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Hello, this is somewhat awkward to me, I have read probably somewhere in the neighborhood of hundreds of thousands a post over the years but this will be the first one I have authored. So please be gentle if I screw this up.
The situation is as follows:
2003 BMW K1200 GT
About a week ago the dreaded ABS lights rear their ugly head. Brake failure light after diagnostics at first crank up flashes and general warning light solid. Poor front brake lever nothing as far as sounds go. Touch the rear brake lever and you hear the servo come on and stays on back to the front brake lever when polled you can hear the servo. Brakes will operate normally for approximately 15 minutes and then the system goes to the residual brakes. I鈥檓 assuming and that happens the servo that has been humming for the last 15 minutes has shut itself off but have checked the lights have Check the battery have checked the fluid levels and the wood color front and rear reservoirs is it clean light gold color.
i鈥檓 hoping with that description that I can be pointed in the right direction without having to go down the dreaded ABS rabbit hole.
thank you in advance for the help.
 

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Hello, this is somewhat awkward to me, I have read probably somewhere in the neighborhood of hundreds of thousands a post over the years but this will be the first one I have authored. So please be gentle if I screw this up.
The situation is as follows:
2003 BMW K1200 GT
About a week ago the dreaded ABS lights rear their ugly head. Brake failure light after diagnostics at first crank up flashes and general warning light solid. Poor front brake lever nothing as far as sounds go. Touch the rear brake lever and you hear the servo come on and stays on back to the front brake lever when polled you can hear the servo. Brakes will operate normally for approximately 15 minutes and then the system goes to the residual brakes. I鈥檓 assuming and that happens the servo that has been humming for the last 15 minutes has shut itself off but have checked the lights have Check the battery have checked the fluid levels and the wood color front and rear reservoirs is it clean light gold color.
i鈥檓 hoping with that description that I can be pointed in the right direction without having to go down the dreaded ABS rabbit hole.
thank you in advance for the help.
Looks like the start of an ABS modulator failure - however we should test simple stuff first - like the strength of battery.
These ABS modulators are somewhat unpredictable with a weak battery.

Checking the voltage at rest with ignition OFF has LITTLE value.
Better if you can have the battery "load tested" - some auto parts can do this if you do not want to buy a Battery load tester.
Even without a load tester , we can make these 2 tests that will give some hints:

A) Remove Seat - check battery voltage at rest (ignition OFF) directly at battery poles. If below 12.5 volts, do not go further before a good charge is applied to battery (many hours). Be carful with certain old chargers designed only for cars - some of these will apply too much amp / per hours OR they will go beyond 14.5 volts during charging process. The older / large battery charger are notorious for this.

B) 2nd test:
Turn ignition ON - wait 10 seconds - do not attempt to start. After 10 seconds , check battery voltage for drop (of course lights are on and some other items like ECU pull some current). Battery voltage should NOT be less than 12.1 volts. Turn ignition OFF.

QUESTION 1: In your post above, it is not clear what are the 2 warnings sequence you have after ignition ON.
Wait 10 seconds , do not start engine and do not touch the brakes:
  • do you see a steady "general warning" ?
  • is the ABS warning flashing fast (4 cycles per sec) or slow (1 cycle per sec) ?
  • does the above warnings change if you apply EITHER brakes in same configuration parked on center-stand (engine off) ?

QUESTION 2: what is the maintenance history of the ABS last bleed ?

QUESTION 3: Do you still have the OEM original black rubber brake lines - front and rear ?
 
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Had similar occurrence on new to me 03 GT last month. First thought was oh crap (or something like that). Turned out to be old/stiff grease in rear brake pedal pivot. Pedal was also slightly out of adjustment. Wasn't contacting micro switch properly all the time.
 

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Along these same lines, can anyone tell me what size wrench to use for making the "special tool" to reach the recessed bleeder valves on the IABS unit? Lots of pictures, but no description. The BMW part is obsolete, so I'll be making my own. I think I need a 7mm wrench, but am not sure.
 

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Along these same lines, can anyone tell me what size wrench to use for making the "special tool" to reach the recessed bleeder valves on the IABS unit? Lots of pictures, but no description. The BMW part is obsolete, so I'll be making my own. I think I need a 7mm wrench, but am not sure.
Correct - you need a 7 mm tool / wrench adapted for available space. Out of 6 bleeders on the ABS modulator, some are a bit awkward to open / close.

I will NOT repost photo of some of the home-ideas done by members in the past - there are quite a few here already in various treads.
 

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I'll send you a pic later of the one I made this spring. BUT, I really think on my GT if you just take the brake line bracket loose so you can push them out of the way a little you wouldn't need a special wrench.
 

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Along these same lines, can anyone tell me what size wrench to use for making the "special tool" to reach the recessed bleeder valves on the IABS unit? Lots of pictures, but no description. The BMW part is obsolete, so I'll be making my own. I think I need a 7mm wrench, but am not sure.
 

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7 mm, buy as skinny of a wrench as you can get and bend as close to box end as possible without distorting the box end. May still need to grind outside of box a little.
Door Wood Tool Lock Metal
Wood Finger Font Thumb Gesture
 

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Thanks, Beech. Works for me. Saves me the time of running down to my local welder, fabricator. Now if I can just find one of the Beemerboneyard funnels, (out of stock) or a good substitute for the rear reservoir, I'll be in business!
 

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2009 K1300S, 2017 S1000R & 2021 Vespa Primavera clown paint job
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If you just keep a serious eye on the level you can skip the funnel. Just use a small funnel to fill as needed with a flashlight. Don't let it get down more than a 1/2 inch or so in the reservoir. It can happen fast due to the pump action. If anyone wants one of the last 3 wrenches, let me know via private message conversation. ten bucks paypal. But so easy to make your own if you have a propane torch and a vice. These nipples only need to be tightened down to 10 Nm or so which is like 6 ft/lbs. Of course if they weep more is needed. I have seen dealers tighten so much it was scary trying to loosen them. This damages the seal surface. We are talking aluminum threads which can be stripped, then you're dead in the water.
 
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