300TD Hot Idle Shaking - apparently solved - Page 3 - PeachParts Mercedes-Benz Forum

Luis448 · #31 06-28-2005, 06:48 AM

Hi ! I have been reading about your vibration problem.
I have the same problem in mine.But I have been said by an expert in Bosch pumps that the problem is the governor.It seems to be that this is a weak point in this mercedes turbodiesels.Note that this problem doesn ´t appears in the 300 D non turbo engine ,so apparently the 5 cylinder is not the fault.

Quote:

Originally Posted by surfblau

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.

Symptoms:
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.)

In summary, ENGINE SHOCKS MATTER.

I hope this helps someone like me in the future....

Gil · #32 10-07-2006, 08:43 PM

I just did my engine shocks at 258k miles; thought there would be more of an improvement than there was, but it did help a little. Still a little disappointed, though. Must be something else causing the idle shakes.

The job was not difficult. I did not replace the motor shock mounts or rubber bushings, not sure if that would have made much of a difference. Anyway, started it up and noticed an immediate improvement, but after driving a few minutes, then stopping at a light, noticed much of the idle shake was right back again -! The old shocks had some resistance left, but no rebound at all. I figured this was worth a shot as it wasn't too expensive and hadn't been done on my car. Not sure how much motor mounts would improve the situation, but that's probably next. No idea of the difficulty level, though.

AdvisorGuy · #33 05-12-2008, 12:39 PM

So let me get this straight cuz I've been doing some searching myself. If the idle is fluctuating with the engine shake, culprit is the rack damper bolt or adjustment but if it's a hot shake only with no dancing idle, most likely culprit is motor shocks/mounts ? Thursday,Friday and Saturday when we had temps in the 90's, I was getting the hot shakes but steady idle.

Dionysius · #34 05-12-2008, 03:11 PM

Excellent thread. One comment.

Should not the logical first step in such an investigation be a compression check at the engine state as close as possible to the problem conditions. So a test at hot idle would be your starting point.

I believe that if the cylinders are not within a good measure of each other (within 10% from max to min) one will always have some vibration. The MB designers are tight lipped on what is the acceptable variance when snuffing out vibrations.

Diesel911 · #35 05-12-2008, 04:23 PM

Quote:

Originally Posted by surfblau

300TD - om617 Hot Idle Shaking - apparently solved

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.)

In summary, ENGINE SHOCKS MATTER.

I hope this helps someone like me in the future....

This may not work for all 5cyls engines. About 30 days ago I changed my Motor Mounts and did not install the Engine Shocks while I waited for 1 new shock to arrive UPS. During that time it still exibited the smooth idle with a cold engine and shaking after driven 20 min. or so hot. Meainig there was no Engine Shocks to heat up.
Putting both shocks on after the new shock arrived did reduce it a little.
I had ask the question on one of the other threads if anyone knew the reason why the engine runs smooth cold and rougher when hot. I still no resonable answer. Also, I have done that whole list of stuff that you did and did my 2nd valve adjustment and installed rebuilt injectors within the last 60 days.

Diesel911 · #36 05-12-2008, 04:30 PM

Quote:

Originally Posted by Palangi

I think I read somewhere that only the 240D's with automatics have engine shocks.

If this is true it brings up a suspicion that I have. I have been thinking that maybe it is something in the automatic transmission that is getting hot that is causing the shaking at idle when the engine is hot.
Is there anyone out there with a stick shift 5 cylinder 300D? Do you also have more shaking at Idle when your engine is good and hot?

Diesel911 · #37 05-12-2008, 04:39 PM

Quote:

Originally Posted by surfblau

The engine shocks (if you have them) are near (probably in front of) the motor mounts.

alec

On my 84 300D you need to jack the car up to get under it but do not need to jack up the engine to remove or install the Engine Shocks. The bottom rod of the Engine Shock has 2 flat spots so the you can put a 7mm open end wrench on it to keep it from turning. If the rod turns it can unscrew from the piston inside of the shock, the rod will come out and the oil will come out of your shock (guess how I found out) and you will be buying another engine shock.

AdvisorGuy · #38 05-13-2008, 08:56 AM

I'm leaning towards engine shocks on mine. In my attempt to undo the left motor mount 2 months ago to replace the cooler hoses, I loosened the left shock. When I tried to button everything back up, it just spun. I tried a pair of vice grips on the piston but it still spun. I then set the vice grips on the body of the shock and I was able to tighten the top nut. Maybe that led to weakening/failure of the left shock.

Bajaman · #39 05-13-2008, 09:03 AM

Quote:

Originally Posted by Diesel911

If this is true it brings up a suspicion that I have. I have been thinking that maybe it is something in the automatic transmission that is getting hot that is causing the shaking at idle when the engine is hot.
Is there anyone out there with a stick shift 5 cylinder 300D? Do you also have more shaking at Idle when your engine is good and hot?

Yes, I do.

Diesel911 · #40 05-13-2008, 11:31 AM

Quote:

Originally Posted by Bajaman

Yes, I do.

Thanks for answering; another theory down the drain.

777funk · #41 05-13-2008, 12:11 PM

Not to be a little skeptical but as someone else said, the engine shocks don't know whether or not the engine is warmed up. If it's smooth running when cold and shaky when hot, I don't think the engine shocks are to blame. Again, they are shocks so they may take some of the spring out of the engine shaking but if it's loping the problem is just being masked by new shocks.

That said, my 124 300d (87 car with a 603) is quite shaky at hot idle. And there are NO engine shocks on this engine. Just the hydraulic engine mounts. One thing I have noticed is that when I ran out of fuel one day (after working on the fuel tank level sender) I dumped all of the burnables (motor oil, trans fluid, etc.) I could find into the tank to get to a gas station. The car immediately idled as smooth as a top. Then when I filled it back up on diesel about 20 miles later, shaky as could be once again. I wonder if it's IP timing. The oil is probably slower burning than diesel is. Maybe Ultra Low Sulfer Diesel?? Who knows. But somewhere we're getting a lot of 20 year old MB's with a shaky hot idle. I had mine timed by the dealer about 6 months ago. I still wonder if it's right. The diesel exhaust smells different than it did before the timing was done. The dealer did it so I'm sure the guy had the right tools and I trust that he's done enough. But one thing I do wonder is this... the harmonic balancer needle has a screw on it that allows it to slide left or right by a few degrees. This means if someone messed with it at one point, the mechanics bearing could be off by a few degrees in timing. So... that makes it really confusing to know if it's right or not. All I do know is it runs perfectly smooth on slower burning fuels (WVO, and motor oil).

pawoSD · #42 05-13-2008, 12:51 PM

My car has a shaky idle, our other two do not. Oh well, it doesn't bother me that much.

Dionysius · #43 05-13-2008, 04:55 PM

Quote:

Originally Posted by Dionysius

Excellent thread. One comment.

Should not the logical first step in such an investigation be a compression check at the engine state as close as possible to the problem conditions. So a test at hot idle would be your starting point.

I believe that if the cylinders are not within a good measure of each other (within 10% from max to min) one will always have some vibration. The MB designers are tight lipped on what is the acceptable variance when snuffing out vibrations.

Let me sell you my theory as something to be first considered since it can save cost and trouble. Let us assume that the head gasket has a slight leak between two adjacent cylinders. Engine will start and run but all of the tea in China will not remove the embedded vibration since the anti-vibration design (engine shocks and mounts and balancers) is/are not qualified to eliminate it. The engine shocks and mounts mainly suppress vibrations in the body vertical plane. They do little or nothing for lateral vibrations (vibrations in the body horizontal plane).

europower · #44 06-11-2008, 06:44 AM

I have a 84 300d with a terrible shake,i just did the motor shocks,found that they were almost gone they were so old,however car still shakes and seems to kind of go put put at iddle,ok at higher rpms but i dont know what could be the problem,the previous owner got it some new injector nozzles and a set of shocks but obviously still no repair.
Any suggestions of better diagnostic ideas from anyone here?
TThanks

nhdoc · #45 06-11-2008, 07:06 AM

Quote:

Originally Posted by europower

I have a 84 300d with a terrible shake,i just did the motor shocks,found that they were almost gone they were so old,however car still shakes and seems to kind of go put put at iddle,ok at higher rpms but i dont know what could be the problem,the previous owner got it some new injector nozzles and a set of shocks but obviously still no repair.
Any suggestions of better diagnostic ideas from anyone here?
TThanks

How are the motor mounts themselves? You need good mounts and shocks to properly damp the vibrations.