Thoughts about Land Rover shocks
The Shocking limits of Land Rover leaf spring
follows are my personal thoughts and current understanding on the
subject of series Land Rover shock absorbers and how they affect
spring articulation. Please do not let them limit your thinking
if you are contemplating something substantially different and innovative.
Before going into this discussion I should state up front that
the #1 limitation to series Land Rover suspension articulation is
shock length and the only way to get beyond that limit is to move
the top and bottom mounts farther apart and install longer shocks.
There is no way around this
The purpose of shock absorbers is not to absorb shocks. What they
do is provide a resistance to the spring's movement that dampens
spring oscillation. Without a shock if a spring is deflected then
allowed to freely return to its rest location the momentum of the
spring mass carries it past the rest point then back again past
its rest point in oscillation. The shock exists to dampen this spring
osculation so the driver does not feel like a jack in the box head
on the end of a just released spring.
Shocks work most effectively when the dampening resistance is matched
to the oscillating characteristics of a spring and when the shock
is aligned perpendicular to the movement of the spring.
Some of the spring movement energy absorbed by the shock turns
into heat. Shocks heat up during off road use and more so in fast
off road use. The hotter they get the less effective they become
at dampening oscillations. There are a number of approaches to handling
this heat and minimizing shock fade, including using multiple shocks.
Shock absorber manufacturers are constantly researching new and
better ways of handling heat and shock fade then offering socks
with their latest technology. I will not go into dampening levels
and heat dissipation. This is one place where you need to check
a manufacturer's current product line for the characteristics you
need when you go to purchase shocks. If you are going to drive washboard
roads at speed, look into a shock's resistance to heat fade. For
most slow cross country trailing the common nitrocharger style will
usually do the job without fade issues.
Land Rover shock absorbers work just fine on stock Land Rovers
operating within the Rover engineer's design parameters. They did
a very good job of matching shock characteristics to the springs
they specified. If you are running a basically stock suspension
system with factory specified spring rates you would be hard pressed
to find better than the original stock shock absorbers.
However if you modify the spring characteristics or replace your
springs with non Land Rover springs such as parabolic springs you
may need to likewise modify your shock characteristics to better
match the springs.
Stock Land Rover shocks are not a good match for parabolic springs.
Most companies offering a parabolic spring have tried different
shocks that fit series Land Rovers and have determined which of
the bunch works best with their parabolic springs. If you decide
to install parabolic springs be sure to get the shock absorbers
that the company recommends to use with their shocks. They have
done the research which can save you from costly trial and error
Series shock length limits spring articulation
Shock absorbers have a fully extended length and a fully compressed
length. No amount of spring manipulation can achieve articulation
greater than the distance between a shock's travel between its top
and lower limits in its mounted orientation. Unfortunately series
Land Rovers have one of the shortest shock travel lengths of any
off road vehicle.
You can increase upper OR lower articulation at the expense of
articulation in the other direction by choosing shocks with different
compressed and expanded lengths. Since there is only so much distance
between the upper and lower shock mounts aftermarket shocks can
not extend total articulation over stock shocks. All they do is
move articulation higher or lower a couple inches at the most.
Some manufacturers or retailers of aftermarket shocks for series
Land Rover claim increased articulation. What they really mean is
that they have increased lower articulation at the expense of upward
articulation. They have a longer extension rod which allows a spring
to extend farther downwards but that longer arm creates a longer
compressed length which hurts upwards articulation.
The upper articulation stop should be the frame mounted bump stop
and not the compressed length of the shock absorber. If you go to
an aftermarket shock that has a longer compressed length you will
want to increase the length of the frame bump stop. The frame bumper
should come into contact with the axle housing at least a half inch
before the shock reaches full compression. This allows some space
for rubber compression. If you are playing around with the new poly
stops, use the manufacturer's recommendations. Most of the poly
stops I have seen are designed to absorb the shock of contact by
compressing to a greater degree than a solid rubber block.
Most people don't pay much attention to upper articulation. It
is the downward articulation that is visible and that people concentrate
on. Here are two reasons to pay attention to upward articulation.
1. The more that axle movement conforms to uneven terrain the
more level the vehicle is likely to sit.
Imagine a vehicle without a suspension system. The axle housings
bolted directly to the frame. If a wheel is unsupported, the body
tends to remain in line with the other three wheels for as long
as the other three wheels support the vehicle's centre of gravity.
However any bump that moves any of the four wheels upward will push
the vehicle upward at that corner and force one wheel off the ground.
The ability of a suspension to articulate upward is a critical
factor in keeping a vehicle level and the other three wheels in
contact with the ground. The greater the upward articulation capability,
the more stable a vehicle is whilst rock crawling.
The ability of a suspension to articulate a wheel downward affects
the ability of that wheel to get enough traction to help propel
the vehicle forward and how abruptly the body tilts if the vehicle's
centre of gravity is no longer supported by the other three wheels.
Of course with an open diff, loss of traction on one wheel spells
loss or power to both wheels on the axle.
2. On solid axle vehicles, the greater the articulation on
one side, the greater the articulation at the other side as long
as the limits of articulation are not reached.
When an axle is on an uneven surface, the forces acting to articulate
one side of the axle act to increase opposite direction articulation
at the other side. Articulation is enhanced when one side encounters
a bump and the other a trough until an articulation limit is reached
at one side or the other.
Increasing lower articulation at the price of upward articulation
will not increase the axle assemblies total articulation and it
will make the vehicle a tad less stable under rock crawling types
Increased articulation through longer shocks
The shock absorber ties the frame to the end of the axle housing.
Land Rover shocks are mounted in the direction of spring travel
for maximum dampening affect. Without changing orientation, the
extended length of the shock absorber will set the lower limit to
articulation and the length of the compressed shock will set the
upper limit of articulation. If you add a shock with a longer rod,
the compressed length will be longer.
If you wish to achieve greater overall articulation you will need
to move the shock mounts and fit a shock with longer travel. Rover
suspension engineers did just that when Land rovers went to coil
springs. A very important part of the reason that stock coil sprung
Land Rovers have greater articulation than leaf sprung Land Rovers
is that the coil sprung vehicles have more shock travel.
Parabolic or low friction elliptic leaf springs alone will just
let you get to the limits of shock travel quickly if you do not
extend them. They will not increase articulation unless the leaves
on the old springs were rusted together.
Front shocks are easy to extend just by using the same bottom mounts
and creating new top mounts.
Modified front shock mount welded to top of original mount (Timm
Cooper's Series I 109).
Here is another implementation very similar to Timm's
Here is a different approach where the tower is tucked in tight
against the frame.
With some modification, Toyota FJ40 and Ford F250 front top shock
mounts would be good bolt/weld on premade top mounts for front shocks.
The key is to keep the mount and shock as close to the frame as
possible since the tyre top swings inward during upper articulation.
Extension of rear shocks is more difficult because there is less
space in the stock shock orientation. The easy solution for a short
shock extension is to adapt Land Rover coiler rear top mounts. But
without Defender lower mount points the added shock length is minimal.
This person picked up a couple inches by
moving the rear top shock munt forward and a little higher. This
gives about the same length as a Defender rear shock top mount.
An approach many vehicle manufacturers make to deal with limited
space in the direction of spring travel is to mount the shock at
an angle to the direction of spring travel. The advantage of this
approach is that the shock needs to extend or compress less for
a given amount of spring movement. The disadvantage is that as you
move the shock travel farther away from the direction of spring
travel the less effective it is. You can compensate with a higher
dampening rate on the shock.
A common rear shock mounting arrangement on leaf sprung 4WD vehicles
is to angle the top mounts inwards towards each other. This allows
longer shocks to be fitted than there would otherwise be space for.
This in turn allows the springs to articulate to a greater degree
without being stopped by a shock that reached the end of it's movement.
Rear shocks on Timm Cooper's old Series I 109
Different view of the top mounts
The bottom mounts are welded to the axle tube.
The Toyota FJ 40 rear shock mounting is this style and can easily
be reproduced at the rear of a series Land Rover.
Some years of FJ40 have bottom spring plates with a built in bottom
shock mount. These can be used at the rear of a series Land Rover
along with larger diameter 'U' bolts. The upper mount can be either
an inverted 'U' channel or 'L' channel welded between the frame
rails at the tops and drilled for upper shock mounting bolts. If
you place the top cross member and mounting holes so that the distance
between upper and lower mounts are the same as an FJ40, you can
use the variety of off the shelf available FJ40 rear shocks. Otherwise
you will need to measure shocks to fit your application and hope
to get one with heavy enough dampening for your application.
A couple thoughts about inward tilting shocks. The closer towards
horizontal they are mounted the less effective they will be, so
placing the top mounts together at the middle of the cross member
may not be the most effective solution. The closer you can get them
to vertical and not interfere with the frame during extreme articulation,
the less dampening they need to be effective with your rear springs.
Also when you angle a shock towards the middle it becomes a factor
in dynamic body lean tending to dampen body movement the same way
it dampens spring movement. I suspect that if you drew a line between
the bottom rear shock mount of a factory stock FJ40 and the roll
centre axis, the rear shock extension rod would be aligned along
If you need to choose new shocks for your vehicle you will need
to measure the distance between shock mounts at both upper and lower
. The maximum upper articulation can be the difference between
the static mount to mount distance and the distance between the
frame bumper and axle where the bumper would contact. Then subtract
an inch for bumper stop compression.
You need a ramp of some kind to measure the static maximum downward
articulation. With the shock removed so it can not limit travel,
measure the distance between the shock mounts when the wheel is
off the ground and the end weight is supported by the upwardly compressed
other wheel. Do not just jack up the front end so both wheels are
off the ground. Add 2 or 3 inches to the static length to approximate
a dynamic length.
Your proper shock length will be where the compressed shock length
is equal to or shorter than the upper articulation length and the
fully extended shock length is equal to or longer than the calculated
dynamic downward articulation.
If you can identify a 4WD vehicle with similar shock length requirements,
axle weight and shock mounting angle as your Land Rover you can
use the shocks for that 4WD and be confident that the shock valving
is close to what your Rover needs. Axle weight and shock mounting
is one of the reasons I keep referring to the FJ40 as a model. If
you duplicate the FJ40's shock mounting, which is much better than
a Land Rover's, the weight is similar enough that the range of off
the shelf specialty shocks for the FJ 40 would also me a good match
for the Land Rover.
If you can not locate a leaf sprung 4WD vehicle with the same approximate
axle weight, get shocks with dialable shock resistance and experiment.
And do not forget every change affects something else to a degree.
Pay particular attention to front and rear propshaft to frame interference,
length of flexible brake lines, propshaft lengths at both upper
and lower maximum articulation and 'U' joint binding.
One change will often require a number of other changes to bring
everything back into acceptable specs. Be careful...be aware..be
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