Why do some autos roll back on a hill?

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Tue 30 Sep 2014 20:03
Why do some autos roll back on a hill? - Pondlife

I've had a few cars with standard automatic gearbox. Some of them will hold the car still on a hill at idle, but other's won't.

Examples: Mercedes W202 2.4 V6 holds, Jaguar S-Type 3.0 v6 holds, Honda CRV 2.0 I4 rolls back.

With the cars that hold, it's not a mechnical holding device because if the hill is steep enough it will roll back, but it will hold still on moderate hills.

With the cars that won't hold, as soon as the hill is steep enough to stop the forward creep, it'll start to roll back. There's no range of slopes that it'll just sit on without creeping forward or rolling back.

It's a minor thing, but I've been wondering about it for ages. Is it something to do with the torque converter design?

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Tue 30 Sep 2014 20:30
Why do some autos roll back on a hill? - gordonbennet

I don't know how either of them work for certain, but neither my old MB or the Outback will roll back no matter how steep the hill is, it's a little disconcerting to be honest, i could release the footbrake and it would just stay there during a traffic light sequence on a max incline for instance but i don't.

I understand the MB box has a simple anti roll back device inside the box itself, must be simple mechanical/hydraulic its working perfectly at 18 years.

Compared to satans automanual and dual clutch things, TC boxes are all lovely to drive especially for hills requiring fine control, found the Matiz TC auto a little peach to drive.

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Tue 30 Sep 2014 20:59
Why do some autos roll back on a hill? - craig-pd130

It must be a combination of the design of the converter, idle speed and so on. I recently drove an Interceptor and that pulled like a frisky dog when the engine was cold and idle speed was about 1,200rpm (auto choke), requiring quite a firm foot on the brake pedal to stop it creeping.

When the engine was warmed up and idle speed around 600rpm, the creep was much gentler, needing only a light brush of brake. Don't know if it would creep uphill as I used to engage neutral when stopped at traffic lights etc (I know this is controversial practice with torque-converter autos :-D)

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Tue 30 Sep 2014 23:43
Why do some autos roll back on a hill? - John Boy

.. I used to engage neutral when stopped at traffic lights etc (I know this is controversial practice with torque-converter autos :-D)

Is it?

Could someone explain why, please?

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Wed 1 Oct 2014 01:05
Why do some autos roll back on a hill? - Happy Blue!

Lots of myths about damage to gearboxes left in neutral or park with engine running (all rubbish) and controversy about keeping your foot on the brake when stopped so blinding the driver behind you. I'm not saying what I do with my lovely Smax and its even better electric hand brake.......

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Sat 11 Oct 2014 23:11
Why do some autos roll back on a hill? - Wukl

"...and controversy about keeping your foot on the brake when stopped so blinding the driver behind you..."

Pure good manners to pull on the handbrake instead. Not that difficult, I manage to do it in my slushmatic.

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Wed 1 Oct 2014 12:34
Why do some autos roll back on a hill? - Pondlife

.. I used to engage neutral when stopped at traffic lights etc (I know this is controversial practice with torque-converter autos :-D)

Is it?

Could someone explain why, please?

I've heard that some autoboxes don't run the oil pump when in N or P. But even if that's true, I don't see that it would be a problem with the engine at idle.

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Fri 10 Oct 2014 23:19
Why do some autos roll back on a hill? - jamie745

Examples: Mercedes W202 2.4 V6 holds, Jaguar S-Type 3.0 v6 holds, Honda CRV 2.0 I4 rolls back.

I've got an S-Type and it has an electric parking brake (the older ones didnt) and it will not disengage until you put your foot on the accelerator.

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Sat 11 Oct 2014 09:10
Why do some autos roll back on a hill? - Hamsafar

Ours applies the service brake (if EPB is not on) over a certain angle and keeps it on until you move off.

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Sat 11 Oct 2014 16:13
Why do some autos roll back on a hill? - hillman

I suppose it depends how fast the engine is running. I reverse up my driveway which is quite steep and if I hesitate and don't hold it on the handbrake it might roll forward. I make a practice of always using the handbrake when stopped, regardless of either manual or auto.

When I was driving to work I used to wind the gearbox up against the handbrake occasionally and gain the extra acceleration. I've been frightened a time or to when doing that whilst driving a hire car where the handbrake is not so good.

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