Mystery Vibration: 300d
 

Please pardon the lengthy details, but in the end, they all become relevant.......

Last spring I purchased a 1981 300d that had roughly 172,000 miles on it. Some time thereafter, I noticed that the CV boots were split and needed to be replaced; so I had the rear axle shafts replaced. When the time came to replace the axle shafts, a variety of other repairs were also done to the car. After the following work was done- there was a serious ‘growling’, ‘whirring’ vibration noise that continues to this day at a certain speed:

1.) Replace rear axle shafts.
2.) Remove/Delete EGR system.
3.) Replace Exhaust intake manifold
4.) Replace Exhaust intake manifold gasket
5.) Replace Air Intake Housing Mounts
6.) Repair certain areas of the exhaust pipe- which in part, required welding the downpipe
7.) Replace front driver side shock absorber
8.) Replace front passenger side strut
9.) Valve Adjustment
10.) Replace Valve Cover Gasket
11.) Oil change
12.) Replace secondary and primary fuel filters
13.) Replace air filter
14.) New exhaust pipe donut hangers

Here are the circumstances under which the noise appears:

1.) Hard to tell if the noise is coming from the front or the back.
2.) When accelerating, must be going over 40mph, the faster the speed, the quicker the pulse of the vibration; “Grrrrrrind, grrrrind, grrind, grind, grind, GRIND, GRIND, GRIND”
3.) Once the speed reaches 60mph, the frequency and intensity lessens a little- but not much.
4.) If I take my foot off the pedal immediately (during the noise), the pitch of the noise will change, but the same vibration and frequency will still be there.
5.) If I slowly take my foot off the pedal during the noise, as the speed decreases the noise will change to the opposite as I described in #2 above.
6.) While driving, the noise goes away if I switch the gear to neutral.
7.) The noise will not occur if in park and pressing on the pedal.
8.) It made no difference if I was going uphill or downhill
9.) It made no difference if I was taking turns.

After the vibration noise appeared, my mechanic did the following subsequent repairs/fixes

1.) Replaced the new rear passenger side axle shaft with another new axle shaft (thinking the first one might have been defective).
2.) Replaced axle shaft bearings
3.) Sanded all four brake rotors
4.) Changed the brake fluid
5.) Added transmission fluid
6.) Drained and replaced differential fluid with another brand.
7.) Put DieselKleen in to the tank and change primary and secondary filters again.

At this point, the noise seemed to go away.

About one or two weeks later, I was preparing to take the car on a trip that lasted 260 miles each way, and wanted to make sure everything else was good to go. So my mechanic also fixed the following:

1.) Front Crankshaft seal
2.) O-ring for the oil dipstick area
3.) A couple other (front) seals related to oil leaks. We did not change the lower oil pan gasket or rear seals.

I took the car for a long/fast test-drive before going on the trip. (Average 80mph; roughly 120 miles roundtrip). The noise did not appear, but I did notice that transmission fluid was spurting out underneath the car. By the time I took the car back to have that looked at, the transmission was not spurting anything out, and the transmission fluid level was appeared fine.

About 200 miles after we left for upstate New York, the noise began to come back. The car made it fine otherwise, 520 miles roundtrip, but with the noise/vibration. While the problem was back again, it was not as severe as before, but definitely noticeable.

When I got back, the mechanic looked at the car and noticed that the differential fluid had changed color, the odor was different, and that there were some metal flakes present. He then proceeded to switch the following parts out from his car and test on my car (his car is same make/model, but two years older).

1.) Differential- made no difference
2.) Drive shaft (including flex disks and center support bearing)– made no difference
3.) Rear axle shafts- made no difference
4.) Switched all 4 tires out- made no difference


He then proceeded to replace the following:
5.) Rear passenger side brake caliper
6.) Rear wheel bearings
7.) Rear sub-frame mounts
8.) Lash washers
9.) Checked the wheel alignment- fine
10.) Adjusted axel bolts
11.) Adjusted emergency brake
12.) Adjusted brakes and bled fluid
13.) Replaced Transmission Fluid, Filter and Gasket.
14.) Re-torque valve cover bolts and bolts from other initial repairs.
15.) Transmission mount
16.) Both front motor mounts
17.) For testing conditions:
a. Removed the engine shock absorbers
b. Removed central exhaust pipe hanger that attaches to part of the transmission


None of this has made a difference.

I continue to drive the car daily. Sometimes the noise almost goes away entirely on a particular drive- but then appears later that day. Otherwise, the noise continues in the same fashion.



The only change is that if I take the car out on the highway when the car is not completely warmed up (i.e. oil pressure gauge not yet reading 1.5 at a stop), the noise is there and is really loud. Once the car has warmed up, the noise is less severe….but still noticeably present.

The car now has about 5,000 more miles on it since the beginning of this saga. As a continued attempt to fix this noise:

1.) Changed the oil/oil filter roughly 3 times
2.) Flushed the engine once
3.) Did a DieselPurge (two bottles)
4.) Drained fuel tank and cleaned (but did not replace) the fuel tank screen
5.) Changed primary and secondary fuel filters probably 3-4 times
6.) Put countless bottles of DieselKleen and Seafoam through the tank
7.) Tried different diesel fuel brands
8.) Wondering if it was a load/tilt issue- took two bags of cement and rotated them to each corner of the car while driving.
9.) Changed tire pressures
10.) Changed brake fluid
11.) Changed all fuses
12.) Tightened fan belts

Other things that have come up and been fixed:
1.) Fixed a couple vacuum leaks
2.) Replaced Transmission Pressure Modulator
3.) Put TransX in Transmission
4.) Not fixed- but needs fixing- rear passenger side shock.

None of this has done anything to get rid of the noise. I should also note that the car has an extraordinary amount of power. No noticeable timing chain noise. Never a problem starting. Given the amount of time, I can comfortably say that the noise has also persisted in different seasons (August through current- Mid-Atlantic region). The rotors are severely warped in the front. Not sure if there are any other sticking calipers (i.e. in the front). However, I jacked the car up and spun all four tires- all four spun relatively freely.

Repairs that the former owner apparently did before I purchased it (within year or two before):

1.) New flex disks
2.) New tire rods


Any Ideas?????

1) Have you tried ear plugs?

Did he replace the brake hoses too? If they deteriorate and collapse it could cause the caliper to stick.

tires?

2) So long as I keep a spare pack for passengers....

No. We wondered about that- but the vibration is still there even when I brake. Also, we also didn't think that was the problem, given that the vibration changed form in one instance if I take my foot immediately off the pedal- same frequency, and in the other instance, if I slowly take my foot of the pedal- in which case the grinding noise gets slower and deeper.

First we rotated them.

When that didn't work, my mechanic switched all 4 tires from his car on to mine. No change.

Thanks for accepting my remark as humor.

All I could add is that it is possible that the noise is still engine related. My car is acceptably smooth but being a 5 cylinder does make it fire 2x on one revolution then 3 on the next.
Your noise may be horsepower related rather than rpm related.

.

you have mentioned drive shaft,
but did you do balance check while replacing things? it might be out of specs...?


cheers

We ruled that out when my mechanic switched the drive shaft from his car on to mine. Same noise.

If I didn't have humor in this mess I would have gone nuts....

Aside from the drive shaft, my mechanic did wonder about other causes- which is why i posted all of the other repairs that were done at the same time. Under your idea, perhaps removing the EGR or the valve job did something?

removing the EGR...doubt that, but wrong adjusted valves,some chain stretch
paired with few low-pop injectors.... I guess it can make all sorts of trouble
but it will be visible as a smoke.

can you take video in cabin while driving? It will be great help
for the big guns here .....


cheers

A warped brake rotor due to a sticking caliper will most definitely cause vibration. That condition sounds like something that a sticking caliper would cause.

I would replace the brake line and rotor on the suspected caliper, and if it hasn't been rebuilt yet (I know you said you replaced one) then rebuild or replace it.

I will certainly look into that more.

I have also been told that the problem might be with the transmission- what do you think?

Very little smoke. I have also been recently advised that this could be transmission related. Any thoughts?

Did you check the center bearing on the driveshaft?

Yes. My mechanic switched out the greater portion (if not entirely) the driveshaft and related components, including center bearing, flex disks, etc. from his similar model benz and put them on mine. Noise was still there.

To be thorough, he also put my driveshaft and related components on his model- noise was not there.

What caught my eye in all of this is when you took it on a 120 mile test drive, the transmission was squirting fluid. Yet, when you returned to the mechanic the fluid level was fine.

Did you add any fluid?

When the level was checked, was the transmission good and warmed up?

I've found that this is critical with these transmissions in order to get an accurate reading. In fact, I've seen nearly 1+ quart variance between cold and hot. I'm not sure why this is but it may have something to do with the fact the pan only holds about 2 quarts. The other factors, you mentioned, are that the noise diminishes when warmed up and is eliminated when shifted to neutral a highway speeds.

I'm not sure what would happen, internally, when a transmission is over-filled but it may be a place to start.

No fluid added when I returned, as then, the mechanic said the fluid level was fine. I believe, though I cannot remember exactly, if the engine was warmed up at the time he measured it.

Since then, had new transmission fluid change, gasket and filter. Also had to put new transmission pressure modulator. When my mechanic replaced the modulator, I realized that there might be a lot of 'varnish'/buildup in the trans....so I put in a bottle of trans x. Since then, no change.

This morning was the first time the noise/vibration started at 35 mph. Because the rpm was low, it may have been in third gear, but I am not 100% sure.

This might narrow the scope to being 3rd and 4th gear specific. Not sure what that could mean- transmission related? If so, any thoughts on what trans issues could cause this?

My first guess would be that it is related to the transmission as it goes away after you put the car in Neutral. However there are other factors at play. The engine being under load at a specific RPM. As was suggested timing, injectors, and poorly adjusted valves (compression?) could also combine for some strange harmonics.
I'd start with the motor. You can test the above without throwing unnecessary parts at the car and they are all just prudent preventative maintenance. With the motor ruled out you can start to look at the transmission or other possibilities.

You didn't mention front wheel bearings. Were they replaced? And what did you mean by "axle bearings?"

I'd start with the motor as was already suggested. You can check the timing, valve adjustement, and injectors before throwing more money at the rest of the drive train. Those things are just good PM anyhow

front wheel bearings were not replaced, as they did not display the typical symptoms after rocking/shifting/turning the wheel while the car was on the rack.

Axle bearings= please forgive wrong terminology, but there were some type of bearings associated with the installation of the rear axle shafts.

Good suggestions. Because my mechanic had already adjusted the valves in the same job as he did with replacing the rear axle shafts, we did not think to look there again.

How would you test for timing and fuel injection? What types of noises have you noticed in the past with these issues?/vibrations

I would disconnect the speedometer cable at the transmission and see if the noise goes away. Your description does not have the classic symptoms of a speedometer or cable problem, but it does match some of the symptoms and it is an easy check.

Injectors have to he tested with a pop tester and timing....well search the forum this has all been written up before. As for noises poor timing and bad injectors can sound all sorts of funky when the engine is under load.
Sounds are hard to diagnose without hearing them. I suspect you have a transmission gremlin but the metal in your diff is suspect as well.
I have read somewhere on here that when looking for these noises start at the engine and go back.

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UPDATE

Earlier this week and today, noise/vibration ocured for the first time below 40mph. Was in 3rd gear with low rpms around 30mph on highway.

I think it is time to make a video with sound of this vibration.

UPDATE- Problem (kind of) fixed.....

Recently had the privilege of having a highly qualified/experienced Benz mechanic review the car. Very quickly, he saw that the center support-portion of the transmission mount was positioned in a way that rendered the mount useless; therefore, it was as if my transmission was sitting directly on the car. After removing the center portion of the mount, the vibration disappeared. At that point I was satisfied. The whirring noise is still there somewhat in the same speed sections.

I know there is still a problem. However, I am enjoying the moments whereI at least have a vibration-free car...finally.