606 Belt tensioner shock, Yes, it can be done relatively easily!
 

I was a bit fearful about tackling this job after reading many write-ups on it. The bottom bolt of the shock interferes with the water pump pulley as you back it out. Some said theirs came out OK, others talked about grinding down the bolt to shorten it a bit, but at least for my bolt there was no way to access the end on the engine side to try to file or grind it.

So I just went for it. Pull the fan shroud and the plastic piece it mounts in to give yourself some working room. I then started on the problem bolt at the bottom of the shock, and sure enough, not enough clearance to be able to pull out the shock. So I just started loosening the water pump pulley bolts to enable the pulley to move forward and give that bolt some room. It is a tight fit for a wrench on the pulley bolts, but my 10 mm did fit in there.

To be able to loosen the pulley bolts, you'll have to have tension on the belt, so I just kept the tension on and started two bolts loose, slacked tension and rotated the pulley by hand to access the remaining two bolts, then tensioned again to start them loose. Once they are started, you can slack the belt and rotate the pulley by hand.

I did have some fear about loosening the pulley bolts far enough that they would come all the way out, which would be a PITA because there is no way to gain access to re-insert them. I did about 1 complete turn on each bolt, moved the pulley, and tried the shock bolt. Lather, rinse, repeat, carefully. I think I wound up with loosening each pulley bolt maybe two turns plus a bit to allow the pulley enough room to be able to move the shock bolt enough to free the shock. Just do it a bit at a time and try the shock bolt each time. Patience helps here!

Once the shock bolt backs out enough to free the shock, you're home free. New shock goes in very easy. Installation is the reverse of removal, as they say.

The reason for doing this job was that at idle, my car had a very loud vibration noise which seemed to be transmitted through the structure of the whole car. It would disappear if the idle was increased just a bit. I could see the old shock vibrating at idle together with the pivot arm. Lived with this for a couple months, but decided it was time. Should have done it much sooner, now I have a nice quiet, Benz-like idle!

Rgds,
Chris W.
'95 E300D, 251K

If the vibration returns check the motor mounts. Sounds like you read at least some of my older posts; MM's was where my tensioner problems originated.

Hi Terry,
Good point. I neglected to mention that I had done the motor mounts several weeks ago as the first try to kill the noise, also because I could tell that the car needed them anyway. New mounts made a HUGE difference in the car, but in my case they didn't help the noise/vibration from the bad tensioner shock. Of course the old mounts may have contributed to the shock failing anyway.

Rgds,
Chris W.

You should change the spring as well. Shortly after I did my first shock, the spring went to bouncy heaven.

If that spring goes, you can't drive the car.

Yes, changing the spring is an excellent idea and save the old one for a spare left in the trunk just in case, along with a spare belt.

Also, you might have taken a couple of threads off the end of that bolt while it was out so that next time you would not have to loosen the pulley to get it out. Those shocks only last a couple of years.

Keep the old shock as well, chances are one of the bushes will be fine. When the bush on the new shock goes, you can just push it out and replace it with the good one from the old one.

How a motor mount defect can damage the tensioner?

Just having a vibrating engine will cause this shock to deteriorate more quickly?

Thanks,

You can read my old threads for more data, but indeed,....partially collapsed mounts resulted in heavy vib at the tensioner on mine. I burned up a couple of damper shocks, a couple of spring, stretched out a belt or two and wore out a pivot arm before figuring it out.

With Gilly's help I ran every test imaginable trying to figure which tensioner component was at fault. Finally jacked oil pan up 1/8" using a big rubber bushing and vib was immed gone.

My tensioner shock upper bushing was making a buzzing sound immediately after startup - I believe during the time the glow plugs were energized and the alternator was working harder than usual. I took the shock off to check it out but I had no real problems removing the lower bolt as I remember. I know it did interfere with the pulley but I somehow got around it...