Defender 90 rear brake forces

[valhalla]

Something that appears to be going wrong on quite a few of the 90" Defenders (Station-Wagons as well as Pick-Ups) of all ages from 1985 to 2010;

I am seeing a perpetual problem of advisories on rear axle brake forces for the service brakes, with low forces coming out on the test-sheet. Quite a few are marginal fails. Yet I cannot see how any of them could be improved over and above the efforts that each of these cars have.

This only seems to affect the short wheelbases, not the long wheelbases, so I wonder if there is a problem with the axle load data on the computer system? Maybe this is a problem with the tyres losing grip on the rollers?

So far, I have had reports from customers on cars that they have taken to 3 different MoT stations across the UK (one down in Devon) including the local one, but these are also cars that have been serviced by people other than me, and have different histories of brake work by different garages, so I'm fairly sure it isn't just my own incompetence!

Has anyone got any direct experience of this problem, or how to get around it (other than filling the rear of the car with concrete blocks)?

[studabear]

Can't ever remember testing a defender, if I have it will have had a decelorometer test.

[Deleted]

valhalla I not convinced that you should be too concerned about brake test results from Test Stations, there are many things to consider with the results of brake tests from stations.

A couple of things to think about;

Are the Defenders permanent 4 x 4 vehicles!

Are the Defenders tested using a 4 x 4 brake tester!

Are the testers still testing to the old standards when roller brake testing?

How many Test Stations actually have computerised roller brake testers and not the old hydraulic rollers fitted?

The test criteria changed a little while back and it seems many testers can't get to grips with the new methods so DVSA advised if you can't test to the new criteria just continue with the old methods.

Are the individual wheels locking at the time of test!

Are the testers actually advising of brake concerns from a lock wheel criteria?

The roller brake test is calibrated to correspond to a road speed of 20 MPH, which is why the decelerometer brake test is conducted at 20 MPH. Nobody actually drives at 20 MPH and all brake test results are indicating the findings from those figures, which are not ideal. A brake test that produces a locked wheel criteria is of no use in the real world, it may automatically meet the minimum mot criteria for a pass, but would you want your brakes locking up when driving?  

It is recognised and understood by DVSA staff that the brake test is not ideal, but until something better comes along for modern vehicles and their technology then we are stuck with that minimum standard unfortunately. 

The Test Stations were also advised by DVSA a couple of years back or so about premature wheel lock up, where this effect could lead a vehicle to fail the test, if that was the case then DVSA advised that testers must complete a decelerometer brake test to confirm efficiency and if the minimum percentage was met, i.e. 50 or 58% depending upon vehicle age, then the testers should pass the vehicles and disregard the roller brake test results.

Its all in the special notices, and they are available online to the public as well, just google DVSA special notices and happy searching 

[Karl]

Hybrid sums it up nicely

[Karl]

All I can add is we have ATL lanes (around 9 years now)

And like hybrid said
Roller brake test changed a while back.

Axles are run together to obtain readings. for the rears this has a tendency to have the rears "ride" out of the rollers

You are meant to chock the wheel

I routinely get low figures. Locked wheels supersede figures anyway.

Plus shouldn't be RBT if 4x4 . Unless you have fancy rollers

[valhalla]

Thanks for all the replies.

To be frank, I cannot answer some of the questions that Hybrid raises, as I'm not party to the details of the test itself. I can only try to work on what I am seeing on the brake test reports that are copied back to me by the couple of owners that have done so - the others have just emailed to say that they "scraped through" on the test, but had advisory points raised to the effect of the rear brakes maybe requiring adjustment before the next test. In the cases of where the sheets have been copied back to me, no note was made regarding wheel lock-up, so I have to assume that the roller brake load was weak.

What I can say, definitely, is that the local station does not have any fancy rollers whatsoever, and that the modus operandi is to run the test as if the Defender was a normal saloon car in 2WD. Every 4-cyl Defender built since 1984, when the LT230 transfer box was first used, has clearly stated on the centre tunnel housing behind the gearlevers, that it must not be run above 5mph on 2WD rollers, unless the centre differential is locked and one or other propshaft is removed (in other words, converting the Defender to 2WD of some sort or another).

The reason I have raised this is that it seems something has changed in the last couple of years, because I have not had these problems before. It's very difficult to fix this sort of problem unless you understand the full measurement system being employed (of which I have none, not even a Tapley meter), but I can categorically state that in only one case would I agree that the brake performance was weak or lacking, and that was on a car that had seized calipers on the front axle. The 90 has considerable bias to the front axle for braking, not least that if the rear brakes lock before the fronts, the car is lethal with such a short wheelbase and high CoG (pitching transfer of load to the leading axle).

[oli]

My disco always gets the same advisory.

I'm surprised it affects all 90s as this would include those with rear drums (pre 93) and the later ones with discs on all four wheels. The rear discs/calipers etc on a 90 are the same as a disco and RRC - on many, my 1984 90 included, they ARE from a disco, where someone has switched from a drum to disc axle.

I can only think it's related to the bias valve they have. Do the CSWs (with self leveller) have any sort of self adjusting brake valve?

With regard to rollers, my MOT place uses standard 2 wheel rollers and he's a member of the local Land Rover club - as are some of his employees. I think it's only a problem for rolling road type power testing as the centre diff can't tolerate a speed difference of 100% for more than a few seconds at any significant speed (Dave Ashcroft has a good video explaining how sensitive they are). A few mph for a few seconds on a brake roller is fine though - think at my MOT place IIRC it's "brakes on" THEN the rollers turn (don't know if this is the standard way of doing it or something to avoid prolonged spinning).

Do SWB Series vehicles throw up the same advisory?

Oli

[valhalla]

Oct 27, 2017 0:46:22 GMT 1 oli said:

I can only think it's related to the bias valve they have. Do the CSWs (with self leveller) have any sort of self adjusting brake valve?

The 110 and 130 Defenders do not have the bias valve on the driver's footwell, and in my experience over the last 20years of driving this sort of model, no - they don't throw this sort of problem on rear brake forces.

The logical conclusion would be that the brake bias valve is the root cause. Except, in one specific case, I have changed said valve for a new item, and the brake forces have not improved on the rear axle! So that would imply that Landrover either sailed close to the wind with the selection of bias valve settings, or that the MoT requires figures that are too close to the maximum theoretically possible for a system that is anything but perfect (as per the factory).

[oli]

Oct 27, 2017 23:30:23 GMT 1 valhalla said:

Oct 27, 2017 0:46:22 GMT 1 oli said:

I can only think it's related to the bias valve they have. Do the CSWs (with self leveller) have any sort of self adjusting brake valve?

The 110 and 130 Defenders do not have the bias valve on the driver's footwell, and in my experience over the last 20years of driving this sort of model, no - they don't throw this sort of problem on rear brake forces.

The logical conclusion would be that the brake bias valve is the root cause. Except, in one specific case, I have changed said valve for a new item, and the brake forces have not improved on the rear axle! So that would imply that Landrover either sailed close to the wind with the selection of bias valve settings, or that the MoT requires figures that are too close to the maximum theoretically possible for a system that is anything but perfect (as per the factory).

I think you are probably right with the former - I.e. Land Rover sailing s bit close to the wind. The rear brakes on an unladen 90 are almost pointloss. They seem to do little more than just give the discs a polish. I've just replaced one of the calipers on mine after finding it was seized solid (I only got it recently in my defence) and it has made no difference at all to the braking!

In defence of Land Rover there really aren't many modern vehicles that have such a very short wheelbase as a SWB Landy and I can imagine over eager brakes on the back end would be terrifying!

Oli