Power steering build, MR2 Electric Pump Options

[drive-ability]

I'm now working on a power steering system for my V8 car. I'm using a Golf P/S unit and a Toyota MR2 electric pump. There will be some pictures soon, I'm building the bracket to mount the power rack to the 914 cross member.
I'll doc the build up in this thread.. (IMG:style_emoticons/default/driving.gif)

[drive-ability]

I have set up one tie-rod, the rack is 48" to the end of the inner tie rod. That's about
8" longer than the old rack. As it sits at riding height the rod has a small rise as it leads out to the spindle. Looks like a 1/4 inch. Like most of us the term bump steer is a bit fuzzy to me. (IMG:style_emoticons/default/icon8.gif)




(IMG:http://members.cox.net/altjamy/Power%20steering%20tie%20rods.jpg)

[byndbad914]

I have set up one tie-rod, the rack is 48" to the end of the inner tie rod. That's about
8" longer than the old rack. As it sits at riding height the rod has a small rise as it leads out to the spindle. Looks like a 1/4 inch. Like most of us the term bump steer is a bit fuzzy to me. (IMG:style_emoticons/default/icon8.gif)

Bump steer is basically what it sounds like, when you hit a bump, the car wants to steer itself off center.

So, if you had perfect, zero bump steer, you could set the tire straight and move the tire up and down thru full travel and it would never turn and remain perfectly straight. This happens when you have perfect rack length to A-arm spacing, etc (a lot to explain but it is easy to google and read up on).

In short, because the rack is so much longer (taking 4 inches out of 930 tie rods is a LOT) you have pivot points for the tie rods that are way wider than the suspension geometry would need, so you are going to have a LOT of bump steer unfortunately. That means as you are rolling down the road and you hit a dip, etc that causes the suspension to compress and rebound, you can hold the wheel perfectly straight and the car will toe in and/or toe out like crazy. If they both compress perfectly the same amount you won't notice anything more than aggressive tire wear, but the typical case is one side moves more than the other, and in a straight line holding the wheel perfectly centered, the car will steer itself in the direction of the largest tire displacement.

I am not sure even aggressive rack relocation could fix that much difference in overall length with a strut suspension. What you might find is a spot that has such an aggressive tie rod angle you would have small bump over a small range of motion (1" each direction maybe) but then it would start getting aggressive.

You really should check out some website searches and make up some simple tools, buy a dial gauge (or two depending on tool design) and check it. Honestly. That car could be scary if you hit a dip on one side on the freeway and it steers in 1/2" on one side.