DennisStehlik

Rebuiliding the steering rack on my 1996 A6. This is a Servotronic rack. I got the o-ring kit from the dealer.

This is the shaft assembly
<img src="http://pictureposter.audiworld.com/23251/shaftassmb.jpg">

The shaft assembly with the shaft removed. You can see the 3 holes where the restrictors get inserted.
<img src="http://pictureposter.audiworld.com/23251/shaftassmb2.jpg">

The Steering Shaft out of the assembly
<img src="http://pictureposter.audiworld.com/23251/shaft.jpg">

The tubes. Inner hydrolic tube, the steering piston, and on the bottom the main steering rack tube
<img src="http://pictureposter.audiworld.com/23251/tubes.jpg">

The piston sealing assembly that is inserted in the hydrolic pressure end of the tube (see last picture) Mine was leaking and thus the rebuild.
<img src="http://pictureposter.audiworld.com/23251/sealingassmb.jpg">

Other Side of the piston sealing assembly
<img src="http://pictureposter.audiworld.com/23251/sealingassmbback.jpg">

Restrictors that are inserted in the shaft assembly.
<img src="http://pictureposter.audiworld.com/23251/restrictors.jpg">

Looking at the (dirty) bottom of the hydrolic section of the gear. The sealing assembly gets pressed into the bottom of this.
<img src="http://pictureposter.audiworld.com/23251/hydtubeinner.jpg">

Thought you would enjoy seeing some of the guts of your car.

Audi Logic

was it hard to get the rack out?

DMW96A6

My rack had been leaking where the O-Ring on the seal carrier (the thing on the left of image 5) sealed against the surface seen in the center of the last image. The hole in the center is where the shaft goes through and the light area around it is where the O-Ring seals. That area on my rack (previously rebuilt by ZF Industries) was badly pitted. I used a very long 3/8" extentsion with a 1/2" adapter and a 1/2" socket turned backwards so that the flat surface of the socket could be used to attach fine grit sandpaper to polish it. I used double-sided carpet tape to hole the small disks of sandpaper that I cut out. After I polished it, I took the tube down to the local car wash where I pressure washed the tube to ensure that there was not any grit left over. I then used compressed air to remove any moisture and then lightly oiled the tube with Pentosin.

When installing the seal, make sure that the inside surface of the 'donut ring' (the thing on the right of image 5) is smooth. It appears that the one in the image was damaged a little bit but it should be OK as long as the Seal Carrier fits flat against the inside surface of the donut ring.

I used the same extension but a different socket (installed normally) to tap the donut ring back into position. I drove the donut ring until it was almost seated which I could tell by the looseness of the seal carrier by feeling it from the rack side of the tube. (NOTE: don't push the seal carrier too far up or you might cause the O-Ring to come out.)

I carefully inserted the hydraulic shaft into the seal to ensure proper alignment of the seal carrier, taking care not to allow the end of the shaft to nick the seal. I then removed the shaft and then seated the donut ring which pushes agains the seal carrier causing the O-Ring on the other side to seal against the tube.

The design appears to allow the seal carrier to have a small amount of lateral movement. The old 5000 racks had the seals mounted directly in the tube.

Question: How did you mark the pinion/rack so that the teeth would match up? The first time that I rebuilt a rack, I didn't mark them and ended up with a steering wheel that was way out of alignment. You can't just adjust it with the steering column spline because the clamping bolt has to go where the flat spot is on the spline.

Looks like you are doing a great job Dennis! Keep us all posted on your methods of doing this so that we can break the monopoly that Audi has on rebuilt racks!

DennisStehlik

Bernie,

Thanks for the E-mail. I have thought about replacing that pesky hard blue o-ring. Was actually talking with my father-in-law and his machine shop to design something different. Seems to me there should be 2 o-rings there, but I am not an o-ring design expert so I hesitate. I have been reading up on it lately and looking at alternatives available via the web and the McMaster Carr catalog I have.

Can you give me more details on the replacement you used? Where you got the o-rings, the exact size, shap, part number, and material it is made of? I would love to look into it.

As part of the rebuild o-ring kit I got a whole bunch of o-rings and seals, but also got the metal insert with the blue ring. That insert has to be placed into the carrier that I pressed out with the old insert. You are right that there is some lateral play in that assembly. I know I didnt have to take the entire thing apart and redo all the rings, but I had them, was interested, had the time....so I did. It was more about the challenge of it rather than actually fixing any problem.

Thanks,
Dennis Stehlik

From: Bernie Benz
To: "Miller, Chris"
CC: 200q20V mailing list
Subject: Re: servotronic rack rebuild
Date: Tue, 14 Mar 2006 10:18:50 -0800

Hi Chris,

Thanks for the link to Dennis? great photos of the ZF rack internals!

Excepting for the addition of the three restrictor plugs added to the valve
housing, this Servotronic rack appears to be identical to the later 44
chassis ZF racks, as used in the ?91 200Q-20V, of which I?ve overhauled
several.

My further comments, as you requested.

Excepting for the high pressure piston rod seal these racks are bullet proof
and IMO never need to be totally disassembled as Dennis has done. I only go
in far enough to remove and replace the rod seal and boot. Apparently rod
seal failure was Dennis? reason for his overhaul.

The complicating factor (which I have resolved by redesigning the rod seal)
is that ZF will not sell separately or include this rod seal assembly in any
overhaul kit, not even for independent rebuilders. They only sell the
complete kit for the older 44 racks which employ a different rod seal
housing design. I?ve talked with the ZF US rebuild facility engineer about
this, they are very protective of their rebuild business and will not sell
parts for any of their later racks. Dennis, what are you using for this seal
replacement?

In these later racks ZF has not replaced the poorly designed and prone to
failure (read cheap) hard plastic rod sealing element that they?ve always
used, rather just repackaged the same part into a new swaged together
housing (pictured). It is the identical plastic part as is included in the
rebuild kits for the early 44 racks and, IMO not worth installing.

For my last overhaul, I have disassembled the swaged together seal housing
assembly and replaced the ZF plastic seal element with an elastomeric Quad
ring backed up with a nylon back up ring. With no leaks for a year now, IM
optimistic O, with this new rod seal the rack should never again fail.

Dennis, feel free to post this as a reply to your AW post.

Regards, Bernie


&gt; From: "Miller, Chris"
&gt; Date: Tue, 14 Mar 2006 11:01:25 -0500
&gt; To: "Bernie Benz"
&gt; Subject: servotronic rack rebuild
&gt;
&gt; Saw this on Audiworld; thought you'd have comments.
&gt; https://forums.audiworld.com/a6100/msgs/57661.phtml
&gt;
&gt; How's the new A6 working out? I just bought a cheap high mileage C4
&gt; wagon needing a few parts...
&gt;
&gt;
&gt; ---
&gt; Chris Miller
&gt; Training Development
&gt; [i] The Information Foundry at Robert Bentley, Inc.
&gt; http://www.infofoundry.com

DMW96A6

He mentioned that it wasn't available from ZF Industries but I got both of my seal kits from the Audi dealer which included a new shaft seal installed in a new carrier. I call it a shaft seal and Bernie calls it a piston rod but we are referring to the same thing.

As far as being "bullet proof", I don't see how these racks can be considered that since there is a high percentage of leaking racks out there. My car already had a rebuilt rack in it that was leaking when I removed it; and my car only had 89K on the clock!

DennisStehlik

He was using some old information. I guess there was a time when you couldn't get the parts because of some liability issue or something. But, you are correct..when you buy the seal kit you get a brand new shaft seal. These parts ARE available from Audi now.

I started talking with my father in law about making a shaft seal alternative. He has a machine shop, and I think we could make a shaft seal part for MUCH less than the $130 or so I paid for the entire Audi steering rack kit. The Audi kit has ALL the seals in it, but frankly I think the only one that needed replaceing is the shaft seal. I think Bernie says bullet proof because of this..the rest of the rack doesnt need any work. The only part that seems to have an issue is that shaft seal. Interestingly Bernie has shared details of an alternative sealing arrangement that he thinks will last a lot longer. From what I see, it seems it will, but time will tell.

DMW96A6

I believe that the reason that the shaft seal fails is because it loses it's elasticity. The only other reason that a seal would fail is if the sealing edge (the sharp ridge on the inside of the seal) is damaged or worn flat.

The seal arrangement that is in these newer racks, compared to the 5000 racks that I'm used to, is that the older racks had the seal mounted directly to the tube and these newer ones have the seal mounted in a carrier. This arrangement MUST cost more to manufacture and therefore there must be a reason that they chose this design.

Because of the lateral movement allowed by the carrier arrangement, that would seem to limit the forces on the seal which should, in theory, cause them to last longer. I imagine that there is something going on in these racks that might not be apparent unless you have a rack mounted in some sort of testing fixture where real-world loads and heat can be placed on it. It's possible that there is some flexing going on within the tube that causes the shaft to move slightly laterally so the engineers designed the 'floating' seal carrier setup to be able to compensate without damaging the seal. When I say slightly, I'm talking about fractions of a millimeter.

A fixed seal has SOME lateral give in the sealing surface but over time, one side of the seal could suffer premature wear. A floating carrier would solve that issue.

However, I'm not conviced that the seals are leaking because of mechanical damage; I think that the seals are losing elasticity because of the Pentosin. I had a power steering pump from another car apart not too long ago and I seem to recall that the o-rings that were used in it were as soft as new ones; and the pump was from a 79 Porsche 928! I also seem to recall that the o-rings from the rack were all stiff; not brittle but certainly not like new.

If I can find the left over new seals (o-rings) from the racks that I rebuilt, I might try soaking some in Pentosin and others in ATF for a few months and see what happens to them.

David