GBMUD Posted January 5, 2012 Share Posted January 5, 2012 I have two Landrovers with DMFs, a Td5 Defender and a Freelander Td4, I also have a VW T5 van with a knackered DMF. What kills them, and can the driver/driving style have any influence on their longevity? TIA Chris Quote Link to comment Share on other sites More sharing options...
fozsug Posted January 5, 2012 Share Posted January 5, 2012 From the Skoda Forum Likely causes of DMF failure and how to minimise the chance of failure. There seems to be a good number of cases of premature DMF failure on cars reported on this forum and others. While the DMF (or a certain design of DMF) may be a relative weak point in the drive train, there are some things can increase the likelihood of premature DMF failure. Racing Starts Driving around at very low RPM Putting a lot of power down from low revs Sharp and harsh application of the power Remap (See below) All of these put much larger strain on the active parts of the DMF and can increase the likelihood of an early failure. Avoiding these where possible and having some mechanical sympathy should reduce the likelihood of problems, but obviously the part is a mechanical items and will have a designed lifetime. Regarding a remap, it should be noted that a remap can cause the car to deliver more power or torque than the DMF is rated for, which will obviously reduce it's effective life. This is not a given for all remaps and it should be noted that the quality of a remap can vary wildly. While some vendors will provide an excellent service, taking into account the DMF and other factors, there are others who may provide a poor quality map which takes no account of these factors and can shorten the life of the DMF and other components. Quote Link to comment Share on other sites More sharing options...
mmgemini Posted January 5, 2012 Share Posted January 5, 2012 What the hell is a DMF ? Quote Link to comment Share on other sites More sharing options...
Retroanaconda Posted January 5, 2012 Share Posted January 5, 2012 Dual Mass Flywheeel Quote Link to comment Share on other sites More sharing options...
steve b Posted January 5, 2012 Share Posted January 5, 2012 .......... Designed Mechanical Failure absolute pants , another built in fail point that ups the cost of running things beyond 5yrs old to a prohibitively expensive level jmho of course Steveb Quote Link to comment Share on other sites More sharing options...
Les Henson Posted January 5, 2012 Share Posted January 5, 2012 The DMF is essentially a 2-piece flywheel - seperated by a cushion of bonded rubber that cushions the impact of taking up drive from the engine to the gearbox. 'Nailing it' doesn't necessarily cause them to fail - frequent gear changes will also cause it, or pulling a heavy weight beyond the capabilties of the vehicle will do it as well. So the purpose of a DMF is just a rather expensive shock absorber - about £730 for a clutch and DMF for a TD5, but then you guys can afford it Apart from the expence of it, I see no real benefit of a DMF over a 'normal' clutch - they are cheaper and easier to replace. DMF failure can cause serious damage to the gearbox - normal clutches don't. DMF's can distort and go out of line, so you need to exert mental pressure on the outer section in order to align the holes to get at the centre bolts, etc, etc, etc, Les. Quote Link to comment Share on other sites More sharing options...
mmgemini Posted January 5, 2012 Share Posted January 5, 2012 .......... Designed Mechanical Failure absolute pants , another built in fail point that ups the cost of running things beyond 5yrs old to a prohibitively expensive level jmho of course Steveb You owe me a keyboard. So true though. Quote Link to comment Share on other sites More sharing options...
mickeyw Posted January 5, 2012 Share Posted January 5, 2012 Dual Mass Flywheeel Glad someone asked before I had to .......... Designed Mechanical Failure Steveb Sounds far more appropriate, now I know what one is. So, WTF is the point of them? Meant to be a shock absorber... but to what... if it can still damage the gearbox? And is there a retro-fittable alternative 'proper' flywheel? Quote Link to comment Share on other sites More sharing options...
Retroanaconda Posted January 5, 2012 Share Posted January 5, 2012 Part of the recent trend in the automotive industry to reduce NVH* levels (something Land Rover are rather late to the game on). Smooths out the transmission changes, so you get less clunks, bangs and wallops from underneath. Also helps with the idle vibrations. You can retro-fit a solid flywheel to Td5s at least yes. *Noise, vibration and harshness - I'll give you that one Quote Link to comment Share on other sites More sharing options...
Les Henson Posted January 5, 2012 Share Posted January 5, 2012 Gearbox is only really damaged if the two steel parts of the DMF seperate and one part attempts to exit the flywheel housing. You can get conversion kits, which essentially are a solid 'normal' flywheel, a clutch cover, a friction disc which has springs within it (to act as a shock absorber), and a thrust bearing. Les. Quote Link to comment Share on other sites More sharing options...
Tanuki Posted January 5, 2012 Share Posted January 5, 2012 The DMF is a way for manufacturers to get driver-acceptable levels of NVH [Noise, Vibration, Harshness] in a vehicle which has rather few large-capacity cylinders and which produces lots of torque/BHP. The alternative to a DMF is to use a big, heavy, traditional flywheel - but that makes the vehicle heavier, and makes the engine feel much more lethargic because the engine's got to accelerate this dirty great lump of metal (it also makes manual gearshifts slower because you have to wait for the heavy flywheel to slow down!). Treated properly, I don't see why a DMF should fail. #1 cause is driving like a taxi-man: expecting the engine to 'lug' hard at low RPM: the DMF is then working its friction-pads off trying to keep everything smooth. In my truck-driving days I was taught to only seriously load the engine when it was in the rev-range between peak torque and peak BHP, and never to use full throttle until you were at least 3/4 of the way up the curve to peak-torque. Build the power up slowly until the engine's happy - only then can you turn up the heat. Drive around town at 35MPH in 5th on a typical Land-Rover product and you'll trash the DMF; the big-end and main-bearings won't be happy either. A free-revving engine loaded lightly is a long-lasting engine (and transmission). --Tanuki. "The human body hits terminal velocity after about 5 stories of falling. So jumping off anything more than that is really overkill." Quote Link to comment Share on other sites More sharing options...
zoltan Posted January 5, 2012 Share Posted January 5, 2012 Being very petrol biased, the DMF is an effective modern method of polishing the diesel t*rd Quote Link to comment Share on other sites More sharing options...
mmgemini Posted January 5, 2012 Share Posted January 5, 2012 NVH.. FORD FORD FORD bull**** when I worked on them in the 1970's and 80's...NVH was force fed into us. The worst vehicles I've driven for NVH have been FORD.... The modern vehicles I'v had the dubious pleasure of being a passenger in including my daughters new Renault Laguna and my son in laws Audi Q5 both suffer from NVH through the tyres..As have most of the other euroboxes I've ridden in. My Defender though not quiet does not have the tyre roar of the modern car...... I should have said Les. DMF just a modern not so good, flat cone clutch LOL Quote Link to comment Share on other sites More sharing options...
Daan Posted January 5, 2012 Share Posted January 5, 2012 #1 cause is driving like a taxi-man: expecting the engine to 'lug' hard at low RPM But that is exactly what offroaders doing all the time. I also do this driving my roadcar to get good fuel consumption; fewer revs means less fuel. So if that kills a DMF, it is not the thing to have these days, even more so on an off road vehicle. Daan Quote Link to comment Share on other sites More sharing options...
GBMUD Posted January 5, 2012 Author Share Posted January 5, 2012 Thanks for the replies and insights. The low revs/high loading thing is interesting. The Freelander is an 'e' model and as well as the 'stop/start' feature it also has a shift light - which, if I obey it, keeps the revs below 2000RPM, usually in the 1500-1800 range. Surely the DMF must be having a hard time of it? The Defender is driven a little more vigorously but still at fairly low revs. At 109k, and despite being chipped it is still feeling fine... The van used to be an AA van and the DMF was knackered when I got it at 102k miles.... I think it spent a lot of time during it's service life ticking over and then towing cars on a dolly. I have done 40k with the DMF knackered and it is a little noisy at idle. Cheers Chris Quote Link to comment Share on other sites More sharing options...
disco2hse Posted January 6, 2012 Share Posted January 6, 2012 So, what does a knackered DMF sound like? Quote Link to comment Share on other sites More sharing options...
Les Henson Posted January 7, 2012 Share Posted January 7, 2012 Drive train can become harsh and a knock or bang felt when taking up drive, vibration as the DMF becomes unbalanced. Les. Quote Link to comment Share on other sites More sharing options...
zoltan Posted January 7, 2012 Share Posted January 7, 2012 To be perfectly fair to DMFs, would there ever have been the huge numbers of petrol drivers going over to diesel that we've seen in recent years without this type of technology? Modern diesels are so far from their predecessors and DMF must play a huge part in this Quote Link to comment Share on other sites More sharing options...
tacr2man Posted January 7, 2012 Share Posted January 7, 2012 its not only NVH there is emissions , lighter flywheel less time accelerating , sprightlier vehicle ( consumer drive) , 6 speed gearboxes WTF ? There is alot to be said for big flywheels JMHO Re truck driving , as pretty well all are FBW the acceleration profile is "managed" by the computer sensing load etc . so acc pedal is pretty well a switch now , start up move off and upto limiter . Quote Link to comment Share on other sites More sharing options...
GBMUD Posted January 7, 2012 Author Share Posted January 7, 2012 6 speed gearboxes WTF ? Smaller capacity, peakier, narrow power/economy band needs a lot of ratios to keep the engine 'on song' at all speeds. Knackered DMF, in my van at least, manifests as a very noticeable rattle at idle. I suppose it is responsible for some of the backlash felt in the transmission too. Chris Quote Link to comment Share on other sites More sharing options...
forkrentfitter Posted January 7, 2012 Share Posted January 7, 2012 my old transit(52 plate)had aknackered dmf,felt like engine mount had split when it was idleing. Quote Link to comment Share on other sites More sharing options...
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