BY Frank Massey I concluded the last topic with a commitment to update you on our Ford Galaxy dtc i 1.8. As you may recall, the owner complained of vibration at initially around 45-50mph. This was addressed with a replacement DMF. Further issues were reported however, now at much lower engine speed. A faulty set of refurbished injectors were replaced by new OE units. This improved engine smoothness combustion noise and overall performance further still. Despite this ongoing cavalcade of success on our part, the owner reported that a vibration still existed, now only present at idle when stationary! Common sense ruled out transmission and wheels, leaving an engine issue as the only possibility. When sitting in the vehicle, a distinct vibration was indeed noticeable. All the symptoms suggested a DMF issue, and depressing the clutch pedal instantly removed the vibration. My initial thoughts suggested that loading the clutch pressure plate could be assisting the DMF, or it decoupled the vibration source. Eureka moment It was frustrating, especially when so much progress and improvement had been achieved, all at quite a high cost to our customer. I never accept ownership for vehicle problems, but out of respect do share a little sympathy. We are fortunate to have a close relationship with Schaeffler who manufacture LuK DMFs in Buhl Germany. They suggested that we ramp the vehicle and check the alternator freewheel clutch, as well as running the engine, less the auxiliary drive belt. The alternator clutch was mounted on a short drive shaft incorporating a cush coupling and was operating normally. However, the auxiliary belt self-adjusting tensioner was 28 AFTERMARKET MARCH 2024 TECHNICAL www.aftermarketonline.net A MONTH IN THE LIFE OF A VEHICLE TECHNICIAN Freewheeling Frank ‘FLUKEs’ his way through a VW T4 problem, before carrying the CAN on a Fiat 500 seized solid. I felt the eureka moment had arrived. My thoughts were as follows; The vibration felt at idle was a result of secondary mass imbalance from ancillary rotating components. Vibration can become more prevalent when resonance occurs, especially if two or more components sharing mass imbalance at close frequency - around 10khz. Then, the mass imbalance is added together, producing a more powerful effect. Resonance will disappear with frequency changes. This is why Ford fitted the selfadjusting belt tensioner. The other method of avoiding resonance is to add or remove weight, shifting the frequency at which it occurs. Part 11 Fig. 1
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