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.

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....

Wow!
Thanks! I think I'm gonna replace my engine shocks too!

Are there engine shocks on an 82 240D? I've never seen anything like that, just the engine mounts, but I'd be interested if they are there!

Thanks!

surfblau
 

Wow! I would have NEVER guessed they were that important. I thought they were only for when you shut the engine off and the ensuing vibration thereafter. This post is going to help a lot of folks. Hey, if we were college budies, I would have moved you up to #1 on the speed dial for this one!!

Question. you show you replace the govenor screw? I am thinking this is the rack dampner screw, on the back side of the injector pump.
Good news on the engine mounts. I will be changing mine out soon. Get a little shake on the 78 300D. And I thought it was just old age.

yup
 

For me, governor screw = rack damper screw.

The naming issues on these cars sometimes get pretty bad. I am looking to do my "subframe mounts" on my 126 this weekend. Depending on which post, they are called

front rear subframe mounts (or bushings)
differential mount (or bushing or carrier)
rear (or back) subframe mount
etc.

Lots of nomenclature for two donut sized pieces of rubber and a brick sized rubber/metal frame. Just plain confusing.



Like I said in the post, most people I have talked to think that these shocks are intended to prevent sudden loads to the engine mounts, like during ignition and shutdown. I don't think the guys in d-land had that soley in mind when they designed the engine mounting system.

With regard to the presense of shocks on a 240. I don't know. If you have them, they will be attached through the engine carrier (the wing from the engine that bolts to the motor mount) near the engine mount. You can see them from below the car looking forward from behing motor mount (which should be an easy landmark to find).

later

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

Excellent run down. You almost sound like a doctor dealing with an unknown disease. But the result was worth the trouble I guess!! Nice work Surfblau.

I have very similar symptoms, will check the shocks on mine too. Thanks

MVK

Engine mounts took a great amount of " torque shake" out of my engine (or rather off the frame) during acceleration and a little at idle also. I am very curious to see if your subframe mounts make a difference. Please keep us posted.

wagging at idle 300 td
 

Great post. I too have a shaking 300, side to side only at low idle, but mine does it when cold as well. Were you exagerating when you said the wheel almost came off the ground?
People have also told me that it's the injectors. Thanks for saving me great time and effort. bowlcole

my shaking was pretty extreeme
 

My shaking has pretty much disappeared. Yours could very well be injectors, or worse, differential compression. Or rack damper.

The easiest possible fix would be to drive it very hard (flooring the accellerator) every chance you get. After 10k miles, you should see some improvement.

This is the so called italian tune-up, and it seems to work over a period of time, especially when everything else is eliminated. It all depends on your desire to get covered in grease.

alec

Surfblau,
Great color on the mount shocks. My local tech told me they were for shut down only but obviously he was not entirely correct. I wonder if the shocks help only with violent shaking or if it helps with the more minor stuff too. By the way, my new, gold rack pin dampener screwed in all the way and I could still start up without a problem just like you. On cold days though I found it took longer to smooth out on my morning startup so I backed it off about 1 turn. It still runs smooth and seems to be better at cold startup. For fun you might want to back yours off a turn and see what happens. No harm done if you just end up screwing it back in.

surfblau, what an intersting chapter in the life of your 300TD.
(You want to sell me the old parts that were good after all... ?)

Say I just saw Gus yesterday too! He is a rare resource isn't he?

Wanna hear my story? I had the IP for my TD (well, one of them) rebuilt by Gus last year. He did an asolutely beautiful job, complete with a computer print out of the performance, idle to test RPM, in multi-color bar graph form. Plus I got to see him doing his magic on a pump calibration station!

After installing the IP I always thought it was running rough, it had a slight loping when the engine was hot (OK cold) and a high idle speed too.
I wasted a can of Lubro Moly injector cleaner, finally changed injectors, installed another rack dampener pin (warranty by Gus), and a few other things I have intentionally erased from my mind.

The mechanic who installed it had said he couldn't adjust the idle speed down below about 920 RPM, which didn't really matter much until I had him install a new rebuilt transmission (due to a sudden surprise when the existing one locked up in low gear - another story!!) Now, the new tranny came up with a new torque converter which has a higher lock rate and caused the car to creep or maybe I should say, accelerate rather violently when the brake was released in gear. Clearly 900+ RPM was no longer acceptable, back we go to the drawing board.
Just as the mechanic said, adjusting the idle speed control made no change. So I go to see Gus for a quick consultation. In under ten minutes he showed me the workings of the IP and suggested that first the linkage between the IP and the rest of the throttle rack be disconnected to see if the idle speed or roughness was affected.
He also informed that if the rack damper pin was adjusted "in" too far, the idle speed would be excessive.

Voila! First the linkage to the IP was removed, and it was noted to be a little too long, causing the throttle to be pressing towards shut off (this is the same as pressing the manual shut-off button) and the damper was turned out slightly. Clearly a lash-up snafu.
Now the engine idles properly and smoothly and the mechanic gets an "F" grade.
Maybe we have passed each other on the freeway and didn't know it!
Dieseldiehard
'71 220 (gas) 4-speed manual "present project car"
'79 300TD w/ '85 turbodiesel engine
'83 300D
'85 300TD

You da man
 

This make total sense Surfblau. Thanks for laying it out so well, but aren't the mechanics supposed to tell us what's wrong.

aren't the mechanics supposed to tell us what's wrong
 

Welcome to the group, 85turbosd.
Many of us here are shirtsleeve mechanics, weekenders, or DIY'ers that like to work on our own cars or have a mechanic do a specified job. I can't speak for everyone on here, but over the years I have been taken advantage of by shops that wanted to shotgun a particular problem, or worse yet pad the bill by performing some work that wasn't necessary.
If you trust a mechanic (I mean you know him well!) its probably OK to let him tell you what is wrong. To walk into an unknown shop and let them tell you what is wrong is open to ones own expectations. Some problems seem simple at the outset but turn out being rather complex in the end.
I am not faulting mechanics in particular as its often the shop manager or owner that drives greed, or in some cases doing a "better" job is what they set out to do.
Anyhow, one can get a lot of satisfaction figuring out on their own what is wrong with their car and fixing it without going overboard, and usually saving some money in the process.
At least an individual in this situation has no one else to blame when errors are made.
Dieseldiehard
1971 220 (gas) 4-spd manual 102600
1979 300TD w/ ’85 turbo engine 287690
1983 300D 234200
1985 300TD 202,820

Interesting write up, I wonder if really bad motor mounts with good shocks would manifest the same symptoms?

Heck, I'm mine own worst enemy at times! Being a mechanic, (just not on cars) I have pretty good troubleshooting skills. BUT...., My employer does not actively discourage shot-gunning, and readily supplies any and all parts needed, as they want things fixed, and they are very adverse to taking risks.

When I don't forcefully change my mindset prior to working on my own vehicles, my wallet quickly feels the pain!

On the issue of outside opinions, it would seems so much of working on and troubleshooting vehicles is tactile, it's hard to fault someone for bad advice on something that they have not seen/touched, plus they need to make a living as much as the next guy.

Gotta Go, I have a big box of assorted parts to install, err, I mean return for a refund. Mack

Mack, interesting topic, a bit off the original re: motor shocks.
I agree that the shotgun approach covers some improvement in the general worth of a car, so that is not bad if overall reliability is improved as a result. Assuming the owner will pay for it, some won't.
I had a fight with the Saab people, I even called the US rep to look into the issue over a transmission cluster that came apart just out of the 1 year warranty, that was the last new car I ever bought! They agreed to split the labor ($800 in 1972!). The factory had an improved locking washer, the type that has several ears that fold over the hex on the big nut that secures the end of the cluster. Of course they never advise of this in a recall or anything. I found the truth from talking to the mechanic, who I had buddied up to over the year that it was in and out of the shop. The manager found out he had told me of the improved locking device and I think he caught hell. I sold the car and chalked it up as a SAAB Story, LOL!

But I have to add, that if a "shop" mechanic tried one thing, that didn't fix the problem, then tried another and so on until they "hit the source of the problem" I can assure you they would not normally then spend any time uninstalling the previous work that was uneffective. It is a way of life in the fast lane here in the US. I suppose in other countries that may be different as labor is much less, and the scarcity of parts might be an issue.
If you read the fine print on some service agreements it probably adresses this issue.
OTOH, a weekend mechanic on his own ticket can do whatever he wants - especially if its their hobby car or one they don't drive every day.
Oh, here I am wasting time on the keyboard (my second job) I Need to change the MSD ignition out in the 220, and the Weber (BBQ) becons.
BTW I wish I were out at Lake Travis watching the skinny dippers, do kids still go up those chalk lined river beds and drink beer on a hot day? (how do I know? - I spent one summer in Austin on the UT campus when I was 18. That was before they called it UTA.) cheers!
Dieseldiehard
1971 220 (gas) 4-spd manual 102600 current project.
1979 300TD w/ ’85 turbo engine 287690
1983 300D 234200
1985 300TD 202,820

Can anybody help?
 

Aloha,

Would like to change both motor shocks on my 116 (1980 300SD). Have not done this before. Is there anybody who can, and would like to give me a run down on how to proceed? I'd love to have your input and instructions.

Appreciate it,

easy
 

I think on your engine, all you do is unscrew the retaining bolt on top and bottom of the shock. You will need an adjustable wrench or a 7 or 8 mm open end wrench (better) to keep the shaft of the shock from spinning as you loosen the nylock nuts on top and bottom. Access is bad for the passenger side shock- you will probably have to do it all from below. Start with the driver side. You probably don't need to jack anything unless you want more access.

Last week, I was planning on replacing my engine shocks (on my S class), but when I got them off, they had plenty of resistance, but the mounts were either broken or cracked. That is, the mount that holds the engine shock top to the engine arm. That may not be a part that is used on your car.

IN OTHER WORDS, IT IS EASY TO CHECK THEM TO SEE IF THEY ARE STILL GOOD BEFORE YOU BUY NEW ONES AT AROUND $50 EACH!

I removed the shocks and the shock mounts in about 30 minutes total. Not too tough.

There is a more complete outline in the factory CD if you need it.

alec

Where exactly are the shocks? I haven't seen them on my 300SD.
Thanks
David

location
 

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

alec

I have same symptom of rough idle when hot. Is changing the engine shock difficult? Do I need to jack up or support the engine? Thanks for any tips.

can't remember, but the manual will say
 

I think that it is just loosen at the bottom and top and remove.

I just changed the shock mounts on my s-class and it went really easy. Use a small (7 mm?) open end wrench to hold the shaft or the shock to keep it from turning.

Remove shocks and test to see if they offer smooth and steady resistance before buying new ones. There is a chance that your shock mounts are broken also.

Before you do anything else, check the motor mounts and the rack damper screw and the valves....

The 84 300SD I am considering also has this severe shake ONLY at idle. However, from the sound of the tailpipe- it has a "miss" sound to it. Someone else said it was that "rack damper screw". I just want to know if it is something that is not going to cost big $$ to repair, before I but it.

it has a "miss" sound to it
 

Odd, that sound might be a symptom of an injector problem or IP problem or valve timing or . . . .?
I'd have the valves lashed if its time.
The rack dampner will not cure any engine problems, it only smooths out the idle to prevent "loping"

Dieseldiehard
1971 220 4-spd manual 104646
1979 300TD w/ ’85 turbo engine 290820
1983 300D 238890
1985 300TD 207980
1976 300D (still waiting to see what it needs to get running

Re: it has a "miss" sound to it
 

What is "IP"? I am dumb when it comes to Mercedes.

The IP is the main thing that makes the engine tick in a diesel, its the Injection Pump. There are rubber seals in it that after a long time start leaking instead of putting the identical pressures into each cylinder they give some cylinders more fuel than others. This is not something that can be rebuilt outside a fully equipped Bosch repair shop (go ahead someone will say it can be done at home...?!)
DD

injector delivery valves
 

(all of this is from memory, so don't quote me too much).

I don't think an 84 SD has too much rubber in the IP, on the top are delivery valves that are seeled with copper washers.

However, the 86 and up SDs and SDLs have rubber and copper washers on the delivery valves of the IP.

All are changeable by an average DIYer and may help this problem, especially if there is leaking fuel from the top of the IP.

The real guts of the injection pump are another matter. But, it has been said several times that injection pumps themselves really don't often or ever fail.

alec

injection pumps themselves really don't often or ever fail
 

Yes, but they slowly get out of spec, and cause an engine to "lope" - why else woud Gus have so many to rebuild over at Pacific Fuel Injection in South San Francisco?
Dieseldiehard

when I last talked to gus,
 

when I last talked to gus, he said it was basically a waste of time to rebuild the IP in a 60x or 61x mercedes diesel. He said that you could get the IP to spec on the bench, but the likelihood was that once you put the IP back in the car, the problem would not be cured. He said there were just too many other variables on these old cars. If anyone out there thinks a new - used IP is the cure to their problems, I have a functioning one from an 84 300D all boxed up and ready to go.

alec

Mercedes 300 Sd Vibration
 

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.

Just did mine - a little improvement
 

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.

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.

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.

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.

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?

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.

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.

Yes, I do.

Thanks for answering; another theory down the drain.

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).

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

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).

300d shake
 

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.

300D shake
 

My 1990 300D shakes pretty good when warmed up--I changed the motor and trans mounts. As far as I know, my car doesn't have engine shocks, or am I wrong? :o

85 300D here. 270,000 miles. New car for me. Shakes at hot idle. I checked compression -- 395/400/400/375/410. That is great. Put new bosio nozzles in it. The old nozzles popped at 133 bar and spayed well so i kept them. Was not expecting them to be so good. I'll try rack damper bolt tomorrow. This is a great thread.

I hope it apply to gasser SEC as well, I also got hot engine shake. Will try and let You know but thanks a lot

My car has been shaking quite significantly now that its hot outside....I raised my idle by about 100-150rpm last winter to aid in cold starting....now that I got my tach working I found out that my "raising the low idle" only brought it up to about 600-650ish.....but my rack damper adjustment was made when it was at the lower idle....which was probably only around 500! :eek:

I have the updated bolt....so hopefully I can make most or all of the shake go away by adjusting it..... :rolleyes:

What if you only have a mild case of the "hot idle shakes" sometimes?

Sometimes after a run on the highway, the first time or two that I stop, it will shake a bit, but after a couple of stops it pretty much quits doing it.

Now what the heck could cause it to come and go like that?