300sd shakes when at a stop or in park
 

I am sort of new to this site, so please forgive any stupidity on my part. I have a 1982 300sd with 250k miles. Just had valves adjusted by mechanic. Car is shaking from side to side while in park or at a stop light. Do I need to replace the engine mounts? I doubt they have ever been replaced. I assume the engine vibration is transferring to the rest of the car. Also the rear end is sitting a little low. Should I think about replacing the rear springs and if yes, then which ones? Should I go back witha heavy duty spring? Would appreciate an honest opinion from someone more knowledgeable than myself. Love my car. Thanks.

Welcome

Shaking could be engine mounts, could be rack dampener. Using the "Search" function will yield a lot of threads that discuss both possibilities, and symptoms.

Rack dampener adjustment is the quickest and easiest, even if the part needs to be replaced.

Also, try posting this in the "Diesel Discussion" Forum for a broader range of advice.

Best Regards,
Jim

I'd post the question over on the diesel discussion where there are lots of guys and gals who drink diesel for breakfast.
Did it shake before the valve adjustment? If it didn't, I'd suspect a mistake in the adjustment.
I'd also run a can of diesel purge thru the injectors, following the directions to run on pure purge. Don't just put it in the tank.
Could also be a bad injector.
I wouldn't change the engine shocks before exploring these other possibilities.
Can't help on the suspension question.

If the engine mounts are original, the answer is an unqualified yes. The mounts need to be replaced. While you are at it, you need to check the engine shocks as well. After 20 years, they frequently will compress easily and will NOT provide any damping for the engine vibration.

If the springs are original, then they are typically soft by now and need to be replaced to obtain the proper ride height. Heavy duty springs are a matter of personal choice. The heavy duty springs have a stiffer spring rate and will offer a stiffer ride, however, they will be less sensitive to the amount of baggage in the trunk or the number of people in the vehicle. They will also last longer than the original springs because they start with a stiffer spring rate. My personal opinion is that the stock springs are more than stiff enough, however, other members have installed the heavy duty springs and are pleased with them.