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Renault Master Mm35 Dci 120 2.5l Vibration Problem Sorted
Renault Master MM35 DCI 120 Converted Panel Van to Motorhome
(Year 2006 16000 miles)
During the last year we notice a slight vibration when going up hill around 40 to 50 mph, this with time gradually increased causing concern. The symptoms are that the whole of the front of the van feels like it is being shaken from side to side. If you lift off on the power the vibration immediately stops, but as soon as the power is applied again the vibration comes back. I carried out a series of tests to try and establish what was wrong, initially we drove a short test route and proved that the vibration was repeatable. The following is a summary of the tests that were carried out:-
1. Datum run vibration present
2. Had front wheels re-balanced conducted test run no change
3. Swapped wheels front to rear and rear to front, test run no change.
4. Fitted vibration sensors to measure engine movement and passengerís seat vibration, carried out test run. Established vibration at a frequency of approx 10 Hz that we could feel and that engine was vibrating laterally at 10 Hz up to 2.5 mm. At 48 mph the CV drive shaft are rotating at a frequency of 10 Hz (600 RPM)
5. Established that the engine in its mounts has a lateral natural frequency of approx 10 Hz changing slightly depending on the torque being transmitted.
Having determined that the engine had a resonance that was being forced to vibrate at the drive shaft frequency, it was a case of trying to work out which drive shaft the vibration was associated with.
To do this the front wheels were jacked up one at a time and driven by the engine then while monitoring the engine movement the drive shafts were loaded by applying the brakes. From this I found that the near side drive shaft was causing the vibration. At this stage I decided to strip out the near side drive shaft, after a detailed inspection of the shaft and trilobe coupling (part of the differential gearbox) I found wear within the trilobe coupling. The coupling was removed by taking out a retaining spring clip and spacer. The trilobe coupling forms one of the sun gears in the differential. Ordered a new sun gear/coupling and assembled into the gearbox, refitted drive shaft and refilled gearbox with new oil. Carried out test drive with vibration sensors fitted, no vibration felt or significant displacement measured.
The question is why did the coupling wear so quickly with only 16000 miles on the clock, first you have to understand what the function of the trilobe coupling is, its primary task is to transmit torque to the wheel via the drive shaft. It has to do this while changing angle and sliding in and out with suspension movement. When the drive shaft is not directly inline with the differential gearbox the three trilobe rollers have to roll in and out with each rotation. If one of the mating faces in the coupling is worn then with the high torque transmitted the drive shaft applies an axial force to the gearbox as the trilobe roller in the worn area resists rotation. Why does this occur around 45 mph? At this speed the shaft rotational frequency is the same as the natural lateral frequency of the engine that it wants to vibrate at. So instead of all three rollers rolling in and out freely one sits in the same position in the coupling and makes the gearbox move laterally instead. Because the roller starts to stays in one position it gradually wears a dent. Therefore once a indent is formed it rapidly accelerates the wear, so my long term solution to preventing the vibration starting with the new coupling is to fit a damper that resists rapid lateral movement of the gearbox/engine assembly.
Every van gearbox/engine installation will have slightly different vibration characteristics varied by normal differences in manufacturing. Then rarely on occasionally when all the conditions come together you may be unlucky and get this type of vibration problem.
Brian, Transmission Development Engineer