Servo-assisted ABS.

[Bear]

Can anyone point me to detailed information about the servo-assisted ABS fitted to my 2006 model GS please. On an occasional basis I lose the servo-assistance to the rear brake (accompanied by the RTOD) but the front brake is still assisted. If it happens it's almost always in heavy traffic with a pillion using only the front brake (I don't use the back brake as I can't easily reach it). My thoughts are that either the servo is drawing so much current that the battery voltage is low (battery is a 3 week old Exide of the same specification as the original) or some sort of sensor in the ABS unit has an intermittent fault. The alternator is working (voltage across the battery rises when engine speed rises) and the fluid levels are correct. The fluid was dealer-changed 1500 miles ago at the last service. The brake light works correctly from both levers even with the RTOD lit up. One interesting oddity is that when I tried starting the bike with the front brake held on the odometer showed 251 miles remaining. Cycling through the display options still worked. The oddity went away after switching the ignition off and on a couple of times. If the problem was always there a dealer should be able to find it but I'm not prepared to let someone take repeated guesses at my expense until the whole bike has been replaced.

 

[RickG]

It's one of the characteristics of the DIY BuMW world that detailed info' of the sort you require is usually hard to come by.

What is making you think you are losing the rear servo?

I'd be surprised if it was a power supply issue and given the intermittant nature of the problem your best initial bet is that the fault is a sensor issue and has been logged by the computer. Reading the code will quickly point you toward the fault. Unfortunately this does mean paying for the priveledge, or knowing someone with a 911 who can be bribed for a beer or two

 

[Bear]

As you say, information is hard to come by. I assume that I've lost servo-assistance to the rear brake because I need to stand on the pedal to make the brake work whereas normally a light touch is sufficient. When I first had this problem about a year ago the only fault my dealer could find was a low voltage error, with no ABS faults reported. It's unlikely to be a rear wheel sensor problem as the speedometer still works, but the front wheel sensor is a possibility, although I can't see why that would knock out the rear brake. I'm more inclined to the theory that corrosion on an electrical connection is causing the problem but want to find out exactly how the system works before diving in.

 

[RickG]

Can you tell if the rear servo is operating OK when you pull the front brake lever? You should hear the servo's whining away with the bike on the stand


does the speedo actually work off the rear ABS sensor or the front? In any case a faulty speed sensor shouldn't stop the brake servo working, just stop the ABS part of the system from being able to function? I'd have also thought the computer would flag up a fault on the display if it didn't pass it's preflight check but like you I've go real info on how the system behaves

Again the idea of an electrical issue is logical but if the bike starts OK it means you have plenty more current available than the servo system needs so any such problem would be localised to just the rear braking system. I'd be trying to test the rear servo alone if possible. If you do a search on brake bleeding the rear circuit you'll see that this involves causing servo to operate as it tries to pressurise the circuit and would at least be a way of testing most of the electrical and mechanical parts of the circuit if not necessarily all the electronics.

Good luck

 

[Pukmeister]

How badly worn are your rear brake pads/disk?

The ServoABS unit has integral fluid reservoirs which are the real braking circuits, the handlebar/footpedal reservoirs are only the pilot operating circuits (and residual braking in the event of Servo failure/bypass).

If the Servo units internal level drops too far due to the brake pistons moving outwards through pad/disk wear, this can affect unit operation.

The only way to know for sure is to remove the fuel tank to gain access to the Servo unit, unsrew the plastic reservoir caps and look inside to gauge the fluid level remaining. If thats too difficult and your pads/disk appear worn, simply fit new pads and reset the pistons back into the caliper.

Could also be a build up of wear swarf on the magnetic pickup inside the final drive unit causing it to fail to read wheel speed, though this usually includes errors in speedo readout.

 

[Bear]

The fluid levels in the reservoirs under the tank are OK, as are the rear pads and disk. The FD is almost new (6000 miles) and had its oil changed 1500 miles ago, along with the brake fluid, so I would assume that the rear wheel sensor was reasonably clean then. The more I think about it, the less convinced I am that it's a wheel sensor problem because I can't see how they are checked until the wheels start turning, and once the problem shows up it stays there no matter how many times I switch the ignition off and on until it decides to go away. The oddity with the odometer I described in my original post makes me thing that something electrical is intermittent (I have 30 years experience in the electronics and computer industries) so unless something else proves me wrong I'm going to pore over the wiring diagram looking for what to suspect first.

 

[GSband]

Can anyone point me to detailed information about the servo-assisted ABS fitted to my 2006 model GS please. On an occasional basis I lose the servo-assistance to the rear brake (accompanied by the RTOD) but the front brake is still assisted. If it happens it's almost always in heavy traffic with a pillion using only the front brake (I don't use the back brake as I can't easily reach it). ...

The exact same thing happened on my 06/'05 R12GS at 55000km in October 2007. Turned out to be faulty servo pump. It was replaced for a new unit FOC which was nice, considering bike was out of warranty. Otherwise some 1200€ had to be paid. I exchanged my bike for a new R12GS without assisted brakes afterwards. I really don't like brakes failing.

I hope your servo pump is still OK.

 

[wrightyboy]

Brake Servos

I have a 55 plate 1200GS and I'm experiencing a lot of the problems people are describing on this and other similar threads, http://www.ukgser.com/forums/showthread.php?t=227070&highlight=servos that is:

• Servos not always kicking in on start up (fast flashing brake failure warning), takes up to 5/6 times to work);
• Brake light remaining on (with servos whining) when all brakes released;
• Apparently dodgy connection with the tail / brake light;
• No servo whine when the rear brake is used (sometimes) so only residual braking;

Only had the bike since the end of November, so it’s still under BMW Approved warranty and its booked in for a 6K service at Roy Piddock on Friday so will be asking them to sort this. (v. useful to have the extra info and background from the forum!!). Anyway, I will post any info or insights that result from talking to them about this.

While I’m posting, would also be interested to know about people’s experience / opinions of Piddocks. Never used then before (and didn’t buy the bike from them), but they’re just down the road from where I now work, so convenient. Would be good to know, as in addition to the brake servo problem, I’ve also spotted an oil leak at the back of the engine that I’m going to ask them to sort under warranty as well. I plan to call them before hand to set their expectations about what I think needs to be done, but it would be useful to know if they’re likely be awkward and / or mess me about.

Cheers

 

[Bear]

I would assume that any franchised dealer would be happy to sort out warranty work on an approved used motorcycle because they will be paid to do it. My only experience of Pidcocks is when Mrs Bear bought her Belice suit from them and they could not have been more helpful. Please keep us informed about how they sort out your brakes.

 

[andyclift]

Brake light remaining on (with servos whining) when all brakes released;

This one is almost certainly a sticky switch but when it happens there is a more undesirable side effect than just the brake light on.

If the switch is stuck on when the bike is started the self testing thinks the brakes are on a will not complete the brake system check. The result is the bike goes into "residual braking" mode and the "brake failure" warning shows.

This happened to me on a fully loaded two up GS in Germany and I didn't realise the brake light was stuck on for some days so struggled with near useless brakes. Only realised what it was when I saw the reflection of the brake light in a shop window at night.

Although the brakes just about work when this happens another danger I found from experience is that if the switch releases while moving the brake test completes. If you don't notice the warning light has now gone out the next time you grab loads of brake cos you think you are still in residual mode, the bike stops on a sixpence and the pillion passenger climbs over your back!!