Skip to content

BMW R1100S iABS Brake Flush

The Correct Way to Service the Servo-Assisted System

Based on the YouTube tutorial “BMW I-ABS COMPLETE BRAKE FLUSH R850, R1100, R1150, R1200, K1200.” The procedure and sequencing below are credited to the video’s creator. The BMW Guy

This article adapts the method for R1100S owners, adds model-specific cautions, and should be read alongside the BMW workshop information for your exact motorcycle. Watch the original video on The BMW Guy YouTube channel.

The servo-assisted BMW Integral ABS system is not a normal brake system with an ABS box added on. It has separate control circuits and wheel circuits, a pressure modulator with an electric servo pump, and multiple bleed points under the tank.

That makes the job more involved than a conventional brake-fluid change, but it is manageable for an experienced home mechanic who understands hydraulic brakes and works methodically.

This guide applies only to R1100S models fitted with the earlier servo-assisted BMW Integral ABS / iABS system. Do not use it on an R1100S with conventional ABS II or no ABS. The simplest check is the modulator: iABS has six bleed nipples on the pressure regulator; ABS II has two, while later non-servo systems have a different layout.

First: confirm that your R1100S actually has iABS

The giveaway is the servo noise. With ignition on, gently applying the brake lever should activate an electric hydraulic pump. BMW describes this system as partially integral: the hand lever applies braking to both wheels, while the foot pedal works the rear brake only.

If your bike has iABS, it is worth taking the service seriously. BMW warns that a fault leaves only residual braking, with much higher lever effort, longer lever travel and no ABS function in the affected circuit.

A quick visual check: BMW or Brembo calipers

The servo sound is the easiest confirmation, but it can be confused with the fuel pump priming when the ignition is first switched on.

There is also a useful visual clue on an otherwise original, ABS-equipped R1100S:

  • BMW-branded front calipers: normally indicate the later servo-assisted iABS system.
  • Brembo-branded front calipers: normally indicate the earlier ABS II system.

The difference is easy to see once you know it. The later iABS bikes use BMW-marked calipers, while the earlier ABS II bikes use Brembo-branded calipers.

This is not a substitute for checking the actual system, particularly on a modified motorcycle, but together with the servo-pump sound it is a very practical way to identify which brake system the bike has.

What you need

  • Fresh DOT 4 brake fluid
  • Clear brake-fluid-safe hose
  • Waste-fluid container
  • 7 mm spanner for bleed screws
  • Small syringe, suction bulb or similar tool to remove old reservoir fluid
  • Rags, water and detergent for immediate spill cleanup
  • Fully charged battery, ideally supported by a smart charger
  • Eye protection and gloves

Brake fluid is brutal on paint, instruments and plastics. Cover the tank, fairing and dashboard before opening anything.

The iABS servo draws substantial electrical power while operating. A weak battery can create problems during the procedure, so do not start with a marginal battery.

The system has two separate jobs

The brake flush is split into:

  1. Control circuits — from the front lever and rear pedal to the ABS pressure modulator.
  2. Wheel circuits — from the ABS modulator to the calipers.

You must service both. Replacing fluid only at the calipers does not fully renew the fluid in the servo-assisted system.

The video’s approach is logical: flush the rear control circuit, then the front control circuit, then move to the wheel circuits.

Part One: Rear Control Circuit

Start with the rear brake-fluid reservoir.

Remove the old fluid carefully, refill with fresh DOT 4, and keep the level above minimum throughout. Do not allow the reservoir to run dry.

At the ABS modulator, remove the relevant covers and identify the three rear-circuit bleed screws:

  1. Rear metering circuit
  2. Rear integral circuit
  3. Rear control circuit

The sequence is important:

1 → 2 → 3 → 1

For each bleed point:

  • Apply pressure to the rear brake pedal.
  • Open the bleed screw.
  • Allow the pedal to travel.
  • Close the bleed screw before releasing the pedal.
  • Refill the reservoir as required.
  • Continue until the fluid is clean and free of bubbles.

The final return to bleed screw number one is deliberate. It confirms that the rear control circuit is fully flushed.

Do not use a vacuum bleeder for this particular method. The procedure relies on controlled pedal pressure and careful reservoir management.

Part Two: Front Control Circuit

Now move to the front master-cylinder reservoir.

Remove the cap, extract the old fluid, and refill with fresh DOT 4. Set the front brake lever to position 4, giving maximum lever travel.

At the ABS modulator, identify the three front-circuit bleed screws:

  1. Front metering circuit
  2. Front integral circuit
  3. Front control circuit

Again, follow the sequence:

1 → 2 → 3 → 1

For each point:

  • Apply the front lever smoothly.
  • Open the bleed screw.
  • Let the lever travel fully to the handlebar.
  • Close the screw.
  • Only then release the lever.
  • Top up the master cylinder repeatedly.

Do not pump the lever aggressively. The point is controlled fluid movement, not speed. BMW iABS owners who have done this repeatedly also caution that the job is not technically mysterious, but it is time-consuming and unforgiving of a dry reservoir.

Part Three: Wheel Circuits

Once the control circuits are complete, the job moves to the two fluid reservoirs on the ABS modulator that supply the wheel circuits.

The tutorial demonstrates a practical alternative to the BMW filling adapter: manually filling the front and rear ABS reservoirs to the top, then using the servo pump to move fluid through the calipers.

That method works, but this is the point where concentration matters most.

The wheel-circuit reservoirs must not run dry. If they ingest air, you are back at the beginning.

Rear wheel circuit

  • Fill the rear wheel-circuit reservoir at the ABS modulator.
  • Switch ignition on.
  • Press the rear pedal gently until the servo activates.
  • Open the rear caliper bleed screw for only a few seconds.
  • Close it before releasing pedal pressure.
  • Refill the ABS reservoir.
  • Repeat until clean fluid appears with no bubbles.

The servo pump moves the fluid. You do not need to pump the pedal repeatedly as you would with ordinary brakes.

Front wheel circuit

Repeat the same procedure at both front calipers:

  • Fill the front wheel-circuit reservoir.
  • Turn ignition on.
  • Apply the front brake lightly enough to activate the servo.
  • Open one caliper bleed screw briefly.
  • Close it.
  • Top up the reservoir.
  • Repeat until clean, bubble-free fluid appears.
  • Move to the other front caliper.

Do not hold the bleed nipple open for long. The aim is short, controlled flushes with frequent refilling.

A Useful Warning From the Video: Inspect the Original Brake Hoses

The tutorial catches an important real-world failure: an old OEM rubber brake hose swelling under pressure and restricting fluid flow.

That is exactly why original rubber lines on an R1100S deserve attention. A hose can look acceptable externally while degrading inside, creating restriction, poor braking performance or visible ballooning at the crimped ends under servo pressure.

If you find swelling, restricted fluid flow, cracking or unknown original hoses, stop and replace them with a quality stainless-braided kit before completing the flush.

This is not cosmetic maintenance. It is safety work.

Final Checks

When finished:

  • Refill all reservoirs correctly.
  • Refit caps and electrical connectors.
  • Clean every trace of spilled brake fluid.
  • Check for leaks at every bleed screw and hose connection.
  • Confirm a firm lever and pedal feel.
  • Listen for normal servo operation.
  • Carry out the BMW pull-away self-test.

BMW states that the iABS self-diagnosis starts when ignition is switched on, and the pull-away test completes once the bike moves off at roughly 5 km/h.

A GS-911 or similar diagnostic tool is useful as a final confirmation, particularly after a complete system flush or brake-line replacement. The video demonstrates both a brake bleed test and sensor-drift test after completion.

What this guide does not apply to

Do not use this procedure simply because your R1100S has an ABS light.

It does not apply to:

  • Non-ABS R1100S models
  • Earlier ABS II systems
  • Later non-servo ABS systems
  • Any bike where the modulator layout does not match the six-nipple iABS unit

The wrong procedure on the wrong brake system is worse than no procedure at all.

Bottom line

BMW’s servo-assisted iABS is more complicated than conventional brakes, but it is not black magic.

The job comes down to discipline:

  • Identify the correct brake system.
  • Keep every reservoir topped up.
  • Follow the control-circuit sequence exactly.
  • Use the servo pump correctly for the wheel circuits.
  • Do not rush.
  • Replace any suspect original rubber brake hoses before trusting the bike.

Do it properly, and the R1100S keeps the strong, assisted braking system BMW intended. Do it casually, and you risk ending up with residual braking, warning lights and a much more expensive problem.