Sunday, July 17, 2011

Integral ABS closed circuit

There are numerous questions about BMW's Integral ABS brake system around the web. Mainly to know how to get rid of it. Designed more than 10 years ago now, it's a rather advanced system but when it fails it's really expensive to fix. There's only two cheap cures when this happens : remove it or have it removed.

One other question that comes relatively often is why simple parts from previous generations of ABS systems - such as the ABS-1 - or non-ABS versions of the same motorcycle are not compatible with I-ABS. Well, let's say you've spotted a nice master cylinder for your R1100S on ebay, if you blind buy this part there are a bit more than 50% chances you get one that fit on your I-ABS equipped BMW. And this is the reason why : 

Brake switch when lever relased

Brake switch with lever pulled

The brake loom works as a closed circuit. That is, instead of requiring to be closed, the brake light won't light up if the circuit is not opened. So the brake lever closes the circuit when it's completely released and opens it when at full grab.

This topic has been discussed hundreds times on different forums, but pics are worth thousands lines of explanation.

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