Nate, I started another thread, since we are on a different topic now. I tried the centering procedure you recommended and ran into a problem. The teeth on the pitman arm and the shaft have 4 wider teeth positioned at 90° around the opening. [See 1st & 2nd photo] The shaft has the same corresponding 4 wider teeth. This limits the positioning of the pitman arm to 4 descrete positions per rotation, correct? The steering gear box has 4 3/4 rotations [1710°] from one end to the other. When I put it in the center [2 3/8 rotations from either end], the wider teeth do not allow me to put the pitman arm at 90° to the ground. See photo #3 for the pitman arm location at the center. Photo #4 shows how far off it is to the connecting rod when the wheels are straight. What did I do wrong? Is it possible that the Sector gear is one tooth off? [See photo #5] Is there a way to adjust this without disassembling the gear box? Can it be done with the lash adjuster? Thanks to all, Greg
Greg: Nate is the expert, but I think what is important is that the drag link is parallel to the ground in the center position of the steering wheel. The further away from parallel to the ground the drag link is the worse your bump steer will be. Bill
Interesting ! Well ; I have not seen this before on an AD box...... You're correct as is Bill . Remember : lube with OIL , not grease ! .
Sorry Nate. What am I correct on? Can I make the adjustment with the Lash adjustment screw on the backside of the gear box? Greg
And another question... And what is bump-steer? Something to do with cattle? Seriously~ I've heard this term, but I don't know for sure. Is it when you hit a bump at a fair speed and the steering wheel starts trying to turn back and forth in a darn near violent way?
You Are Correct In That The pitman Arm only fits on the sector shaft in one of four different positions . No , you cannot adjust the centering with the Lash adjuster , that is for setting the freeplay (' Lash ') between the worm and sector . You might try slacking off the lash adjuster then adjusting the bottom BIG locknut and adjuster to a tiny bit of pre-load , measured at the steering wheels outer spoke , a couple inch pounds (fish scale) will do , IIRC the book wants about 10 Inch Pounds on a new box but that's far too tight for my liking . then adjust the lash when the box is as close to dead center (usually the loosest place) . Then Bill was correct about having the drag link paralell . BTW : don't let Bill kid you , he knows as much as I if not more judging by his posts over the years . -Nate
Bump Steer Is the dangerous condition caused by lowering the vehicle so much that the caster angle is lost to hitting bumps or pretty much anything in the street causes the steering wheel to jerk out of your hands , hitting a RR crossing at speed , this can cause total loss of control ....... One more reason I like 'em fairly stock , they drive far better . -Nate
There are probably many causes of bump steer, but the cause that I am familiar occurs on any of our trucks to some slight extent. Example below has some rediculous statements in it to make understanding bump steer easier. Park your truck on a flat concrete pad with both the front wheels in a puddle of oil so they can turn easily. (Nate, you could park yours on a front end alignment machine with the "turntables" unlocked.) Lock your steering wheel in the straight ahead position. I assume that the drag link is parallel to the ground like GM meant it to be. Now get some really big guy like me to stand on your front bumper compressing the springs. As the frame moves down the pitman arm is held in place by the locked steering column. The drag link is no longer parallel to the ground, effectively trying to become "shorter", so it must be exerting a "pull" on the steering arm attached to the left front spindle. That pull translates to the spindle turning to the right on the kingpin. This causes the tires to move slightly to the right. Now get my fat a$$ off the front bumper and everything returns to straight ahead. Put a jack on the front bumper and start lifting. Even though the vertical direction of the front end is opposite, the exact same thing occurs including turning to the right. As designed, this isn't much of a problem because of three things: 1. Front end springs on our trucks are pretty stiff. There really isn't a lot of vertical motion. 2. The position of the drag link is parallel to the ground, minimizing the amount of "pull" or "push" that occurs when the axle moves up and down in relationship to the frame mounted steering box. 3. The drag link is pretty long which also minimizes the amount of "pull" or "push" that occurs when the axle moves up and down in relationship to the frame mounted steering box. But then I started to fool with Mother Nature (or was it GM?) I installed a Brother's power steering kit on my GMC. The length of the new drag link was around 11" vs. the 20" of the original GM part. And the drag link goes uphill quite a bit from the pitman arm to the steering arm. When I stand on my front bumper the motion of the frame relative to the axle makes the drag link want to pull, translating to a left turn of the tires. When I jack up the front end the motion makes the drag link want to push, translating to a right turn of the tires. Real scary crossing railroad tracks at 30 MPH and makes you $hit your pants as you change lanes at certain bumps at freeway speed. I replaced the Brother's pitman arm with an arm for a "lowered" front end and the drag link is now a lot closer to parallel, though it is still short. Still some bump steer, but not near as bad. A good example of what I have now is this: Drive 30 MPH straight on a road. Remove my hands from the steering wheel. Apply brakes about 3/4 hard, not a panic stop, but harder than you would doing a normal stop. As the front end "dives" the steering wheel will crank 90 degrees to the left, but the truck continues straight because I am not holding the wheel. If I were holding the steering in place the truck would be turning right. Once the truck comes to a stop the "dive" rebounds and the steering wheel returns to the straight ahead position. You guys that passed 10th grade geometry (and can still remember any of it) could jump in here and and give actual values for how much turning angle of the front wheels occurs when the axle is deflected an inch in either direction.
Zig: If you are talking cattle and old trucks, maybe you are thinking of a "bump gate", not "bump steer".
Bill : THANX ! that's as clear and concise an explanation I think I've ever read about the causes ofbump steer . Who even wants to remember Geometry as taught in High School .
Back on subject... Well, I dismounted the steering box and disassembled it. My pitman arm alignment was due to the sector being off by one tooth. I centered the steering wheel and moved the sector gear to the center of the ball nut teeth. The result was the pitman arm alignment is now perpendicular to the ground. Problem solved! Greg
