Hopefully my adventure and this thread on replacing the steering box and engine mounts will be helpful for other owners.
My car is a '91 560SEC with 156,020 miles
There has been at least one really solid thread on replacing the steering box by member foolio2 which was an excellent reference.
I agonized for weeks and weeks on replacing both the steering box and the engine mounts but it was not too bad once you get into it and mostly mind over matter and if anything just VERY time consuming. It took me two weekends to complete everything. On a difficulty level I would rate it at 6-7/10.
The main reason for the steering box replacement was due to the loose, vague feel of the steering on my car coupled with power steering fluid leaks, which leaks are a major vice for me.
The engine mounts on my car were collapsed so they were very due for replacement.
Specialized tools required:
1) 36mm Socket (1/2" drive)
2) Impact Gun
4) Steering Gearbox Centering Pin (MB Part No:116 589 06 21 00)
Remove all the power steering fluid from the reservoir, I used a rubber tube I had lying around and sucked it into the tube which I then emptied into a gallon jug. Careful not to swallow any!
All the oil sucked out with the top of the power steering filter visible:
Carefully remove the 10mm bolt and the spring and plastic collar combo to get the filter out:
I then centered the steering wheel by using a ratcheted harness strap from the wheel to the brake pedal and cloths to make sure the leather on the wheel was not damaged. To remove the steering box will require wiggling the splined shaft to the steering coupling, so it is essential to keep the geometry perfect. I also extended the steering wheel as far outward as possible and removed the key to lock the wheel.
I then jacked the car up, removed the passenger side wheel and placed the car on jack stands. Now time to see how bad the steering box is:
(pretty bad, worn and very wet with leaking fluid)
I removed one of the 10mm bolts holding the exhaust shield and bent the shield out of the way to access the steering coupling.
I then used my impact gun on the steering coupling allen head bolt as this bolt has Loctite from the factory and was worried about rounding the inside of the bolt by using hand tools. Naturally it came out easily with the impact. I then pried the coupling open with a large screw driver and sprayed some PB Blaster on the splines.
Time to remove the high pressure feed and return lines to the steering box. Even though I have line wrenches designed specifically for this task, open ended wrenches would work equally as well. One of the lines came free with no problem, the other one was unfortunately stubborn and corroded / welded to the fitting on the steering box and even though I tried to save it, it ended up twisting and becoming permanently damaged.
After a few choice curse words due to the damaged power steering line, I gathered my thoughts and removed the other end of this damaged line at the pump, which required a 17mm crow's foot socket (3/8" drive) and a bracket on the inner fender (which was tricky to access).
Time to remove the 36mm bolt on the Pitman arm, which came out without any issue using my Impact Gun. Although sourcing the 36mm socket took a couple of hours and a visits to several Tools and Auto stores.
Note the alignment of the Pitman Arm and the spline shaft on the steering box - very important!
I then used my very strong Craftsman puller to remove the Pitman Arm:
In the above picture you can see how wet everything is due to the leaking steering box.
I did heat the Pitman arm with a bit of MAPP Gas before it broke free.
The steering box is ready to come out and I loosely threaded the 36mm nut back on the Pitarm to catch the box once I removed the three 17mm bolts securing the box to the chassis of the car (accessible on the left side fender well)
Note: The steering box is heavy 30lbs so you don't want that dropping on your head as you remove it!
Old 156K box (right) next to the rebuilt CM box that I bought from AutohausAZ.
AutohausAZ gives you $450 for the old core, so I have to make sure and send that bad boy back pronto.
Note that the feed and return line fittings have to be transferred to the new / rebuilt box. I also bought new copper crush washers (MB Part Numbers 007603016401 and 007603012405).
New parts waiting to be installed including the new OEM engine mounts and Stabilus engine shocks:
The part number for the new hose (to replace the one that was damaged) 1264660381
Getting ready to install the self centering tool in the new steering box:
I also cleaned the surface rust off the shanks from 17mm bolts that secure the steering box to the chassis and applied graphite anti-seize:
New steering box installed and the splines greased:
As I am stickler (maybe fanatical) when it comes to fasteners and very careful to examine each one upon removal in detail in this case I did not re-use the allen bolt for the steering coupling and purchased a new one (MB Part No:2029902101), note it comes with Loctite from the factory! Having one of these back out on you while driving would be fatal.
Everything else is the reverse of the removal for re-connection, playing special care to line up the hash marks on the Pitman Arm and the spline on the new Box and carefully tighten up the power steering hoses and fittings. The 17mm bolts holding the steering box to the chassis is torqued to 52ft.lbs.
I used genuine MB power steering fluid (about 1.5 qts required) and a MB power steering filter (Part No: 0004662104):