Vibration at 2200 rpm


Created: 06. 06. 2003
Updated: --. --. ----

Model:
406 with XU10J4R engine.

Symptom:
A loud vibration can be heard in a very narrow engine rpm band near 2200 rpm. The noise is reminiscent of an exhaust baffle of catalytic converter vibration and it could be easily mistaken as such.

Possible Cause:
Perished or split bush at the rearward end of the upper engine torque reaction rod. That's the smaller bush which inside is the alluminium housing, bolted to the body.

Left photo: Engine torque reaction rod whith the big bush at the front and the small bush at the back where it bolts to the body.

When you hold the engine at 2200 rpms (not easy to do) You will see how the bolt inside the larger bush starts to oscillate up and down at a high frequency. The movement up and down can be about 1cm. The engines own internal vibration drives this oscillation.

Usually a new rear bush will prevent this oscillation from occurring. In order to further reinforce the damping effect we have filled the spaces inside the front and rear bushes with polyurethane.

Always remove the rod and rear bush for inspection. Often the rubber is only split and this can be easily missed. A split rubber is sufficient to cause the problem.

 


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