Spring-Over Axle Conversion
By Jim Van de Ven
Last updated: 6/1/98
Drop me an e-mail: email@example.com
-A spring-over with shackle reversal will give you about 4 1/2"-5" of lift.
-A shackle reversal up front will improve on road handling, will improve rock crawling by allowing the tire to come back as it climbs, producing a smoother climb, although dropping off rocks will be a bit more abrupt. The shackle reversal also improves approach angle by eliminating any shackles hanging down in front (with spring hangers right under the frame).
-By putting the springs above the axles, you gain clearance under the axle tubes.
-You can run 35" tires with very minimal trimming of the rear fenders. I just had to trim the very front of the rear fenders as the tires tuck up inside the fenderwells.
-Cheap, if you do your own labor. Only costs are the bent spring perches, shocks, some steel, and a double steering arm (or build your own).
-You raise your center of gravity, increasing body roll, and the chance of roll-over.
-Have spring perches bent up at a local steel yard. I had mine bent out of 1/4" steel. The plates I had made were 10" long to avoid axle wrap. The width of the perches are 2.75" and are 2" sides. Once home, I cut semicircles out of the sides of the perches, and drilled the centering hole for the springs.
-Get ahold of a second right steering arm, or buy a double steering arm from Fabtech or Wardens.
-Buy a 1 3/8" hole saw.
-Have some 3/16" steel on hand to box the front frame rails.
-Wash off the undercarriage of the Cruiser.
-Lift the rear of the truck, chock the front tires, and place stands under the frame.
-Remove the rear springs, shackles, and shocks. At this point you could also disconnect the brake lines and completely remove the rear axle housing if you would prefer to work with it on a bench.
-Place small saw horses under the stock spring perches.
-Using your dial gauge, set your new spring perches on top of the axle directly above and perpendicular to the lower perches. Depending on the length of your rear driveshaft, and the amount of lift you are attempting to achieve, you might want to rotate the rear pinion up to improve driveline angles. I found that I did not have to because the adapter on my SM420 rotates the t-case down and improves driveline angles.
-*Tack weld the perches into position and recheck your measurements.
*Make sure you disconnect the ground cable from the battery before welding, otherwise you will fry your battery.
-Set up your spring perches with a gauge as on the right, then weld.
-Take your stock springs and remove the center pin. Remove the shortest leaf and put the spring pin back in, but reverse it so that it faces upward.
-Put the springs into position above the axles. I used shackles that were 1/2" longer than stock.
-Put jackstands under the axles and lower the rear end onto the rear axle. Put the rear driveshaft into position and check your angles. If you wish, install the U-bolts and carefully drive to check for vibrations.
-Finish welding the rear perches into position.
-Reattach the U-bolts and torque them to 65 ft.-lbs.
-Remove the front bumper, the front triangular bumper supports, the shackle hangers, and the spring hangers. You will have to remove quite a few rivets, so find out which method works best for you. Take care removing all hardware except the shackle hangers which are also welded. You only need to keep the sleeves that the bushings ride in.
-Box your left and right front frame horns. I would recommend using a 2 1/2" hole saw to cut a hole in the new 3/16" piece of steel, this will allow you access to all the nuts that need to be installed on the inside of the frame rail. This would be a good time to do the Saginaw PS conversion if you are planning on it.
-At this point you have the option of lengthening your frame rails 1 1/2" to maintain stock wheelbase, or to simply put the spring hangers flush with the end of the frame. I chose to simply put the hangers on the end of the frame. There is even a hole that lines up with a hole in the hanger. Clamp the hanger in position, and weld it into position. Drill holes and bolt the hanger in with quality hardware.
-Take your 1 3/8" hole saw, and cut a hole in the frame just behind the rivet hole where the spring hanger was. Make sure you do not cut into the bottom of the frame. Beware of gas lines and wires in the frame.
-Remove the extra steel from around the shackle sleeve. Insert the sleeve into the frame, orientating it toward the outside of the frame, with only enough inside to allow for a good weld. Align the sleeves so they are perfectly in line with each other, and perpendicular to where the springs will mount. The will avoid bushings from binding. Weld the sleeves into position.
-Take the stock front springs and remove one leaf and reverse the center pin. Put the springs in place and measure the angle that the bottom of the springs are compared to what they were before the shackles were reversed.
-Put the new spring perches on the front axle and rotate them the appropriate amount to maintain stock angles. I had to rotate it 5 degrees. Tack weld them into position. Check your measurements, and fully weld. Attach U-bolts and torque.
-You now need to deal with your steering linkage. One way to go is to use the cast arm made by Fabtech. I opted to make my own arm by cutting a right arm and welding it upside down to the existing right arm. I then welded in a 3/8" gusset to strengthen the arm. You can now place the drag link above the springs.
-You will most likely need to lengthen front and rear brake lines.
-You may need to modify driveshaft lengths.
-You will need to measure for shock lengths, and make new shock mounts on the rear. I ended up using Rancho 9000's so that I can firm them up on the road to minimize body roll.
-You might want to extend bumpstops.
Rancho 9000 Shocks:
I ended up calling Rancho at 1-800-574-6257 to get the model number of front and rear shocks that would fit my application. I ordered RS9112 for the front, and RS9118 for the rear. The RS9112 can vary from 16"-26 3/4" eye to eye, and the RS9118 can vary from 14"-22 1/8".
-If I were to do it again, I might extend the front frame rails 1.5" to keep the front axle in the stock location. I am currently considering reversing the front springs, thus moving the front axle forward about 3.5-4" from it's current location. This would mean that the axle would be 2" forward from the stock location. This would give me a better approach angle, and a longer wheel base is nice on the road.
-Some people swear by cutting the front knuckles and rotating up the front pinion while leaving the knuckles at the stock angle. I found that I was able to keep the knuckles at the stock angle and keep my front driveshaft angle decent (I don't have any vibrations front or rear at any speed). As I said before, the adapter I have for my SM420 to 3spd t-case rotates the t-case down and thus improves my driveshaft angles.
This conversion is at the owners risk and I assume no part in any ill fate that might occur because of my directions. Use at your own risk.
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