down to about 20% tread remaining, under braking, I too get a slight judder through the front wheel.
I think it is due to the different rubber compounds, on different areas of the tread, wearing at different rates. The shape of the tread changes noticeably as the tyre wears.
I’ve now had 3 sets of these tyres and each set has exhibited the same tendencies.
This might not be the case for you, but it’s worth a look.
They might sound like crap tyres because of the wear issue, but I’m doing about 80/20 road / offroad and seeing around 14,000 miles off each set. I’ve been doing a lot of riding two up with heavy loads and even in the sand these tyres are incredible. Performance in the wet is also bloody good too.

 

[CallMeSnake]

Michelin Anakee Adventure for me. Same problem since brand new, about 5k on them now. Front tire still looks almost new.
Agree that severely used front offroad tires can make the treadblocks sloped, which leads to feeling that under braking. The old Avon Gripster fronts did that. Not the case for me since the Adventure tread has close spacing.

 

[cagiva50]

By the way, in my case, I dont feel that the “tight spots” are regular

They are unpredictable and random, which gives me more reason to think its electronic instead of mechanical

I'm curious, did your brakes work correctly before the dealer serviced your bike? If the problem is new, I'd suspect issues with the hydraulic fluid (assuming original pads/rotors).