I`am trying to set up the Vega steering box in my 30` Model A. I`ve got the box where it needs to be but the drag link is 2.5" lower than the tie rod. Pete and Jakes diagram shows the drag link 1/2"to 1" inch higher than the tie rod at ride height. The car is on jack stands at the moment but can`t see that it is going to change much by setting the car on the ground. I can`t go higher with the box because the header is in the way. Does the drag link need to be higher? Any ideas. Thank you.
Sorta.....the drag link should be paralell with the tie rod, WHEN ALL THE WEIGHT IS IN THE CAR, if not, then I set them up about an inch higher than the tie rod, move the box higher, make a different header if you want it to steer properly with little or no bump steer. You could heat and bend the drag link arm on the box, but I suspect the box already sits too low and can be seen under the frame.
Try reading your OTHER thread with the same question??? https://www.jalopyjournal.com/forum/threads/draglink-height-for-cross-steering.1131129/ .
This is wrong and basically an Urban myth and Pete and Jakes are correct here. Most bump steer is an issue when the suspension is under higher loads [ meaning going over a bump] when the suspension is under extension or droop you don't feel it [eg: a wheel dropping into a pothole] So the idea is to have the bump sideways deflection within a usable range [deflection: meaning the sideways movement when the draglink moves in an "Arc" from the pivot] Note: the pivot is the end that has no vertical movement I'll do the math here using basic trigonometry for compression only [this is all that matters] 90% of all suspension compression is 3" or less on the road With a 48" draglink at horizontal = 48" , at 1" of compression it Arcs towards the pivot by .010" [this is unnoticeable] at 2" of compression it Arcs towards the pivot by .040" at 3" of compression it Arcs towards the pivot by .090" [starting to get dangerous here] Now with a 48" draglink with the draglink mounted 1" higher than horizontal = 47.99" at 1" of compression it Arcs away from the pivot by .010" [this is unnoticeable] at 2" of compression it Arcs back towards the pivot = zero [this mirrors the static position] at 3" of compression it Arcs further towards the pivot a total of 0.030 P & J are suggesting you to keep it in a safe useable range , but most "cowshed engineers" use "rule of thumb" decisions without fully understanding what P & J are recommending.
Thank you all for this valuable information. I was pretty close, so only need to make a couple adjustments to the box and pitman arm.
How much offset in the pitman arm ? Can you heat and flatten it or find one with less offset to help cure your problem... Did you mount your engine "low" to help fit the firewall ? Header clearance can then be a bear... My $0.02 …. from the grand state of Maine...
One correction is to straighten the pitman arm. It has a 2" offset. Straightening it will put the draglink even with the tie rod. Secondly is to do some work with the header. I have (2) different style headers and that will be a "bear" to rework. Right now the top mounting bolt of the steering box bracket is just below the frame. I do have the frame boxed in, in that area. Just a little more tweeking.
If your pitman is tapered on both sides, try tie rod from the top on the pitman and on the bottom at the steering arm. This is a bad picture but viewed from top my drag link and tie rod are parallel. You will need to check full lock to lock for clearance between drag link and wishbone though.
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