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Three Link and Coil Over Shock Conversion

Tech Article

  1. 85m1009
    Article/photo's courtesy of:
    Steve Frisbie

    Three Link and Coil Over Shock Conversion
    Let me first start by saying that my original intention was to convert my truck to cross over steering only. After several discussions with Stephen Watson at Off Road Design, I decided to completely remove the existing suspension, in favor of a three link with coil over shocks. I spent many nights "dreaming" up ideas and not knowing quite where to start. I eventually dove in headfirst and found that it was not as difficult as it first seemed. The end result was well worth the effort and money.

    I started out by cutting the front half of my Suburban donor frame and mounted it on four legs to mock the suspension on. The frames are exactly the same to about the transfer case cross member, which was all I needed. I found an old small block, acquired a 700r4 case and scrounged a 203 adapter, which duplicates my drive train with an ORD Doubler. I bolted these parts in place and started taking measurements.

    The ideal three link set up would have two links on the bottom and one center link on top of the axle. Due to clearance problems with the motor and the center link I decided to reverse the set up and put the center link on bottom. After obtaining some basic dimensions I spent several days "testing" the suspension on graph paper and using cardboard links with thumbtack pivots.

    The suspension on a Suburban frame
    If all the arms were equal length, and parallel to one another the caster would remain constant throughout the travel of the suspension, however this causes the pinion angle to suffer and put unnecessary stress on the u joints. I managed to come up with a happy medium. I ending up using 33" upper links and a 38" lower link. The center line measurement at the axle between the upper and lower links is 10". This tapers to about 6" where they mount to the frame. The end result is a maximum caster change of 4 degrees and the pinion remains in line with the drive shaft throughout the entire travel.

    I then turned to making the mounting brackets on the frame. I removed the stock body mount brackets and the spring hanger plates and built 3/8" plate brackets to mount over both locations using the existing holes to index them. I made a new body mount bracket from 3/16" plate and welded it to the 3/8" plate. I have a 2" body lift installed so I moved the body mount bracket up 2 inches to eliminate the puck at this location, since this is one of the tie in points for my roll cage.

    The center link mounts to the 203 cross member. I had to reinforce the cross member and build in a "tunnel" for the front drive shaft to pass through. I welded the mounts to a piece of 3/8" plate and bolted it to the cross member. After the suspension was installed into my truck I integrated the mount into a complete skid plate that ties both the 203 and 205 cross members together for added rigidity.

    Body and upper Link mount combined

    203 Cross member with center link mount and full skid plate
    I acquired a Dana 44 front axle and removed everything down to a bare housing. The mounting tabs for the links were fabricated from 3/8" plate and welded in place. 3/16" plate was wrapped around the axle tube and welded to the mounting tabs on both sides. The lower mounting bracket was made large enough to allow full movement of the heim joint and was skid plated to protect it from rocks.

    Dana 44 with truss, skidplated cover, and link mounts

    Link arm threaded 1 1/2" 3/8" wall DOM tubing
    I purchased stainless steel; Teflon lined heim joints from Off-Road Design. The heim joints used in the links utilize a 3/4" hole and 7/8" thread. All the steering heim joints are 3/4" hole and 3/4" thread. All of the link mounting points has a hardened washer welded on the inside of the tabs to allow for maximum misalignment of the heim joints without binding. After the mounting tabs were installed I put the axle in place on stands, set the pinion angle and measured for the length of the links. The links were made from 1 1/2" x 3/8" wall DOM tubing. The tubes were threaded with right and left handed 7/8" taps. This was done in a lathe to ensure alignment of the threads and it is a lot easier than doing by hand.

    The links were then installed along with the axle. I set the axle at ride height, which was determined by measuring the distance from the bottom of the frame to the top of the axle. I used the dimensions obtained from my truck. I wanted to retain the same ride height as my existing six-inch suspension. Once the ride height was set, I set the pinion angle and tightened the jamb nuts on the heims. It was now time to set the caster back to factory (8 degrees). I had already removed the knuckles from the axle and a piece of bar stock was machined to fit in through the upper ball joint hole and turned down to fit into lower one. The bar stock extended above the top hole enough to use a smart level. A torch was used to remove the weld around the knuckle mount. The knuckle mount was heated up and "tapped" (big hammer!) to the proper location. The knuckle mount was then welded into place. Gussets were installed on the bottom and top of the knuckle to strengthen the axle.

    A pair of gussets was placed on top to make a mounting point for the coil over shock. I then made a plate from 3/16" steel to fit between the differential housing and the cover. The lower corners of the plate extended past the bottom edge of the housing. I took an old Dana 44 solid tie rod, cut it, and welded it between the lower gussets and the plate making a stout axle truss. The bottom of the differential housing was ground smooth with the edge of the cover. Two gaskets were used to seal the plate and cover to the housing. A 2" x 1/4" piece of plate was welded to the differential cover over the ring gear to protect it from damage. The axle was removed and then reassembled with 4.88 gears and an ARB locker. The passenger side knuckle was machined flat and tapped to accept a steering arm. A custom steering arm was made from 3/4" plate and bolted to the knuckle using factory studs and tapered washers. The axle assembly was put back into place and centered side to side.

    Custom Steering arm, drag link and tie rod

    King coil over Pre Runner series shocks
    I purchased a pair of King Coil-over shocks through Stephen Watson at Off Road Design. The shocks have 16" of travel and use a 150 over 250 set of coils. The shocks were custom valved by King for the weight, sprung and unsprung, of my truck. I determined the height of the upper shock mount and designed a shock tower from cardboard. After determining that it would work it was made from 3/16" plate. The tower was welded to a 3/8" steel bracket that bolts to the top and side of the frame. The bracket was indexed off the motor mount bolts. The upper mount for the shock is adjustable and can be moved up or down 2 inches and is held in place with 6 3/8" bolts. I determined that the engine cross member would interfere with the cross over steering so it was removed.

    A new cross member was constructed from 3/16" steel and bolted in between the two towers. An upper support was made to bolt between the towers and cross over the top of the engine. A cut out was made to clear the air cleaner. Once the towers and supports were completed and put into place the shocks were installed with just one coil to check for clearance problems. The shocks lean in 3 inches from bottom to top to eliminate tire contact during suspension travel. The next obstacle was the cross over steering.

    Shock tower

    New cross member
    The tapers in the knuckles were drilled out to 3/4" to accept heim joints. A tie rod was made from 1 1/4" x 5/16" wall DOM tubing. The steering box was replaced with a 2WD version and fitted with a 1995 Ford F250 stock pitman arm. The index grooves were off 45 degrees and had to be removed with a triangle file. Brackets were fabricated from 3/8" plate to allow the steering box to be rotated down on the frame to a horizontal position. This was done due to reduce the extreme angles placed on the heim joints at maximum suspension travel. A length was determined for the drag link and it was fabricated from the same tubing, as was the tie rod.

    The drag link was put into place using 3/4" heim joints and chrome moly misalignment bushings. A track bar was fabricated the exact length as the drag link. A track bar bracket was welded onto the axle as close to the knuckle as possible on the passenger's side. The track bar was run parallel with the drag link and a bracket was made off the frame from 3/8" plate. The track bar was mounted on the backside of the axle due to congestion on the front side. The suspension was cycled to check for binding and 4-inch bumpstops were installed to prevent bottoming out. After all the bugs were worked out the entire suspension was dismantled and all the brackets were painted. It was finally time to install the suspension on the truck.

    Out with the old parts

    Steering box, pitman arm, Borgeson jointed shaft, and track bar mount
    I removed the old suspension along with the engine cross member and all the unnecessary brackets including the body mounts. The inner fenders were also removed. The new brackets were bolted into place with 3/8" grade 8 hardware. The rest of the suspension was installed and everything was bolted up without any problems. A piece of 3/8""plate was made to fill the gap on the side of the frame between the link bracket and the tower bracket. This portion of the frame angles out from front to back. The plate was welded to the two brackets to stiffen the frame and prevent it from flexing.

    Since the steering box was rotated down a new steering shaft was fabricated using Borgeson u-joints and a 3/4" solid shaft. I mounted the shock remote reservoirs to the crossover bracket in the engine compartment. I reinstalled the inner fenders having to cut them to fit around the towers. Rubber guards were made to fit tightly around the shock towers to prevent unwanted debris from entering the engine compartment.

    Reservoir mounts

    Finished inner fender
    The front axle was finished up, by installing Warn Chrome Moly axles. The Warn hubs received fusible clutch rings. New brake lines were run across the axle and are fed to each side from a center mounted stainless flex line. The air line, for the locker and the vent line were run together with the brake line up to the frame. Limit straps were made to limit the downward travel, just short of the extended limit of the shocks, to prevent damage. All the hardware was retightened and the 37 x13x 15 Boggers were installed. The toe in was set and the power steering was bled. The final ride height was adjusted by running the threaded adjuster down the shock body and compressing the coils. The shocks were filled to 150psi with nitrogen. The K5 was road worthy once again.

    Shock tower
    All I can say is that the truck handles beautifully on and off road. There are new driving characteristics that take some getting used to. Under hard acceleration the suspension unloads causing the front end to rise up a few inches and then settles back down. Since there is no sway control there is a little bit of body roll in corners but it is much better than running the sway bar disconnected with the leaf springs. Since my track bar and drag length are the same length and within a couple degrees of parallel there is no bump steer. The only thing I am going to add is a center limiting strap to prevent complete unloading of the front suspension, during steep climbs off road. The approach angle is better since the front axle was moved forward 1 1/2".

    The family at the Ozark Jamboree

    Up on the testing block
    The entire building process took place over a four-month period. Stan's Custom Fab of Warsaw, MO performed all the fabrication work. I drew most of the bracketry using Auto Cad and the brackets were burned out on a torch table using a plasma cutter. The drawings are still on disk and can be replicated. The actual installation into the truck took about 2 days.