4 Link Rear
Suspension - Page 2
The next decision was
how to connect the links to the frame and axle. The options
include rubber bushings, Johnny Joints, heim joints or a combination
of the these. One factor to consider is whether or not your
rig will see a lot of street driving. Many people believe
rubber bushings are better at reducing the shock loads the joints
will see from street driving vs. heim joints. If any of your
links are going to see a lot of side load you'll want to avoid using
a heim or Johnny Joint. A good example of this is on a 3 link
suspension where the upper links converge into one joint at the top
of the axle. That single joint will all that keeps your axle
centered and it will see enormous side load. Since I was
going to triangulate all four links thereby spreading the stresses
amongst the links I decided to go with 3/4" heim joints.
Under lightweight buggies, these joints have a good track record and
appear to hold up well. If I were building a heavier rig I'd
go a combination of rubber bushings and Johnny Joints.
Materials and Sources
1.50", .250 wall DOM tubing. All the links are
40" long. After running these for a few months I
would recommend either using .50 wall or bracing the links
with a rib along the top. The .250 wall lower links both
had a slight bow in them from dragging them over obstacles, I
added a stiffening rib made from a piece of 1 x .375 steel to
Threaded tube Insert
from Coleman Racing (get enough for one spare link while your at
Heim Joints - #AUR-XM10
from Spidertrax, ask for teflon race (don't forget to order the
Link Tabs - Flexy
Flyer (local race car shop).
Gussets - #950
from Coleman Racing (1 bag of 24).
Coilover Shocks -
Sway-Away 2" Coilovers, 16" travel (I recommend going
14") w/ dual rate kit.
Springs - Initially
Eibach 2.5" dia, 14" long 90lb and 100lb coils from Polyperformance.
I also needed a helper spring since I couldn't get 16"
coils in a low enough spring rate. This is why I recommend
going with a 14" travel coilover for a light rig, it'll
save you having to buy the helper springs. As of 6-03 I am
running a 150lb spring under a 120lb spring. The 150lb QA1
springs are from Summit Racing, the 120lb set is borrowed, I
will eventually order a 130lb spring from summit (the closest to
120lb they have).
Now it was time to get
my hands dirty. First, with the frame sitting on jack stands
at the desired final ride height, the old suspension was
removed along with the back half of the frame. Next I
positioned the rear axle to the desired wheelbase and squared it
with the frame.
From here on out I had
my friend Erik lending a hand. First we built a small
outrigger and braced it in all three planes. the outrigger was
located as close to the plane of the t-case output flange as I could
get it. Next, we attached the link brackets to the heim joints
on the link. Holding the link roughly in place we moved it as close
as possible to the CV joint on the passenger side, this put the two
links about 21" apart. We marked that mounting point.
With Erik still holding the link I positioned it roughly where I
wanted it on the axle tube. I made a mark roughly on the
centerline of the tube and 17.5" from the center of the
differential. The link brackets can now be tack welded onto
the outrigger and axle. We eyeballed the other side and made a
few measurements after the link brackets were tack welded to confirm
the second link's placement.
As you can see the
link angle isn't very steep, I measured about 10 degrees. We
moved on to the upper links.
I cut some access
holes into the floor so could get to the top of the frame.
Since all my links were the same length, we just needed to locate
the upper mounts on the differential housing and that would
determine where the front mounts would go. The mounts on the
housing were spaced 10" higher than the lower mounts and as
close as possible to each still allowing me to get a bolt and nut
thru the brackets (4.5" apart). I utilized my
previous traction bar mount, bracing it with an axle truss.
This upper mount needs to be very strong so don't be afraid to go
overkill on the gussets.
Holding the upper
links so they were parallel to the lowers showed us where the front
link brackets needed to be. I made a cross member and welded
it to the top of the frame. Next we tack welded the front link
brackets to the cross member. They ended up being about
6" above the lower link brackets and roughly 22" apart.
Here's a side view
showing the angle of the links in relation to each other.
A view looking from
the axle forward. Notice how crowded it got with all the
linkages? I checked each link for chassis clearance and drive
shaft clearance before welding the tabs on for good.
Here's a good diagram
drawn up by Nate Moore. It clearly shows why my links ended up
the way they did due to the loaction of the transfer case driveshaft
With the link mounts
figured out I set about bracing the link brackets and cross member.
Each link bracket is braced by one of the small roll bar gussets
mention above in the materials list. The cross member was
braced via a tube from the frame seen in the second picture above.
Next, I ran a 1" dia tube from the cross member to the
Locating the coilovers
proved challenging. I wasn't sure how much the springs would
compress so I had to mount them and put the weight of the rig on
them to get a good idea on where to place the upper mounting points.
The lower mounts were initially mounted perpendicular to the axle
tube as shown in the first picture but the ball joint would bind
before full droop or stuff was reached. The final
configuration looks like the second picture with the mounting
brackets inline with the axle tube. The coilovers are angled
inward appoximately 20 degrees and forward roughly 25 degrees
to cut their dampening rate a bit and to allow a little extra
Here's the dimensions
for the final coilover mounting location.
Page - Page 3