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Tuesday 30 September 2014

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.

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.

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.



Suspension bits:

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