W123 Skid Plate Install w/pix
 

W123 Skid Plate Installation

The first four photos are in this post. The second post has photos five through eight.

Having crunched an Oldsmobile's transmission on a big rock some years ago, I'm leery of things that hang down in harm's way. :D Reading here of how the W123 diesels lead with their chin (the oil pan), I decided to install the factory skid plate. This item, part number 123 520 03 42, was $132 from Phil (free shipping) and arrived a few days ago.

There were no instructions with the skid plate and none of my books mentioned it. Perhaps there is a Mercedes option manual out there somewhere. Without instructions, I had to use "logic" and "common sense" to figure out what to do. I apologize to all if I have the thing in upside down. :D

I began by jacking up the front of the car (until the wheels were almost off of the ground) and putting the weight of the car on my jack stands. This was just to make a little more working room underneath. There is nothing that has to be removed for this installation (unique?).

Photo #1 shows the underside of the car with the oil pan ready to snag on a high curb. The two red arrows point to frame brackets to which the rear of the skid plate mounts (you wondered what they were for, right?).

Photo #2 shows the hole (red arrow) to which the front of the skid plate mounts. This is the passenger side of the vehicle; there's a matching hole on the driver's side, close to the A/C compressor. The white arrow points to the slot through which you will be reaching to put a lockwasher and nut on the bolt that goes through the skid plate and the hole. This is the challenging part of the installation; the rest is trivial.

It's easier to do this work if someone or something holds the skid plate up in position while you work to install four bolts. I used a bottle jack but a block of wood, cardboard box, small child, etc., could also be used.

Photo #3 shows the skid plate in place with an 8x1.25-24mm bolt through the hole (red arrow). I used 8mm because I had a bunch of them. I wouldn't use anything smaller than 8mm; 10mm would probably be too big. You could also use 5/16" SAE but I don't advise mixing types. YMMV.

The white arrows show the electric clutch wires for the A/C compressor and the place where they plug in. I removed them to make it easier to work. If you unplug this connector, remember to put it back when you finish or your A/C won't work. Yes, the label on the compressor says "Delphi." Blame the PO, please.

[The other red thing in Photo #3 is the aftermarket block heater that I installed in my lower radiator hose (Diesel Giant, $74 including shipping). My car is a California smog version; the plug for the factory block heater can barely be seen, much less removed, so I went this way.]

Photo #4 shows the bolt from Photo #3 (actually it's same thing on the other side of the car) peeking at you through the slot. You must now reach up through the slot and put a lockwasher and nut on that bolt. This is a b*tch of a job; in my younger days I would have thrown more than one tool in frustration before finishing. Here's how I did it.

It's fairly easy to reach up using a pair of needle-nose pliers or a surgical clamp and put a split lock washer on the bolt. Take your time; if you drop the washer, it will probably land inside the frame member and be there forever. Get another one and try again.

[continued]

Skid Plate Installation, part two
 

[continued]

The four photos in this second half of the skid plate installation procedure are numbers five through eight in the procedure.

To get the nut up through that slot and onto the bolt, I used a tool from my previous life in the semiconductor industry. Photo #5 shows an inexpensive tool used to pull chips out of their sockets on a PC board. The left tool holds a chip; the right one holds an 8x1.25mm nut. I added the rubber band to hold the tool closed on the nut.

Using this tool, I lifted the nut up through the slot and held the nut against the end of the bolt while I turned the bolt with my free hand. Once the nut had caught on the bolt, I removed the holder. The slot is just big enough to admit a 13mm box-end wrench and it is then easy to tighten the nut and bolt.

The rear of the skid plate is easy to bolt to the frame brackets with two more 8mm bolts, nuts, and lock washers (Photo #6). Other interesting things in this photo are the hole for draining engine oil (white arrow) and the "drip hole" at the lower rear of the skid plate. Anything falling on the skid plate from above will drip out this hole or the oil drain hole.

Photo #7 shows the finished installation from the driver's (left) side and photo #8 from the passenger's (right) side. It took me about an hour including taking the photographs. Remember to remove the jack stands before driving the car.

Jeremy

So cool, thanks! If you get a chance would you mind posting a photo from in front of and below the car, like a "curb's-eye" view?

This is great and reminds me of the great factory skid plate excitement years ago at TDIClub: http://forums.tdiclub.com/showthread.php?t=37626

Ted

Curb's eye view
 

Here it is. (I had to enhance the photo a bit.) Now what I want to see is someone (like you?) to put a skid plate on their car and run it over a curb to see if it works. :D

Are those available to purchase? Looks pretty cool! How sturdy are they/how much do they weigh?? Would they really hold up under 3.5k lbs of a MB slamming into a curb? I'd install one if they are real strong and worth the effort. :D

Ground clearance
 

The lowest point of the skid plate is the drip thing at the rear center; on my car with new Bilsteins, 212000 miles on original springs, and newer Pirellis on 14" Bundt cake-pan wheels, the skid plate is 6-1/2 inches off of the ground.

I forgot to measure the ground clearance of the oil pan before installation of the skid plate; could someone measure their similar car and post it here?

Update: Clearance without the skid plate, floor to oil pan, is a little over 7 inches, so the skid plate costs you less than an inch of ground clearance.

Looks good but what is involved in removing it to work on the car???

Our SDL had the sound encapsulator and it was easy to remove. I view this as more of a Deepest, Darkest Africa survival panel.

Dave

Excellent. I did not realize these were available. And what a great price.
A very worthy option .

Nice photos too.

What is the red tee coming off the lower radiator hose ?

Removal is the reverse of installation. Four bolts and a pair of 13mm open-box wrenches. For most "work on the car," removal is not recessary. What had you in mind?

Your comparison is apt. The skid plate was indeed built with rough road/no road conditions in mind.

Go back to the first half of the post and read it again, please.

"[The other red thing in Photo #3 is the aftermarket block heater that I installed in my lower radiator hose (Diesel Giant, $74 including shipping). My car is a California smog version; the plug for the factory block heater can barely be seen, much less removed, so I went this way.]"

First oil change after skid plate install - no problems
 

I just changed the engine oil in my 1985 300D for the first time after installing the skid plate. There were no problems.

Since the drain plug is so easy to remove, I had initially planned to do the oil change without driving the car up on my ramps. However, I discovered that there was only a little clearance between the skid plate and my drain pan. So, up the ramp! Then it was easy. The hole in the skid plate is positioned so that you can get either a 13mm box wrench or a socket wrench (I prefer the latter) on the drain plug.

After most of the oil had drained, a little did dribble onto the skid plate but it was easy to wipe off. There was even room for my torque wrench when I tightened up the drain plug with its new crush washer.

Sorry, forgot to take pictures. Next time!

one of my 560's came with a skid plate, you bet i pulled it off and saved it before selling the car :)

Skid plate looks great. But I do have a few questions.

If you hit something hard with the plate what will happen to the points of attachment of the skid plate to the car. Will those attachment points bend or break anything? Will that be an issue if they do bend? If they do bend will the cost of repairs exceed the cost of an oil pan and gasket?

Ron, those are exactly the questions that I hope the factory asked before they designed the skid plate. Clearly, the skid plate is not designed to protect the underside of the car against all possible situations. It is a compromise solution -- oil pan protection at minimum cost in dollars, inconvenience, and weight.

Looking at the underside of my car, I would say in reply, that a hit by something big enough, hard enough, will buckle the tubing frame of the skid plate or bend the skid plate, which will then hit the oil pan. The skid plate, which is 3mm thick steel, will spread the force of the impact over a wider area, as opposed to the lighter gauge oil pan (anyone have a number?), which will take the force of (a large rock?) at one point and puncture or buckle, possibly damaging the oil pump and its pickup.

The result will be a damaged skid plate but an undamaged oil pan. I do not see any resulting damage to the car's frame members, which are even heavier steel, unless the impact is so great as to do lots of other damage. In that case, the damage will be much worse than the attachment points for the skid plate, probably involving tearing of the engine from its mounts. That is beyond my ability to imagine.

Jeremy

Very
 

Very cool my next upgrade I drive a lot of dirt fire roads and know the rock through the oil pan will happen its only a matter of time. Now I have a souliton and something to buy. Thanks for the information
Dave S