The sage Jeeping guru Jefe once said "Eventually, every serious rock
crawler will go spring over." The virtues and faults of SOA have been
debated many times, but eventually all discussions come to the
conclusion that going SOA is the only way to free up the very
significant space under the axle tubes where the spring packs normally
reside. The only real disadvantage of going SOA is the possibility of
inducing wheel hop, but as I will explain later wheel hop is easily
controlled. SOA has been used by many manufactures on both front and
rear ends, and these OEM SOA setups prove that it works well.
You can get your CJ to ramp 1000+ by using Wrangler YJ springs.
YJ springs can often be found for free from a friend who has installed
lift springs or purchased cheaply used from a 4wd shop.
Wrangler springs work well for CJ spring over axle (SOA) conversions
because their length and their arc. The YJ springs are slightly longer
than CJ springs and a longer spring has more droop than a shorter
spring. The stock YJ springs are almost flat under load which
makes them good for a spring over because they do not provide
any more lift. A spring over alone normally provides more than
sufficient lift. Another advantage of the flat springs is flat
springs articulate better than arced springs during compression.
With flat arch front springs such as YJ springs an expensive shackle
reversal becomes unnecessary and even counter productive. With flat arch
front springs that are anchored at the rear the tire will move towards
the rear on either compression or extension. The reason is the flat arch
places the tire at it's farthest forward point when the suspension is at
rest, and when the spring arches either positively or negatively the
arch will cause the tire to be moved slightly rearwards.
With the flat arch springs on a SOA you can also angle your front
shackles further forwards than most people normally would. The reason
you can do this is similar to the reason a shackle reversal becomes
unnecessary, the shackle end spring eye will move towards the rear on
either compression or extension. This has 2 benefits. First it gives the
shackles more room to move rearwards and frees up more droop. Secondly
having the shackles raked forwards makes it less likely that you will
pop one over center to the rear and bend a spring.
Springs
The rear springs used in CJs and YJs are the same width, so the rear
springs bolt right in. The YJ front springs are a little longer and
wider than CJ front springs. The fixed spring hanger for the CJs
front spring is the correct width because the CJ front spring uses
a wide bushing in the back. It is the shackle side of the CJ that
is not compatible with the YJ front springs.
For the shackle end of the front springs, CJ rear spring hangers are
the right width and only cost about $14.99ea new. They need to be
moved forward so that the rear hole in the spring hanger goes where
the old front hole used to be. There is a rivet in the frame at the
location where the new front hole needs to be. The rivet holds the
cross member in place. I welded the cross member to the frame, ground
the heads off the rivets and punched them out. The bolt holes lined up
perfectly.
The picture to the left shows where the front spring hanger needs to
be modified. The red arrow points to the rivet to be removed and the
blue area shows where to weld. Weld before removing the rivet so
everything stays in place. The rivet hole will be used for the
forward bolt on the spring hanger.
Moving the hanger forward leaves a space between the steering box
bracket and frame where the back part of the spring hanger used to be.
I cut off a piece of the old spring hanger and used it as a shim.
The red arrow points to the spacer for the steering box made from
the old front spring hanger.
The rear hangers do not have an extra hole to clear the rivet
that you knocked out, so they are much stronger than the stock front
spring hangers. This swap makes expensive after market hangers
unnecessary.
Bushings
I used polyurethane bushings meant for the rear of a CJ in the frame
part of the shackles and the fixed spring eyes on both the front and
rear. I left the factory rubber bushings in the shackle ends of the
springs, but I will probably replace them with polyurethane eventually.
The shackle end bushings for CJs and YJs can be purchased separately
or about $1 or $2 a piece, so it won't cost much.
Shackles
For shackles I used 2" x 3/8" bar stock all the way around and I made
the bolt holes 4" between centers. The shackles have a good rake
forwards on the front and rearwards on the rear, but because the YJ
springs are flat they shackles move inward on both compression and
extension and the rake is actually an advantage since it gives them more
room to move and less chance of getting stuck over center.
U-bolts and U-bolt Plates
If you have kept the stock Dana 30 you will probably need to
fabricate some spring plates to
accommodate the wider YJ springs, but your stock U-bolts should still
work. If you have gone to a Dana 44 FSJ spring plates work well and
U-bolts can be purchased locally at a good auto parts store. Mount your
shocks parallel with the bottom of the axle tube and for early CJ 7's
you will want to change to the later CJ7 shock towers to allow a longer
shock, FSJs also use the same towers and are good donor vehicles. Lower
swaybar mounts from a FSJ fit between the springs and spring plates and
have worked out very well for me.
Brake Hoses
If you want your CJ to ramp over 1000, you'll need to give some
attention to brake hoses. If you use stock hose in their stock
locations, it is very likely your hoses will limit travel.
To complete the swap full size Jeep (FSJ) or Chevy Blazer brake
lines relocated to mount off the bottom bolt of the shock tower
work well.
Drag Link and Tie Rod
Since The CJ drag link attaches to the knuckle and the lift will
cause it to run at an angle, it will most like hit the spring if left
in stock form. There are several potential solutions to this problem.
One is to convert to a custom "Y" style tie rod and drag link
similar to what is used in the Wrangler YJ and other vehicles.
Another solution is fabricate a bracket to move the drag link
over the spring.
For my personal project I converted to spring over steering. Because of
the serious nature of steering work I'm going to say "If you have to ask
how you shouldn't try to build it yourself." Although I designed the
arms myself I enlisted the help of a fellow 4 wheeler who is also an
expert machinist to do the actual work. Many of the companies that make
custom width front ends are selling similar spring over steering kits.
The kits consist of steering knuckles from a '74-76 FSJ or Chevy and
some custom steering arms that bolt to the flat area on top of the
knuckle. These kits put the tie rod about as high as the top of the diff
cover, which works out perfectly for SOA with YJ springs.
By custom designing my steering arms I was able to retain the use of
stock wide track CJ linkages even though my Dana 44 front is 2" wider
than my Dana 30 was. This gives me extra tire clearance and makes
finding spares easier.
Spring Wrap and Wheel Hop Control
The biggest problem with a spring over conversion is spring wrap
and the resulting wheel hop. The problem is accentuated with soft,
flat springs that articulate well. You will need some kind of spring
wrap control or you will break u-joints, drive shafts, and even yokes.
When the spring wrap unloads, it causes wheel hop which can cause
a roll in an off-camber situation. Some sort of anti-spring wrap
measures must be taken.
I used a ladder bar with a shackle and threaded section on the leading
side and a fixed mount to the axle tube on the trailing side.
It controls axle wrap and wheel hop completely while
still allowing full articulation. My ladder bar does this by controlling
the pinion angle while still allowing every other type of movement
including twisting. If the pinion angle can't change the springs will
not wind up and wheel hop is prevented. I bent my ladder bar and
broken the axle tube mount by testing on pavement and rocks, but
even in this half functional state it still worked fine. I've been
driving with this setup for a whole season already and so far I've
experienced no wheel hop.
I fabricated the axle end mount for the ladder bar to put the bottom bar
only an inch or so below the axle tube and the top bar about 8 inches
above. The front end of the bar mounts to a frame cross member I built,
but many people mount them to their skid plate. All three points of the
ladder bar and the other end of the shackle have polyurethane bushings
to somewhat absorb shocks. The bottom tube of the bar runs parallel to
the rear driveshaft but about 1" below to protect it from logs and
rocks.
Spring Rates and Sagging
A common complaint of CJ owners who have used YJ springs SOA is that
they are too soft or sag easily. I suggest using YJ 5 leaf rear spring
packs for both the front and rear of your CJ. Mine haven't sagged after
a season of 4 wheeling. If sagging becomes a problem or if more lift is
desired add-a-leafs can be purchased from many lift kit manufacturers or
made from another YJ spring pack. Try to buy or make adda leafs that are
as long as the main spring in the pack and put them in the second
position. If this isn't high enough or stiff enough you can add even
more leafs further down in the pack.
Conclusion
The end result with my CJ7 was RTI scores over 1000 by using springs
that someone gave me for free and no expensive conversion kit. The
SOA leaves plenty of room for tires, my 33s don't rub at all and
it looks like there is plenty of room for 35s.
SOA, 1" body lift, and 33" Swampers.
