[DeTomaso] Bump Steer

Bjoern Flesland bflesland at gmail.com
Sat Mar 26 21:43:28 EDT 2011


You should open a Pantera restoration shop! 
Cheers Bjoern


Den 26. mars 2011 kl. 23:37 skrev GW <gow2 at rc-tech.net>:

> I am getting to my front suspension. I am still waiting for my A-Arm 
> Jigs to be laser cut. Business is first so my projects get done when we 
> get time on the laser.
> 
> This has been a long ongoing project on the side burner...till now.
> 
> As you may know I am doing a power steering conversion. This is a rack 
> which was used on small cars and sold as a conversion for an MGB. It 
> uses an electric pump which can be turned on or off which means the rack 
> can be manual or electric.
> 
> One thing I have really worked on is getting the geometry correct. As 
> many of you know shimming the rack for bump steer is not a fix but a 
> patch. All it does is shift the parabolic arch to where it is less 
> noticeable in bump; far worse in droop.
> 
> The real problem in bump steer is the rack length it self; specifically 
> the length between the tie rod pivot. I started by pulling in suspension 
> dimensions. I bolted tubing into the suspension mounts and welded it all 
> up in a frame. I pulled it off the car and used it to measure suspension 
> geometry:
> 
> http://www.rc-tech.net/pantera1/frontsus/jig.jpg
> 
> I took the numbers and loaded the program Susp Calc the best I can. I 
> played with rack length and height in the program. I tweaked one, then 
> the other zeroing in on the best of both. Basically, rack height will 
> determine the balance of bump steer, rack length will determine  how 
> much bump steer. The two do work together. By working them into the 
> funnel so to speak I came up with numbers of total variance of  .01 
> degree or less in bump and .03 degree or less in droop. In my book 1/100 
> of a degree is zero.
> 
> Here are the numbers:
> http://www.rc-tech.net/pantera1/frontsus/bump.jpg
> 
> The key number is 11.862.....x2 = 23.724". That is the width of the 
> pivot point in the steering rack. The stock rack is about 28".
> 
> Now garbage in is garbage out. How close is my measurements? ! could be 
> within a 1/16", I could be within a 1/4". The rack may need to be 23", 
> or it may need to be 24" or somewhere in between. The final tweak is on 
> the car.
> 
> To do this had to cut the power rack. The power rack was too short to 
> begin with. I needed a way to change the length of the steering rack to 
> make in car measurements. One issue is welding on the original ball 
> joint melts the inner liner and is not re-build able. My solution was to 
> use a ball joint off an MGB rack I had. It has the same threads on the 
> tie-rod and the shortened length will be exactly what I need.
> 
> What I did was cut down a threaded tractor implement pin and weld it on. 
> The nut was welded to the ball joint end. To do so allows me to check 
> travel at different lengths. I have about 3/4" travel. The idea is I am 
> starting too long. I can check the travel at 2 different distances, then 
> shorten the threaded shaft till I get in range. If I had 100% confidence 
> in what  have transfered to the computer program I would cut it down to 
> 23.724"....In fact I know better. I need proof of concept on the car. 
> Here are some photos
> 
> http://www.rc-tech.net/pantera1/frontsus/sus.htm
> 
> Gary
> 
> 
> _______________________________________________
> 
> Detomaso Forum Managed by POCA
> 
> Archive Search Engine Now Available at http://www.realbig.com/detomaso/
> 
> DeTomaso mailing list
> DeTomaso at list.realbig.com
> http://list.realbig.com/mailman/listinfo/detomaso



More information about the DeTomaso mailing list