I have a 2000 model Peugeot 406 HDi that I purchased earlier in the
summer. There is an intermittent fault with the braking system that
causes the ABS to operate when braking gently at slow speeds, typically
less than 20 mph, which results in pulsing felt through the brake pedal.
This is typically annoying but there have been a couple of times when
stopping on a dry road that the car has felt like it's braking on ice
(with the ABS pumping way) and considerable pedal pressure has had to be
used to stop the car before it hits the vehicle in front. The ABS works
fine if I try and force it to engage when braking heavily from moderate
to high speeds.

I have tried a couple of things to cure the problem including bleeding
the brakes, replacing the front discs and pads and cleaning the front
sensors and toothed rings. When replacing the discs I noticed that the
toothed ring that the ABS sensor reads on the OSF could be turned around
the driveshaft and would also slide along it (I estimate about 10 lbs ft
of torque was need to turn it around the circumference of the
driveshaft). It is also split like a circlip that results in the teeth
on either side of the split being further away from each other than the
corresponding teeth on the rest of the ring. I imagined that this
toothed ring would be an integral part of the driveshaft rather than the
separate, relatively loose part that it is. I am wondering whether this
is as the car was manufactured or whether in the past someone has bodged
replacing the driveshafts. The toothed ring on the NSF is also split but
takes a bit more effort to move.

Can anyone confirm whether the toothed ring and driveshaft should be
like described? Any ideas where else could be causing the fault. I have
now pulled the ABS fuse for greater peace of mind whilst driving but
would like to get this sorted before winter sets in.

TIA

Marc