I started this post asking about factory setting of caster on my Workhorse chassis. The thread morphed into setting the caster to a higher than stock value in order to improve straight line stability.
I posted earlier caster measurements that I made. Please disregard those measurements. I goofed and those values are not accurate because of mistakes on my part.
See the first picture. If you look at the spring pack, it contains from the top to the bottom; a cap, 2 springs, a spacer that extends to the rear and becomes the bottom shock absorber mount and 2 wedge shims. The top shiny shim is the one I added and the rusty one the original. This all sits on top of the axle on a flat machined surface. The complete axle pack is clamped to the axle with 2 u-bolts.
I have a 7” android tablet. It has an app that allows accurate measurement of surface angle relative to level ground. Second picture shows the tablet sitting on the spring machine surface next to the u-bolts displaying the angle of the spring pad relative to ground. It repeatedly measured 2.6° on both left and right sides. These measurements are close enough to the measurements that an alignment shop measured on CamJam1’s MH to give me confidence that I had an accurate measurement.
I decided to add alignment wedges to attain a target of ≈5.5° caster. I needed a 3° wedge. Refer to next picture. It shows the wedges I purchased. They are 159 mm long 11.2 mm at the thick end and 3.4 mm at the thin end. The math says 2.93°. Close enough to 3° for me! The slot allows the wedge to be inserted without removing the center bolt that holds the spring pack together.
Things needed to install the wedges:
• A means to raise the Motorhome by the frame high enough to get the front wheels off the ground about 1”. I placed Lynx levelers under my front jacks so the jacks contacted the levelers after traveling about 1”. Some may say this isn’t safe…I think it is as safe as jack stands. I do it my way…you do it yours!
• 2 medium size C-clamps.
• A deep 15/16” socket and healthy impact wrench…or a breaker bar and big muscles…or all the above and a good cheater bar to go on the breaker bar.
• Penetrating oil like PB Blaster. Start using it about once a day for a few days before starting!
• 3/4” socket or wrench.
• Vise Grips
• 2 bottle jacks
• A small soft hammer. I used a brass surface hammer. The nylon hammers would do as well. A steel hammer is OK if you have a very soft tough with it.
Procedure per each side:
• Safely jack Motorhome by the frame so that front tires are ≈1” off the ground.
• Place the ignition switch in the unlocked position but not far enough to turn on the instrument panel.
• Place a C-clamp on the spring pack between the shock absorber mount and the rear of the axle. This holds the shock from expanding when the u-bolts and center bolt are removed or loosened.
• Place a C-camp on the spring pack about 7” in front of the axle. The two C-clamps hold the spring pack together while you work.
• Place a bottle jack under the spring near the front C-clamp just installed. Jack until the jack barely takes weight. It isn’t meant to lift anything…just hold the spring where you want it.
• Place a bottle jack under the axle. Jack until the jack barely takes weight. It isn’t meant to lift anything…just hold the axle where you want it.
• Remove the 4 nuts on the U-bolts. It is okay of the spring lifts off the axle. If it starts to lift more than ≈1”, jack the axle a little to maintain that distance.
• Tap the bottoms of the U-bolts with the soft hammer to push them up. Remove the front U-bolt completely, the rear can be left with the bottom of the bolts flush with the axle.
• Remove the cap from the top of the spring. It should lift right off.
• Clamp the vice grip onto the bolt head of the center bolt that is visible on the bottom side of the springs pack between the spring pack and the axle.
• Use the 3/4” socket/wrench to loosen the spring bolt enough to slide the alignment wedge in above the existing wedge.
• While being careful to not allow the alignment wedges to rotate tighten the center bolt. I didn’t torque this bolt. I just got it really tight with an 8” long wrench. The same wrench I took it off with.
• Re-install the cap on top of the spring.
• Re-install the U-bolts and tap them down until you can install the washers and nuts. The u-bolts may be slightly wider across than the holes they go in. The bolts are springy. You have to squeeze them a little get them started in the hole.
• Start tightening the U-bolt nuts. The head of the center bolt must go into the hole in the spring. The axle may have moved a little bit so that the bolt and the hole don’t line up. I used a ratchet strap to pull the axle into position.
• Going from one nut to another tighten the u-bolts nuts. Torque to 140 ft/lbs.
• Take out the jacks, remove the C-clamps.
• Rinse and repeat for the other side!
• Lower Motorhome.
At this point I measured the Caster Angle again. See pictures 4 and 5. I got 6° on the right side and 5.6° on the left. I went for a test drive of about 5 miles. The steering was definitely heavier at low speeds but about the same at highway speeds. There was a definite improvement to the ‘on center’ feel! Less road wander, more stability. Just what I wanted.
I returned to the shop and re-checked the torque on the u-bolts. Things had shifted enough that the torque was down to ≈100 ft/lbs. I re-torqued to 140 ft/lbs. I re-checked the caster angle. See pictures 6 and 7. Now the angles are 5.5° on the right side and 5.3° the left side.
The last picture is a shot of work in progress.
The steering wheel center will be off. Use the procedure outlined in this
THREAD to re-center the wheel.
I have a ≈1000 mile trip planned for this next week. I will re-torque and measure the Caster again when I get home.
Cautions:
• The u-bolts on the back side of the axle may be too short after adding the wedges. Mine were OK.
• The center bolt may be too short after adding the wedges. It was really marginal on mine. The bolt lacked about 2 threads from coming out the top of the nut! I think that is enough in this case. Once the u-bolts are properly tightened they will keep the spring pack tight. The head of the spring bolt will still do its job of inhibiting the spring from sliding back and forth on the axle.
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Everything is big and heavy. Be careful and do this at your own peril.