griffiths

worf928,

OK. I "think" I understand your complaint on your rack. If I'm still missing it here then feel free to call me directly or pm.

- With the rack centered and on a bench
- Turning the input shaft clockwise approximately 10 degrees results in NO "immediate" movement of the rack shaft

There are many probable causes for "lack of initial response from input". Some may apply to your symptoms and some may not. Some may have come about during a rack rebuild, some the result of installation, and some we will never know the cause. However we'll recite a few here in general terms as it may answer other questions or comments from readers I see here, and you can pick out the potential cause and effect based on the specific symptoms you observed in your particular circumstances.

1. There is too much "backlash" between the rack shaft gear and the pinion gear. The amount of backlash (space or clearance between opposing gears) is determined based on design; sometimes undesirable and sometimes required for lubrication, deflection under load, manufacturing tolerance,
or differential expansion between components.

A) The backlash is set by washer shim located under the steel diamond shaped cover held against the bottom aluminum pinion housing. If you take a 13 mm socket and remove the two 8 mm bolts you can remove this cover plate.
Underneath or inside should be a shim washer, a spring and a "shoe". If washer is missing or undersized you will have excessive backlash. There is a spring that sits between cover plate and blind bore in the shoe. The spring provides a "float" for the backlash. If the spring is missing you backlash may "float" excessively. If the shoe assy. is frozen in position in the bore (from corrosion) you could have excessive backlash. The shoe has two sides, the visible side when you remove the cover plate has a blind counter bore to hold spring. On the opposite side of the shoe should be a (nylon) "glide" or bushing for the term of the moment, that seats in shaft side of the shoe. If the glide is missing, broken or excessively worn you wll have excessive back lash.

B) The opposite side of the input shaft sits in a needle roller bearing in the bottom aluminum pinion housing. If for some reason the needle roller bearing assy. is missing or a needle is missing then you will have excessive back lash.

C) The rack gear's tooth profile(s) is(are) compromised. This means the shape and dimensions of the rack's gear teeth on each side of the given pinion gear's tooth is not in conformance. Assume you have the vehicle tracking set up in a "dead center running position"; you are driving the car down a straight road, a particular pinion gear tooth will be between a "set" of rack gears. The profile of the rack gear teeth on each side of the pinion gear tooth is either worn or damaged. Wear normally appears over time as the rack gear teeth are "softer" (in RC terms have you) than the pinion gear teeth simply based on the design ratio. The two gear teeth (in the set of gear teeth on the rack) which just happen to fall into place when the vehicle's rack is aligned to its straight running position naturally see more contact over time than other gear teeth in the rack .... so you will get worn teeth or a what ends up to be a larger backlash over time. A damaged rack gear tooth profile can result from failure to properly hold the rack shaft from twisting when installing or removing inner tie rod assemblies; the rack shaft will twist against the pinion tooth which can result in the harder pinion gear damaging the face of the softer rack tooth.

(As a side note we typically screen cores coming in for what we described as "worn center teeth" ; when rolling the rack gear you feel an extensive "thump" over the center position. We had a retailer we'll call them years back we use to rebuild for. Suddenly we found we were receiving many racks for repair, from them, that had excessively worn center teeth; meaning from a stats. standpoint we were getting too much junk as compared from other clients. We would return these cores back to them as "non" rebuildable as we usually found when we got done with the pre-inspections, cleaning, disassembly, cleaning, sub assembly or component cleaning and inspections. etc, that is just was not cost effective to pursue these particular troubled cores. Naturally we lost the retailer as a client, though there were other issues we had with them, such as they were sending back compressors to us for warranty which were not ours but from one of their other suppliers, etc. So frankly we don't miss them. Thinking back we believe they probably had an installer, who purchased many racks from them, and he simply did not know how to R&R a rack without damaging gear teeth, or when retailer was pulling the racks out of cars to ship to us they did not know about twisting shafts and tie rod removal. Anyway it was an isolated problem we resolved;>)


2. One or more (there are two) of the pinion's valve springs is broken or missing.

A) When you turn the "input shaft" you are turning the pinion valve body assy. From the outside we see a splined shaft entering the aluminum pinion housing; the outer diamater of the shaft is splined to grip the universal steering joint or yoke, and on the inside of the input shaft there is a "torsion bar". The torsion bar presses against the valve mechanism to open the hydraulic circuit for LH or RH power assist. The first 15 degree's (for simple measurement) in either direction is a gradual increase in flow, or power assist, from 0 to 100%. The valve mechanism has a set of springs. If a spring is missing or damaged the symptom is typically lack of power assist in a given direction. We have seen broken springs I'd say in the probable circumstance of 1 out of 50 racks for overhaul. The broken spings appear more commonly in early racks, 1978-1981. The spings are hardened so from a casual observation the broken spings appears "fractured". Since we do not see many broken springs and they appear more commonly in early racks, we sense the cause could be related to a heat treating problem (the usual suspect). Why one particular early rack with a broken spring has this problem and not others could be either the batch of springs or that the input shaft was "over driven" ... meaning excessive force was applied. Again, the symptom or complaint is typically lack of power assist, however the symptom could be overlooked if one was not familiar with how the steering effort fell or how it should be.

Digressing from your question, however helpful to a reader someday, here are a few other causes we have seen related to both felt or observable symptoms with the rack in the car:

I) Lack of rack gear movement when turning the steering wheel a few degrees left or right:
a) worn universal joint.
b) loose steering mounts (four mounting bushings), the rack shifts on the mounts
c) loose inner tie rod joints or outer joints
d) loose wheel bearings (however at this point driving in the car usually sounds like you are in train)
e) an alignment issue
f) don't laugh .... underinflated tires

II) Lack of power assist:
a) a loose, dismounted or worn power piston on the rack shaft
b) failing power steering pump or low on fluid (which usually has excessive noise)
c) the broken spring as mentioned before
d) rings grooves in the aluminum spool valve housing, or a broken high pressure seal ring.
e) not common, but things you see going down this road from our end:
"something blocking the lines", or "collapsed suction hose" and finally.....
"no fluid in the PS tank".

Assuming you now understand the problem I describe, what I would like to know is:

a) does this problem represent the result of an improper rebuild technique?
b) does this problem represent an infrequent failure of post-rebuild QC? Or
c) would a rack rebuilder expect the end-user to 'deal' with this issue?


These last questions are difficult to give you an "answer" , but I'll assert what we can speculate:

A) With out looking at the part first hand I nor anyone else I assume could say the symptoms you are observing are the cause of the rebuilder, whether the cause is their MMM (methods, materials or manpower). If you inspect the rack "out of the box" and it is OK and not OK during alignment, then you have to look back on what transpired after it came "out of the box/OK".
B) The observation or complaint of: "..... driving down the highway there is a 10 to 20 degree 'dead spot' in the steering wheel. I can drive straight down the road and saw back and forth on the wheel by 10 to 20 degrees with no movement of the front end of the car because the shafts are busy moving forwards and backwards rather than left and right".. I would say, from our position, that we do not hear this often; looking at over 2,000 928 racks overhauled here. And, if we cataloged the incoming phone calls or emails regarding either help with or complaints about something of this nature then I would say we seldom here about it; seldomly about other rebuilders and seldomly (for what remains in long term memory today) about ours.
And if "QC" after the product has been rebuilt is in the eyes of the rebuilder then I would have assumed they would have screened for this. I would assume a good installer would screen for this problem during alignment or test drive prior to releasing the vehicle to the client.
C) In my state of mind today, after having two cups of coffee and forgoing the Becks at the Christmas party, I would not expect "our" customer to "deal with it"; assuming they have contacted us and gone through all the troubleshooting.
If it is our rack then I'll blame it on the Becks.

Of course. I ran a business for over a decade that was based upon patented and/or proprietary technology and methods. The challenge in sales was to educate our prospective clients without giving away the farm. I have no interest beyond technical curiosity in why the problem I observed occurs.
I appreciate your candor. However there are some readers that simply expect or demand everything that is in life for free ... some that can't tell the LH from the RH.

Let me know if these notes have helped you. And you wish us to inspect the rack in question just pm me and we'll give you a ship to address.

If we don't hear from you before Santa arrives then have a Safe, Happy and Merry!

griffiths

Actually on a RH turn in the U.S. the smooth side of the rack is retracted rather than extended.

The design does not have a weakness in terms of how far the smooth side extends as that is function of the desired turning radius and the ratio.

I'm not convinced yet that the design as it was 30 years ago is a weakness today, however I would explore what 30 years can do to any design.

BC

I see that was me. It has been corrected. Note to self _ Don't post from the throne. Not enough focus.

BC

As I mentioned in another area, Looking at newer technology in person tells me that more attention has been paid to extended strength. If there is so much movement under load at the full extension that we CAN see, how much movement is there in a moderate high speed turn - where any mm or amount of deflection in any non-intended direction is amplified through the inner, then outer (tie rod), then hub, and finally the tire.

The same idea says that a very good alignment on a performance vehicle can make a world of difference in directional stability and responsiveness, all all being equal, and the different in Camber, Toe, Caster and total toe can be milimeters.

griffiths

Ahhh, heck no. That was not you; was it?

Its the quantity of posts that counts not the quality. Right?

griffiths

I'm not convinced yet that the complaint noted by the posters is the same across the board in this thread, nor for all 928's on the road. However the complaint is a valid complaint and more than worth the time to resolve.

Granted there is a frenzy feading on the subject here but not a concensus as to the cause, effect and solution for each member or across all owners. I've owned 3 (78,84s,89s4) and never had "slop" right or left, " a dead spot" in the center", or "wondering" in center. However they had fresh GTI rebuilds put in them soon after purchase. However I do recall symptoms alike the topic, caused by wheel bearings, tire inflation, worn inner tie rod joints and simply a poor alignment.

What will be interesting is to see what the solution is in each case.

I guess that holds true for my: 911, Grand Voyager, Jeep Cheroooookeee, Allis Chalmers tractor, my kids skate boards and Ferris zero turn lawnmower (do you know how upsetting it is to pay $7,000 for a lawnmower only to see zigzag tracks across the lawn? I want it to look like Yankee Stadium during the playoffs).

worf928

What you posted in bold-italics is not what I wrote.

In my post above I wrote:
Thus, there was "immediate" movement of the shafts. However, for approximately the first 10 degrees of input shaft rotation this "immediate" movement was fore and aft and not right or left. After 10 degrees of input shaft rotation the shafts would cease their fore/aft translation and begin to translate right (or left) along the shaft axis. At the point where the proper shaft axis translation began the shafts would remain displaced along the pitch axis in opposite directions and would stay thus displaced while translating along the shaft axis.

With the rack on a bench - fresh out of the box - and the shafts centered, if you turn the input shaft 10 degrees clockwise and then 20 degrees counter-clockwise and then 20 degrees clockwise and then 20 degrees counter-clockwise etc. you see the shafts move front/back, back/front, front/back etc., with no right /left movement. In other words - rotating the input shaft back and forth 10 degrees off rack center either way results in one steering shaft moving towards the front of the car (had the rack been installed) and then towards the back of the car while the other shaft moves back/front in opposition to the other shaft. All the while the shafts move not at all right or left.

There is "immediate" movement of the steering shafts - it just isn't to the right or to the left.

It doesn't seem to me that this description fits the 'back lash' model assuming that the gears are straight-cut.

Ron_H

This is consistent with my experience also. When I would attempt to correct perception of wandering (pulling slightly at the wheel), my immediate input did not result in immediate response of the car, but add a bit more and suddenly the car would jump toward the direction steered, rather than smoothly. This of course caused me to begin correcting the other way, but would be accompanied by a delay in response that way, until suddenly the correction would occur and back and forth, etc. This is usually accompanied by some rather foul language, as if that will make the car steer more correctly !!

griffiths

You are correct, I did not quote you verbatim. I keep forgetting my verbum dicendi when I jump to conclusions.

I think your last full paragraph sums it up? .... in this sense, and if I may paraphrase for myself:
"I turn the steering wheel, or the input shaft, and the rack shaft does not immediately move, it kinda wobbles there". So you are not getting immediate "linear" movement.

Consider that the pinion gear is not a "straight-cut", in simple terms like a common spur gear, rather in this design you could say it is helical in nature, a spiral or a "twist". And the rack gear is not a horizontal cut either, rather diagonal or helical again.

This design is probably used in auto rack and pinion sets, as opposed to a straight set, because the teeth in a helical wrap are stronger and the amount of surface contact is greater; hence they can carry more load, however not as efficient I would remember than straight cut sets.

This type of design wants to "thrust" if you have a member, rack or pinion, that is not held in place (the rack along its intended linear direction, or the pinion within its intended axis) ..... say from excessive back lash, or a glide or bushing, in simple terms, that is not doing its job....such as being out of place, then what you may observe is the fore and aft or the rack gear walking or twisting away from the pinion.

On the 928, if this is excessive "twisting", you may see the "translation" down the shaft to the RH side although is it more easily seen at the LH side.

Based on what you have observed with your complaint (excessive fore and aft movement) I would suggest inspecting the "shoe" assy. and its related components under the diamond shaped cover plate, and while you are at it check the backlash.

Hope this helps you. Again I apologize in assuming what you were observing was a lack of linear movement as a result of possibly not having the pressure and backlash properly set.