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1986 420SEL/1995 E300D/4 BMW’s/2 Vanagon’s
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After 15x,xxx miles, the steering gearbox on my 420SEL has obvious play, an internal knocking sound, and a couple drips a night when parked. It’s time for a replacement.

From research on this site, it seems the most recommended rebuilt unit to go with is from C&M Hydraulics. AutohausAZ sells this unit for $400 and free shipping. They charge $450 core in addition which in theory I will get back when I return the old unit.

As a side note, they send very specific return instructions so pay attention to those if you want to get your core back.

I also purchased the “special tool” for keeping the steering box centered while putting everything back together. I think this is something that can be easily made, but, since I did not have the specs, I had to buy it.

I would rate the difficulty of this job at a 3 out of 5. I actually thought it was going to be much more difficult than it was. The factory shop manual has the procedure pretty well laid out but as usual some things just aren’t clear. Between the FSM and internet research, I had all the steps figured out before I started though. As you can see in the photo’s, I do have a midrise lift and that did help for some parts, but, I think this job could easily be done with just the front on jack stands. Also, you’ll see I have the spring removed. That is not necessary but since I had done my guide rod bushings right before, I just never put the spring back in. I suppose it made access to the bolts holding in the steering box slightly easier. All in all, I probably spent about 4 hours doing the swap.

Supplies:

New/Rebuilt Steering Box ( C&M Hydraulics)
New Power Steering Pump Filter
Mercedes-Benz Steering Gear Lubricant
Pitman Arm Puller
Steering Gearbox Centering Pin (special tool 116 589 06 21 00)
Steering Column Coupling (123 460 02 10) – not required but I replaced it since I had it apart
36mm ½” socket for pitman nut
New low pressure power steering return line – again, not necessarily needed but I replaced mine cause it was leaking.
Various Sockets, tq. wrench, breaker bar, penetrating oil, etc.

First step I did was to use a turkey baster to suck out the power steering fluid from the reservoir. Use an 8mm deep well socket to remove the spring retainer and needle nose pliers to reach in and remove the old filter. Be careful removing the nut holding the spring retainer as it will be under tension and could spring away across the garage:



Fluid and filter removed:



I also replaced the low pressure return line at this stage. That is just hose clamps and cutting two pieces...no need to really get into that too much.

Couple views of my box from the side and below. You can see it is wet with leakage. Location wise, it is just forward of the carrier bushings and above.

Side view:



Below view:



Even though I sucked all the fluid out of the reservoir, I could not get it all out of the lines or the box itself. I have a large flat oil drain pan that I put under the box with an old t-shirt to help control splashing for when I removed the supply and return lines from the box itself. After removing the lines, I turned the wheel back and forth a few times to get the fluid out of the box.



Lines take a 17mm and a 22mm open end to remove. If you have a flare wrench, that may be better but mine came off pretty easily:



Next, you need move an exhaust heat shield to get access to the bolt that holds the steering coupling to the box. There is an 8mm bolt that holds the exhaust heat shield to the frame. I removed that and just sort of bent the shield up and away from the coupling. Then, the FSM says to fully extend the power steering column (not sure why) to remove the bottom nut to slide the box off (eventually). I removed bolt the bottom and top nut since I was replacing the coupling. This is done with a 6mm hex drive.

Side note, there is a good reason to make sure that the steering wheel stays pretty much centered throughout this process. The steering wheel is clocked in such a way that the turn signals will not self cancel right of you happen to get the wheel off 360* or more. You don’t have to be degree perfect here but at least eyeball-close. I noticed that the steering wheel will lock itself in the center position with the key out. I also used a bungee cord to make sure it stayed roughly center. I did have to move it around a bit to get to the steering coupling bolts but I always made sure I got it locked back in center before I continued.

My set up to keep the wheel centered:



In the photo below, the red arrow points to the exhaust heat shield, the yellow circle is the lower coupling bolt and the green circle is the upper coupling bolt:



Once you have the coupling bolts out, you can go about removing the box itself. First step is to remove the pitman arm. Note, I did not even bother removing the drag link or steering links while doing this. There really was no need. Literally, the only thing you have to remove is the wheel (to gain access to the steering box bolts) and the box itself. I originally thought I was going to have to disassemble half my steering and suspension to do this, but, that is not at all the case.

Some tools I bought at Autozone…36mm socket, some pitman pullers. I ended up using the big one, but, I didn’t want to make two trips since they were only $15 a piece.



I used my impact to remove the pitman nut:



I used a 20” break bar on my pitman puller and it came right off without too much drama. Don’t get me wrong, it was tight, but I did not have to use a cheater bar or anything:



Disconnected!



Next step is to remove the box itself. Since I am a one man show and the box weighs about 30lbs., I slipped the pitman arm back onto the shaft and put the nut back on a few turns. My thought here was, once I get everything disconnected it would not drop to the floor immediately and break my foot or something.



Here are the three 17mm bolts that hold the box to the frame:



After I got the bolts out, I sort of just tapped the box with a hammer to slide it off the coupling. Yes, I left the coupling attach to the column here. I could have loosened to the top bolt of the coupling and took them out together as well but I did it in two separate steps.

Out!



New box all shiny and nice!



The new coupling and special tool:



You have to swap over the fittings for the lines from the old box to the new box. I almost missed this step…that would have sucked:



The box comes delivered centered, so I took out the covering nut and put the special centering bolt in to hold everything in place. Technically, you could probably do without this, but, I did think it made things a little easier.
Here is a picture of the centering bore. I don’t know if you can see because the flash sort of ruined this photo but for demonstration purposes, I slightly move the box off center so you could see the hole the centering bolt screws into:



Here is the centering bolt installed:



If I had to do it again, I would probably do this next step a little differently. I installed the coupling to the column, then, installed the box to the frame. Doing it again, I would have installed the coupling to the box, then, installed them as a unit. The problem was, the splined shaft was a tight fit onto the coupling. Not only do you have to line it up perfectly, but you have to use a fair amount of force to slide the shaft onto the coupling. This was difficult doing by myself due to the box weighing 30lbs. and having to hold it above my head. I was at least one, if not two, hands short.

Again, I used my trick of first putting the box loosely onto the pitman arm to help hold it. It was still heavy and cumbersome to maneuver into position and slide onto the coupling though. The upper part of the coupling is not a splined shaft. It slid on very easily. That’s why I think it would have been easier to install the coupling to the splined shaft on the box first, then, slid the coupling onto the column.

I used blue locktite on the coupling bolts…don’t want these backing out…ever. Coupling installed first (notice the exhaust shield bent out of the way for access):



Box installed. Note the centering bolt still in place:



Notice the hash marks for getting the pitman arm properly clocked on the pitman shaft. Make sure these line up before permanently re-attaching pitman arm:



I was too lazy to look up the torque settings for the pitman arm nut so I just put my impact gun on full wood and torque’d it till it would not move any more…again, don’t want this falling off.

After doing this, I removed the centering bolt.
The bolts that hold the box to the frame are torque’d at 80nm.
Next, I pretty much just put the spring back in (since I had mine out), put the wheel back on, and filled and bled the system.
The system took about 1.5 qts of this fluid I got at the dealer. Smelled like ATF but was yellowish in color:





When I got everything done and the car back on the road, HUGE difference. There has virtually no play in my steering any more. It is very tight and the car centers itself nicely. This must be what it feels like new. Very worth it. Before, it was so bad you could move the 1.5” in either direction with no movement of the wheels, there was a knocking when you moved the wheel back and forth when stationary, and when you hit bumps, you could feel the gears knocking together and reverberating up though the steering column. All that is gone now. This has to be one of the biggest differences I have felt in all the different jobs I have done on this car. Now I just have to pack that old one up to send it in to get my $450 core back!
 

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84 500SEL AMG, 90 560SEC AMG, 85 500SEC AMG Widebody
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1,784 Posts
Great write-up - needs to be moved to the DIY post.

Interesting point on keeping the steering wheel centered and the gear box centered because of the turn signal cancel. My 91 SEC had its gear box replaced at some point and also the turn signal stalk assembly on the steering column. My turn signal cancel only works part of the time - hit or miss. I wonder if the install of the gear box was messed up or the steering wheel replaced in the wrong orientation or....

Al
 

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'91 560SEC, '98 SL500
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1,936 Posts
Wow...brilliant tutorial / thread!! Like you my steering box leaves me a drop or two of fluid and with 156,000miles on my car, this is next on my to do list. I VERY much appreciate the pictures and the pointers - thanks!
Yasin
 

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'82 Euro 500SEL, '85 Euro 500SEC AMG WB Cabriolet,'86 Euro 500SEC RUF
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9,487 Posts
Once again a great tutorial!
 

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I just did this job. Removing the old unit is not difficult. The pitman arm nut came off with a breaker bar. The pitman arm required a breaker bar + cheater. Installing the new gear box is better with an assistant. I used a 100 lb picture framing cable , tie it securely to a washer, put it through the top hole on the box & put it through the top hole on the frame. My assistant will pull the box up so it’s elevated while I line up the coupling to the steering shaft. Then my assistant will insert 2 large screwdrivers into the bottom holes to support the box. It was difficult to install the steering shaft into the coupling as it’s a pinch bolt slot . Once I get the shaft somewhat into the coupling, I remove the screw driver & insert the bolts. I don’t tighten it. Then I have my assistant turned the steering wheel so the shaft seats in the coupling better. Then I removed the supporting wire/washer from the top hole & insert the bolt and tightened it. Then I used a pickle fork to push the coupling further up the steering shaft so the Allen bolt is locked onto the grove in the pinch slot bolt. Then I tightened both the bolts on the coupling. I find I have to remove the tire rod & the center stabilizer in order to hammer the pitman arm back onto the pitman gear. Remember to line up the marks. Then I screw it the large nut & used an impact to tighten the nut & push the pitman arm home. It’s not easy & definitely needed an assistant.
 

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1988 560SEL
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64 Posts
I am in process of doing this too. However I ran into a problem with the pitman arm removal. I didn't have the one OP had but the smaller one. So I tried to use a pulley puller but it messed it up. I decided to disconnet the driver side tie rod and drag link from the pitman arm. Again I didn't have the right tool for the drag link ball joint so I took the drag link with damper and gearbox out all together. Then I had an easier time removing drag link from pitman arm. Took the gearbox with pitman arm attached to a friends shop who removed it for me. It actually took a good amount of impacting on it. I guess mine was on pretty good. I'm not looking forward to sliding the spline into the coupler. It will be a one man show.

Side note: I decided to change the 2 low pressure hoses since it was easy to get to and it was leaking from the clamped areas. Hoses were hardened with age. Clamps looked great after I cleaned them up a little. While waiting for my rebuilt gearbox I already changed to new power steering filter and gasket seal.

Wish me luck!
 

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Install the coupling onto the gear box first, making sure you line up the split slot from the shaft end to an indentation on the spline gear. If it’s a one man show, I would insert couple of big screwdrivers into the 2 bottom hole of the frame from the tire well just so you can see the tips of the screwdrivers. When you push the gear box into place, push the screwdrivers all the way home so the box is supported & you can have time to fit the coupling onto the steering shaft. It’s frustrating to line up the shaft end precisely into the coupling but since the screwdrivers are supporting the weight of the box, you have both hands free to line up the 2 ends. Let me know how you manage !
 

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1989 560SEC, 1989 560SEL, 1995 E420
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Great idea with the screwdrivers!

Additionally, I sometimes drive a screwdriver into the slot of the spline clamp to open it up a little. Makes a big difference on getting the splined shaft in. I also lock both the steering gear and steering wheel in the straight ahead position before installing the gear.
 

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Great idea with the screwdrivers!

Additionally, I sometimes drive a screwdriver into the slot of the spline clamp to open it up a little. Makes a big difference on getting the splined shaft in. I also lock both the steering gear and steering wheel in the straight ahead position before installing the gear.
I installed the spline end of the coupling onto the gear first. Then I installed the gear box as a unit. Once the weight of the box is out of the equation, then it is simply line up the split slot & the steering shaft & insert the shaft home. I wiggle the steering wheel to get it started, then I used a pickle fork to shift the spline end towards the split slot end until the split slot is completely home. Then tighten the Allen bolts.
 

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1988 560SEL
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64 Posts
Updates? Nursing some busted knuckles?
If you are talking to me I got it in...twice. I read that the rebuilt units come pre-centered from the re-manufacturer so I didn't bother checking. I was also affraid if took that bolt out it would never seal back again completely. After installing it would only turn half a turn to the right. That is when I decided to open the sight hole and noticed the alignment hole was only showing half. Had someone steer slowly until I visually saw it was centered and then took the gearbox out again. Recentered steering wheel and slid it back on. The hard part was the spline. I thought about what someone mentioned to take the coupler out and install onto the gearbox first since the other side isn't splined. I decided to just try into the spline again but with a pry bar after getting it started a couple millimeter it went in with some force. Since the coupler/column moves inward it made it difficult everytime I pushed the gearbox onto it. I bolted the gearbox in and used the pry bar to push the coupler onto the spline. The rest was cake. I'm just having a issue with the steering being stiff to turn. I am waiting on response from remanufacturer to see what I should do. Some are saying to screw in 1/4 turn CW increments to loosen the steering up but that will be my last resort. Steering is definitely tighter and almost no freeplay left or right. Since I was doing new steering components and driver side suspension at the same time I only drove a couple hundred yards to flip the car in the garage so I can get started on the passenger side suspension refresh. I'm halfway done and after everything is back on I will give it another bleeding to make sure I got all the bubbles out. BTW the steering now turn 1.5 turns left and right from center after redoing it. Just got to get alignment and see whats up with the stiffness.
 
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