Renew Your Steering
by Brad Ripley
You’ve spent considerable time and money on the body and trim of your 356, but have you paid attention to the running gear? Often the most forgotten area is the front suspension, and especially the steering part of it. You’ve probably rebuilt the outer spindles and replaced the tie rod ends. But, most often neglected is the steering gearbox. If you’ve got a half inch of play in the steering wheel, your steering box needs attention. Beyond too much play, you may experience a “notchiness” driving straight down the road. In extreme cases, the steering wheel will want to catch when turned just off of center. Any of those symptoms means the steering gearbox will probably need a rebuild.
For 356A T-2 thru 356C cars, the steering box was manufactured by ZF-Germany. It’s referred to as a Ross design, or better known as worm and peg. Here’s an exploded view of this box.
At first glance, it looks simple but it’s really a precision mechanism with tight tolerances. Your 356 may have several hundred miles on your steering box, so it’s inevitable some wear has occurred on the internal components. The most prevalent wear item is the peg where it intersects with the worm gear. Badly worn pegs are probably in 50 – 60% of the gearboxes.
Here’s a photo of a peg with typical wear. You can see the erosion of the surface hardness. With this wear, you will have increased play and eventually the worm will be ruined by the bad peg. Additionally, there can be a safety issue with the catastrophic failure of the peg.
A few notes about replacement pegs – first, there are no new pegs either from ZF, nor from Timken. So any new peg has to be at least equal quality to what was made back in the 60s. We have enlisted a precision machine shop to manufacture our pegs from the best steel alloy. Running surfaces are ground and the part is heat treated to 50-53 Rockwell C. It will probably outlast the originals assuming no damage to the worn gear has occurred. The nut at the top of the peg should be adjusted close to zero tolerance and locked in place with the lock plate provided with the peg.
You can purchase our new steering box peg HERE.
If by chance the peg and roller bearings are OK, then a slight adjustment can be made with the set screw in the top casting to hopefully take out some of the play in the steering wheel. You’ll find instructions the Porsche Work Shop Manual for adjustments.
As for replacing the peg, it normally is a professional operation. Careful attention should be paid to the roller bearings and to the upper cap holding the rollers. There are no new rollers available. The same careful inspection has to be done on the worm gear. Of course, where the peg normally rides is in one common part of the worm. If that area is worn excessively or the peg has been driven into it by an accident, then another used worm has to be found; there are no new ones being made.
For complete and professional steering box rebuild, we recommend Martin Willis http://mwthemachineshop.com/356-zf-steering-box-rebuild Martin uses our pegs and has well-developed methods for curing other problems with these ZF boxes.
