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Rebuilding a ZF Steering Box

September 24, 2010 | Troubleshooting & Repair

By Bill Sargent


Q1: How do I replace the seals in my ZF steering box?

I rebuilt the ZF box in my 64 C earlier this year. I assume yours is a similar. To replace the seals you will have to remove the steering box from the car and take it apart - at least partially. You will need a tie rod end remover to get the tie rod ends out of the pitman arm.

Once they are off and you remove the steering damper from the pitman arm you can unbend the locking plates on the 4 bolts securing the steering box to the upper torsion bar tube (be sure to replace the locking tabs on the mount bolts with new when reinstalling - Stoddards, NLA and others have them).

Once the steering box is out of the car you will have to remove the two eared connector from the smaller of the two shafts coming out of the box. This is the thing that connects to a similar connector on the steering shaft. Unbend the lock tabs on the clamping bolt and remove the bolt. If you are lucky the two eared connector will come off the shaft with a little work.

Be very careful with a puller on this part as it is easy to snap off the ears. If you are not lucky the two eared part will be rusted on. Mine was and I ended up having a machine shop press it off.

Next you will need to pull the pitman arm off the larger of the two shafts. Remove the cotter pin and then get an air impact wrench to remove the large castle nut from the shaft.

Next find a very stout puller to remove the pitman arm or take the thing to a machine shop to have both the pitman arm and two eared connector removed. Note the position of the pitman arm on the shaft before removing. There should be a stamped line on both parts to mark the correct orientation on the shaft. If the line is rusted off, use a cold chisel to (gently) add a new mark before taking things apart.

Now that all the things are off the shafts, clean all dirt, grease and corrosion off both shafts. There are bronze bushings inside the steering box and if you try to take things apart with junk on the shafts you will score and scratch the bushing surfaces.

If all you want to do is replace the seals, you can stop here and remove the old seals and replace with new.Since you have grease in the box, I suggest you continue and take the box apart and clean things up before putting in new oil.

Now, before you take things apart, check if you have any end play on the smaller of the two shafts that you can feel by hand. You should have none. If you do have some end play it may be due to wear and you may be able to correct it with more shims under the small end cap that is held on with 4 by 6 mm bolts. Now you can take things apart.

Take notes or make drawings of where everything goes (or see the good drawings in the factory parts and shop manuals). Make sure you know which ball bearing race came from where as they must go back in the same place unless you are replacing both the balls and races. Clean all parts. Inspect the worm and peg parts for serious wear. Some shininess is OK. Galling or other wear is not.

If you have serious wear, be prepared to shell out $500 to $750 for a rebuild kit that includes the worm, peg, all new bearings and new seals.Assuming you have no serious wear, get new seals from any one of several vendors - Stoddards, NLA etc. They cost about $9 each. Reassembly is the reverse of taking it apart with the following notes:

  1. Make sure the bearings go back where they came from unless replacing both the balls and races. Pack the bearing near the small end cap with grease and make sure the spacer ring goes back in after the bearing before you install the end cap. Use a very thin layer of sealer on both the end cap/shims and the top of the box. I used the orange locktite sealer recommended for engine case halves. Blue Hylomar also works well. If you have any noticeable end play on the worm shaft, you need to add shim(s) under the small end cap. Not sure where you can get these - maybe Parts Obsolete or EASY. These shims are metal. Do not be tempted to use paper. Fill the box with 0.25 liter of SAE 90 gear oil.


    Set the high point by adjusting the allen head bolt on the top cover of the box until you can feel light binding in the rotation of the worm shaft at the center of its range when rotated by hand. Lock the allen bolt with its lock nut after adjustment. Reinstall the two eared connector with a new lock plate on the clamp bolt (lock plate again available from Stoddards, NLA etc.) Reinstall the pitman arm noting the correct orientation on the shaft by the lines on the arm and shaft. The nut holding the pitman arm onto the shaft should be torqued to 112 foot lbs per the factory shop manual. Get some soft jaws for your large bench vice and a good torque wrench, or take it to a machine shop. No impact wrenches here. Once you hit the required torque, go just enough further to line up a slot in the castle nut with the hole in the shaft. Insert a new cotter pin. Reinstall the box in the car using new locking plates on the bolts that mount the box to the torsion bar tube. Use new cotter pins in the tie rod end and steering damper bolts on the pitman arm.
  2. Probably a good idea to have the alignment checked when you are done.

Cosmetics, if you are so inclined - paint the whole thing black. Yellow paint dot about 3/8 inch diameter on the large top cover. Yellow paint dot about 1/4 inch diameter on the seam between the small end cover and the body of the box on the bottom of the box as installed in the car.

Good luck on duplicating the lead sealing tag. Maybe your local gas or electric utility repair man will do one for you.