Thread: Brake Mystery.

With the complexities of an ABS system I wouldn't mess around with the brakes, but I would take it to a brake specialist and have them diagnose and fix the problem, Regards Frank.

If you have done all of the simple (common) things with no result, can't help but agree with Underover

Cheers

RF

get a Nanocom evo and do a modulator bleed, just enter the wabco menu and its straight forward.

I have a similar problem on 96 Disco with a WABCO ABS. I have done quite a bit of looking around the web and what I found is this: Bleeding Brake after ABS Module fix - Land Rover Forums : Land Rover and Range Rover Forum

Look at the comment by "Rovin4Life", it seems to be backed up by the manufacturers instructions for bleeding the system on pages 13-16: http://www.meritorwabco.com/MeritorW...nt/tp99124.pdf

I am going up to Nelson Bay (from Bathurst) this weekend hoping that this works.
I'll let you know how it goes

Good luck,
Tom.

Thanks for the info.

I have bled the system so the brakes are perfect (which seems to be no real issue) and have disconnected the power to the ABS.
In the event of it being something within the unit creating the air, I'm hoping that it may eliminate one more maybe. I am of the understanding (correct me if I'm wrong) that the ABS has a pump of some description within it that activates it. If this is faulty, deactivating it may help pinpoint the issue.

Also a safety recall which I was not privvy to (and I did buy it new) also makes me suspicious.

Hmmmm...



HomeRecall categoriesCars, boats, bikesCarsLand roverLand Rover—Discovery Series II and Defender Vehicles
Land Rover—Discovery Series II and Defender Vehicles

PRA number: 2004/6875
Date published: 22nd March 2004
Product information

Product description

Model Years 1999 - 2004. Campaign D148 Identifying features

N/A What are the defects?

After use of the traction control system in off road conditions, longer brake pedal travel and additional effort may be required. What are the hazards?

Brake failure. Where the product was sold

• Nationally

Supplier

Premier Automotive Group Australia Pty Limited - Trading as Land Rover Australia What should consumers do?

Contact your authorised Land Rover Dealer. Other regulator reference numbers

D148

How are your wheel bearings ?

I'd be checking there too.

Any play at all in the bearings will give you pad knock back.

As the wheel wobbles it pushes the pistons back into the bores, so the next time you go to apply the brakes you need to push the pistons and hence the pads out further just to meet the disc face.
This gives you a very long pedal on the first application requiring a second stab to give any decent pressure and retardation. (if you're aware of it, it becomes a quick few pumps coming up to a corner)

Pads with little material left can also create a similar situation as the pistons retract slightly with friction against the seals.

Rough roads can also do it, I've gotten onto the habit of a little security tap of the middle pedal just to bring the pads up when driving on dirt.


And sorry to be nit picky, but a long pedal isn't fade.

Fade is a heat related issue and there are two types.
1. Where the pads overheat and their coefficent of friction goes down, (they're overheated) resulting in a normal feeling pedal but no retardation or
2. In extreme cases it can be when the fluid can start to boil behind the pistons, obviously resulting in a long pedal.

Sorry, can't be much help with the ABS stuff other than what Don suggested re the Nanocom, never had to work on it.

Quote

Any play at all in the bearings will give you pad knock back.

Unquote

Lightbulb moment! My 99 D2 when it was actually new used to do this. With the D2 the front brakes would sometimes go "bang" on the first application.

On dirt roads the pads would move back. Visiting LR tech eventually agreed it was the pads or the pistons/discs. Just changing out of the front pads cured the problem.

Might be all???????????

Bit more for clarification.

Quote

Fade is a heat related issue and there are two types.
1. Where the pads overheat and their coefficent of friction goes down, (they're overheated) resulting in a normal feeling pedal but no retardation or
2. In extreme cases it can be when the fluid can start to boil behind the pistons, obviously resulting in a long pedal.

Unquote

Braking is converting mechanical energy to HEAT energy. Fade is not really pad thing though they can play a small part. It is a function of the amount of HEAT in the Disc or Drum and its ability to absorb and dissipate more "HEAT". Hence extra finning and Aluminium clad drums, and thicker and thicker ventilated discs all the way up to very sophisticated disc materials such as Carbon/Carbon ceramic. Slotted or drilled discs are not for this, though it is an aid.

The slotting or cross drilling is to quickly dissipate the gases generated by the ablating of the pad to allow the pads to remain in 100% contact with a disc and prevents the (a long bow) something similar to the pad aquaplaning on the disc; gives a more solid feel to the pedal under heavy hard braking. (Obviously getting rid of those very hot gases very quickly will also aid in keeping the disc cooler longer.)

Brakes "fade" when the Drum/Disc cannot absorb/dissipate any more HEAT fast enough.

The Pads - Pad materials become a factor only when the pads start to cook and the the pad material ablates faster due to the excessive heat. If one puts a standard road vehicle on a track and starts to punt, standard road pads just disappear!

Fluid boiling is very nasty, normally caused by moisture in fluid. Brake fluid is Hygroscopic. It absorbs moisture from atmosphere, hence the recommendation to change fluid every couple of years. If your fourby does fair bit of paddling try 12 months. It is nastier still when after an accident one says "brakes failed" and plod puts his size twelve on the now "hard" pedal.

I understand some Dealers and Brake places now have a gadget like the one I use on my pot plants. Dip it into the reservoir and it gives a Go/No Go moisture reading



Cheers

RF

Originally Posted by Rick Fischer

[snip]

The Pads - Pad materials become a factor only when the pads start to cook and the the pad material ablates faster due to the excessive heat. If one puts a standard road vehicle on a track and starts to punt, standard road pads just disappear!

Fluid boiling is very nasty, normally caused by moisture in fluid. Brake fluid is Hygroscopic. It absorbs moisture from atmosphere, hence the recommendation to change fluid every couple of years. If your fourby does fair bit of paddling try 12 months. It is nastier still when after an accident one says "brakes failed" and plod puts his size twelve on the now "hard" pedal.

I understand some Dealers and Brake places now have a gadget like the one I use on my pot plants. Dip it into the reservoir and it gives a Go/No Go moisture reading



Cheers

RF

Pads have very specific temperature working ranges for the optimal coefficent of friction (mu)

Road type pads operate best at temps far below high performance or race pads, when you exceed that specific temp range, often less than 400*C, you will get pad fade.
Yes, it's a function of the discs/drums not dissipating the heat fast enough, but it's still pad fade.
These 'soft' types of pads are used on road cars as they bite and work well at low temps and on the first application when cold, they don't need to be worked hard and brought up to a specific heat range before optimal performance or bite is reached.

With pad fade the pedal is rock hard, the brakes smell like all buggery and you don't stop.
This is so easy to bring on just going down a mountain pass on a 4WD.

There are actually two types of pad fade, green fade, which is something you get with brand new pads that haven't been 'bedded' in yet (Aussie/English term) or 'burnished' is the term used in the US.
What happens here is that the resins and fillers used to bind the friction material need to be 'burnt' out of the pad/lining. As these resins evaporate, gasses are formed which creates this type of fade.

What people don't realise is that a certain amount of material also needs to be deposited onto the disc face for best performance too.

This green fade happens at a far lower temperature than the pads normal operating temp range.

Straight pad fade is where the pads maximum normal operating temperature has been exceeded.

Yes, fluid boiling mostly occurs because of moisture contamination, this is why fluids have rated wet and dry boiling points, but fluids can also boil when their rated maximum working temp has been exceeded.
Rare on road cars, ceramic heat shields and pistons are used on race cars to reduce the occurrence which can happen even with iron discs and 'normal' friction materials.