Ineffective Brakes

[hitechcpa]

Over the weekend the brake system startup light along with the red triangle warning light began flashing while riding. I assumed low brake fluid since the light only seemed to come on (and stay on) once I leaned over through a corner. Staying upright after starting the bike seemed to keep the light from activating. If the light comes on it stays on until cycled through by turning the key off. I checked the rear reservoir but not the front. The rear was fine.

 

While coming to a stop last night and using only the front brake lever, I had only about 10% stopping power, if that. The only thing that saved me from hitting the car in front was applying the rear brake pedal.

 

I got home, changed my shorts, and checked the front reservoir. It was a little low, but still within the bubble. I took the cap off anyway and topped off. The light seemed to stay off for good now, so I thought all is well. Then first thing this morning another low speed attempt to stop and the front brake again gives me something less than 10% stopping power. The warning lights had not come on.

 

Any thoughts? Could this be associated with the ABS sensor? Brakes seem to work fine at speed. I did notice that the warning light came back on just as I was getting to work (34 miles after the one time stopping experience). Thanks for your thoughts.

[T__]

hitechcpa, what year BMW 1200 do you have? That makes big difference on where or what the problem could be.. The early 1200’s have the actual brake master cylinders & reservoirs in the ABS controller under the fuel tank.. The ones that are on handle bars & above the rear pedal are just for the control circuits..

 

 

Twisty

 

[Ogri]

If the Brake Failure warning light is flashing as it normally does while it waits for the pull-away test to complete, this normally means an ABS sensor fault.

Ive had a similar fault on my bike where the Brake Failure light would randomly come on & was sometimes followed by the red warning triangle illuminating. I too lost a lot of braking power which I think was down to the ABS system not seeing a sensor and assuming I had a locked wheel, putting the brakes more or less permanently into ABS mode, if that makes sense.

Anyways, problem for me was a damaged cable from the front ABS sensor. Replaced the sensor and all is good.

[BanjoBoy]

Sounds like another whizzy brake failure. What kind of bike are you riding?

Here's my exellent experience with whizzy brakes on my '05 R1200ST.

Linkage

There is a little micro switch up at the hand brake lever that got bug juice in it. That made my brake light stay on (check yours) which, for whatever reason, disabled my whizzy brakes. That's some real fine engineering!!!

 

Good luck with yours.

[hitechcpa]

I have a 2005 R12RT.

[T__]

hitechcpa, OK now we know you have the IABS system with power servo assist..

 

The actual brake fluid reservoirs that supply brake fluid to the front & rear calipers are in the ABS controller under the fuel tank.. You need to remove the fuel tank to check those fluid reservoirs..

 

Low brake fluid might not be your problem though.. It could be a sticking switch (usually rear pedal switch),, or speed sensor,, or other..

 

OK, now that we know what bike you are working with we now need to know EXACTLY what the warning lights are doing.. Such as:

 

Are the both lights on constant?

 

Or- Are they both flashing?

 

Or-Are they flashing together?

 

Or-Are they flashing opposed to each other?

 

Or- is one on & the other flashing..

 

If flashing how fast are they/it flashing?

 

This is all needed as how the lights are on or flashing helps to point to what the failure fault is..

 

 

Twisty

 

[hitechcpa]

When the lights come on, they come on together and both are red. But, only the Service Brake light flashes. The triangle warning light stays solidly lit. The Service Brake light flashes at about once per second.

 

The problem does not appear to involve the back brake. It works at all times and all speeds. The problem is just the front brake and then only at speeds under about 5 mph. It acts as though the ABS is being activated. That is, if I'm going slightly faster than 5 mph and lightly apply the brakes they will work, but as I slow they act as though the ABS is activated and as I get below 5 mph the front brakes are all but inoperable.

 

Does this situation only get worse?

[T__]

hitechcpa , your brake warning light sequence of (Gen warning light ON, ABS light flashes at 1 Hz) means at least one brake circuit is without ABS.. (that is about all the flashing lights tell us on this failure sequence)

 

That is strange failure you have as most ALL ABS systems are designed to turn off the ABS & ABS wheel release below about 3-5 mph.. If they didn’t you could never come to a complete stop..

 

Not sure if your ABS controller is getting errant speed sensor input or there is a problem in the ABS controller itself..

 

Maybe start by looking at your front wheel sensor wire where it routes near the brake rotor.. There was a service bulletin or that wire routing & the possibility of it touching the brake rotor & wearing through..

 

Otherwise probably a trip to the dealer to have them read the stored ABS failure codes..

 

Twisty

 

[Ogri]

I would still suspect an ABS sensor or sensor cable fault. U can visually inspect these for damage yourself but I wouldnt do any more than that. Take it to your nearest dealer and have them check the ABS fault codes. This doesnt always work however as in my case 3 seperate checks showed no faults and yet I still had the warning lights.

[MadDuck]

You might also check your rear brake lights/circuit. I had a bulb fail and it screwed up something like this. A lot of circuits seem to tie to rear brake lights, YMMV as its been four years since I had my ABS problems with my 05 RT. Sensors and wires had a few recalls in the 05 model year so check to make sure that work has been done. You may need a really good BMW service person to get this resolved as that system is odd/quirky when a component fails.

 

Best of luck.

[hitechcpa]

Awesome responses. Thanks to all of you for your time.

[T__]

MadDuck, a failed rear brake or tail light can bring the warning light on (not flash though) but won’t make the ABS or brake system act up..

 

Twisty

 

[hitechcpa]

Update: On the front brake I found the ABS wire unclipped from the brake fluid line. The ABS wire is clipped to the brake line for support. I think the wire may have been tweeked while unclipped. After clipping back to the brakeline for proper support, I notice that the ineffective slow speed braking is much improved.

 

The warning lights are still coming on. Again, this seems to happen after leaning far into a curve. Could this mean fluid is needed in the reservoir under the gas tank? Is that the only way to fill? If I have to take off the tank, should I do a flush? Without doing the search, is special equipment needed to flush? Thanks, again.

[T__]

hitechcpa, as a rule low brake fluid in the under thank reservoir(s) is indicated by BOTH dash lights flashing alternately.. Yours aren’t flashing like that so your problem is probably something else..

 

Carefully inspect that front sensor wire for nicks & rub throughs.. Especially near the rotor area..

 

Twisty

 

[Bernie]

Check your ABS wire. I think the brake disc has rubbed through the insulation. This will cause a short and a ABS fault. Maybe it only touches metal when leaned over.