First, this article is an outshoot of the excellent thread posted by Flatlander757. If it were not for his initial research and article this tutorial would not be possible.
Flatlander's thread Inside the 2003-2006 TJ steering gear(Mercedes-built)
The 2003-2006 steering box commonly referred to as a Mercedes box is actually manufactured by ZF (ZF Friedrichshafen AG) a huge automotive (tractor, rail, truck, and aviation) supplier. Obviously these steering boxes are not as common as the Saginaw boxes and will not swap out without modifying the frame mounting holes. The aftermarket does offer rebuilt gear boxes but I have yet to find a specific rebuild kit for our Jeep ZF boxes. I also used the Mercedes Steering Gear Seal Kit Part number 124 460 01 61 it, thankfully, had the one seal I needed.
• To remove the Steering Gear Box, start by removing the drag link cotter pin and bolt. I couldn't get my tie rod end puller in there, which turned out fine as I used it later when I had more room. (don't blame me for the swollen dust boot, the PO was alittle grease-gun happy).
• If you can access it, now would be a good time to remove the steering shaft collar pinch bolt. I have a 1" body lift that helps give access but my Mile Marker hydraulic winch lines are kinda in the way. I did manage to snake a flex head 13mm socket in there, otherwise your doing it from the underside.
• If you could not get a good shot at that pinch bolt fear not. I found if you remove the bottom and rear steering gear mounting bolts and just loosen the top/forward bolt the whole box pivots down nicely. Now I could access those power steering lines, slide the steering shaft/pinch coupler off, and have enough room to get my tie rod end puller on. I had to spread that pinch coupler on the steering shaft with a chisel, and even then it took some mild coaxing with a pickle fork to slide the pinch off the splines.
• Be ready when you pull that last bolt, it's got some heft to it. From here clamp it moderately in a vise, input shaft up. (I started on the bench before I wised up). Grab your 6mm allen wrench and pull the cover bolts off. I had to seat my allen with a few taps of a hammer, cause they painted over everything.
• Make sure you put a pan or bucket under you vise cause there's still alot of fluid in that box that will come out when you lift the piston assembly out.
• Now I unscrewed the box cap to give me a little wiggle room here. I only went an inch or so, and thankfully, no ball bearings dropped out across the floor.
• Next that outer spanner lock nut needs to come off. It's snug but not hard to remove.
• Now there's an inner spanner nut that needs to come off. I have a two-post spanner wrench but couldn't locate in my mess. None the less, this nut comes off real easy.
• The offending seal...
• New replacement seal...KACO DGS 21338/9.5 VO1 HT891056
• This is the special gasket that fits under the cover, that Flatlander757 mentioned in his thread. It's looks like a MLRS type steel rubber lamenent of sorts. It is NOT included in the seal kit, so be carefull with it. Mine came loose after handling the piston assembly, so I took it off so it wouldn't get damaged. We need to reuse it.
• I drove the old seal out, cleaned the gear box cap were seal sat of any dirt or rust that got in behind it. The new seal I could push in mostly with my fingers, a socket and hammer drove it flush with the inside of the cap. Before I slid the box cap on the shaft, I needed to remove some of that rust on the shaft that may have caused the seal to wear.
• One last look at the thrust bearings. Notice that what looks like a fat thrust washer in the middle is actually part of the shaft. Another thrust bearing follows it, and there's an outer bearing after that.
• Putting back together is easy enough. The inner spanner nut is tightened down just enough so it tight but does not drag on the steering shaft. So tighten it little then twist the steering shaft splines with your hand to feel for too much drag. It was very obvious when it was too tight, so I had to sneak up on the proper tension. Then I tightened down the outer spanner lock nut. This one you can tighten pretty snug (so it won't come loose). Just make sure your inner nut doesn't move by rechecking for drag on the steering shaft.
• Put that special cap gasket back on if you took it off, and smear ATF+4 around the outside of the piston assembly. Set the assembly back on the gear case. At this time make sure the box cap is screwed all the way down by spinning the cap.
• Notice the cap is bottomed on the piston. Now look at the four teeth on the (left) side of the piston assembly. These teeth mesh with the four teeth on the pitman arm. If you need to, lift the piston assembly off the case and look inside as you move the pitman arm, you see the pitman arm teeth I'm talking about. As you slide the piston assembly into the case move the pitman arm to engage the teeth. Align the gasket and cap with the bolt holes and torque them on; Flatlander757 measured 25 ftlbs removing the allen bolts.
• Putting the steering gear box back in is easier than coming out. Loosely put the one bolt through the frame into the gear box. Reconnect the power steering lines. Align the pitman up to connect to the drag link (but don't connect it yet). Align the steering shaft pinch collar with the flat notch for the pinch bolt on the splined shaft from the steering box. Reinstall you pinch bolt on the steering shaft and reinstall the bolts holding the box to frame 70 ftlbs. Reinstall the tie rod end drag link 55 ftlbs with a new cotter pin. Do the steering pump bleeding drill and think of the coin you just saved!
EPILOGUE: So far the repair seems to be working (knock wood). I thought I had it fully bleed out, but there must have been an air bubble some where 'cause it started whining and the fluid level dropped. Added some more ATF+4 (and left the rest of the bottle next to the driver's seat, just in case) and it seems good now.