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Old 08-08-2002, 02:44 PM
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surfblau surfblau is offline
neue Dieseler
Join Date: Feb 2002
Location: san francisco - immer kalt, immer windig, I want to move
Posts: 382
300TD Hot Idle Shaking - apparently solved

300TD - om617 Hot Idle Shaking - apparently solved

So I have been using this board for several months to fix up my 1984 300TD, and things have been really working out. One elusive problem that I have been working on since day one is a moderate to severe shaking at hot idle only.

Shakes (sways in the engine compartment, harmonically, side to side, wide osscilation) at hot idle in park or in neutral at 600 rpm.
Completely smooth in any gear at 900 rpm.
Runs smooth at cold idle at any rpm.
Always starts easily.
Never smokes.
Always idles smoothly (rpm wise), never hiccups, stalls, misses, etc.

In short, everything was perfect except the sometimes violent shaking that at times seemed to be lifting the wheels off the ground.

Based on what I could read on the board and what I could find out from other people around town, here is what I did in order.
- Changed motor mounts (one was 50% pancaked- no real improovement, but everyone says this is the first thing to check)
- Changed transmission mount (no real improovement, but learned the importance of liquid wrench)
- Changed the front shocks (I did this unrelated to the hot idle, but figured that there was a snowballs chance of helping - it didn't)
- Adjusted valves (no real improovement, but got a little more power and mileage)
- Diesel purged - twice (idled smoother, but still shook)
- Injection pump governer screw (rack damper screw) replacement (the new gold one) (no change, but could make the problem worse if I wanted to). Current adjustment is all the way in which seems as though it should not allow startup, but it starts easily
- Biodiesel - 2 and 10%, seemed to help one time, the other time had no effect
- Injection pump delivery valve seals - made problem worse, which was interesting, probably because of crud in the valves getting liberated into the injectors
- Injector testing - all had the correct opening pressure and spray pattern, testing was done by Gus at Pacific Injection who gave me some ideas on this post

At this point I was getting fustrated and was pondering
- compression test
- IP timing check
- IP replacement (in fact, I got a used one on ebay as a contingency ($50), but Gus (who has somewhat of a legendary reputation in injection pumps- and drives a 300CD) said it would be very unusual for that IP to ever need maintainence, and that a rebuild and bench test would cost a lot and probably not work in the end because when installed back in the car, his experience was that the car would continue to shake. There are just a lot of variables in the system)

Before I went that route, I figured that I would change the engine shocks. The techs at the dealership didn't think that they would matter and thought that they only affect shut down, but weren't too sure. The board here doesn't really talk too much about them. No other sources I could find seem to say much about it. Furthermore, when I was changing the motor mounts, I unbolted the shocks and they appeared to have at least some resistance, which is all the dealer techs said that they needed.

As a side note, Gus said that the 5 cylinder engines are notorious for having problems with resonance and shaking because of their design. This got me thinking that the shocks function was at least partially to dampen the ossilations of the 5 cylinder engine.

So I changed both engine shocks, but not the shock mounts or external rubber pieces.

And the shaking is gone, though there is still some vibration, but it seems fairly normal.

Both old shocks had only resistance to finger pressure, and had a grinding sound on compression or extension.

My guess is that at cold idle, the shocks still provided some resistance, but after 20 minutes of driving, the heat thrown off by the engine reduced their shock absorbing ability and the engine ran with it. Wide ossications were the result. ( it could still be a compression problem, or the IP could be crudded up, maybe someday when I have a garage I will get around to tinkering with it more.)


I hope this helps someone like me in the future....
84 300TD - 235k - Farbe "Surfblau" bought at 213k
87 300SDL - 131k - Farbe "PimpGold" bought at 115k
00 Klepper Faltboot Expedition Double

Last edited by surfblau; 09-26-2002 at 01:21 PM.
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