rough idle when warm - 81 300TD

A five cylinder engine is inherently unbalanced - so M-B added a damper to overcome the shaking. Look at the aft end of the injection pump - right where the two oil cooler lines pass it. You'll see a bolt and a lock nut. The bolt is a spring loaded pin called the "rack damper pin" and it does just that - dampens the oscillations of the fuel rack.

You rack damper needs to be adjusted inward a bit. Two wrenches are needed a 10 mm and a 12 or 14 mm for the lock nut. Loosen the lock nut and turn the smaller bolt inward a 1/4 turn at a time and snug the lock nut. Adjust, drive it a bit, adjust again if needed. You can also do this with the motor running or not. Too much inward adjustment will cause the motor to stall. Too little and it will shake as it does now. The last time I adjusted my car's rack damper pin the motor was shaking like crazy and with a 1/4 turn it got quite smooth.

You should also know that there's a "new" style pin with a heavier spring that's sold by dealer for $25 or $30. So first try adjusting the old pin.

Experimented a bit this pm, and it seems to be better. It appeared to be as far in as it would go, so I backed it out a bit. Will keep playing with it !

Thanks!

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Buy a new rack damper pin.

"-->> T.G. Lambach damper pin" and it does just that - dampens the oscillations of the

Make sure your valves adjustments are correct and all other filter maintenance is done before playing with the rack damper.

Tried it yesterday, and it seems to have helped. It was already as far "inward" as it would go, so I backed it out a bit.

THanks

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This is the third mention of filters that I have read today. I was wondering if and when I should change my fuel filters. I've only had the car for about 5 months, but I have no idea when the fuel filter was last changed. (Yes, I have run Startron through it Tiger) It doesn't really seem sluggish, but I can't really tell since it is a diesel. Any recommendations on this? The repair manuals I have suggest once a year, is this frequent enough? What signs should I look out for to let me know the filter needs to be changed?

If you've had the car for 5 mths and don't know when the filters were changed, I'd do it now. They only cost a few bucks. I change mine about every 20K miles on my 300SD and have no problems.

Here is my catharsis on my old diesel........

In my old 300sd I used to change mine every second time I changed the oil and filter (6K miles). We had dodgy diesel fuel in town because not enough people used diesel at that time. If I bought my diesel on the interstate at a truck stop where there was more usage and the diesel did not sit in tanks for as long a period of time, the fuel filters did not need changing as much. I would also blow out the air filter with an air compressor and rotate it 180 degrees, and check the banjo fitting, throttle linkages and little micro switches on top of the valve cover as well. I only used Shell Rotella oil and Mann filters.

Every third oil/filter change I would adjust my valves and replace the air filter.

Every fifth oil/filter change I would change the transmission fluid and rear axel fluid.

This schedule along with keeping an eye on motor mounts and replacing them as necessary kept the old girl (Stella, my streetcar....) running smoothly enough to stack wine glasses on the hood and she started everytime.

Back on the old Mercedes mailing list, Stu Ritter had a tweak to adjust the ALA compensator for the turbo charged models. It is a very delicate adjustment that allows the altitude compensator to inject more fuel (basically adjusted by Bar) and the turbo to kick in a bit earlier (as I remember). The problem with the adjustment was that if you turn the screw to far you broke a little ceramic bit in the ALA and trashed it (expensive). I performed the adjustment on my car and noticed a fairly remarkable increase in power resulting in a slight increase in exhaust soot and a slight decrease in mileage. Later I backed it out. YVMV, and I do not recommend the change.

I also made sure all of the throttle linkages had the correct measurements in mm (yes there is a spec on that and it is important), replaced the Rack Damper spring with the stiffer one and made sure it was in synchronization. adjusted the transmission modulator to the point of a reasonably stiff but not head snapping shift (better transmission life), and replaced the flex disks, motor and transmission mounts. The cruse control amp needed resoldering, and the tachometer amp/sender needed replacing once. I also replaced the plastic bushings on the rear torsion bar that cause that annoying thump when going over bumps.

That is about it other than tires, belts, brake shoes/rotors and brake fluid, glow plugs, a battery, wiper blades and washer fluid. Occasionally I needed to take the console switches out and clean them too, when the fader control messed up the radio because I spilled coffee. I also often needed to either replace or clean fuses, especially in damp weather.

All in all that car ran pretty much flawlessly and lasted seventeen years and almost 300,000 miles before I sold it (as far as I know it is still going) for $4000.00. It did not use oil, the transmission still shifted crisply, although it was getting a little slow going into reverse.

No mcbrue, it never left me by the side of the highway and Hanz and Franz never got their mitts on my car. I found a good honest Mercedes diesel mechanic locally and he could always advise me or do stuff on the car when I was too busy or it was beyond my competency. Yes the rexus is probably less effort, but as you point out, not nearly as much car.

me

- driving over the bridge with the trailer under it down by the river.

A nice encapsulation of how to keep the old gals running. Thanks for sharing your experience. I'm due for a weekend under the hood, and will take a look at all of the items you've mentioned. I'm due for fuel filters (have a K&N air filter). Wouldn't have thought of throttle linkages - do you have specifics?

Also, the thought of the valves isn't overly daunting to me - something a decent shade tree mechanic should be able to accomplish?

TIA

tweaks

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Adjusting the valves with the correct tools helps:

The 2 bent ones are used together to loosen and tighten the lock nut and top nut. The middle one keeps the valve from turning.... you don't always need it but boy, when you do need it you need it!

HZ 2769 Set here:

Not cheap, $99.00 but good to have.

More information at

A great synopsis of what it takes to keep the old gals running! I'm thinking I'll take the plunge and try the valve adjustment - invest in the proper wrenches, etc. They probably don't cost as much as having it done for me, eh?

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