Land Rover Hinged Radius Arm
This is a picture of a modified Land Rover radius arm. It has been modified
to allow it to rotate for increased articulation while off roading. The
rear pin is removed for off roading and returned for on road driving. With
this approach, you get greatly increased articulation and stability off
road while retaining stock manners on road. Another major benefit of the
design is that is a true bolt in requiring no other modifications or fabrication
on the vehicle. You only use one of these arms, not two. Essentially, in
the stock setup, both arms control rotational loads from braking and acceleration
along with fore and aft location of the axle housing. With one unpinned,
hinged arm and one stock arm, the stock arm controls the rotational loads
by itself while both still control fore and aft location. When you reinstall
the pin for highway travel, both arms work like stock.
You can see the hinge bolt, removable pin and welded on outer plates.
Not visible in the picture are the 2 hidden pins which go through the arm
and outer plates. These act as additional structural reinforcement of the
outer plate attachment to the rear section of the arm. The hinge pin also
uses a spherical bearing in the main arm. On early Bronco arms, I fill
in the I beam section of the arm with 1/2" thick filler plates and do not
use a bearing. On the Rover arm, the dished shape of the I beam did not
lend itself to easily filling in the cross section with additional material
so I elected to use a bearing to fill the gap. It has a side benefit of
reducing wear although this has not shown to be a problem on the Bronco
arms.
This is the baseline test with the arm pinned and the shocks still in
place. The sway bar was removed to make room for the prototype arm. This
will not be required on future models. RTI for this test was 585. This
score should only be used as a reference for comparison to later runs since
the ramp was setup on an uneven gravel surface.
This was the second set of tests where we ran up the ramp with the arm
unpinned. The shocks are still in place for this run. Score improved to
an RTI of 760.
This picture shows the extended side of the vehicle in the same position
as the previous picture. You can see the great deal of angular misalignment
between the 2 halves of the arm. This gives you an idea of the amount of
misalignment that the stock bushings are trying to allow while articulating. The
axle on the far side is the original unmodified Rover arm. It keeps the
axle from rotating for braking and acceleration loads while the unpinned
arm only controls fore and aft location.
Unfortunately, I forgot to get a picture of the last run up the ramp
with the arm unpinned and the front shocks removed. I found a problem with
the outer plates hitting the gusset of a body mount on the frame. This
problem was noticed when the two runs up the ramp with the front tires
did not give equal results. The interference problem only effected the
test where the left front tire was in compression. The RTI score for the
right front tire on the ramp (arm extended so no interference problem)
was 862. John Lindblom also took some pics (it's his Disco in the pics)
of the final run and I'll post them once he gets them developed and scanned.
The problem itself is easily corrected by moving the plates forward about
an inch and my second prototype is in work.
If you want to see more and don't mind waiting, click here
to go to the photo page.
Initial results:
First a few test configuration notes:
1) 1995 Bone stock Discovery with stock tires and suspension pieces
2) Front sway bar was removed due to some interference with the rear
removable pin.
-could be left in with a minor redesign of the pin (reduce the amount of
protrusion)
3) Hinged arm mounted on driver side
4) Hinged arm strut bushing washer (the cupped one) was reversed so cup
pointed toward axle
-this is a common Bronco trick to give a little more movement at the strut
bushing
5) We never touched the rear suspension shocks or sway bar for any of the tests
6) We also were set up on gravel which gave some problems getting maximum
scores due to spinning with an open diff vehicle.
7) Tests were conducted at Randy's Off Road in Smokey Point, WA.
On Saturday morning, John Lindblom (Disco donor and closet early Bronco
owner), proceded to remove and replace the stock arm on the driver side
with a hinged and pinned radius arm. As noted above, the sway bar was also
removed due to some potential interference with the rear pin during
testing. We had to remove the tie rod from the knuckle in order to remove
and replace the radius arm. The procedure went reasonably well considering
that this was the first time John or I had worked on a Rover, but from some
tips I had gotten from Q, it went okay. It took us about 2 hours to remove
and replace the arm. When I switched it back, it went much smoother since I
had a better understanding of the steps needed to be done.
The test results below are the vertical height of the center of the tire on
the ramp. The tire indicated is the one on the ramp.
Baseline Test (Essentially stock except for no sway bar)
Arm pinned, shocks installed, sway bar removed
Right Front 20" 585 RTI
Left Front 21.5" 629 RTI
Right Rear 20" 585 RTI
Left Rear 20.5" 599 RTI
Test # 2
Arm unpinned, shocks installed, sway bar still off
Right Front 26" 760 RTI
Left Front 25" 731 RTI
Right Rear 21" 614 RTI (potential unnoticed interference, discussed later)
Left Rear 24.5" 716 RTI
Test # 3
Arm unpinned, upper shock attachment disconnected, sway bar still off
Right Front 29.5" 862 RTI
Left Front 25" 731 RTI
Right Rear N/A
Left Rear N/A
During this last test, we found a problem with the design of the prototype
arm. Essentially, on compression, the arm went up and interfered with the
body mount. The frame has a triangulated gusset beneath the firewall body
mount. When the arm moved up close to it, it eventually hit this gusset.
This was due to the 1/2" thick outer plates of the modified arm. I need to
move the plates forward by about 1" to clear the body mount. I can't do
this to the original one, but I will do it on the second prototype. I guess
this is what I get for making a piece in the dark with no vehicle to look
at for potential interferences. BTW, those shocks were a real pain to
remove. Apparently LR really likes Loktite. We spent a lot of time trying
to remove the nuts off the stud.
For test 3, we first went up the ramp with the left front tire and recorded
the 25". We then went up with the right front and got the huge 29.5". We
were confused about this difference, so we went up again with the left
front tire and found the interference problem. We elected not to continue
with the test for the rear wheels since it wasn't really cool to maneuver
with the shocks just disconnected at the top. It was also getting pretty
late in the day and we needed to return it to road worthiness and get it
back home. My guess is we also ran into that problem for the right rear
result of 21.5" in test 2. We didn't notice until later though so I'm not
positive. It makes sense since the left front is in compression when the
right rear is on the ramp.
Anyway, in summary, you can see that an unpinned arm will add a good deal
of articulation to a stock vehicle going either forward or reverse. Test #
2 shows a nearly balanced articulation at all 4 corners (with the exception
of the right rear). I think we successfully demonstrated that it will work
going forward (which was Q's buddies Matt's concern) and will give quite an
increase overall. It will be much more telling to mount this to a trail
ready Defender 90 which is capable of more travel and has worked out things
like longer brake lines and anti lock brake sensor wires.
For pictures of the hinged arm in action on a D-90, click here
for pictures from Alan E. Foster, click here
for pictures from Chuque Henry