Automatics and rolling backwards ....

[g8dhe]

So is it a myth or is there an mechanical explanation relating to rolling backwards or not on a hill start with an automatic, especially a Bongo ? I wonder if Alacrity or someone with professional knowledge has an answer ?

[Bob]

There's a little drag from the fluid fly wheel which will tend to move the vehicle forwards (assuming in a forward gear) if the brake isn't applied, but this will be overcome by gravity if facing up hill.

Tip: to do a hill start in an auto put your left foot on the brake, apply gentle power, and release the brake as you feel the transmission 'Bite'.

Covering the brake with your left foot is also handy when manouvering in a tight spot, but don't try and use your left foot while travelling above walking speed. You will brake far too sharply.

[g8dhe]

Well that confirms my own thoughts on the subject, I've yet to try a hill start in the Bongo! But I have seen several people over the years say "you can't roll back in an auto" and the matter just came up on on FB, so after my normal googling it seems there is a "myth" that you can't roll back, but no real explanation other than the fact that the various boxes are set up differently with the amount of bite varying.

[mikeonb4c]

Well that confirms my own thoughts on the subject, I've yet to try a hill start in the Bongo! But I have seen several people over the years say "you can't roll back in an auto" and the matter just came up on on FB, so after my normal googling it seems there is a "myth" that you can't roll back, but no real explanation other than the fact that the various boxes are set up differently with the amount of bite varying.

They're sort of right but its largely illusory. On a slight incline the fluid drag will stop or delay/reduce rollback. For steeper hills a little throttle may suffice to do the same. What is no longer necessary is the balancing of clutch let out when moving off (cos there aint one!). I still use my handbrake in traditional hillstart manner. Helps to stay that way for when i'm driving a manual car.

[Bob]

Trust me Geoff, an auto will roll back on a hill.

Your thoughts are correct, vehicles vary, and there will be a gradient where a particular vehicle won't roll back, but load it differently tomorrow and it will either run forwards with the gearbox drag or backwards with the weight.

Most of the nonsense talked about auto boxes is spouted be people who have never driven one.

'You're lazy', 'I like to be in control', 'They creep forwards at traffic lights' (that's what the brake is for), plus 'They can't roll backwards' and many more.

[Diplomat]

There's this useful thing in the centre console called a handbrake..

..saves ever putting your left foot anywhere other than on the footrest!


Frank

[Bongolia]

Well that confirms my own thoughts on the subject, I've yet to try a hill start in the Bongo! But I have seen several people over the years say "you can't roll back in an auto" and the matter just came up on on FB, so after my normal googling it seems there is a "myth" that you can't roll back, but no real explanation other than the fact that the various boxes are set up differently with the amount of bite varying.

Really depends on the type of transmission fitted.
Its more common on semi automatics and CVT`s the vehicles body stability sensors are used to tell the transmission control unit that the vehicle is facing up hill and adjust the throttle to compensate while others work by applying the service brake, the brake is released by a signal from the TPS.
Mercedes use their electronic stability programming to do this.
My wife's Smart car ( developed in conjunction with Mercedes) holds itself on inclines this is a semi automatic. I believe that vehicle achieves this by "slipping" the clutch so not really a good idea to use it for any length of time.

As for the Bongo it is fluid so as Bob says there will be some drag that will have the effect of resisting the roll back on slight inclines.
Pre TCU days I would set the idle speed up to have a slight pull forward in drive. I dont know if the Bongo can be adjust manually like this I suspect it cannot without switching out the ECU/TCU first or whether it`s programming is clever enough to balance the roll back automatically.


I know the norm is to use the right foot for both brake and accelerator but I almost always use left for the brake and right for accelerator in city and B road driving just seems easier that way.

[Bob]

Interesting info on the workings of modern autos, thanks Bongolia.

[MalcW]

I just use the handbrake in time honoured fashion. And I tend to put it in neutral if I'm stopped for any length of time, the theory being that if it's trying to creep forward and I won't let it I must be wasting fuel.
In fact the problem I'm more likely to have is almost stalling my MX5 or my wife's Astra because I just remember at the last moment that there's a 3rd pedal I'm supposed to do something with...

[Bongolia]

I just use the handbrake in time honoured fashion. And I tend to put it in neutral if I'm stopped for any length of time, the theory being that if it's trying to creep forward and I won't let it I must be wasting fuel.
In fact the problem I'm more likely to have is almost stalling my MX5 or my wife's Astra because I just remember at the last moment that there's a 3rd pedal I'm supposed to do something with...

Been there, done that...and still do.

[Merlot man]

I just use the handbrake in time honoured fashion. And I tend to put it in neutral if I'm stopped for any length of time, the theory being that if it's trying to creep forward and I won't let it I must be wasting fuel.
In fact the problem I'm more likely to have is almost stalling my MX5 or my wife's Astra because I just remember at the last moment that there's a 3rd pedal I'm supposed to do something with...

I thought I was the only one
The mx5 and 5 series seem " crude " in comparison
Bongos all the way !
Brian

[Alacrity]

It isn't so much 'fluid drag' that makes an auto creep but the fact the torque converter is trying to do its job & connect the engine to the gearbox. It acts as a sort of pump forcing oil from the engine side (i.e. the casing that is bolted to the engine drive plate) - the impeller, to its opposite number that is connected to the input shaft of the transmission. On the way it passes through the stator (which is the difference between a torque converter & a fluid flywheel (which has no stator)) which gives you the torque multiplication (noticed as a rev increase when you apply the throttle to pull away). Fluid is pumped through the converter so they are always operating in pressurised oil. So on a slight incline it will hold you in place but on a steeper hill you would have to increase the revs to get the transmission to hold you staionary. OK if only for a short while but it generates a lot of heat so not a good idea to do it for a sustained period. As others have said the handbrake is meant for that.

Modern auto vehicles will use various ways of holding on hills, but again it is not intended for sustained periods or for steep hills. Some will, as in the case of the Smart car mentioned (which isn't a true auto but an automated manual transmission that has computer controlled servos & pumps to work the gears & (standard manual type) clutch) slip the clutch (funnily enough as you would in a manual!), but most conventional automatics with a torque converter will put two gears on at once which locks the transmission solid so it cannot roll back, leaving the converter doing nothing. If the hill is too steep, the driver opens the throttle or if it is holding for too long it will release or not apply at all. DSG's, CVT's all slip a clutch (both wet & dry) to hold a car - assuming it doesn't have hill assist which will involve the brakes.

Here endeth today's lesson.

[g8dhe]

Thanks Geoff, that makes sense, and yes now I'm driving and found a few hills I've been experimenting but haven't found a really steep hill yet!

[Bob]

Splendid info, thanks Geoff.

[Glenda]

Thanks Geoff, that makes sense, and yes now I'm driving and found a few hills I've been experimenting but haven't found a really steep hill yet!

Just had some super steep hills in Portugal. Bongo stood still on most. The ones it had trouble on would be the equivalent of the Bostall near you. It is the road from Steyning going by Steyning Bowl and the South Downs to Sompting Church. You should find it empty enough to stop on mid week and do your test.....Otherwise drive around Hanover in Brighton.