Speedtoys

Bill/Etc:

How does this axial play...turn into play affecting toe?

jcorenman

The steering tie-rod is not in line with the rack rod. So as the rack rod moves back and forth (i.e. at right angles to its axis), the tie rod end at the wheel moves in and out a bit, and changing what direction the tire is pointing. It does not seem like much but the steering arm is short, and a little movement has a big effect on toe.

BTW, I've always called that "radial" play-- axial would be in line with the rod axis... or am I wrong?

A proper fix would be new internal bushings, but they are not readily available and I don't think the rebuilders pay much attention-- the focus is on hydraulic leaks (not unrelated of course). The pool of rebuildable racks is not growing, and fitting new bushings-- and then properly shimming the pinion against the rack-- is a nuisance.

The external bushings are a good retrofit I think. But they do need to be hand-fit, the internal bore at either end is not machined-- it may be cleaned up but it is not a precise dimension.

What about making the bushings a little undersized, with some locking grooves on the outside, and then boding them in with something like JB-Weld? That would locate the bushings properly without stressing the internal parts (e.g. the pinion gear) and provide a nice large bearing surface.

928porschepatrick

You're right in my mind it was radial but my hands were typing something else

Aspkiller

Be aware that there are three different diameters for steering rack ends, 26mm, 25mm & 23mm. Only the latest rack (-24,-26 and -27) has both ends the same at 23mm.

So, the -22 rack is 26mm on the driver side and either 25mm or 23mm on the pass side.

No idea what the od might be on any of these.

One of the reasons I buy rebuilt from 928 Intl.

Bill Ball

You can see the head of the screw in the 2nd pic. With the bushing installed drilled a small hole in the rack snout just deep enough to enter the bushing. Tapped the hole in the snout and put in a machine screw cut to just the right length.

Bill Ball

I get these confused all the time. Most written definitions don't help me. Your diagram does.

RFJ

Sorry for budding in ,i just want to say thank you again to Bill. Thanks Bill.

928porschepatrick

Problem reduced to a minimum.
I've done this with the steering rack under the car. Loose the big nut
with a hammer and pin punch. Make sure you tighten the two 17mm nuts.
pull rack down and loosen the oil line nut on top of rack, with a long Hexagonal Key 6 (those can be tight)
Not a big job, just have patience.

Attachment 641087

First we had to center the bushing because the internal bore at the end is not machined, so the steering shaft would not be in line with the end.


Attachment 641088


Delrin bushing with 3 screw

Attachment 641089

Bill Ball

Patrick: Can you describe how you went about "centering" the bushing to take into account the unmachined end. I was there when my machinist buddy, Jim Morton, lathed this bushing for me, but I don't recall the whole process. We did not disassemble the rack. There was a little trial and error to get the final fit. In the end, the amount of radial play was reduced to less than 10% of what it was originally in this freshly rebuilt rack. Everything still looks good 70 or 80K miles later.

928porschepatrick

ffff

Kevin in Atlanta

I have a clunking noise. It seems to come alive after I have been driving the car for a while. Last weekend I tightened the wheel bearings and this eliminated the clunk on the driver side that I heard when tapping the brakes. But, I also found that when grabbing the tire at 3 and 9 o'clock the clunking was coming from the steering rack as the rod wiggled in the rack. There is a lot of play but no leaks.

Is this another form of steering rack failure?

-Kevin

Tom in Austin

I think the only 'official' form of failure is fluid leakage ... sure sounds like there's a good opportunity to reduce/control excess movement of the rack in the rebuild process

Kevin in Atlanta

So, there is a bushing internal to the steering rack that needs to be replaced?

Sander_Baas

Bump on this thread.

I replaced all seals and bushings in my steering rack, I could get my hands on an original ZF rebuild kit with also all the needed internal bushings,

But I also have the radial play as discussed here, I took the steering rack apart again but all the bushes are fine (new)

Is this play normal? Can’t find so much about in on the forum (making me think it is not normal) but are there any other fixes then the extra bushing described here? I have a lathe so making the part described here is not a problem but I can’t imagine that this play is “normal”

Thanks
Sander.

jcorenman

No, not normal, but no simple fix so this often gets ignored. The result is a car that does not steer as nicely as it should.

Is the radial play in your rack at the driver's end, or the passenger? (Or both?)

The passenger end of the rod is controlled by an internal plastic bushing, item #24 in the drawing below. Those do wear but I presume it was replaced-- this part seems to be part of the rack refresh kits sold in Europe but not in the states. If there is still play at the passenger side then either the rod is worn, or the ID of the plastic bushing is not right. In either case it would be a simple matter to make a new bushing with proper clearance on your lathe.

The driver's side is a little more tricky, because of the rack teeth. The bearing on that side consists of a "saddle" (item #30.1 below) on one side and the pinion-gear on the other side. In other words, the rack rod at the driver's end is located between the u-shaped saddle and the mesh of the gear teeth.

Normally the piston (part #30) for this type of rack is adjustable, to set the gear lash (clearance) to near-zero which also eliminates any radial play. Instead, on the 928 racks, a shim-washer (item #33) sets the clearance-- I believe these are selected at the factory, and the shim thickness will depend on the machining tolerances as well as the thickness of saddle 30.1. As the saddle wears, or is replaced, the shim needs to be replaced-- but rarely is.

Again, your lathe can be a great help here. Assemble the rack, make a simple fixture to push the piston #30 firmly against the rod (and fully meshing with the pinion gear), then measure the clearance that will need to be taken up by shim-washer #33. Subtract something for clearance (I found 0.1mm for a similar Volvo rack) and machine a new shim. The material is not critical, it is only in static compression-- aluminum or brass or bronze would be fine.

Assemble it and check it-- it is possible that the rack teeth are worn in the center, and some additional clearance may needed to prevent binding at full travel. Don't forget this step.

Cheers, Jim