The closer the pitman is to the bottom of the top beam,, the less bump steer. I think
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| Author: | hillaholic [ Mon Feb 23, 2009 2:25 am ] |
| Post subject: | Bump Steer |
Bump Steer I just about have my front end complete. Last season I was having major problems with bump steer. I have an S10 gear box on a stock balljoint beam with 2.5" raised thing spindles. When I measure my tow at full extension its 51” when it’s at full compression it goes to 53-1/2”. When the suspension is at full extension, the pitman arm sits about 1” higher than the steering knuckle (where the heim joints attach). I think this is my problem. I put 1” spacers under the outside heim joints and it changed the compression tow to 52”. I think I need to move the gearbox so the pitman arm is higher. I just want some feedback before I do this because there will be allot of grinding and I have to add another steering u-joint to tilt the pitman arm up. I can't fab up a new pitman arm to make it higher because it's about 1/2" away from hitting the gearbox. Thanks, Brad |
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| Author: | Firebug [ Mon Feb 23, 2009 7:09 am ] |
| Post subject: | Re: Bump Steer |
The closer the pitman is to the bottom of the top beam,, the less bump steer. I think
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| Author: | Strong [ Mon Feb 23, 2009 8:58 am ] |
| Post subject: | Re: Bump Steer |
Marty, The pitman and tierod junction should be at same exact point as a rack and pinions tierods junction mounted for 0 bumpsteer. Also changing the length of the pitman arm to acheive this will change the steering ratio (how many turns lock to lock). Longer pitman arm equal less turns. |
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| Author: | hillaholic [ Mon Feb 23, 2009 10:53 am ] |
| Post subject: | Re: Bump Steer |
Strong wrote: Marty, The pitman and tierod junction should be at same exact point as a rack and pinions tierods junction mounted for 0 bumpsteer. Also changing the length of the pitman arm to acheive this will change the steering ratio (how many turns lock to lock). Longer pitman arm equal less turns. Are you saying the tireods should be level? My steering is 3 turns lock to lock. |
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| Author: | Strong [ Mon Feb 23, 2009 8:05 pm ] |
| Post subject: | Re: Bump Steer |
Hill, I am saying there are beams you can buy with the rack mount already welded on for 0 bumpsteer. You would need to copy that location for your tie rod ends. Hope this is helping,bumpsteer is difficult to correct on a beam. |
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| Author: | Firebug [ Mon Feb 23, 2009 8:13 pm ] |
| Post subject: | Re: Bump Steer |
I think of it as a triangle..One side of the triangle is the trailing arm,the trailing arm that is nearest to the steering knuckle,,,,the second side is the beam,,,the upper or lower,,,which ever has the trailing arm nearest to the steering knuckle,,,,the third side is the tierod. the points where the 3 sides join,,well nearly join,,can't be perfect but get them close as you can. Center mounted,,whether box or rack and pinion.,,sounds like a bunch of garble,,but it worked for me,,another thing to remember is use factory offset wheels if possible. 
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| Author: | Strong [ Mon Feb 23, 2009 8:19 pm ] |
| Post subject: | Re: Bump Steer |
Factory offset wheels cut down the scrub radius. |
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| Author: | MadMike [ Mon Feb 23, 2009 9:08 pm ] |
| Post subject: | Re: Bump Steer |
Brad, set your toe at 1/8" in at ride height and make any measurements from that point, then see what you have at full compression, it should be less. |
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| Author: | hillaholic [ Mon Feb 23, 2009 9:28 pm ] |
| Post subject: | Re: Bump Steer |
Thanks for the responce it will help. I am going to try to figure it out tonight. I had it towed in ¼” on the original measurements. Last night I took out 2 of the 3 bolts holding the gearbox in and leaned the pitman arm up and it seamed to help a lot, but I need to tack weld it in position because 1 bolt wouldn’t hold it good enough to get any numbers. |
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| Author: | hillaholic [ Tue Feb 24, 2009 2:27 am ] |
| Post subject: | Re: Bump Steer |
I’m about to give up on it. I can’t really move the pitman arm up because the bolts will hit the gear box. I can’t rotate the gear box to move the pitman arm forward and up because the arm will hit the front down tube. If I could move it up and forward it messes with the tow big time. It almost seems like I need just leave it and tow the front in 2” at ride height then when it cycles through the suspension I will have no tow out on full compression. Take a look at the pictures and please give me some thoughts before I take the BFH to the gearbox. This is what the front tires do when I rotate the gear box to move the pitman arm closer to the beam and 2” higher at ride height.   This is how they sit with the box in the original spot at ride height     This is how bad they get when compressed with it towed in a 1/2" in on ride height. 
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