Brake Shudder ???

[Baggy]

Hi All, style_emoticons/<#EMO_DIR#>/smile.gif style_emoticons/<#EMO_DIR#>/smile.gif

Have 96 Disco, wife mentioned to me several times, and I
experienced it for the first time in shopping centre carpark (last
weekend), at low speed (braking for speed hump) feel shudder through
brake peddle and did'nt want to pull up as normal? style_emoticons/<#EMO_DIR#>/sad.gif

Had pre inspection done prior to purchasing vehicle in Jan this year,
Brakes were given clean bill of health??

Any Thoughts???

[defute]

Hi Baggy,

does your Disco have ABS brakes?

Generally, a pulsating sensation which comes back through the brake pedal when braking is caused by an excessive amount of runout in either the vehicle's front or rear disc rotors. This is normally most noticeable when slowing down from high speeds and generally doesn't effect the braking performance of the vehicle - it's just a very uncomfortable and disconserting sensation for the driver. This fault can be rectified by either machining the effected disc rotors (if there is enough useable metal still on the disc) or replacing the rotors with new ones. It is also advisable to replace the brake pads at the same time.

On vehicles fitted with ABS brakes this braking sensation will also occur if you have driven over a pot hole or speed bump while braking and a tyre has momentarily lost traction!! As traction has been reduced while transversing the obsticle the ABS system will operate, the brake pedal will pulsate as the system reduces the hydralic braking pressure the effected wheel.

It is also possible for the ABS system to operate (go into an ABS mode) even though the tyres are not locking up. When this happens, the brake pedal will pulsate and the vehicle won't slow down as rapidly as you would normally expect. This can occur if there is an electrical fault with the ABS system, i.e wheel speed sensor. Is the ABS light on in the vehicle while driving? It should illuminate when the vehicle is started and then extinguish when the vehicle is driven over 7kph. If the light stays on, this suggests there is an electrical fault logged within the system.


I hope this helps.

[mickus]

Wish there was an on/off switch for the ABS, I hate it offroad. Do a lot of limestone tracks and the ABS drives me nuts. Brilliant on wet bitumen though, has saved a couple of dogs in the last few years.

[Baggy]

Thanks Defute style_emoticons/<#EMO_DIR#>/smile.gif style_emoticons/<#EMO_DIR#>/smile.gif

Yes we do have ABS, and it has occurred when tranversing an uneven
surface (ie where our driveway meets road surface) and on speed humps
however I would'nt have thought tyres lost traction with road surface.
Has never happened at high speed.
Will also look at speed sensor, went to York last weekend and ABS light
came on and stayed on. We pulled up for coffee break started engine and
ABS came on, and went off as per normal.
Q: Is there 1 wheel sensor per wheel?, how does one check them or is it
best left to LR specialist.

Appreciate your Assistance

Cheers !!!!!

[Baggy]

mickus, style_emoticons/<#EMO_DIR#>/smile.gif

When you say your ABS "drives you nuts", do you experience similar
symptoms I discribed ie pulsating through the pedals???
or ABS comming on through momentary loss of traction because of
uneven limestone tracks as discribed by defute.

Haven't done any real "off road stuff" :cry: since got the Disco and would
be interesting to know what to expect from my ABS when I do go offroad.

Cheers!!!!

[mickus]

Baggy did you buy your bus second hand?
If so, at a guess I'd say your shocks are on their way out.

I average 700km a week in mine and noticed the ABS brake shudder thingy(technical term) became worse as the k's clocked up. Usually at least 50km of that weekly average is offroad. So you could say my disco has had a reaonably hard life.

Whether it's through momentary loss of traction through uneven surface(limestone/gravel) or one wheel slipping in the wet, the end result is the same; ABS kicks in and it feels like your car is falling to pieces.
Buuut... thats just what it's meant to do so it's all good.

I do a lot of k's on gravel and limestone and like to travel at a reasonable rate of knots, so ya get a bit of braking on tight corners etc. Thats when the ABS does it's thing. Prolly way safer than a car without ABS, just that shudder takes a bit of getting used to.

Before you worry too much about replacing shocks /springs etc let me see how the new shocks affect the performance of my disco this weekend at Wagoe.

Gettin new shocks fitted on thursday and plan on givin the poor old girl a solid thrashing over the weekend.

Will keep you posted.

mick

[defute]

Baggy,

yes, there is one ABS wheel speed sensor per wheel. Each sensor is wired directly into the ABS ECU to supply it a wheel speed signal.

If the ABS light has remained illuminated while you're driving, this suggests that there is an electrical fault with the system - these faults will either inhibit the system from working or can quite often make the system more sensitive than normal, hence the sensation that you are experiencing.

The easiest way to diagnose an ABS problem is to take the vehicle to your Land Rover Specialist so they can interogate the ABS ECU with their Diagnostic Computer. This will identify the suspect component.

There are 2 faults that can exist with ABS wheel speed sensors - 1. an open or short circuit in the wiring between the sensor and the ABS ECU - this will require the sensor to be replaced, or, 2. an excessive 'air gap' between the ABS sensor and the reluctor ring (which is inside the wheel hub) - this will require the ABS sensor to be 'tapped' back into position and possibly the sensors brass securing cage to be replaced.

If I was you, I would try gently tapping downwards each of your vehicles ABS sensors back into the hub until they bottom out. From there, they will find their own position relative to the reluctor ring.

If this is unsuccessful, take you car the dealer and have them diagnose the fault.

Good luck!!

[Baggy]

Mickus,

On per inspection report, did advise that front shocks needed
to be looked at, doing some research and will probably replace
with Koni or Blistein type, but will be interested in hearing how your
new shocks go..

Cheers!!!

[Baggy]

Defute,

Your knowlege is invaluable and appreciated!!!!!

Will pull off Wheels and have a look, but before I do, not having
taken the wheels off before?

Q: Are these wheel sensors easy to spot :? :oops:

Cheers!!!

[defute]

Hey Baggy,

the ABS wheel speed sensors are very easy to identify.

The front sensors are mounted into the centre of the top swivel pin in the front hubs, inboard of the front discs and the rear is mounted into the hub almost directly opposite the brake caliper on the front side of the axle case, parallel with the diff housing. They are on the end of a wiring harness that comprises of 2 wires (hidden) housed within a black insulation approx 4mm-6mm thick. All that you will see is a thick black wire going into a round tube approx 10mm-12mm in diameter. The round tube (which is the sensor) will protrude approx 10mm out of the hub.

These sensor should be knocked (very gently) all the way home, after which time they will 'centre' themselves when the car is driven.