Safe Speed Forums

Are you saying that preventing gearbox wear is a higher priority than safety?

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Theres no safety issue.

As someone hinted at earlier in the thread, since dual circuit braking systems became mandatory fitment, the efficiency requirement for handbrakes was reduced, as they were no longer considered to be necessary as a secondary emergency system. That's why modern handbrakes don't tend to be that brilliant.

From my own limited experience of reasonably powerful automatic cars I'd say that most handbrakes will resist the creep of the engine at tickover if firmly applied, but would be overcome fairly easily by an accidental burst of throttle, as might happen if someone shunted into you unexpectedly.

I'm also not comfortable about the idea of leaving the engine pulling against the handbrake, in case it hasn't been firmly applied.

But I do admit that this is the minor side of the issue, and as long as you are confident of the efficiency of your handbrake then fair enough. The main point is NOT to sit holding the car on the footbrake alone.

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Nope, you don't even need to push that hard on the throttle to overcome the hand/footbrake on some autos (the two I have experience of-Merc E240 and VX Omega 3l-will both do it with ease), so flooring it would definitely get you moving at a fair old lick-probably knacker your brake shoes as well...

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Chris

I could put my foot to the floor on my parking brake, and the car wouldn't move.

It does help that its RWD, and that the brake shoes are on the back.

What sort of car is it?

My experiences are mainly with BMWs, which tend to have very poor handbrakes.

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1997 E-class, 3.0 turbodiesel.

Mt car (E class Merc) will defeat the parking brake if it's only lightly applied (a couple of notches) but the parking brake will hold it easily enough if I apply the brake firmly (which I do when stopped on a significant slope). However, apply some power and the drive will defeat the parking brake even if fully applied.

I have to say I rarely apply the parking brake unless expecting to be stopped for ~30 seconds or more. If on level road, with nothing behind, I may select 'park' (that doesn't flash the reversing lights because there is a delay of ~1s before they illuminate). If stopped on a slope, I probably will apply parking brake (and select neutral). If several cars have stopped behind and the road's level, I'll just select neutral.

I have tried holding in drive and using parking brake but it can cause an uncomfortable lurch when it's released.

Even more reason to put it into N!

I don't buy the excuse on gearbox wear - yes an auto is more expensive to replace than a manual, but does putting it into N REALLY cause that much wear to the box itself and not just the lever latch button/mechanism?

If it really IS that much of an issue then maybe its a question of looking and planning further ahead so you can allow the car to creap along at tickover rather than having to come to a complete stop (not always possible, I know).

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Science won over religion when they started installing lightning rods on churches.

So you put your car into P or N while stopped at the lights. Meanwhile, you notice behind you a vehicle that obviously isn't going to stop in time before hitting you.

On a cold transmission, it can take more than a second to shift from P to D, decreasing to half a second typically on a warm transmission. Keep the car in drive, all you have to do is release the brake and you're instantly on the move? Also, by continually moving from N to D you're increasing wear on the drive bands, clutches, and all transmission mounts. By keeping it in D, all you're doing is heating a bit of fluid in the torque convertor, burning slightly more fuel.

http://www.roada.org/articles/automatics.pdf

Also, I would never use P without the parking brake. The Park position is designed to lock the transmission, not to stop the car from moving anywhere. The pin is tiny, and is also designed to use the weight of the car to help release it when you want to move.

So that's a valid argument for leaving a manual in 1st and depressing the clutch. This is considered (as far as I was taught) VERY bad practice.

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Science won over religion when they started installing lightning rods on churches.

Thats a manual transmission, for which different driving rules apply. You can't begin to compare the two, its foolish.

I still haven't seen any good, valid reason for leaving the car in D when stationary. As some have said, brakes don't hold powerful autos back very well which would suggest that leaving the transmission in D is bad practice!

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Science won over religion when they started installing lightning rods on churches.

This particular comparison looks perfectly valid to me. An auto left in drive is exactly analagous to a manual with first gear engaged, with the clutch held at the bite point and the throttle slightly depressed ready to go. Definitely not a good idea, especially if someone runs into the back of you!

Is there any appreciable difference between the time it takes to get an auto into drive and moving, compared to the time it takes to depress the clutch in a manual, select first and let the clutch out again?

I'd say that if you are alert to the possibility of someone arriving at speed from behind, as indeed good drivers should be, then you will also be ready to act in good time should one appear, including allowing for the time it takes to engage gear should you need to go for an "escape". Actually, if I was last in the queue and couldn't see a fair way behind me then I'd be in gear and ready to go anyway - manual or auto, but that's not what the original question was about, it was about the "stable" situation where you are sat at the lights [presumably with cars behind].

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The manual for my car recommends leaving the car in drive at lights etc. The Rospa document on automatics does the same - and points out that this reduces gearbox wear.

So that's the ONLY reason?

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Science won over religion when they started installing lightning rods on churches.

You're comparing chalk with cheese. Riding the clutch requires both feet and one hand. Idling in D requires one hand to release the parking brake.

Get shunted in D with the foot on the brake, and the car might creep forward if you released the brake during the impact. Not good.

Get shunted in D with the parking brake on, and the car might skid a bit, but will stop immediately. No braking is required. Best outcome.

Get shunted in N with the foot on the brake, and the car will roll whereever it pleases, presuming the impact caused you to release the brake. Not good.

Get shunted in N with the parking brake on, and the car again might skid, but will stop immediately. No braking required. Best outcome.


As you can see theres no real advantage to selecting N when stopped, other than increased fuel economy. I believe that this extra fuel economy is more than outweighed by the extra wear caused to the gearbox by moving it in and out of drive.


In a manual, waiting at the lights in 1st gear, foot on the brake and other foot on clutch. Get shunted, if you release the brake, the car will either creep forward or stall. If it stalls, it will not move. Not brilliant, but ok.

Wait at lights in neutral, foot on brake. Get shunted, car goes wherever it pleases until you press the brake. Not good.

Wait at the lights in neutral, handbrake on. Get shunted, car skids a bit, then stops. Best outcome.




An automatic takes much longer to get into drive from neutral than a manual car, which is pretty much instantaneous.

Have a look:

http://www.rospa.co.uk/drivertraining/i ... omatic.pdf

Going from N to D causes minimal wear on the low gear brake band. Holding in D causes the oil temperature to rise due to the 'slip' in the torque converter, making oil thinner and not as efficient. Which do you consider worse?

7 litres of ATF, a gasket, and filter cost less than £90 for my gearbox. The ATF lasts for typically 60,000 miles. To change the fluid, filter, and gasket takes about 30 minutes, and is an easy DIY job.

I'd rather change that, then have to take my gearbox to a transmission specialist after 100,000 miles. I wonder which is cheaper?

Also, my gearbox has an intercooler for the ATF.