300 Tdi brakes - occasional scares.

[dooroy]

My brother has a 96 300 Tdi ES and over the past few weeks the brakes have given him a few scares .

What has happened is that when he applied the brakes the pedal pulsated (as if the ABS was working )and he felt the brakes were having very little effect . He was on tarmac on each occasion . He hasn't hit anything - yet .

It hasn't happened when travelling in a straight line - on each occasion the front wheels were turned left or right .

The SRS light has been on for some time now following the installation of a mobile phone kit and he will have to go to a main dlr to have it extinguished .

I don't think the SRS has any connection with the ABS system - or has it ?

Any suggestions welcomed - if there is an ABS problem could it be picked up when having the SRS light sorted ? (€95 + VAT)

[thebiglad]

Sounds to me like the abs is activating on a wet road, like it's supposed to. When the abs works, you will feel a pulsing through the brake pedal - perfectly normal if on low-grip surface.

However if your brothers concern is about the speed with which the car is slowing down (rather than the pulsing) then other areas need to be checked such as: tyre condition, tyre pressures etc

[dooroy]

His concern was that he felt the ' stopping distance ' was excessive . He has had cars with ABS before so was familiar with the action of the pedal .

Will have to ask him about road conditions at the time - I had told him before that ABS couldn't always save the day if grip was very poor .

[Rolly]

You probably have a dodgy wheel speed sensor which is triggering the ABS when braking. I had this with my 1996 Discovery. New sensor required but first you need a Testbook to tell you which one.

Hope this helps

[thebiglad]

His concern was that he felt the ' stopping distance ' was excessive . He has had cars with ABS before so was familiar with the action of the pedal .

Will have to ask him about road conditions at the time - I had told him before that ABS couldn't always save the day if grip was very poor .

Has your brother had 4x4's before?? The weight (over 2tons) and the compromise(offroad/onroad) tyres often used on them make for significantly longer stopping distances, by comparison to a std family car.

Cheers

Dave

[BogMonster]

Rolly took the words right out of my mouth

On mine it probably increased the stopping distance by a factor of at least 2 which is quite scary!

[pinny]

Hope this helps

i had a very similar instance this year and found it to be the wheel bearings allowing the pads to be ppushed further from the discs resulting in more pedal travel to stop just a thought

[dooroy]

He has been driving Discoveries for about 4 years now so he is well used to them .

I was thinking along the lines of a wheel sensor also due to it only occurring when on lock . Wheel bearing play pushing back piston I have come across before but that would allow more pedal travel before applying the brakes and this is not the case .

I also considered intermittent servo failure which can be quite scary - used to be common on older VW dsls when the vacuum pump diaphragm split and could fail to develop vacuum occasionally . Hard pedal - very slow to stop. But he says the pedal does not go hard etc.

When you say Testbook would this be what the dlr will use to put out the SRS light - if so he could kill 2 birds with one stone .

Would there be fault codes stored even if the ABS light didn't come at any time while driving ?

Thanks for all your help - this kind of fault could have serious consequences .

[Richard Mills]

Hi There,

The wheel sensors go faulty mainly because of hitting the castleations on the hub. The first sign is iron filings stuck to the end of the sensor, then later the sensor fails short or open circuit.

This process can be started by wheel bearing play, or rust getting into the sensor mounting. The required gap is rather small, so any change in normal position between sensor and castleations will cause intermittent then permanant failure.

My disco also has the SRS lamp lit, I let the battery go flat, and it will have black PVC tape over the lamp for the rest of it's days, just like the other 2 cars that live with me!

[disco300tdiman]

Hi
I have had a nightmare with my braking system and i know what you mean when you say the abs kicks in but only at very low speed the problem is the pedal goes hard and you cannot stop you there are no brakes and as you know try stopping a car that weighs nearly 2 tons. I have had my 1996 2.5 tdi for over four years now mine is my passion and i dont like being beat. i have changed abs sensors on th front, new servo, new vacuum pump, new vacuum pump pipe, changed all brake fluid, it come to a point my wife would not drive it, you would never know when it would happen. in the end i changed the abs pump and i can safely say it cured the problem but please remember this did not show any faults logged on the onboard computer.

[steve58]

Your stated brake issue you experienced like so many I have read about on the net is almost identical to mine. Just bought a 96 tdi auto and after 30 years as a mechanic and engine machinist I am absolutely appalled at the ABS set up on these vehicles. After checking the fault codes and clearing same, and checking the relevant factory manuals in a hope to find a solution to the issue (non-existent) I have decided to revert the system back to a complete non ABS system (Removing everything relative to ABS in the process) and using all components including brake lines unions etc off an earlier non ABS vehicle.

Land Rover clearly state in the manuals that if the ABS system fails the brake system reverts back to a normal system which is absolute rubbish. To my way of thinking, just 1 occasion of a failed backup brake plan is enough to scare the carp out of the driver and at worse cause an accident.

At a new genuine cost of $5900 Au for the ABS pump I decided to buy another SH ABS pump cheap to pull apart to actually find out what it does and how it functions.

Despite what Wabco make out there is no rocket science involved. Interesting thing is the ABS pump is merely a collection of 8 "On-Off" solenoids together with a 12 volt eccentric shaft "Pump" motor which in turn drives 2 hydraulic spools to marginally increase-direct brake pressure-flow. It is very easy to check the ABS pump assy with a pressure brake bleeder and a 12 volt power supply to check the function. The problem turned out to be the ECU for the ABS which decides to turn off the brake flow in the ABS assy as it sees fit and me as the driver just has to lump it. Really interesting for me on 1 occasion when I was pulling up at some toll gates to pay the second toll on the motorway

Hi

I have had a nightmare with my braking system and i know what you mean when you say the abs kicks in but only at very low speed the problem is the pedal goes hard and you cannot stop you there are no brakes and as you know try stopping a car that weighs nearly 2 tons. I have had my 1996 2.5 tdi for over four years now mine is my passion and i dont like being beat. i have changed abs sensors on th front, new servo, new vacuum pump, new vacuum pump pipe, changed all brake fluid, it come to a point my wife would not drive it, you would never know when it would happen. in the end i changed the abs pump and i can safely say it cured the problem but please remember this did not show any faults logged on the onboard computer.