Chapter 8: Steering

1 - Steering System Upgrade

2 - Bump Steer Kit

1 - Steering System Upgrade

     The steering system used on the 924 is reliable and responsive. The rack is taken from the VW Rabbit, but uses a shorter ratio in the 924. The 931 uses an even shorter ratio. The lower control arms are also taken from VW production and are made of stamped steel. These are also lightweight and do not have the cracking problems of the later aluminum units. The steering column uses two u-joints at either end and will collapse in the event of a crash.

     The steering system can be upgraded by making a few simple changes. The steering rack has a small hole on the bottom. This hole is intended for a VW dealer alignment tool. This tool would be screwed into the hole with the wheels centered before an alignment. A rubber plug is used to cover this hole. These plugs will dry up and fall out over time. When this occurs, grease from within the rack will leak out. Water and dirt will also get in, and over time the rack will fail. The cure for this problem is to remove the plug and in its place install an M10/1.5mm bolt,10mm long. The hole in the rack is already threaded to this size. This bolt cannot be too long or it will hit inside and bind the rack. Do not over tighten this bolt.

     If the rack is contaminated with dirt and water, it can be taken apart and cleaned:

  1. Remove the rack from the vehicle, counting the number of turns on each tie rod.
  2. Clean the exterior of the rack and secure it in a vise.
  3. Remove both rack boots and inner tie rods, again counting the turns of each.
  4. Remove the plastic cover on the top and then the two screws under it.
  5. Pull off the round plate.
  6. Turn the rack over and drive out the pinion bearing using a ¼” extension and hammer.
  7. Slide out the rack shaft.
  8. Remove the two bolts on the tensioner. It is spring loaded and will pop out.
  9. Remove the tension slider inside.
10. Clean and inspect the rack.

     The dealer does not stock the pinion seal and bearings. These can be purchased at a bearing dealer. The rack shaft and pinion are machined in sets and cannot be individually interchanged with other units. Any good wheel bearing grease can be used for lubrication. Reassembly is as follows:

  1. Grease sliding and bearing surfaces.
  2. Slide the rack shaft back into the rack.
  3. Place the small pinion bearing onto the pinion shaft and place the pinion back into the rack.
  4. Align the pinion with the small bearing hole and gently drive it back in with a hammer.
  5. When the roller bearing is flush with the top of the rack, it is seated properly.
  6. Grease the seal and reinstall the top plate and plastic cover.
  7. Reinstall the rack slider and spring loaded cover.
  8. Set the rack tension by turning the bolt on the cover ½ turn from tight.
  9. The rack should turn freely with some resistance.
10. Reinstall the inner tie rods, counting the turns, and the rack boots.
11. Center the steering wheel.
12. Reinsert the steering column shaft into the pinion and install the pinch bolt.
13. Bolt the rack back up to the cross member.
14. Reinstall the outer tie rods, counting the turns.
15. Have an alignment check performed on the vehicle.

      The lower control arms, or A-arms, are quite strong and aren’t known for many problems. Strength can be improved by removing the three 7mm bolts that hold the ball joint to the arm and drilling out the holes to allow 8mm bolts of the same length to be used. This is a simple procedure and can be done right on the car. Remove only one bolt at a time so that the ball joint cannot move inside the arm. For even more strength, use class 10.9 fasteners throughout the steering system. The pinch bolts and nuts on the column shaft must be class 10.9. Do not use inexpensive replacements for these. The arms can also be reinforced by welding additional material around the edges, also known as "boxing" the A-arms, providing additional rigidity. The best results are obtained by bead- or sand-blasting the arms prior to welding, and re-painting afterwards.

   The two spoke steering wheel used on most non-turbo cars is not very appealing .A three spoke or other steering wheel is easily swapped in. Make sure to set the road wheels straight ahead before removing. Pull off the horn pad and disconnect the wire. Use a 24mm socket to unbolt the wheel. Remove the nut, washer, and then the wheel. Installation is the reverse of removal.

     Steering column u-joints cannot be replaced individually. Oiling may help remove some roughness. If there is play in the column, it must be replaced. Removal is difficult because the brake booster is in the way. The steering rack must be dropped down for clearance, but does not need to be removed. A small chisel can be used to spread the column ends if they are tight. Again, do not replace the pinch bolts and nuts with inexpensive hardware. Grade 10.9 must be used. - Daniel Varholy


2 - Bump Steer Kit

Jonathan O'Connor, a retired chassis engineer, has commented that the stock 924/944 suspension has a characteristically large amount of bump-steer. Bump steer is caused by the wheel and the end of the tie-rod moving in different arcs as the suspension is raised and lowered by the road surface. Ideally, they will move in the same arc, so that the wheel continues to point in the same direction. This is rarely possible, if at all, in a real sports car suspension, so that (all else being unchanged) as the wheel moves up and down relative to the vehicle, the wheel steers in and out a bit without the driver moving the steering wheel at all. This is most noticeable on bumpy roads, but also can have an effect on high-performance driving because of the change in stability and effective alignment (therefore handling balance) change as the car progresses through the corner.

This is only aggravated when the geometry is changed by such modifications as lowering the car. In order to allow this effect to be minimized, he has come up with a design modification which allows the vehicle owner to adjust and tune out the bump steer as desired. The following is his explanation of the procedure. The parts do require basic machining abilities to make, but are relatively simple. The tuning, however, is up to the driver - whatever feels comfortable! Jon's not giving away any secrets here:

Making a bump-steer kit for our cars is really easy...make a 6061 (aluminum) sleeve 1.125 OD (outer diameter)...about 6 inches long...drill and tap one end for rack thread (14mm I think) and other end for a 5/8 heim joint (aka rod end, available at most motorsports supply houses for $10-20))....then you drill out the taper in the steering arm of the upright (where the ball joint previously went through)  to accomodate a 5/8 can then shim the rod end up or down (using washers on the 5/8" bolt between the rod end and the steering arm) to tune the toe change out of the suspension...the tuning is a time consuming nuisance, but yields HUGE improvements  in turn-in and mid-corner balance.