Rear Suspension

The standard Jaguar rear end uses 4 coilovers but I am planning on using an airbag setup at the rear.  This has proved to be a bit of a problem in that I foolishly believed that I could just get some standard off the shelf air/Shock units that would fit the standard Jaguar setup. 

Unfortunately, I have since found out that this is just not possible.  The problem is that the standard Jaguar coil-overs  are quite short.  They are only 13" long fully extended.  The minimum length of a combined airbag/shock unit is governed by its construction.  Effectively you have to build a shock then build an air bag over the top of it.  But you have to ensure good seals between the shock oil and the air.  Otherwise you start to get problems with oil leaking from the shocks.  This means that the minimum length of the unit is considerably longer than a standard shock as there are so many more seals needed. 

I have decided to go with the Air Ride Technologies 7000 Shockwaves.  They are specifically designed for rear setups and come in 3 standard sizes.  The size I am using is the intermediate version that has a stroke of 5". 

The overall dimensions are:

Compressed Height Ride Height Extended Height Stroke
11.56" 14.5" 16.56" 5"

This is what the Shockwave looks like, it uses a Firestone sleeve type airspring that offers more travel and a softer spring rate.

The design of the Jag Rear axle uses 4 spring/shocks, two on each side.  I had considered just using one airspring on each side to try and keep the cost down, but the loading on the suspension bottom arms would be completely one sided and in my opinion would potentially result in twisting and binding of the arms.

So in the end I decided that I would have to bite the bullet and go with 4. After I had decided what I was going to do it was now time to work out how to do it.  It was clear that I was going to have to modify the top mounts as they were now in the wrong location for the longer units. 

I decided that the best way to go about sorting the mounts was to make some mock spring/shock units by drilling some box section at the ride height length of the airspring/shocks and then set the chassis to the required ride height and rake.  I could then work out how to make the mounts to suit. 

One factor to consider when placing springs is that the angle they sit at has a direct effect on their efficiency.  The more they lean from vertical the less effective spring rate they offer.  So the idea is to keep them as close to vertical as possible, but work within the limits of that space available.  To get the required stroke the ride height length of the airsprings is 14 1/2".  This is about 2 1/2-3" longer than the standard units.  The only problem now is that to get the extra length I either needed to put the springs over at a severe angle (Reducing their efficiency and risking bending the rods) or raise the mount so that it would be above the normal bed height.  In the end I decided that I would raise the mount and worry about the bed later. 


Here you can see the mock up with the box section in place of the springs set at the correct ride height.

All that is required now is to weld some 5/8" bore tube to the new sections and then fully weld it all up.


Here you can see the new mounts with the tubes cut ready to be welded up.



All welded up with ends capped off, ready to be ground.



Ground and ready for welding to the chassis.



To ensure that they were aligned as well as possible I got some 16mm tube to put into the ends of the mounts holding them together in line when I welded them to the axle mount.

You can see the temporary box sections at the ride height of the airsprings in place ensuring everything is where it should be at the correct ride height of the chassis. I haven't decided if I will grind off the welds to make the extra mounts look more like part of the original cross- member.  I think that they just look like an add on as they are, but that may just be because I know they are.  I might also weld up the original mounting points to make everything look a little neater.  I will have to cut the old tubes off anyway as they will be in the way.

I cut the old tubes off and ground the inner faces completely smooth.  With these out of the way, I turned the chassis upside down yet again and decided that now there was good access for an angle grinder that I would also clean up the corners of the triangulated notch sections.  It just looks a bit neater now.  I don't think I will bother with filling the old mounting holes up.

Here you can see the finished rear end upside down after the grinding.





I now have the 4 Air Ride Shockwaves, I took a few pics of them before attempting to fit them.

Here you can see the 4 Shockwaves together, they look pretty neat.  They are a billet alloy custom made shock unit with a Firestone roll over type air bag fitted over them.  They are supplied with Poly bushes and two different size of bush insert to go over either a 1/2" or 5/8" shaft.  I have fitted the 5/8" inserts, as that is the size of the shafts on the Jag axle lower arms.  I have used Metric M16 stainless bolts for the top mounts but these are so close to 5/8" that the bush inserts fit over them fine.

The shocks have adjustable rebound valving via the control knobs on the bottom as you can see here.  They have 16 positions so adjustments can be very fine.  They are actually available in a double adjustable configuration too, providing adjustable compression and rebound.  I decided to just go with the single adjustable units on the basis that the the truck will not be doing any racing so the need for double adjustable is not really there and also the cost of the double adjustable units is considerably higher.

Here you can see the top crimp ring that holds the airbag on.  It's quite a site when the bag blows up and you realise that it is just that little ring holding it all together.  You can also see where the air line fitting screws in. 


I tried  fitting the Shockwaves to the frame to make sure that they fitted correctly and that clearances were as expected.  It was a good job that I did.  What I found was that the rear bags when inflated got very close to the frame.  They don't actually fowl but they are just too close.  It looks like the axle is not mounted at exactly the right angle for the shocks to meet up with the top mounts.  I can make them fit but it puts a stain on the bushes and the shafts.  It is not out by much but I need to sort it. 

When the bags are inflated they get within a couple of millimetres of the rail.  That is just too close.  The bag will probably get larger in diameter after a while under pressure and it will probably flex when compressed when driving over a bump in the road.  It is also possible that dirt or stones could be thrown up from the road and with such a tight clearance something could get stuck between the bag and frame and inevitably lead to failure due to abrasion.

I decided that I had to do some surgery on the rails.  I am notching the rear support rails to give at least a half inch of clearance all round.  Unfortunately it means that I will have to strip everything down again to do it, but it has to be done.


I spent the day sorting out the rear rail of the suspension support to provide the required clearance around the airbags.  I decided that as it was only a little more clearance that was required it was not going to be much of a job to just cut a couple of notches out.  Not much of a job, Huh.  After messing about for ages working around everything I removed the rear axle to provide a little more room to work in as I was struggling to get an angle grinder in the right place to make the cuts needed.  I want it to look as neat as possible so I made sure that both sides were the same. 

Here you can see the notch that I had to cut out.  you can see the old tube still inside.  This proved to be a real pain as I had to cut right through this too before I could remove the cut section as it was still welded in place. In the end I managed to cut it using an ultra thin (1mm) cutting disc on an angle grinder.

Here you can see the left hand notch complete with the new boxing plates welded in place ready to be ground down flush.



The Right hand side after being welded and ground.



The finished rear rail now with the notches in.  It is not very clear from the photos, but if you follow the line of the shadow, or the bottom edge of the rail you can see the extra clearance now available for the shockwaves.