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-   -   Manual car rolls when parked in gear, normal or not? (https://www.team-bhp.com/forum/technical-stuff/266723-manual-car-rolls-when-parked-gear-normal-not.html)

I have a 2022 Suzuki 1.5L Petrol Ertiga with only 7.5k kms on it, almost 1 year 5 months old

Recently I had parked my car, in my apartment drive-through, which is a ramp leading to the basement, in first gear, and I tried to leave the car.

It has a moderate slope, (as most ramps do)

Suddenly while leaving the car, I noticed the car lunges forward in jerks, and stops again, before lunging forward again with a jerk, covering inches/ or a few cms continuously.

Is this normal?

I have been driving for years, and I had always thought that when parked in gear, it would be impossible for the car to move. So initially I got shocked to see this happen :eek:

Why does this occur? Is this normal or not?

If the car was parked facing the direction of slope, and engaged in 1st gear - then it will roll forward. Forward (slope) + Forward (gear) = Forward Movement.

I guess this is why people suggest to use the gear opposite of the slope direction in order to aid parking on slopes.

If the slope is too steep then you will see that behavior because the gear is not able to resist the forward weight of the car. Did this happen even when you applied parking brake? Like condor said, put reverse gear when parking nose down and first gear when parking nose up.

I was under the impression that it is the vaccum pressure inside the compression chamber in engine helps vehicle to hold. Imagine closing the top of syringe and trying to pull it. So it would require very high load (I suspect more than what a steep hill provides) to move it. Would any fault with inlet valve cause it to loose vaccum pressure?

Now I'm not sure about my hypothesis, but I suggest it would be good to check with a trusted mechanic / raise it up during next service to rest your mind.

Interesting topic. Does anyone know how electronic parking brakes work? Is that a physical brake like the hand brake or does it electronically apply a gear too? How good is it at keeping the car stationary on a slope?

If the force of gravity becomes higher than compression pressure of your engine, and your car is facing the slope, it will start rolling and as you said the engine will try to stop it again only for the gravity to make it roll again, causing the jerking motion you mentioned. That's why you are supposed to engage the opposites gear i.e forward gear if facing the upward slope and reverse gear if facing downward slope.

One interesting aspect of parking in gear is what happens when the car gets towed when opposite gear is engage?
AFAIK, this will either cause wheels to skid throught the tow, ruining the tires.
Or worse, force your engine to turn in opposite direction, which it isn't designed for, making your timing belt jump a few teeth and next time a piston moves upwards, your engine goes kaput.
Or maybe it might just damage your transmission.

Regards,
MiSiMa

Given a steep enough slope, it will still roll, turning the engine over in reverse. The concept of engaging gears so that the engine turns over in reverse, was due to engines self-starting once they start to turn over - especially diesels - and the car running away on its own power. Nowadays, with electronic control of fuelling, there is no way a modern engine will self-start even if turned over, since there is zero fuel supply.

The best options when parking on a very steep slope are 1. Turning the front wheels towards kerb (facing downslope) or away from kerb (facing upslope); 2. Handbrake & appropriate (low) gear for MT cars; and 3. Chocks (bricks, stones etc.) on at least 2 wheels - all applied together.

This is an useful relatively inexpensive product to buy and store in the vehicle(s).
I have a pair of these in each of my Jeepy things.
Available on Amazon.

For a ramp with a moderate slope (as you say) this does not sound like "normal" behaviour.

Does this happen every time? Or was there some instigator - like getting out of the car with a jerk to initiate the movement?


As others have said:
• Engine compression is what keeps the engine from turning over, and as a result keeps the car stationary when in gear.
• Lower gears (1st / reverse) use the gear ratio to the engine's advantage - making it harder for any movement of the car to rotate the engine.
• If the car was parked in 4th/5th, you might even be able to push it on flat land.
• If the force (slope+gravity) pulling on the car exceeds the resistance of the combination of engine compression & chosen gear, the car will move.

Your car is very new, so this feels like overkill to suggest, but if you get the chance to do an engine compression test, go for it. Might even save you from some bigger engine work later on.

Slipping clutch could also be another suspect, but due to the jerky movement (ie. engine actually turning over), it seems less likely here.


e-Parking brake (EPB) is an electronically actuated mechanical brake. In most cars you can hear the electric motor whirring as it engages & disengages.

Parking brakes ("emergency brakes") are usually not reliant on the hydraulic system, so that in the case of a catastrophic hydraulic failure, they can still be of use.

The EPBs sometimes piggy-back onto the hydraulic caliper, but actuate using electric motors. (example)

They usually do not tow the car on the driven wheels when it's in-gear, so opposite or same direction doesn't matter.

Old-school (manual tranny days) way was to pop the door lock and pop the car into neutral.

Nowadays with ATs, car alarms, FWDs/AWDs and EPBs, it's definitely trickier. But generally they will tow the car with the non-driven wheels rolling on the road.

Very interesting! Didn't think of that.

In my mind i wasn't sure about the "engine can't turn in reverse", but I always believed there was a slightttt advantage depending on whether 1st or reverse had a shorter ratio :)

My suggestion would be to use the parking brake to the max point and then engage in a gear. If the car moves forward even then, the other solution would be to use some bricks to keep the car from rolling.

And what does the Park mode do in automatic transmissions?

Well, the K15 engine has a decent compression ratio and this shouldnt be happening for moderate slopes. I'm guessing this has something to do with tech that makes the engine more efficient.

Also, as habit, it's always good to use the handbrake + drivetrail as parking brake and not just any one.
I'd suggest use the gear with the highest reduction. In most cases its the first gear.

It inserts a metal shaft called a pawl into the mainshaft of the gearbox, locking the gearbox with the wheels - so there is no way the wheels can turn at all.

Sorry, I might have a bad judgement, it is moderately steep slope, i.e, the slope is on the steeper side, as it leads to my basement parking.

I tried with an older WagonR on it,(with 1 lakh+ kms on it) it has the same behaviour.

Considering The 2022 Ertiga to be fairly new, with barely 7500kms on it, do I need to be concerned?

When I use a higher gear, like 2nd, on that slope, it rolls down a bit more steadily, with constant jerks, and banging noises.

To secure the car, I need to pull on the handbrake really tight, like almost in the vertical position, such that the brakes don't skid.

Here's the video of it, please have a look:

https://youtu.be/kNgZKRN5fXc

Since you bring this up:
I am some how not comfortable with engaging the opposite gear. A forward gear engaged, and the car rolls back-ward - or- vice-versa. Fuel injection or not.

*

In such cases, I try to use a stone to prevent the roll-back. Of course, in a city and where there is a kerb, I turn the steering so that the wheels rest against the kerb, or are close to the kerb.

My fear is that I will forget these things and drive away :(