ABS II is BMW’s earlier non-servo anti-lock braking system used on some R1100S models before the later iABS system.
On the R1100S, ABS II is an electronic anti-lock system that monitors wheel speed and helps prevent wheel lock during braking. It does not provide servo assistance, and it does not have the same partially linked braking behaviour as the later Integral ABS system.
In simple terms: ABS II is the simpler, earlier ABS system.
It still needs correct maintenance, but it is much less complicated than iABS.
Why it matters
ABS type matters on the R1100S because it changes both ownership and maintenance.
Many R1100S discussions become confused because owners simply say “ABS” without identifying which system the bike actually has. That is not enough. An ABS II bike and an iABS bike do not have the same braking system, the same bleeding procedure or the same ownership concerns.
ABS II is generally regarded as the more straightforward system.
There is no servo pump sound when the brakes are applied. The brake lever feels more conventional. The system still uses a pressure modulator, but the service procedure is simpler than the later servo-assisted iABS system.
For buyers, identifying the ABS system is one of the first things to do.
For owners, using the correct brake-bleeding procedure matters.
Typical characteristics
An R1100S with ABS II should feel:
- conventional at the brake lever;
- free of servo-assist noise;
- stable during braking;
- predictable at low speed;
- mechanically simpler than an iABS bike;
- protected by ABS intervention if a wheel begins to lock.
It should not have the high-pitched servo pump noise associated with iABS.
It should also not be ignored just because it is simpler. Old brake fluid, poor bleeding and neglected modulators can still cause problems.
What owners should know
ABS II still needs brake-fluid service through the ABS unit and calipers.
Do not treat it like a simple non-ABS brake system. The brake pressure modulator is part of the hydraulic circuit, and old fluid should not be left inside it.
When servicing an ABS II R1100S, the system should be flushed correctly at:
- the ABS pressure modulator;
- the front brake calipers;
- the rear brake caliper.
The exact bleed sequence matters, and the procedure is different from the later iABS system.
Use the correct guide for the system fitted to your bike.
ABS II versus iABS
The easiest mistake is confusing ABS II with iABS.
They are not the same system.
ABS II is the earlier, non-servo ABS system.
iABS is the later servo-assisted Integral ABS system, where the hand lever operates both brakes and the foot pedal operates the rear brake. iABS also has a more complex bleeding procedure with separate control and wheel circuits.
A simple owner clue is caliper branding.
On an original ABS-equipped R1100S, Brembo-branded front calipers normally indicate ABS II, while BMW-branded front calipers normally indicate later iABS.
That is not a perfect rule. Bikes can be modified, parts can be swapped, and transition-year machines exist. But it is a useful first clue.
Do not rely on registration year alone.
Identify the actual system fitted to the bike.
ABS II and brake-fluid changes
Brake fluid absorbs moisture over time.
That matters in every R1100S brake system, including non-ABS, ABS II and iABS bikes. On ABS II, old fluid sitting in the pressure modulator is not something to ignore.
The system is simpler than iABS, but it still deserves regular service.
A good baseline service on an unknown ABS II bike should include a full DOT 4 flush through the ABS unit and calipers.
Do not just bleed the calipers and assume the job is complete.
Common ABS II issues
Old brake fluid
This is the big one.
If service history is unclear, flush the system properly.
Incorrect bleeding
Bleeding only at the calipers can leave old fluid in the ABS unit.
Use the correct ABS II bleed procedure.
Confusing ABS II with iABS
This leads to wrong advice, wrong procedures and unnecessary fear.
Identify the system first.
ABS warning lights
Warning lights may be caused by low battery voltage, sensor issues, system faults or other electrical problems. Diagnose before replacing parts.
Wheel-speed sensor gap or damage
ABS depends on wheel-speed signals. Damaged sensors, incorrect gaps or wiring issues can cause faults.
ABS II is not something to fear
ABS II should not put buyers off a good R1100S.
It is an older ABS system, but it is mechanically simpler than iABS and generally easier to live with. The important point is maintenance, not panic.
A well-maintained ABS II bike can be a very sensible choice.
A neglected ABS II bike simply needs proper inspection and fluid service.
As with most ageing R1100S issues, owner neglect is usually a bigger problem than the system itself.
Bottom line
ABS II is BMW’s earlier non-servo anti-lock braking system on the R1100S.
It is simpler than later iABS, has a more conventional brake feel and does not use servo assistance. But it still has an ABS pressure modulator, and that means brake-fluid service must include more than just the calipers.
Identify the actual system on the bike, use the correct bleeding procedure and keep the brake fluid fresh.
That is the difference between sensible ownership and confused ABS folklore.
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