Posted by John Eickhof on Thursday, January 12, 2006 at 0:03AM :
In Reply to: Wrong!! Still had bump steer posted by Keith in Washington on Wednesday, January 11, 2006 at 5:59PM :
1st. imagine the pitman arm in a vertical position. 2nd. a perfectly horizontal drag link to the steering knuckle on the front axle. ( THE AXLE KNUCKLE AND PITMAN ARM KNUCKLE ARE ON THE SAME LEVEL PLANE ) OK, this is the ideal set up, however, once the front knuckle either moves upward or downward, a slight oblique arc(because the flexible shackle will allow the axle slight forward or aft movement)and with a drag link that is a is straight then a slight pull or push against the steering knuckle will happen. This is the best case. Now, take the same situation except the knuckle is lower than the pitman arm..and then a straight drag link is now at an angle downward to the knuckle, when the axle raises from its normal position, the arc will force the knuckle forward thus steering to the left (in a typical set up) and when the knuckle lowers from normal the knuckle will be pulled against by the drag link and it will steer to the right. But, due to the angle of the drag link, the first action will move the knuckle more than the second. Now, with an offset or double bend drag link, the deflection when the axle is higher or lower than its normal position will indeed happen BUT the amount of deflection will be closer to the original amount with a straght horizontal drag link with knuckle & pitman arm in the same plane. ALL VEHICLES with a straight axle and a standard drag-link type steering HAVE some amount of 'bump steer'. The only way to achieve zero 'bump steer' is to have an axle with NO vertical movement and the steering knuckle connection on the same plane as the pitman arm knuckle. And of course there are many variables as all things will change with the amount of vertical axle movement, the arc, and the length of the offset drag link. But no matter what, if the axle steering knuckle and the pitman arm knuckles are not on the same plane, the double bend offset drag link will be much less 'bump steer' than an angled straight drag link. I guess I may have to post a diagram if you can't visualize what I have typed...
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