Center Steer Rack n Pinion Steering
I was under the original assumption that GM new what it was doing in 1947 so I remachined a 1990 Sunbird power rack n pinion unit to fit the car. The Sunbird rack has the power steering pump separate from the reservoir. I've also got another unit from a 1990 Cavalier that has the pump and reservoir together as one piece. I received some pictures of a simpler way of using the center steer rnp and added them to the bottom of this page.
By the way, center steer rnp have the tie rods attached to the center of the rack as opposed to the end for end steer rnp.
The stock configuration for a Sunbird is to have the rack mounted on the firewall with the tie rod ends facing the front of the car. I've machined the rack so that the tie rods face the rear of the car (turned the tie rods 180 degrees). In addition, the rack was shorten 1" so that the center of the rack was centered between the rails and the hydraulic control head turned about 30 degrees to clear the frame. Here's a picture of the machined rack.
Bare rack n pinion modifications
The complete rack parts
Now, the rack is manufactured with nonstandard components and dimensions. The bolts are neither SAE or metric. The bearing is a unique part that is 1 mm smaller than a standard bearing (I've searched over 30 bearing manufacturer's catalogs to find a replacement!). The idea is that you should not be playing with your steering components. They've made the rack pretty well none serviceable to discourage people from modifying or repairing them.
I've mounted the engine in place and the front crossmember is mounted where it should be. With the driver's side exhaust manifold in place, I found that turning the tie rods 180 degrees to face the rear is too much and the steering wheel linkage faced directly at the exhaust manifold. I will have to machine another rack for a lesser angle. This time I will wait until the front suspension is rebuilt and in place...
90 Cavalier/Sunbird tie rods cut down
I'm going to use two righthand side tie rod ends from the 90 Cavalier/Sunbirds. The above picture shows the nice bend at the rack rod end and I've already cut off the other end. I will be threading about 4 inches of the rod for 5/8-18 (UNF) left hand thread close to the rod end. I've left the extra flat portion shown so that I can hold it in a 4 jaw lathe. The rod end is too big and awkward to hold rigidly in a lathe chuck.
A 0.812" dia bar about 17" long will be used for the tie rod and connect the rack rod end to the tie rod end. The tie rod will have 5/8-18 inside thread with the tie rod end being right hand thread and the rack end being left hand thread. This way, when you turn the tie rod (bar) the wheel will either toe-in or toe-out.
The tie rods are already made and took about 4 hours to make including running out and buying a left hand thread tap. The choice of 5/8-18 thread is because that's whats on the 73 Nova tie rod ends I'm using at the wheel side.
90 Cavalier rack rod ends on left, rod bar I made in the middle and Nova tie rod ends on right
Example of an Installed Rack n Pinion
I would be very interested to drive the following car to see what the bumpsteer would be like. Don Bowman was nice enough to send me some pictures of a 54 Chev that had a 1986 Grand Am rack installed. Kudos to Don for the excellent photographs taken during a snowstorm! It's fantastic that we are able to share information on the Internet because I never thought of using a mating plate between the rack and tie rods. This opens up a whole new ballgame. Maybe I won't have to knotch the oil pans. You also get to use stock 54 tie rod assemblies.
Driver's side mount for rack. The steering box is pointing straight up just behind the mount.
This shows the mating plate between the rack and the tie rods. You can modify the plate to fit.
Passenger's side mount for rack, The angle I'm told is 30 degrees.
View of the steering linkage from column to rack. The rack's steering linkage is pointing directly up.
Another angle to view the steering linkage.