OK, specs first.

12/95 X300 3.2ltr Base XJ6, RHD, NO traction control, NO sport mode.

Yesterday whilst driving in peak hour crawl the application of the brakes sometimes gave a chattering/hammering feeling from the the LHF wheel.

I have NO lights, or codes.

I am thinking a sensor telling the brains that the LHF wheel has stopped rotating, hence the activation of the ABS. My only concern at the moment is that my basic understanding of ABS is that it does NOT sense anything until a pre-set road speed is obtained, and that will certainly NOT be at idle in "D" in my opinion. My gut feeling is 50KPH?????.

The fact the thing is workin takes my thoughts away from the module once again.

At "normal" road speed the brakes are "normal", and this only happens at sub 20KPH, and only sometimes, kinda daunting at times. The car stops fine, just this activation, and the weird feel to the brake pedal, pulsing sensation.

I am tempted to unplug the motor drive terminal at the moment, mmm.

What say the brains of JF.

 

Off hand it *does* sound like unwanted ABS activation.

The ABS self test is at 20kph. I *think* the system is supposed active at anything over that speed but, search as I may, I haven't found anything that actually says so.

Not much help, sorry.

Have you ruled out a mechanical issue? Loose caliper, maybe?

Cheers
DD

PS- Ok, now you have to help me with my air bag light :-)

 

If the sensor for that wheel had backed off from the encoder disk a little or had an intermittent internal connection, so that approximately every 3rd pulse (or less often) was sent to the module, would the module interpret that as a wheel slip?

Yes, you said you were crawling, but...

Maybe this is just a manifestation of regular brake chatter? Mine grunt from 1 to 0 mph. Kind of fun to feather the brake pedal to make the car groan at the light.

Yeah, yeah, its a sound unbecoming of a Jag. Guess I need to replace the pads with something softer, or put a silencer behind the pad.

Did I pass the brain test?

 

Thanks Doug.

Front wheels off today, calipers off, pins are fine, nice and tight, no slop in the slides, nothing as it should NOT be, bugga.

Sensors out AGAIN, and the 2 metal strips on each were caked in brake dust, and I reckon causing a signal "clitch" to the point the system "thought" the wheel was "stopped", and ABS needed to release the pressure to do what ABS does. I run "Semi- Metallic" pads, and that may be the issue.

Back on the road again (Willie at his best), and the system is as good as ever. 60kms covered in all this dumb Christmas traffic, and not a shudder/whatever happening. I did a few deliberate panic stops, and all sweet, time will tell.

I have ordered some Non-Metallic pads for it, and when they arrive I will fit them, and see if anything changes.

The air bag light, bugga. I had my airbags de-activated when I bought the car, I HATE them things. Was in a Golf a long time ago and they simply went off, no reason, and damn that hurts, so I just do without. I know all the negatives, I can live with that.

When I was Parts Manager for Jaguar we had some airbags on the shelf in the parts dept, and an audit deemed NO WAY, these are explosive devices, and must be stored blah, blah, blah. The bottom of the blah was that these things have a "use by date", and that is the problem, same with the pre-tension seat belt units, same explosive device apparently. Static electricity can trigger them, so they say.

The new S Type is a different beast, and I have to leave them as is, coz they are in the seats etc.

 

Yep, brain test passed, with flying colours.

I know that chatter well, the XJ-S was great at it, the MK10 is fantastic at it, annoys other people something serious, with this HUGE Jag groaning next to them, waiting to pounce.

NO, this was definately ABS activation, as the pedal had all the normal pulsations I have read occurs when ABS activates.

 

I get ABS activating when I brake at the end of our drive + it's muddy - at less than 5 mph so I guess there's no lower threshold.
It wouldn't be very helpful (I suppose) if the ABS 'gave up' at low speed on ice.

 

Check the gap between the sensor and reluctor. I had an XJ40 in the shop once that had the same issue and someone had pried against the sensor bending it slightly. As the car slowed down almost to a stop the signal would drop below threshold and the ABS module would interpret that as a locked wheel and thus cycle the ABS.

Good luck.

 

Yep, out again today, good as ever.

Going away on the 23rd, back, whenever, some 4000kms maybe more, so if it plays up, it just might get traded, there is sure to be a Jag in a car yard somewhere.

That sensor "angle of the dangle" makes real sense, coz when I got the car the front wheel bearings had "just been replaced", haha, and the wheels were quite loose in the hub area, so I nipped the bearings up to spec. That was 50000kms agao, so I reckon I will bite the bullet and change those bearings again, "my way" when I get back, and check that clearance at the same time.