Discovery 2 Air Suspension Setup

The car was tilted at a slight angle. It was obvious that the rear left suspension was pumped up higher than it should be.

From past experience I know this is most likely caused by a faulty height sensor. If the suspension drops overnight it is most likely a leaking bag, if it raises to full height it is most likely a faulty height sensor.

A quick search on the Internet found a very useful blog post. I've saved this as a PDF for future use.
That article warns that an over inflated air bag risks exploding and therefore could be dangerous if the car is driven.

Luckily I had spare sensors in my stock of parts so I planned to swap out the faulty one. The instructions suggested loosening a valve to deflate the air suspension before carrying out the work however I have a Nanocom for the TD5 which can control the SLABS, so I plugged that in to lower the suspension without having to open up the compressor box.

The Nanocom can also read the settings and much to my surprise the sensor was still showing movement. Just by bouncing on the car it was easy to see the values change! Perhaps my 2 minutes of brushing away the mud from the sensor pivots had done some good.

Without replacing the sensor, I used the Nanocom's SLS calibration utility to raise and lower each side until I got both sides level. It only works with the engine running and all the doors and bonnet closed. I opened the window so I could make changes and more easily measure the heights.

It's a bit trial and error as lowering one side also slightly lowers the other so that side then needs raising to compensate. Each press of the raise or lower button on the Nanocom moved the corresponding air spring by about 1cm.

The workshop manual uses calibration blocks but I know from looking in the past that these are expensive and I don't know anyone who has them. Most people, myself now included, just measure from the centre of the wheel to the highest point of the wheel arch.

I don't know what the correct heights should be so for the time being, until I know better, I have assumed that the car should ride level and matched the rear heights with the front heights at 47cm. I have standard size wheels and tyres and normal height suspension.

When I started, the left side was just over 50cm and the right side only 46cm.

After having made the adjustments I pressed the 'Store Heights' button. It then instructs you 'To load to the ECU turn off the ignition and wait 60 seconds.' I did as instructed.

It had well over 60 seconds because it took me a while to get the cat off the roof before I could head out for a test drive. The roads round my way are quite uneven and at one point in our single track road I had to pull over on the grass to let another car past so the suspension got a good work out on the 10 minute run.

I measured the heights when I returned, while the engine was still running and both sides were still at 47cm. Hopefully that's sorted but I still have the option to replace the sensor if it should re-occur.


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Since carrying out this work I have been told on Facebook and found on a forum that the correct height for the suspension is 61.5mm (2.42") measured from the tip of the bump stop rubber to the axle. I have been unable to verify that measurement from any definitive source.

D2 Workshop manual 99MY extract

The nearest confirmation of the calibrated size, that I can find, is the above reference in the workshop manual which indicates the distance must be at least 60mm.

I'd be interested to know if the exact size is mentioned in a newer workshop manual.

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Air Springs and Hoses

The mornings after we took the Discovery off road we awoke to find it sitting on its haunches.

We have been to off-road courses twice in the last month and it has happened both times.  Its not a big problem because in both cases starting the car pumped up the suspension and it drove properly. After that the springs remained inflated and behaved as expected.

I did a bit of reading and apparently the air spring should be replaced every 5 years.  I've had the car over 5 years so I know they have not been done.  Swapping the springs for new ones sounded relatively straight forward.  There are several other sites with guides plus the workshop manual is clear.

http://www.discovery2.co.uk/Rear%20Air%20Springs.html

http://www.landyzone.co.uk/lz/f38/disco-ii-air-suspension-definitive-guide-61211.html

I ordered the air springs (RKB101200) and the clips to go with them plus a few spare clips (NTC9449) just in case I dropped any.  

The genuine Land Rover air springs are very expensive but there are OEM versions for considerably less.  My original Land Rover air springs have the manufacturer stamp of Contitech in addition to the Land Rover stamp and part number.  The Britpart OEM versions are made by the same people.  According to various forums the Dunlop springs were never fitted to Discoveries but have been used on other models and are frequently used on lorries.

Having the parts I thought I needed I started the job.  After jacking it up and getting the axle stands under it I spotted two snags!

Snag One

The air hose on just the drivers side of my car was already very taut and all the instructions and some advice on the phone from Torque Performance, who I had phoned on an unrelated matter, confirmed that the only way to remove the old spring was to cut the hose. 

The cut should be close to the brass collet and this would not normally be a problem but on mine the remaining hose would be too short to fit the new spring!

I tracked the hose back and removed some clips but getting any extra slack was going to be tricky.

Snag Two

You need to deflate the spring to be able to remove it!

The official method is to attach the TestBook computer and instruct the Self Leveling Anti-lock Braking System (SLABS) ECU to deflate the springs.

That was the final confirmation that I needed my own Nanocom which is now on order.

There were three other methods to deflate the springs.  Cut the hose, stab the spring and remove the connection from the compressor.  Two out of three of those are destructive and the other assumes that the collet removed would go back in and seal when refitting.

I did not want to take the chance of having the vehicle undriveable because I did not have any replacement hose or connectors.

I carefully put the vehicle back on the ground and checked it was all still functioning correctly.

What Next?

I could buy the Land Rover replacement air hose harness.  Not just one hose but you have to buy the whole lot!  That appeared to be unnecessarily expensive and a fiddly job under the car to fit.

After a bit of investigation I found that the hose can be repaired with  standard 4mm pneumatic hose and some straight push fit joiners.  I could use the same idea to extend it.

As this is a significant part of the suspension I was being safety conscious and not just trusting a single eBay advert.

Further investigation into the air spring setup indicated that the compressor can reach just over 10 bar.  I cannot confirm that by other sources but as I could only find two types of hose, polyurethane and Nylon, the choice was easy.

The polyurethane is only rated at 10 bar but the Nylon had ratings starting at over 26 bar and it had a more appropriate working temperature range typically from -35C to +70C.

http://www.kingindustrial.co.uk/pneufnm.htm

The easiest place I found that could supply the 4mm Outside Diameter with 2.5mm Inside Diameter Nylon tube was on eBay.  

I also found the Legris straight joiner from RS was probably the better choice for the joiner because theirs are rated at 20 bar where the more common make available on eBay and other places appear to be only rated at 10 bar.

But What Did I do?

I decided, after having done all that research, to let the garage do it.

With it up on their ramp they were able to find enough slack in the existing tube and they replaced the air springs.

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Appendix

Tube cutter: http://uk.rs-online.com/web/p/tube-cutters/0722198/

Suspension bits:

http://www.famousfour.co.uk/search?string=air+spring+hose&veh=disco_2&sec=spst

http://www.johncraddockltd.co.uk/land-rover-discovery/discovery-2/parts/suspension/