Roll-back in D

[Shude]

If my is car pointing up a steep hill, transmission in D, with the W/S switch set to W then the car holds it's position. If I select S it slowly rolls backwards. Both my current W202 and previous did this.

Does your car do this?

 

[Seamster15]

My ML does, I have to keep my foot on the Gas to stop it.

 

[BTB 500]

Surely it depends how steep the hill is?!

Having said that I don't recall my '97 SL ever rolling back in D (and it's always on the S setting).

 

[Doodle]

No, but in both of ours there are rather grunty engines to hold the car up.

 

[robert.saunders]

There are no steep hills in the fens....

I'm off to Scotland in October, will try it then

 

[nickmann]

same as yours, yes in D, no in W, both for my 202 and the 210.

 

[Shude]

No, but in both of ours there are rather grunty engines to hold the car up.

I don't think engine grunt has anything to do with it, there is clearly no attempt made to hold the car's position in S, it just rolls backwards yet in W it stays put.

I really want to hear from someone with a more modern car with C/S (I think) automatic options.

EDIT: some more info!

http://www.mbclub.co.uk/forums/showthread.php?t=3648

 

[nickmann]

I think the explanation is as follows -

In S you have creep, for manoeuvring. Creep means the gearbox is in normal mode, the power from idle is enough to move the car on the flat. A hill will overcome it, so you will rollback. This is fine, indeed useful, when parking on a slope in the dry.


In W you do not want to creep. This would be bad on ice, you would creep, front wheels locked, into whatever you are manoeuvring around. You don't want to roll back either. If it is icy then setting off is going to tricky enough without having to arrest the momentum first. The gearbox is not in normal mode, it can move only in the direction indicated by the selector lever.

 

[Doodle]

As per Nick's explanation, it is definitely the creep that is holding it on the hill, as on a really steep hill the C250 still tries to roll back. It does have a 5sp electronic autobox, but still with the S/W switch.

Ironically, the SL is less able at this trick than the humble C-class, hurray for the TD motor!

 

[Shude]

Ironically, the SL is less able at this trick than the humble C-class, hurray for the TD motor!

I honestly do not think it is related to the engine at all. The W211 E270CDI does the same thing!

 

[Doodle]

Possibly leading back to your earlier point regarding the C/S switch, as opposed to the earlier S/W?

 

[Dieselman]

The reason why they don't roll in W mode is because there is a sprag clutch which stops the gearbox rotating backwards. I suspect this is because hte gearbox transmits less torque in W mode due tot eh higher gearing and roll back would more prevelant. This would defeat the object of W mode as that is to give smooth starts when on snow or ice.

I've only ever known my car roll back once on a very steep hill. Normally I have to brake it to stop it creeping forwards even on steep inclines. This is due to the available torque from the engine.I think the newer gearboxes will allow roll back in disels due to the gearbox de-coupling at idle as an economy measure.
Even Der-Clunker does this but not much.

Try this as a test;
Stop the car and hold on the brake, now release the brake but only enough to allow infantisimal movement. In my car the engine note changes even though the car really isn't moving. When you stop the car again the note changes again.

 

[se97mlm]

Mine is the same as yours shude, in S it rolls back on the slightest incline, but in W it holds even on those super steep ramps onto a ferry. In fact then, i could feel it "catch" just before rolling back.

if i get the chance over the next few weeks i'll try a test car on the inclines on the test track at work: they've got up to 30% slope

 

[Shude]

I've only ever known my car roll back once on a very steep hill.

I live in Rochdale and I'm moving to Lancaster, every road is a very steep hill! This is why I notice the roll-back

Try this as a test;
Stop the car and hold on the brake, now release the brake but only enough to allow infantisimal movement. In my car the engine note changes even though the car really isn't moving. When you stop the car again the note changes again.

I'll see if I can spot that, I have a test hill which is seriously steep with traffic lights at the top, most people try to creep up the hill because hill-starts are so hard there (regular driving test location in fact!) for those that know the area it's the top of Queen's Park Road, to join Bury Road.

if i get the chance over the next few weeks i'll try a test car on the inclines on the test track at work: they've got up to 30% slope

Ahh, this is what I like to see, science at work! It'll be like mythbusters!

 

[BonzoDog]

I really want to hear from someone with a more modern car with C/S (I think) automatic options.



http://www.mbclub.co.uk/forums/showthread.php?t=3648

2005 280CDI automatic. Most of the time no. However we were just on hols and stopping on a steep hill the car would roll slowly backwards. Putting it into S slowed this effect.
SBC of course holds it completely.

 

[Shude]

2005 280CDI automatic. Most of the time no. However we were just on hols and stopping on a steep hill the car would roll slowly backwards. Putting it into S slowed this effect.

Ok that's helped a lot