Mystery Vibration: 300d

[sam2850]

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?????