DIYing*** – A Cautionary Tale In Car Repair

(in the introductory voice of Rod Serling)*

This all happened probably 20 years ago, but when I detailed my tribulations to a now-defunct Mercedes-Benz internet list, I achieved my Internet 15 minutes of fame. I was known far and wide as “that guy”. I have, for much of my adult life, derived some pleasure and satisfaction in fixing things on my own cars – starting with my 1967 Camaro back in the late 60s.

But lately, with my accrued years, I am seeing the wisdom in letting a pro, with the proper training, tools, and a lift, just do the job.

This attitude started, I think, when I changed the motor mounts of my 1996 Mercedes SL500. The car was on jack stands, I am on my back for a week cursing all the junk I had to get out of the way, just to replace a simple motor mount secured by 2 small bolts on the bottom, and one bolt on the top. And of course, with it all apart, you aren’t going to throw the parts in a box, tow the car with your tail between your legs and plead with a shop to fix your mess! You are committed to finish it one way or another!


I was saving close to $1000 in labor costs! These days I think I’d be glad to let someone with the proper tools do it.

Today’s cautionary tale involves another set of motor mounts on another car. It was a 1986 Mercedes 300E. There was no “junk to get out of the way”, being a simple inline 6 cylinder engine, just a stubborn bolt that would not move.

For starters.

By the way, the reason these had to be changed is that Mercedes has fluid-filled mounts, to cushion the vibration of the engine and over time and miles, that fluid will dissipate. When you notice a vibration at idle, that is usually a good sign that they need replacing. I can’t speak for the rest of the automotive world, but I believe most of these mounts are solid – rubber?

The story starts innocently enough. I was going to spend a Saturday morning and do a simple job. I had read the factory manual, had my tools ready, had the car up on jackstands, and was ready to go. Should have been an easy job – the mounts, which held the engine off the subframe, were clearly visible on each side of the engine, didn’t seem bad for access.

This was the job where anything that could go wrong did go wrong – with a vengeance. 

After I read the manual, I put the car up on the stands and raised the hood to a full vertical position, as per the manual.

Mercedes have 2 positions on the raised hood for easier service – regular and full vertical (90 degrees). With the hood at full vertical, mechanics do not have to stoop under the hood to work on the engine.  

I then opened the garage door.

This was the first sign of trouble, when I saw the door was going to catch the now full vertical hood, and I am running to hit the button to stop it’s march to destruction . Like a slo-mo segment in ABCs Wild World Of Sports, I see the door catch the hood and push it back to a place it has never been. Fortunately only the hood hinges were bent. 

Now this might have dissuaded a normal person from continuing, but people over the years have maintained that I am not normal. Say of that what you will.

If I had been actually thinking, rather than simply following the manual by rote, I would have known that the reason they wanted it to the full vertical was to make it easy to lift the engine up from the top. I was going to push it up from the bottom as most do. A piece of plywood on the oil pan to keep it from deforming and use a floor jack on that plywood to lift it ever so slightly (an inch?) to remove the old mounts and install the new ones.

I started to undo the bottom bolts to the motor mounts. Unfortunately these were the original internal hex-bit design** , and because of a bit of rust in the threads, that bolt wasn’t moving.

I tried using a 6’ pipe for leverage (you know because if 2 feet is good 6 feet has to be better) 

All I was doing was galling*** the hole where the Allen bit went. The hole was eventually so torn up that I learned that I would have to drill it out.

Learned about carbide bits that could drill through steel, and had to drill the !@#$%^&*’s out. Hours and hours doing that. 

FINALLY replaced the mounts, lowered the car and made an appointment with the body shop to fix the hinges next morning. 

Came out next morning and the left rear tire is flat. 

Used the factory jack, raised the thing up and on the smooth garage concrete the jack slipped., The car came crashing down and the wheel missed my foot by an inch or so. 

Finally got the tire changed, tied the hood down with rope making the car look like something from the Beverly Hillbillies, and went to the body shop, where they fixed (replaced) the hinges. 

I arrived to pick up the car, and it wouldn’t turn over. The battery chose that particular moment to give up the ghost.  It worked for the people at the body shop, but apparently wouldn’t work for me. And this was a premier Optima battery, 7 year guarantee, that was 2 years old.

Spent the rest of the afternoon getting a new battery and hitching rides. 

BTW the factory realized their error and updated the motor mount bolts the following model year with the conventional type (shown on the left).

Thus endeth the lesson.

** As I have gotten older, I have come to the realization that some younger people have no idea what I am occasionally talking about. Maybe more than “occasionally”! Which probably includes Rod Serling. He was a screenwriter who was behind one of the most creative shows of the 50s – the Twilight Zone. With commercials, he had about 20 minutes to develop a story with an unexpected ending that would knock your socks off. He would always begin with an introduction to each show. Here are some samples of that introduction .

*** Hex-bit (or Allen) bolts. For decades, Daimler used these in many of the car components. I know of no other manufacturer who used these so extensively. And they really had no advantage other than perhaps manufacturing efficiency. They were actually worse than a conventional 6-sided bolt, because a socket will securely grip those sides, whereas an Allen bit can tear up the hole if the bolt won’t move (as I learned). I had heard, years ago, that after the war, they simply had a huge inventory of Allen bolts, and used them from the 50s. Although I don’t know if there is any truth in that.

Today, for manufacturing efficiency (and making life easier on the factory robots), they use primarily internal Torx and occasional external Torx). (think male and female).

**** DIY – Do It Yourself

05-01-2022 many on the Facebook group wanted to give me suggestions as to how I could have removed that bolt other than drilling it out. IIRC The head was round. You had to use an Allen bit inserted to tighten or loosen that bolt and with the hole for the bit torn up there was nothing left to do. And as I had mentioned the factory had changed these bolts by the time I re-ordered them so they were already getting feedback from shops.

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