So in the process of changing the lower power steering hose, I had to pull out the radiator fan in order to get at the hose clamps on the power steering fluid fittings on the radiator, and I figured while I was in there, I'd pull the power steering fluid reservoir and get at the exhaust cam magnet, which was the last one left un-updated ... boy that reservoir is funny, even though I have the three screws out, something is holding it in place, let's see ... SNAP!

Oh, snap, I forgot about the retaining ring. No matter that it's a retarded design; this one is on me.

Saying a quick prayer that Dorman is able to make a plastic part that fits correctly. I recall their cam housing plugs were a little undersized. But this was the unit that shipped for a reasonable price and reasonably promptly.

While I am in there, I am going to change the upper power steering fluid return hose. Think I'll just order some transmission cooler hose. The moulded hose is (a) unavailable and (b) stupid expensive when it is. As long as it is not bent enough to kink, it should be fine.

Stupid plastic reservoir. Stupid me, too.

 

That cam magnet is always the one that fails too. I currently have a check engine light for P0025 on my GL because I don't feel like taking the reservoir off again and messing with that stupid snap ring to replace it. I've found that using a small pair of vise grips to hold/push it and putting a thin wire on it to retain it when you inevitably fail to get it to snap in place makes it somewhat less miserable to replace.

I'm replacing the reservoir on my new-to-me W164 ML550 when I change the fluid and I'm going to preemptively replace that cam magnet while I'm in there.

 

It is a bizarrely bad design. Three screws that are quite difficult to get to, and a retaining ring that holds the reservoir on ... in case the screws are missing?!? I am seriously tempted to not reinstall the ring. Which makes me wonder why I am replacing the reservoir when the only thing broken is the portion of the mount to do with the apparently unnecessary snap ring.

Curious you say the exhaust magnets go bad. I changed the intake magnets, and the bank 1 exhaust magnet was changed by the dealership in a separate repair a long time ago. I only happened to notice the P0025 preliminary DTC when I was noodling with the ECU recently. Ironically, this was just after I had sold the two magnets I had bought but never installed - so I had to re-buy one. In any event, I had the old bank 2 magnet in there for 190k miles without even a prelim DTC up till now.

If you don't want the ring to fly into the neighbor's yard, you can pry it off with a flat screwdriver, with a magnet on the shaft at the tip. It is a trick for preventing valve keepers from disappearing.

 

The screws drive the reservoir in to the point where you can easily insert the snap ring. It is getting it off without letting it fly that is the challenge.

 

So the snap ring does not actually do anything besides aggravate the mechanics.

The crazy part is, the fluid all that rigamarole is holding back isn't even under pressure.

I looked at WIS to see if there were any special instructions regarding the reservoir. Nope, just as one might expect. I wonder if the clip is there as a last-resort backup to stop the combustible fluid from potentially getting on the exhaust.

WIS also notes that air in the steering rack is "very difficult to remove". I am puzzled by this; I would think it would eventually find its way to the reservoir.

P.S. the clip / outlet is not centered in the three bolts. So I guess the clip nominally serves some sort of purpose.

 

If you don't bleed properly, air in the system gets turned into really small bubbles by the action of the PS pump that don't come out of the fluid in the reservoir so the fluid ends up being foamy and compressible. I forget the details of the MB procedure, but the usual method is to elevate the front of the car and turn the wheels lock to lock several times to get all of the air out before the vehicle is started. If you want to be really careful, you can turn the wheel back in forth while cranking with a fuse pulled to keep the engine from starting. Just doing the back and forth worked on my GL when I replaced the PS pump.

 

Perhaps the foaming is the reason the Pentosin ps fluid is so watery.

I discovered a potential reason for changing the reservoir. Apparently some reservoirs include a filter. Mite not be a bad idea to change it, idk.

 

I'm planning to replace it on my newly acquired ML for that exact reason when I flush and replace the PS fluid.

 

I peeked inside the new unit I received. Indeed there is a fine mesh filter inside.

 

Reassembled. All seems well. The replacement washer did not arrive on time, so I reassembled with the old, and Permatex Black. I did not reinsert the clip ring. I am still confused as what engineering fetish specified that clip ring in the first place.

I used a Dorman reservoir. It fit just fine, despite one Amazon reviewer's complaint.

You may disagree, but I recommend changing out hose clamps from the spring type to worm drive whenever possible. They are cheap these days; buy bulk bags of every possible size and you will never be out.

After following the prescribed turning lock to lock with the motor off, I did same with the motor running. I saw some bubbles surfacing in the reservoir afterward.

 

i just changed out a leaky resevoir and i literally broke the old one out with a chisel and a big hammer.
managed to lose 2 fkn c clips which i found require 2 humans to install. one to line up and one to push a big *** flathead

 

if you tighten the retainer bolts first all the reservoir needs is a wee push with one hand, while you insert the clip with the other hand, and with your third hand, pat yourself on the back.

 

I dunno, when I tightened the three bolts, that reservoir was stiff as anything. It's rock solid. I don't see that pushing it would change its position at all.

I am still confused and wondering if I am missing something.

 

The first time I replaced the O ring, I used a pry bar wedged against the ABS module. As beautifully described in this video here.


The second time, and the easiest, was taking out the steering pump and assembling the steering pump and reservoir outside the vehicle and installing them as a unit. You can't believe how easy it is to insert that clip when you can see where it is going. It requires taking out more bolts and nuts, but it is the by far the easiest and stress free technique.

 

I bet this explains the clip! During manufacturing, the reservoir is mounted to the pump, and then the two are installed on motor together.

 

Not the exact circlip, but still accurate: