With the top mountings now secure, use the
large 'U' bolts to secure the bottom of the air spring to the axle
casing. On this vehicle I found the one brake pipe was in a position
that was likely to rub on the 'U' bolt, so using some of the sleeving
supplied with the kit I used it on the 'U' bolt to help protect the
brake pipe as shown by the arrow below. Its not very clear on the
photo below, but there is quite a large gap between the axle tube and
the U bolt, unless your fully confident of your skills and the gaps,
fit the U bolt between the brake pipe and the axle tube.
Something to be aware of, and that is to
make sure the bracket on the axle is parallel with the top bracket to
avoid misalignment of the air spring. Whilst your aiming to keep the
brackets parallel with one another, do check the gap between the air
spring and the shock absorber shown below, as you don't want the air
spring resting on the shock absorber (also check when inflated to
maximum pressure) as it will eventually wear a hole in the air spring.
Once both air springs have been installed,
you need to decide where to install your optional extra gauge and
valves, or at least where to fit the compressed air filling point.
Most people like them installed in the cab, however on this vehicle
the owner wanted them in with the gas bottles as shown below.
The gauge and valve assembly comes in
several formats of hose connections. If installing in the foot well of
the cab, its best to have the hoses coming in to the assembly from the
side, however in the above its best for vertical connections. The
colour coding of the hoses and valves I use, is with red on the left
as all the markers on the left of the road are also red, so that
leaves blue on the right. Yep the above looks opposite to my
description, however the photo was taken looking towards the back of
the vehicle. Where ever the hoses pass through any holes or possibly
likely to be rubbed, I always use some out sleeving (large sized
hose in this case) to help protect the inner hose.
The hose connections are real simple to use,
providing you have cut the hose reasonably square, you simply push the
hose in to the fitting until it stops. To release, you have to push the
coloured ring in to the fitting, then pull the hose out. They do seal
extremely well, though if they do leak slightly, increasing the air
pressure for a week or so usually does the trick. I have found
installations carried out in cold weather are more prone to leaking as
the pipes are hard and don't bed in so well. As mentioned earlier,
raising the pressure for a while will help.
I normally add a loop of hose to aid
working on the gauge assembly, but as this isn't such a tight
installation, I felt there was no need.
from front of axle, looking towards offside rear)
There's no need to start drilling holes
everywhere (apart from where the hoses went through the back of the
gas locker box) to use the cable ties, as you'll find plenty of
convenient places to fix to as shown above. Again, personal choice, if
the tie is long enough, I
like to wrap cable ties round several times to help excessive stress
in one place as shown above.
from rear axle looking towards nearside locker)
With all the pneumatics finished, the
brake load sensing valve (LSV) needs to be checked and adjusted if
necessary. The LSV is shown below (left arrow), and actuated by a
lever (right arrow)
The LSV is plumbed in to the rear brakes
and controls the amount of brake pressure applied to the rear axle.
Through levers, it senses the height of the chassis in relation to the
axle. With the chassis low, it applies maximum break pressure, but
when the chassis is high with no load, it applies minimal pressure.
The reason for this is to avoid the rear wheels locking up with no
load on the chassis. If this happened going round a corner, you'll end
up with a situation like a handbrake turn and find the rear of the
vehicle overtaking you. With motorhomes, they are always loaded (you
never go home and remove the body, or do you?) so the LSV quite often
seizes up. Most MoT testers are switched on enough to realize its not
an issue with motorhomes so don't worry about it.
With the semi air suspension lifting the
body away from the axle, there is a chance that the LSV thinks there
is no load on the rear axle and starts to limit the braking capacity.
There are kits available to counteract the LSV getting it wrong, but
these are generally only fitted to empty vans or flat bed trucks where
the load is removed. To avoid the LSV getting it wrong on a
permanently loaded chassis (as with a motorhome), you'll need to alter
the LSV linkage. On the rear axle you'll find a slotted/slider
adjuster, as pointed out by the red arrow below.
(View from front of vehicle, towards the rear axle)
photo is a close up of what's pointed out in the photo above)
If not already done, as was this vehicle,
you need to loosen the fixing screws in the middle of the slider, and
move the two halves apart as shown above. If your unsure of this, and
its effect on the brakes I thoroughly recommend you pump up your
suspension to its highest position and have your brakes tested at a
MoT station (Not sure, but I don't think there is a charge for this),
then at least you'll know whether its set correctly or not.
That completes your installation, and your
system is ready to use.
I didn't take any photos of the before and
after effect from outside the vehicle, however the two following
photos will give an indication of what to expect. The differences are
not very great, as the vehicle had empty water tanks etc.
top photo is with the air springs inflated, also notice the bow in the
leaf spring and the gap between the upper and lower leaves.
photo shows the air spring deflated. The leaf spring in this case is
almost flat, infact when loaded it is flat and there is no gap between
the upper and lower leaves.
For a list of frequently asked questions
on semi air suspensions, click here
A good starting point for what pressure to
inflate your air springs to, try 40psi and experiment up and down from
Always have a minimum of 5psi in the air
spring when not being used for long periods.
DON'T jack up the body with any pressure
above 5psi in your air springs (jacking up the axle will be fine).
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