How to select steering components
The Rack n Pinion Steering page details how I determined the width of the rack by measuring and graphing the toe-in play while putting the front suspension through its travel. I guess the question that many people might wonder is how did I know that an 86 Buick Park Avenue rack would work?
I used Federal Mogul's "Steering & Suspension Parts from TRW Catalog X-4000" as a reference. It's main purpose at auto parts suppliers is to look up suspension parts based on the year/model/make of a vehicle. What it also supplies is the dimensions of inner tie rod assemblies, outer tie rod ends, sway bar links and rack n pinion units. Plus it provides a cross reference that lists which vehicles use which parts by part number. It is a great resource but you still have to do a lot of page turning to find the part that will work.
Once I had determined that the rack needed to be an end steer rack and was close to 20-24" in length from inner tie rod end to inner tie rod end. I looked up the Rack and Pinion Specification table. The racks are in ascending order based on the overall length.
Important rack and pinion specs
The overall length is measured from the end of one tie rod to the end of the other tie rod. The tie rods can be shortened and rethreaded if needed. The Inner to inner tie rod center to center length is the important measurement. It is dependant on the rack and cannot be modified. The outer tie rod end thread determines which outer tie rod can be threaded on to the rack.
The Rack and Pinion Specification table is divided into two parts: manual and power racks. Both tables are otherwise identical in format and the column headings are as follows:
- Part # - TRW part number
- No of Turns Lock to Lock - How many times the steering wheel must be turned from one end of the rack to the other
- Total Rack Travel - The distance that the tie rods move side to side as the steering wheel turns
- Steering Front/Rear - Whether the rack is used with front steer steering arms or rear steer steering arms. This determines which direction the steering wheel is rotated to turn the wheels
- Inner End Ball Socket Center to Center distance - inner to inner tie rod center to center length
- Driver side mount - type of mounting bracket used on the driverside (better to just look at rack!)
- Passenger side mount - type of mounting bracket used on the passengerside
- Overall length - measured from ends of tie rods (does not include tie rod ends which screw on)
- Input shaft length - Length of shaft from rack to where the steering wheel shaft connects (not very useful)
- Inner end thread size - the inner tie rods are replaceable with the tie rods which is great cause you can get tie rods all different lengths. Usually the outer threads are the same size.
- Input shaft to rack angle - the angle the steering shaft sits in relation to the rack (not too useful)
The closest GM racks to what I needed from my testing was 1985-91 Cadillac, Olds and Buick fullsize cars with FWD. Racks are available in center to center lengths from 13.90" to 33" and overall length up to 50". Next I had to find a steering arm that would fit.
The steering arm was really hit and miss. There are so many variables involved that it is really trial and error. I went to the wreckers and basically pulled off every bolted on steering arm that I could find. I tried measuring them on the vehicles but it didn't work. I actually had to compare them to the ones that I had. I used the 67 Chevelle's as a starting point as it was the closest to what I wanted. I used a large piece of white cardboard and drew the steering arms mounting holes and their tie rod end centers on it. Even then it didn't tell the complete picture as the tie rod end center was in 3 dimensions in relationship to the mounting holes where the paper only showed 2 dimensions.
Steering arms starting at the bottom: 70 Nova, 63 Biscayne, 70 Ford van, 69 Ford 1/2 ton, 69 Impala, 63 GMC 1/2 ton, 67 Chevelle.
The other problem was the distance between the two mounting holes and the path of the steering arm between them. There had to be enough clearance for the lower balljoint and the lower control arm. The 70 Ford Van had ample clearance for the ball joint but had major interference with the lower control arm when the wheel was turned.
The 63 Biscayne had major clearance problems with the lower ball joint and was an inch too long. The 70 Nova's tie rod hole was 3" too low and so. The steering arms are the most difficult to find and to fit.
The 73 Ford Courier's steering arms worked the best and with some 1 7/8" standoffs made of 1" dia thick wall tubing were the closest to ideal. Next was finding an outer tie rod end that would mate the steering arm to the rack.
The criteria for the outer tie rod ends are: length, steering arm taper, small diameter, large diameter, type, thread and availability. The TRW book lists the specs for outer tie rod ends by length in ascending order.
- Length - this is the length from the steering arms tie rod hole to the end of the tie rod where the rack is threaded on to.
- Steering arm taper - the tie rod shaft has a taper so that it "jams" into the steering arm. The taper must be the same as the steering arm. The common tapers are 1:6, 1:8 (imperial calls it 1.5"/ft), 1:10 and 1:12. Basically the shaft is smaller at one end than the other.
- Small diameter - diameter of small end of taper
- Large diameter - diameter of large end of taper. These two dimensions are important cause they describe how thick the steering arm is at the taper hole. You want to match these specs closely to the ones used by a standard Ford Courier's outer tie rod ends (in my case) otherwise you may not have enough threads showing or too much threads. The preferred is too much as you can put washers under the nut so that the cotter pin can slip in.
- Type - the outer tie rod end can be 90 deg to the steering arm or be 60 deg or so.
- Availability - this is not part of the spec but makes a big difference on which tie rod end you choose. Besides the VW's tie rod ends, there were two others that would work: BMW 2002 and Porsche. Both were not available at the auto parts suppliers and had to be special ordered. They also cost 4 times the VW's tie rod ends.
VW outer tie rod end in black connected to Courier steering arm in silver.
Outer tie rod ends are available in lengths from 2.283" to 23.45" in roughly 0.050" increments so there are a lot choices that can be made. There is typically about 2" of thread on an outer tie rod with up to 1" of adjustment. The best choice for my application was a VW outer tie rod end. It was used on almost every VW Jetta, Passat and Golf for the past 20 years. It was plentiful and inexpensive. I did have to trim down the racks tie rods about 1 1/2" on each side and thread another 3/4" to make them work but what the heck? I also liked the use of a locking nylon nut instead of using a cotter pin. It makes the width of the steering arm not so critical.
If you were stuck and needed longer tie rods, you can change the inner tie rod assembly. There is a table that lists the inner tie rod assembly by ascending length.