Help - front brake pressure too high - RED WARNING flashing BRAKE FAILURE

Hello

Fairly new to this forum, just come over from a CB500 one ... maybe I should have kept it :-( .... and the fireblade ....

I've owned my 2006 ABS servo assisted R1200GS for about 8 months now. I have been falling in love with it more and more as the days go by, I commute ~40 miles a day - in all weathers.

Monday this week I was on my way home only to be confronted by a solid red triangle and brake failure flashing warning. I tried the brakes, they were fine. Trawling a few forums sugested this could be low voltage.

So I charged the battery overnight, went to bed and in the morning started the bike - all the way to work, fine. Problem solved..... On the way home, same again. Red warning triangle, brake failure flashing. Tried the brakes, they were fine.

Thought OK - maybe it needs a new battery - it is >4 years old after all. Fitted, charged ... off to work next morning.

Half way to work I get the warning triangle again, flashing brake failure. Tried the brakes .... no servo assist. That was scary. Get to work, turn off engine, back on, brake failure straight away. B*llox, go into work hoping fairy will fix my bike. Back out 8HRS later, no brake failure.... half way home, same warnings come up and again no servos.

Today I took the bike to a BMW dealer. He plugged in his GS-911 diagnostic tool, pressed buttons on his laptop then told me "oh dear, this is expensive. Your ABS unit is failing for FRONT BRAKE PRESSURE TO HIGH". He quoted me £1650 for the work to fix!!!!!

I said I'd go and think about it...

Anyway, back in my garage an hour later I had a play.

Ignition on, wait a few secs while clocks cycle through normal sequence, then greeted by triangle and flashing text. Pull in the front brake lever = no servo noise (engine is not running at this point). Step on the back brake = servo noise, which remains when I remove my foot i.e. the rear servo is stuck on!! Now when I touch the front lever it's servo also comes on, but goes off when I release, the back remains on till I cycle the power with the ignition key.

So what the hell is going on here? I find it very difficult to think it's as simple as plugging in a laptop and saying that will be £1650 please?

I've checked the switches, handle bars fouling, handguards etc... all seems OK.

Is there ANYTHING else silly I can check to sort this out?

I'm kind of wondering if it may still be a voltage issue and I happen to have replaced a failing battery with a dud one ... unlikley I know, but possible. Certainly in my unlucky life The reason I think this is ... you can bet tomorrow after a full charge I'll flick the switch, get no warnings, start her up, half way to work .... warnings??

Any help very greatfully received ...

My 20004 bike had the same warning on my GS911. It reset and was fine. It sounds like your rear brake switch on the pedal is sticking, keeping the servo on which rapidly drains your battery. Clean or replace the switch, recharge the battery and get a mate with GS911 to clear the fault code from memory. Don't pay for a replacement servo unless all else has been sorted.

Thanks for the rapid reply dude.

New to these GS things. Is the switch easy to take apart? I take it you means the switch directly connected to the brake pedal, and not some other hidden trickery...

Pukka Pies? Are you South Wales? I'm Cardiff myself...

Hi

I found the switch, took it off. Cleaned, chased the wire up to behind the battery, dissconected and checked with a DVM. All is OK.

I'm convinced now this issue is the servo as you say, hence I get the red triangle and flashing lights when the battery goes below ~12.65V. A good overnight charge brings it back over the threshold and I don't get an issue again till I use the rear brake, servo sticks on and hey presto ... back to square one.

Question is, what else, if anything, can cause the rear brake servo to stick on ALL THE TIME?

Any more help appreciated.

Had a servo failure myself-similar symptoms but would check the rear abs sensor just in case its covered in crud. This way throw the speedo and brake off.

Be careful going down the 2nd hand route.The part numbers may be the same across the R1200 and K1200 range but the problem comes when the unit is programmed. The abs ecu retains the previous model software so you can only replace gs with gs not with an rt etc.

The speedo is fine, so I'd doubt it will be the rear sensor - having said that I will take it off and clean anway.

With a good battery charge I get no warning when I turn on, if I start and ride off I could probably ride all day as long as I don't use the rear brake.

As soon as I do the servo sticks on = draining battery = ABS goes into fault mode = red death triangle and flashing brake warning.

I am trying to get my head around what could make the servo stick on?

So I guess there is not enough pressure in the rear line to satisfy whatever reads the pressure i.e. the modulator? That or the thing that reads the pressure is f-ecked, again the modulator - God I hope not = £1650

So whay can't it get pressure .... I intend taking apart tomorrow and looking for:

1. any leaks
2. poor electrical connections
3. bleed and re-fill rear brake line

Please point out if I'm off down totally the wrong tack .....

The switch contacts check out using a meter, but if the servo is staying triggered by the rear pedal then presumably it is the mechanical action of the pedal itself that is keeping the (good) switch made, or the pedal is not returning properly under spring action to the off position.

Did you check the pedal arm action??

FWIW It takes hardly any pedal travel to operate the switch/servo.

Note that by design when the rear brake servo operates, it should cut off after a period, followed by the odd pulse to build/restore pressure. This is different to the front servo, which stays triggered all the time when the front brake lever microswitch is operated (lever pulled). I used to recommend that owners keep the bike held on the rear pedal on hills for this reason (to prevent excess servo drain on the battery). I don't understand why your rear servo isn't shutting off after a fashion.

If I were you I would check the front brake lever isn't fouling the handguard and that the front servo circuit cuts in/out when the lever is operated, just in case one problem is masking another.

BTW my surname is Puk (Polish family heritage), hence the Pukka pie related nicknames from my childhood, and no I'm not in Wales I'm in Hampshire.

Good luck with the bike, keep us posted.

EDIT: You may need to remove the fuel tank to gain access to the servo pump, then remove the reservoir filler caps on the servo pump (not the front/rear brake lines) and check the internal fluid levels in the servo. The system works by using the handlebar/footbrake circuits as a pilot to trigger the servos own secondary hydraulic circuits. A low servo (secondary) fluid level could cause the constant pump operation. A low servo level is usually due to excessively worn rear brake pads, causing the brake caliper pistons to travel too far outwards using up fluid. Another cause could be hydraulic leaks so check for that too. My guess is that your rear pads are probably worn excessively (the GS eats rear pads at an alarming rate anyway)

Hi

Pad inspection is on the list for tomorrow.

The front servo does switch in and out when the lever (front) is applied. Interestingly if I turn the ingition on and go straight to the front, pull in the lever = no front servo?

If i then apply and release the back lever the rear servo comes, and stays on.

If I then go to the front lever again i get the front servo as i pull/release the brake. The front servo switches on and off as expected.

Other job for tomorrow is brake fluid levels etc - thanks for the explanation on this - very helpful.

Regards pads - i was going to give the pistons a big lump of wood to push on - see if that makes things better - if so = new pads.

cheers

Psst, look [URL="http://www.ukgser.com/forums/showthread.php?t=254383&highlight=servo"]HERE[/URL].

I was only reading that 10 mins ago ...... great link

out of interest - what brake fluid do you recomend?

this is good too

http://www.youtube.com/watch?v=YLM25NYvlas

You ideally need to remove the rear caliper to check for pad wear properly, they usually wear excessively on the left hand pad looking from rear of bike more quickly than the right hand pad. They are meant to wear an indicator hole in the left hand pad backing material so you can easily tell its due changing, but they are typically metal to metal by the time you notice and hence score the disk.

Be sure NOT to operate the brakes or ignition until you have refitted the caliper/pads in order to prevent popping out a brake piston under either manual or servo action and causing yourself a whole load of hassle.

Don't refill the internal servo reservoir to full level unless you have just fitted new pads and reset the pistons in the caliper, otherwise when you do eventually fit new pads you'll hydraulically lock the servo and lose brake fluid via the overflow pipes.

Obviously everything must be spotlessly clean before and during the opening of the hydraulic circuits (if necessary).

I couldn't wait till tomorrow, so have spent an hour in the garage making ready for the assault tomorrow. Tanks etc is off and i've taken a look at the first modulator filter and inside the two modulator fill ports. The back brake liquid in particular looks almost brown in colour and there are little bits floating around in the fill port .....

Questions - what do you suggest as a cleaning agent for the filters?

Will flush through and fill with nice new DOT 4 tomorrow. No doubt it will be the same when I get it all back together, but hey ... a day 'fettling' is never a wasted day

Brake fluids vary in colour depending on makers: some are clear, some are slightly golden. Never seen new brown Dot4 which suggests old fluid/a lack of changes, there could also be microscopic wear particles or moisture/corrosion that needs flushing out.

Brake fluid should be flushed/changed every 2 years according to BMW, I got dealers to do the first one on my old 2004 bike, then made a funnel adaptor for the servo reservoirs (which isn't essential) and did my own the second time with a friends help/guidance. Having seen his GS911 and been impressed I bought my own, which is essential for reading fault codes and resetting.

Lets hope that flushing through the primary and secondary fluid circuits fixes your fault, it looks intimidating but is only bleeding through hydraulic circuits. Be sure not to let the ABS pump run dry/cavitate when flushing, plenty of info on the procedure for changing ABS fluid on this site/Advrider/other web sites.

I would probably spray the filters with an aerosol of brake cleaner (which evaporates) then blow dry with low pressure compressed air from the inside to push debris off the mesh screen against the flow rather than embed it into the screen.

So today I set to it ...

Stripped everything down, took out the ABS filters and cleaned, bled/flushed ALL the lines, cleaned calipers etc etc etc. ...

Got the back brake back together and thought I'd give it a go.

Back brake servo going on and off as expected - brilliant !!!

Then stuck everything else together and went for a mile ride down the road, still OK. All brake servos going on and off as expected.

Put the bike in the garage idling for five mins - then noticed the red triangle of death and brake failure was flashing.

Pressed the back brake - servo stuck on.

Turn ignition off, then on, red triangle of death ... press rear brake ... servo sticks on when lever is release. Does the same if I start the engine .... A&e.

Go figure???

I've left the bike and spare batteries on charge overnight - if it isn't that now I'm baffled.

It's booked into the main dealer for diagnostics Monday afternoon.

Any other ideas anyone? Could this really be battery........

I guess I'll find out tomorrow.

With an immediate caveat that I've got a lot to learn about my servo brakes, and will cheerfully accept any comment that I'm talking out my @rse, but could it be that the servo is reacting to pressure in the rear brake primary circuit... my logic...

The servo is activated by pressure in the primary circuit. (Possibly the brake light switch electrics don't have much to do with it or else you'd not have a variable braking force and the rear brake would fail if the switch failed).

If there is residual pressure in the primary circuit, the servo would see that as a signal to pump.

Residual pressure might be caused by either an incorrectly adjusted master cylinder pushrod, or there might be a blockage in the master cylinder itself (on fronts there's usually a small hole which is covered by the piston when the lever is pulled but uncovered when released, so letting fluid pressure back into the resevoir to stop the system 'pumping up' pressure.

Please don't go chasing shadows, someone with experience will be along shortly to tell me the logic's flawed I'm sure.

Rich.

I'll listen to any logic at the moment....

I would hazard a guess that either your rear brake pedal master cylinder is sticking on (worn/jammed seals) or else you have some sort of Servo ABS pump fault.

Now that you have exhausted the stuff you can do yourself, I guess a dealer diagnostic is the next logical step.

The only other simple possible cause I can think of is a chafed or worn signal cable between the brake switch and ABS pump (some folks reported this problem on early bikes a while ago - ABS wiring loom chafing on a bracket under the tank somewhere.) I believe that the ABS switching is 'normally open' according to an earlier post by PatZX12, so a break in the loom changes nothing, but a grounded connector could possibly make the switch and operate the servo.

A bit gutted that you had it working, then it went tits up again which makes me wonder if it could be an intermittent wiring fault (loom).

My worry is I'll take it to BMW on Monday - they plug in their GS-711 and say "modulator gone - that's £1650 please - and I'm not so sure you can 100% believe a test routine like that. That's not fault finding - plugging in a laptop .. and module swapping what-ever box it says is faulty

What if the £1650 doesn't fix the problem, do I get my money back? I wouldn't think so.

Just to confirm, fault status is:

Key in, turn on, initializes, then red triangle and brake failure on dash (no servo wine), press rear pedal and servo wines, then stops if I press harder on the brake. When I take my foot off the pedal the servo starts again and continues to wine (on it's lowest setting if that makes sense) ... till I turn the key off.

What the hell failure mode is the bike sensing when I turn on the system - that then results in the rear servo sticking on?

Is there any way to test the rear master cylinder? I'm thinking it's always open - is that plausible ... How about I mole grip the tube after the cylinder to stop any potential flow and see if the servo shuts up??

Does anyone know what the switch looks like, if there is one, in the master cylinder. Or does it just act like a non-return valve ... or maybe not in my case.

Why was the fault cleared this morning?

Is it now as simple as I didn't put enough fluid in the ABS unit ..... maybe it's found it's level and is too low. By pressing the brake pedal I am compressing what is in there and allowing the servo to shut up... I'm not sure it was shutting up yesterday when I pressed hard - I don't think so - wish I could remember.

Why me?

You just know what they will say on Monday .... "Front brake line pressure too high!" DOH ...

Back to square one

Was scouring the forum and found this ... could it be final drive??

http://www.ukgser.com/forums/showthread.php?t=112016

piebaps said:

Mine kept losing charge too. After two batteries it was finally narrowed down to the rear brake servo which was sticking on and while it wasn't applying any braking force it was using more juice than the alternator could cope with. End result was ride 20miles with a fully charged battery and then get off the bike at the other end with a flat un.

Final drive replaced under warranty sorted it out.

Good luck

Click to expand...

Is PIEBABS still on the site - anyone have his email - I'd be really interested in messaging this guy? Sounds like he had exactly the same issue... I'm struggling to se ehow this could be final drive?

You will get the red triangle on initialising the ignition/ABS, you may get a brief whine/buzz from the servo as it builds pressure if necessary, then the 'brake failure' light will flash at approx 1HZ.

Once the bike is in motion at about 5mph, the ABS unit will detect the rear wheel speed from the ABS/Speedo sensor fitted in the top rear face of the final drive unit, and clear the brake failure warning.

If there is a build up of swarf/debris on the (magnetic) rear wheel ABS/speed sensor, it can confuse the speed sensing function of the ABS unit. Simply remove the rear wheel on centrestand, undo a torx screw, pull out ABS/speed sensor then wipe clean and replace.

I can't see how it would affect servo operation, but might be worth giving it a clean to see if it helps with your warning.

A pity you aren't local to me, I have a GS911 and would be happy to check your bike over. Perhaps a forum member more local to you could do the same ??

A BMW main dealer should use a BMW GT-1 diagnostic computer, which has far more functionality than the rather straightforward (but excellent nonetheless) GS911.

To be honest, the possible expense of fixing the ServoABS was a major factor in my decision to part-ex my old 2004 GS (although it never went wrong).