1989 300TE, 240,000 miles.

I had a leaking rubber hydraulic hose (to the rear suspension). Following advice from this forum I replaced the rubber portion of the hose using the metal fittings from the old hose. I bought a rubber hose (from a local hydraulics shop) that had similar specs to the original Gates hose for around $20. The job was not too difficult. Rear suspension self-leveling is now functioning normally.

HOWEVER, there is now a loud buzzing noise invading the passenger compartment whenever the engine is running. The frequency of buzz is proportional to engine speed. An engine stethoscope verifies that the buzz is coming from the hydraulic line, but placing the stethoscope on the pump itself reveals no such noise (just the normal whirring sound that bearings make). I begin to hear the noise in the stethoscope as I move along the rubber portion of the hose just after the pump.

Presuming that the pulsations in the line were normal, I proceeded to check all the rubber attachment points for the hydraulic line as it heads for the rear suspension. All the mounts were good and the line was not touching the frame directly at any point. I proceeded to remove the attachments one-at-a-time, to see if any one of them was the culprit, but the noise in the passenger compartment just diminished slightly with each mount I released (still loud). I now conclude that the pulsations (buzzing) in the line are NOT normal and that the rubber mounts were not designed to isolate that amount of vibration.

I see two possible sources of excessive pulsation: (1) perhaps the pump was slightly damaged during the hose replacement operation (debris?) and is producing an abnormal pulsation in the line, or (2) the pulsation is normal and the replacement rubber hose I selected is somehow amplifying the normal pulsations to abnormal levels.

Would someone with a 300TE please check their hydraulic hose (adjacent to the coolant reservoir) to see if it has a pronounced buzzing vibration? If you don’t have a stethoscope, you can just use a screwdriver between the hose and your ear.

Any other thoughts or suggestions?

Thanks, Eric