DMF vs. Solid.

A question about : DMF vs. Solid.

A neighbour with an Avensis had DMF problems and had it replaced by a solid clutch/flywheel assembly. He says that he can't feel any additional vibration as a result. Is this general experience? If so why do manufacturers instal DMF,s?

Best answers:

• DMF is to absorb the vibrations from the engine and gearbox.
  Without the DMF the vibrations are transferred to other components such as the main shaft and bearings inside the gearbox or the crank shaft and supporting bearings inside the engine.
  DMF was to bring some refinement to diesel engines. It keeps them nice and quiet and with less vibrations. Less vibrations was meant to allow them to cruise at lower RPM (longer gear ratios) and helping the environment by delivering more MPG
  Using an SMF when sitting idle and the clutch isn't pressed then they normally sound like an early 90's Transit.
  Using one long term is usually ok if it's a good kit but i've seen some cheaper kits fall apart from vibration funny enough (clutch broke up then made big gauges in the SMF)
  Some cars don't like the added vibration and i've heard of gearboxes wearing prematurely and in extreme cases crankshafts snapping.
• Noise, Vibration, Harshness is a subset of vehicle engineering that has really split in to two camps. We have had very simple clutches since the invention of cars but of late, instead of building better balanced engines or adding balancer shafts or harmonic pulleys, DMFs have been introduced to hide the shortcomings of many diesel engines.
  Some cars do just fine if converted to "SMF" clutches (some commercials can be specced that way from the factory), while others seem to add unacceptable vibrations and shorten the clutches lifespan. You really have to check with forums to find out which ones work and which ones don't like it.
  Skoda Octavias for example are surrounded by myths of bone-jarring vibration and snapped crankshafts as a result of conversion. One taxi boy I know says his seems to "burr" a bit at idle, but has done this since he converted it 120,000 miles ago.
  So, in short, lazy engineers masking a symptom instead of proper engine development, coupled to bad driving equals introduction of the unnecessary DMF.
• How good is your neighbour at detecting mechanical noises though?
  Sometimes drivers dont spot obvious faults and thought that some noises were normal.
• Too large a swept volume on a silky smooth Jaguar? My 944 at the time, with what was considered old-tech, competition clutch as standard, was equally smooth with its balancer shaft, and a greater swept volume in its 4-potter.
• Jag were probably more interested in preserving the gearbox than refinement. Maybe the Porche gearbox didn't need kid gloves.
• While no Jaguar suits a Spanish gearbox, I've never seen a broken one. They are well designed, engineered and built pretty tough and even during the notorious Leyland era, didn't seem to need any special protection from the not very peaky, engines.
• DMFs have improved since they were introduced.
  There was a decent article in Car Mechanics Mag a few years ago with input from the manufacturers.
  If you ensure you start and stop the engine with the clutch depressed and don't labour the engine in too high a gear you will get much longer life from a DMF.
  The wifes Clio is on the original DMF and it has been driven mostly round London. From memory it is on around 130k.
  My V50 had over 150k in the original DMF.
  My old mk3 Mondeo was on the original DMF when the bloke I sold it to traded it in, over 250k on it.
  There have been issues with crank failure due to a solid DMF being fitted.
  They certainly are not perfect, anybody that has driven a Transit will tell you that, to prevent DMF damage the vehicle was made ridiculously easy to stall, if the ECU thought you didn't have enough revs it would cut off! Likely improved in later ones.
• Engines and gearboxes never used to need DMF's so why do they suddenly all need them now?
  A cheapskate fix for a busted DMF is just to weld it up (must be really well or the welds break) and thus create a solid flywheel. But if you are paying for the job to be done, then it probably is better value to replace the DMF or fit a proper solid conversion.
• Buy an automatic, then you don't have to worry about any of this.
• There is a specialist company in Ipswich that machines SMFs out of aluminium. They are made for racing and are designed for that make/model of vehicle.
  If these kits could cause damage to the engine or gearbox, then I doubt they would make then.
• I wouldn't bank on it. Racing engines are often rebuilt between races.
• A great deal of his customers buy them to fit on road cars.