DMF's, Clutches and reversing!

[TerryIvybridge]

Well! you may or may not remember, we were trying to change our towcar, for nearly a 12 month! Things have changed, the DMF went a month ago and that cost over a grande. New clutch, starter and other bits and car's a good 'un now. Along with fitting reverse sensors means my wife can safely do the weekly shop with it, sorted.
Now, I've took it back to the clutch people for checking. Its a Mk4 Mondeo 2.0 140, supposedly a good Tug for towing. The reason for taking back was that whilst I engaged reverse to park in our drive, I felt a scraping at the clutch pedal and some rumble sort of sound, only very briefly. After a check at the clutch centre, it happened again. Just for a 3-5 second period. I'm monitoring it now and we'll see if it develops!
My point is, I' ve been told that reversing in particular puts an enormous strain on the DMF and clutch and slipping the clutch whilst reversing should be avoided when ever possible!
This, as a towcar worries me. Has anyone else here found the same please? Terry.

 

[ProfJohnL]

Hello Terry,
Yes there has been considerable debate about DMF's and towing. Tow must put extra load through the clutch, and especially so with low speed maneuvering.

There is a suspicion the DMF's are more vulnerable to damage caused by excessive slipping when towing, possibly down to manufacturers cost saving in the clutch department, but DMF are definitely more expensive to repair.

I suspect there are two main differences between reversing and pulling forward, In many cars the choice of the reversing gear ratio is not as high as 1st gear, so it means you have to apply more throttle to prevent stalling in reverse. And secondly in general drivers are more confident about moving forward so there is less tendency to slip the clutch, by contrast we are more trepedacious about reversing and this shows by slipping the clutch more.

I have found that with many modern fuel injected vehicles (both Petrol and diesel) there is enough engine torque at tick over to get an outfit moving. This limits the amount of clutch slippage, and then only apply more throttle when the clutch is fully engaged. I try to use the same technique when reversing and so far in 41 years of motoring and towing I haven't had a problem with a clutches burning out.

 

[colin-yorkshire]

hi Terry.
I have heard this before mate and never quite understood it.
if you know a little of how the gear train works you will understand that the clutch does not turn the opposite way in reverse, and neither does the input first motion shaft. reverse is engaged within the gear box its self, (well after the clutch has done its bit) only the output and idler shaft gears reverse, so no matter which gear is engaged the rotation is the same.
there should therefore be no difference between going forwards in first or reverse (similar gear ratio) exept for the ammout of clutch slip used in order to manouver. especially with the weight of pushing the van.
burning of the clutch in reverse is symptomatiic of a worn DMF where separation of the plates imparts greater movement in the dampening coils leading to vibration, clutch slip, and heat,
what I am trying to say is, if there is a problem with burning in reverse the DMF must be faulty in the first place but only noticed when trying to reverse the van.
reversing with the van will not cause the DMF to fail this is a myth, riding the clutch with exessive slip from new will however shorten it's life,
notably many diesel cars and vans have DMF's but most failures seem to occur on LD's and mondeo's.

 

[TerryIvybridge]

Thank you Prof' and Colin. Both good replies to my Questions. As an ex HGV driver, I've alway's fully engaged the clutch as soon as possible and let the engine rev's take the vehicle at the appropriate speed. Never liked slipping the clutch, or riding it whilst on the move. The only explanation for early clutch demise is either "slipping" or poor manufacture in the first place. The same "new" material is used in today's LGV's as in our modern car's, therefore, clutch size for both cannot be relative?
As to my new signs of rumblings and scraping sounds, I'll do as I previously said and let things develop I guess? The clutch repairers are aware of what I experienced. I'm just concerned that in the event of more clutch related problems, they don't attempt to fob me off because I tow a caravan! I'm going to log my tow miles and keep this forum updated, Terry.

 

[colin-yorkshire]

hi Terry.
like the Prof in 45+ years I have not had to change the clutch in any car I have towed with (touchwood) which in it's self is remarkable as just about every car I have owned has been pre-used and previous owner driving techniques unknown,
however I once did have a clutch problem with the Mondeo shortly after purchase where the clutch showed signs of slipping in high gear, on returning it to the dealer for inspection the workshop found the clutch self adjustment quadrant had failed, owing to the fact I towed a van I insisted on a complete clutch inspection which they reluctantly did and also found some burning of the friction plate. this was replaced along with the pressure plate and thrust bearing together with a new self adjustment assembly, for which I agreed to pay half the cost minus labour charges. it was fine after that.
I only mention the above because it was a Mondeo a 1.6 petrol version without a DMF I am in no doubt that had it been fitted with a DMF this would also have been damaged as well, the thought occured to me that seeing as how certain models are more prone to DMF failure than others there may be other factors involved besides driver techniques.

 

[Dustydog]

The Prof and Colin have summed up very well.
Our 9 yr old Sorento is still on the same DMF and clutch.
Luckily we have a low ratio option which turns reverse Into a crawler get where the clutch can be engaged avoiding slipping.
The real issue for me is that the clutch hydraulic slave cylinder is mounted inside the bell housing. If it fails the gearbox must come out.Then you have the Dilemma whether to change all the other bits.

 

[bertieboy1]

Whats a "DMF" - I was always taught to use abreviations only when you are going to run out of space,if space allowed then the full text should be used.

 

[WoodlandsCamper]

Whats a "DMF" - I was always taught to use abreviations only when you are going to run out of space,if space allowed then the full text should be used.

Google says it's Dual Mass Flywheel

 

[Wilbury]

Dual Mass Flywheels have gained a lot of stick in the Motorhome fraternity being blamed for bad clutch judder
especially in reverse due to badly specified very high rev gear ratios requiring much slipping.
It is not a fault of the DMF's as a principal but the fact that they are badly engineered in the first place and only exist at all to try to cover up short falls elsewhere in the design and manufacture.
It is all down to making something that they can hopefully get away with for average applications and failing to engineer for worst case sinarios.
Rgds

 

[ProfJohnL]

Whats a "DMF" - I was always taught to use abreviations only when you are going to run out of space,if space allowed then the full text should be used.

Hello Bertie,
I agree in principle, but unfortunately caravanning is full of abbreviations and acronyms. To help clarify posts I tend to write the full description and immediately follow it with the acronym in brackets. Then further down the document I simply use the acronym. Its no so much to save space, but to prevent tedium.

 

[JonnyG]

hi colin -yorkshire. had it not been for you last line concerning most failures occur in Ld's and Mondeo's i would have done a thank you but were do you get the facts that state these have the worst failure rates? i mean frankly have been reading about DMF's for well over 15 years and given the amount of cars fitted with them ie millions upon millions have always taken it all with a pitch of salt.. main cause of problem? well the DMF is a wear part end of and there are so many poor drivers out there burning the arc spring grease off them with poor clutch control thinking they are still driving a petrol engined car lacking any lowdown grunt. am surprised they last as long as they do.. never the less they are a wear part but millions last for 150 plus K. which for a wear part is acceptable...So we have poor drivers then we have poorly maintained cars ie an unbalanced engine due to worn or faulty injectors can add undue stress to the DMF making its job load even harder and indeed shortening its life more so....of course car manufacturers do push there luck after all DMF are fitted to lorries and don't suffer anything like cars do but those figures? were are these figurers coming from concerning which make is renowned for its failure? is it forum gossip ! or actual figures that state mondeo's are the worst and is it mk 3 or mk4s or both? and given the mk3 is shared by jaguar one would assume jaguar are also renowned for it. and if its the mk4 then Citroen/ peugoet would be as renowned for failures too?
personally i don't know which is the worse or indeed the best come to think of it as i've never seen any info that could help me dicide.. never the less a good and interesting post colin

 

[colin-yorkshire]

hi JonnyG,
thank you for pointing out my omission I had intented to use the word "seem" in relation to the last paragraph my mistake.
this was based purely on reports from members complaining of problems with DMF's both on here and on the boating forum on which I participate. the vast majority of complaints SEEM to relate to Mondeo's and Landrovers, with typical problems of juddering and burning clutches while reversing. while other models that use them SEEM less problematic from the reports posted.
there could be other reasons for this of course, as I doubt driver technique is solely to blame afterall mondeo and LD drivers cannot be worse than any others "can they".
possibly one reason is the sheer numbers of Mondeo's and Landrovers used as tow cars in relation to other makes, or there is something amiss in the ford design.
one thing is for sure we only get reports of failure when someone complains. or has a problem while units that give faultless service go unnoticed.
it is rather like the statement that british made vans have damp problems from the number of complaints aired were clearly others remain damp free for 20 years or more, but we hear very little of those.

 

[xtrailman]

IMO the main reason for failures while reversing is the often higher reverse gear, and the need to overcome the caravan brake reverse mechanism.

This often requires slipping of the clutch, and excessive revs.
Another factor is clueless drivers with little knowledge of what's really going on under the bonnet.

I have been driving since the days of Austin A40's, and in all that time have only ever changed one clutch plate, and I mean just the plate, not the entire clutch along with the thrust bearing.

That failure was only oil contamination due to leaking oil from a crankcase seal, on a Mk1 Cortina.

Even back then people were writing about clutch problems, so its nothing new.

Obviously some cars may be more susceptible due to poor design, but the driver is a major factor, I use a mover when possible.

 

[seth1]

Well up to now ive not come accross a single heavy commercial vehicle with a dmf fitted,plenty with twin plate ceramic clutchs.I would think the problem lies with tall reverse gears and backing up with the clutch not fully released.Can an outfit be backed up with the clutch fully released on tick over because that would equate to around 20mph in reverse?Also as engine powers rise in the trend flywheels dont seem to get bigger,i understand Nissan are ready to launch a two stage turbocharged 1.6 diesel with around 160hp.This is great but the architecture of the engine will still be small.Meaning small flywheels and clutches.

 

[Wilbury]

Hi Seth,
I could not agree more re reverse gear ratios.
Over the years I have driven many dozens of different vehicles and consider them all to have a reverse gear ratio that is far higher than is required. It is a pure case of putting cost/profit before function.
Rgds

 

[JonnyG]

bit confused about this talk concerning reverse gear, as generally reverse gear is [corrected] a fraction taller than 1st gear and always has been, so as we are talking modern diesel with reference to DMF's they wont be doing 20 mph at tick over, and certainly will be no faster than 1st gear is.. ie.. first gear 5.7mph per 1000 rpm reverse 6mph per 1000 rpm.. just check out the gear ratio's of whatever diesel you drive to confirm reverse is as short as make no difference as first gear.

 

[seth1]

Whether its 6 or 20mph and your calculation sounds closer than mine,there is still not much chance of backing a van up with the clutch fully released.So in other words the clutch would be slipped most of the time.Not good for a dual mass flywheel.

 

[emmerson]

So buy an automatic!

 

[macandy]

DMF's?

The more I read about them, the more I thank God I always drive automatics.

 

[DeliDave_]

Well up to now ive not come accross a single heavy commercial vehicle with a dmf fitted,plenty with twin plate ceramic clutchs.I would think the problem lies with tall reverse gears and backing up with the clutch not fully released.

Havent got a Mondeo but used to work on them and there are posts on the Owners club forum about fitting the solid flywheel from the transit instead of the DMF

 

[JonnyG]

Well up to now ive not come accross a single heavy commercial vehicle with a dmf fitted,plenty with twin plate ceramic clutchs.I would think the problem lies with tall reverse gears and backing up with the clutch not fully released.

Havent got a Mondeo but used to work on them and there are posts on the Owners club forum about fitting the solid flywheel from the transit instead of the DMF

which with the Mondeo already being a tractor style engine is asking for trouble. all for the saving of at best 250 pounds, for more noise more gearbox issues for starters and mounts[ gearbox/engine] which no doubt will elevate any savings made in the first place. and actually finding which single plate flywheel from the transit collection is properly suited, due to the fact the transit has less bhp and less torque, than the variant engine fitted to the Mondeo.. .. companies like LUK do offer single plate conversions for popular cars, but not the mk3mondeo....which is what the forums talk about...