DMF Flywheels Sleeping Policemen (France)

[Swanny87]

I kind of agree with the brakes - slow, gears - go mantra. For example; if I'm coming up to a set of lights on red on a 50 dual carriageway, I'll tend to slow down in 5th leave it a bit then grab third. The way I see it, if you slow down all the way in 5th and the light changes just before you come up to it, you're not in a suitable gear. I definitely don't agree with sequentially changing down gears though, it's a bit of a wasted effort and only useful on a track where you need to be in the optimum gear through the corner.

Edited by Swanny87 on Friday 7th November 11:16

[PhillipM]

nawarne said:

To OP!

Gears for GO....Brakes for SLOW.

See that so many times - easier and cheaper to replace a set of brake pads rather than a new clutch..even if it's just the friction plate.
Nick

I assume you release the clutch and coast every time there's a hint of overrun then?

I'm not sure why people seem to think overrun braking is bad on clutches...

[B'stard Child]

PhillipM said:

nawarne said:

To OP!

Gears for GO....Brakes for SLOW.

See that so many times - easier and cheaper to replace a set of brake pads rather than a new clutch..even if it's just the friction plate.
Nick

I assume you release the clutch and coast every time there's a hint of overrun then?

I'm not sure why people seem to think overrun braking is bad on clutches...

Either he's had IAM or Class 1 training as that's a pretty common expression used in both

it's not a bad thing but it isn't the whole picture/story

[anarki]

I was taught when learning to drive to read the road ahead and anticipate situations, slow the vehicle accordingly using the brakes and change down gears before the engine/drivetrain labours. Then if the traffic is moving and you're in 2nd gear doing 15-20mph you can then accelerate and begin to change up. If you do have to stop then the engine/gearing/braking in tandum works to bring the car to a nice calm stop.

Passed first time with 3 minors and have never ruined a clutch/gearbox in 10 years of driving.

Saying that my 13 year old S3 is going in for its first clutch and flywheel replacement next Monday after doing over a smidge of 100k miles and it was remapped 8k miles ago. Not to shabby for a car with 260bhp and 270lb/ft of torque

[lbc]

nawarne said:

To OP!

Gears for GO....Brakes for SLOW.

See that so many times - easier and cheaper to replace a set of brake pads rather than a new clutch..even if it's just the friction plate.
Nick

That is apparently how they teach people to drive these days.

No wonder there are so many accidents!

I have never replaced a clutch in over 30 years of driving.

If you are in too high gear for the conditions, brakes alone will not save you.

[wst]

lbc said:

If you are in too high gear for the conditions, brakes alone will not save you.

If you're in too high a gear for the conditions you should be changing to be in the correct gear for the conditions, but you should not be using the changing-of-gear to slow the vehicle down.

My car labours in 5th at 30mph on the flat. I don't change into 3rd at 60mph and use the engine braking to slow me down. I slow down to 30 with brakes (or coast down gradually) and then change into 3rd.

Brakes are slowing down devices (ok and vehicle balance but that's not in this type of situation), gears are for letting you control your speed more easily. If you're going down a 20% feel free to change into a lower gear to stop melting from your brakes. But just dropping gears instead of using the brakes is far less controlled and wears harder-to-replace components more, and isn't at all necessary for modern vehicles.

Off topic, but don't trot out the old "I've been doing it this way for ages it must be right" fallacy, as an aside. They said that about slavery once. Hell I probably said it when I was being potty trained.

[liner33]

I was always taught , "Gears are for slowing, brakes are for stopping" and be in the correct gear for the road speed at all times , drive the car dont let the car drive you.

[JamesL]

lbc said:

That is apparently how they teach people to drive these days.

No wonder there are so many accidents!

I have never replaced a clutch in over 30 years of driving.

If you are in too high gear for the conditions, brakes alone will not save you.

How does slowing on the brakes cause an accident?

Edited by JamesL on Friday 28th November 09:30

[McSam]

Howard- said:

McFarnsworth said:

Doesn't anyone revmatch while downshifting anymore? Can't say I've ever needed to replace a clutch on any of my cars, some of which went well beyond 250k km (~150k miles?)

Indeed. Shifting down a gear or two in order to increase engine braking is not going to hurt the clutch or gearbox if you rev-match appropriately.

Exactly this. Both of my cars appear to be on their original clutches, and one has a DMF. Both 2.8 litre sixes, both over 150k miles, neither shows any sign of any clutch wear despite one being used on track days and seeing dozens of hard launches.

Anyone saying you shouldn't use lower gears to slow the car because it's somehow "more wear" simply isn't driving properly.

[The Wookie]

Personally I heel and toe (although not screaming the nuts off it on every downshift) but I don't subscribe to any dogma, acceptable mechanical sympathy should be obvious to any half decent driver and any variance of driving style within that spectrum is likely to have minimal effect on the wear of any components. The type of driving you do (e.g. city or motorway) will have massively more effect on clutch, brake and gearbox wear.

[dvs_dave]

Failing to rev match on down shifts is poor and sloppy car control, and wears out the clutch prematurely (OP's problem). Also it can land you in trouble, especially in lightweight large engined rwd cars. Failure to rev match (especially when pressing on) can unstick the back end very suddenly and is very hard to recover from.

[sparkyhx]

SLCZ3 said:

Gears and brakes should be used together to slow down, in this day and age of 5+gears for forward it is even more essential to be in the "right gear" for the situation in a manual gearbox, an automatic is, as it says automatically in the right gear (supposedly).
Who approaches a roundabout or halt/stop/redlight situation in top gear and stops completely on their brakes, I pity your clutch/gearbox/and drive train.

er I do, and have done for 20 years since passing my advanced

[Countdown]

SLCZ3 said:

Who approaches a roundabout or halt/stop/redlight situation in top gear and stops completely on their brakes, I pity your clutch/gearbox/and drive train.

I do that if I'm approaching a red light and I know it won't change.(Not top gear, just whichever gear I was in on approach)

Could you clarify why it's "bad"?

[JamesL]

Countdown said:

I do that if I'm approaching a red light and I know it won't change.(Not top gear, just whichever gear I was in on approach)

Could you clarify why it's "bad"?

As long as you don't slow the engine below below idle speed or attempt to accelerate at unreasonably low revs it does absolutely nothing to decrease the wear and tear of your drivetrain.

Lots of rubbish being spouted in here IMO.

[BritishRacinGrin]

dvs_dave said:

wears out the clutch prematurely (OP's problem).

No, the OP's problem is with the DMF. The clutch plate almost certainly has tens of thousands of miles life left in it.

[GSE]

What are the symptoms of a failing DMF?

[weekbladder]

The Wookie said:

OP, I'll have a guess and say you either left it in gear and ran the engine at very low revs for the hump (which then probably put a spike of torque through the driveline as you hit it), or after going over it you declutched in 2nd or 3rd at low speed and laboured the engine.

Either of those would have finished it off, and lugging at low revs regularly is what will kill a DMF in less than 50k

I am not arguing with what you say but if it is correct then you illustrate what is wrong with these things.I drive a transit pickup for work which spends most of its time heavily laden often crawling over building sites at low speed so I will soon be replacing the starter,flywheel and clutch again.But what annoys me most about these things is they solve a problem I never knew existed,started driving with high mileage 70's cars and the only thing that never gave trouble was clutch/gearbox

[Matthen]

GSE said:

What are the symptoms of a failing DMF?

You can feel the engine power strokes through the clutch pedal when the DMF is on the way out

[GSE]

Matthen said:

You can feel the engine power strokes through the clutch pedal when the DMF is on the way out

Thanks. I was wondering if the damping properties of a DMF diminish with usage over time and mileage - or do they just go bang and fail in one swift move? It might just be my imagination, but I'm sure the drive train on my car doesn't feel 'as smooth' as it used to be. The car has now done 120k miles though, it might just be general wear and tear. I can't feel anything untoward through the clutch pedal, if I depress and release it whilst driving, so I'm not going to worry.

[Bobley]

I dont make a habit of engine braking but I tend to try and match the gear to the situation so I may grab 2 gears just before I reach an obstruction so I can accelerate away at the correct engine speed, but that speed is rarely higher than 2000rpm in a diesel so engine braking is subtle but the inertia of the engine can help stabilise the sheel speed in low grip conditions. The wife on the other hand will drive up to a stop line from speed and brake (clutch up in top gear) to 0 and often have the idle control fighting the brakes and juddering the f#ck out of the DMF. Her DMF is decidedly sloppy now (60k miles) it'll need doing soon. She also drives at low engine speed often (thinking its economic) ignoring the gear change indicator asking her to change down a cog (and raise revs) - you can sometimes hear the DMF rattling away (assuming she's not listening to the Archers or arguing with the kids).

In quiet traffic if I'm approaching a red light then I'll drop a gear and coast and use the brake at the end as a last resort as usually I plan my approach such that the light wont be red (or the junction will be clear) by the time I get there (I'm forunate in that respect that I live in a rural area so I dont have people behind me). My car has the same mileage as 'er indoors yet its as slick as the day I drove it off the forcourt new. So the engine will be doing some braking but it does turn the fuel off for a while?

If you want to use it, the diesel engine has plenty of engine braking potential as the piston secondary loads (skirt and ring pack) are higher due to the higher gas pressure and then the bearing drag is higher too. By comparison a petrol engine with the throttle open (ignition off) would only drop 30% motoring torque at 2000rpm compared to closed throttle, and ~no loss at 4000rpm, so in some cases a diesel will give higher braking.

The only time I use engine braking is when I'm on holiday in my van and I find myself driving down some steep lane to reach a MTB trail (Winnets Pass in Edale for example). In that case I'll let it spin away in whatever gear to about 3000rpm. It almost holds it! I just use the brakes for the occasional dab and then they cool while the engine takes a turn. When its motoring like that the piston loads will be lower than the firing load, the only usual concern is lack of gas pressure relief on the con rod so the rod bolts and bottom shell of the big end will see a higher load for part of the cycle but the engine will have been ran on the limiter at no load for 200hours during sign off so no load at 1000rpm less shouldn't be an issue.

As far as hitting speed bumps and level crossings I often dip the clutch just to reduce the large transient torque going through the transmission to the engine. Its a bit like MTBing in that respect. Brake before the obstacle, roll through, power away.