Surprise after parking on slight incline
09-02-2005, 07:18 PM
#1
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Surprise after parking on slight incline
I came home this evening and left my max parked in my driveway, which has mild incline. It's a 6-speed and I left it in 1st gear. Since it's mildly sloped I didn't even think of using the parking brake. Well about an hour later I went outside and was amazed to see the car down at the end of the driveway, about 40 feet from where it was originally parked. At first I thought someone had let it roll down, but as soon as I got in it the car moved backward a few inches. About 10 seconds later, same thing again - it moved backwards a couple of inches. 10 seconds later again...
Our driveway is not that steep - my 6 year old daughter can ride up it on her heavy steel Huffy bike. Yet even with the car in 1st gear, the engine resistance was low enough that it could slowly roll back. My previous car (4-cyl Accord, also a manual) never did this. Even on fairly steep hills it wouldn't roll when in 1st gear.
Has anyone else ever experienced this in their car?
I'm not concerned anything is wrong with the car. I did quickly pop the hood and verified the engine was actually turning as it rolled back, so it's not a slipping clutch. In fact, knowing the engine turns that easily is probably a good thing. On the other hand, I will have to start using the parking brake more now...
Our driveway is not that steep - my 6 year old daughter can ride up it on her heavy steel Huffy bike. Yet even with the car in 1st gear, the engine resistance was low enough that it could slowly roll back. My previous car (4-cyl Accord, also a manual) never did this. Even on fairly steep hills it wouldn't roll when in 1st gear.
Has anyone else ever experienced this in their car?
I'm not concerned anything is wrong with the car. I did quickly pop the hood and verified the engine was actually turning as it rolled back, so it's not a slipping clutch. In fact, knowing the engine turns that easily is probably a good thing. On the other hand, I will have to start using the parking brake more now...
09-02-2005, 08:01 PM
#2
I've actually noticed the same thing myself. Both of my other vehicles, both standard obviously, seemed to hold a lot better on hills than my max, 5 speed. I have a driveway with a pretty steep incline and my Nissan pick-up always held in 1st gear(parking Brake was stuck off). My max will not hold at all. Wasn't a worry for me either, but I did find it interesting as well. Just had to relearn to use a parking brake.
09-02-2005, 08:23 PM
#3
Yeah I've noticed the same thing with my Max. My Nissan pickup also holds pretty well in gear without the parking brake on. Now, I always leave it in neutral and pull the parking brake every time.
09-02-2005, 10:52 PM
#6
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Originally Posted by xtantmaxima
seriously, i can't believe you don't use the parking brake. In my old car I would place in gear + the parking brake because I didn't want it rolling away.
09-03-2005, 06:36 AM
#9
what if you leave it in 4th gear? that's what i ususally do+ e brake. i have had some work done on my car, and after picking it up, the dealer always left it in 4th. would the gear resistance be higher or lower in 4th gear?
09-03-2005, 08:29 AM
#11
Originally Posted by Nomad
Man I'd suggest you to check compression in your cylinders. How's yo max rides? does it eats any oil? It's not a good sign
Clutch problem?
09-03-2005, 09:52 AM
#14
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why is that not right? compression pressure bleeds off after a few seconds, allowing the engine to turn with no problem. not only that, but the 6 speed is geared rather short, making it that much easier to turn... dont leave it in gear, use the ebrake.
09-03-2005, 06:24 PM
#15
I started to talk about copression because i've seen some cars which moved backwards downhill. compression problem. Actually i saw few cars one of them move second did not. Guess who had problems? BTW both cars were geared on 1st gear and neither of drivers used e-brake.
09-03-2005, 07:17 PM
#17
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Originally Posted by chr0nos
would the gear resistance be higher or lower in 4th gear?
Originally Posted by MaximaPolak
Clutch problem?
Originally Posted by Nomad
Man I'd suggest you to check compression in your cylinders. How's yo max rides? does it eats any oil? It's not a good sign
Originally Posted by BewstAdd1ct
but the 6 speed is geared rather short, making it that much easier to turn...
In general, I'm thinking the more cylinders your engine has the more your car might be prone to this. Think about it. If you had a 1-cylinder engine then you would have to apply a lot of torque to push the piston through the compression stroke. If you have four cylinders, then at any one time one piston is in the compression stroke and another is in the power stroke. The torque needed to push the first piston through compression is somewhat balanced by the torque provided by the second piston. (We're talking with the engine off here.) So compared to the first engine, the 4 cylinder one turns more smoothly. Increase this to 6 or 8 cylinders and things smooth out even more. You don't end up with such high peaks in resistance. Of course more cylinders also means more friction, so you'd have to factor that in. Anyway, it's just an idea.
09-04-2005, 07:55 AM
#19
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Originally Posted by weltonw
Higher gear = less resistance
That would help explain this. The 3.5 engine does have good low-end torque, so maybe that lets it have a shorter 1st gear.
In general, I'm thinking the more cylinders your engine has the more your car might be prone to this. Think about it. If you had a 1-cylinder engine then you would have to apply a lot of torque to push the piston through the compression stroke. If you have four cylinders, then at any one time one piston is in the compression stroke and another is in the power stroke. The torque needed to push the first piston through compression is somewhat balanced by the torque provided by the second piston. (We're talking with the engine off here.)
yes and no... compression doesnt become relatively difficult until 30-45º ABDC, and eases up again around 25ishº BTDC, so really weve got around 120º of compression force to overcome, and once were past it, weve got another 600º of free rotation, not to mention any pressure thats left in the cylinder after the compression stroke will be helping us along for part of the power stroke.
600º of free rotation might mean the momentum to get the snowball started down the hill.
more cylinders means less degrees of crank rotation before another compression event, slowing the process, meaning less compression pressure to assist on the power stroke, and still more cylinders on their way to compresison.
i guess its a tossup, really i think it comes down to gear ratio, incline and vehicle weight and not much else.
09-04-2005, 10:23 AM
#20
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Originally Posted by Nomad
Man I'd suggest you to check compression in your cylinders. How's yo max rides? does it eats any oil? It's not a good sign
Every car does it. Ever heard of "popping the clutch"? A manual transmission should always be left in gear AND parking brake on. Sorry you had to learn the hard way. I learn the hard way when it comes to most things so I know how you feel. Life is a constant process of learning through trial and error.
09-04-2005, 02:17 PM
#21
Bewst, great post. I'm glad someone understands compression ratios. IF the car was rolling because of a compression, which its not, it would be virtually undrivable. The powerloss would be too signifigant. If a car has compression issues it will generaly be in one cylinder which would not allow the car to roll far, one sixth of a rotation basically. If all six where suffering from cmpression issues the engine would be worthless. It is a simple issue of the Max havng different gear ratios than the other cars mentioned. Plus the original post mentioned the car "clicking" back which relates directly to the transmission "slipping."
Agree with you last qoute MD.
Agree with you last qoute MD.
09-04-2005, 10:58 PM
#23
damn people.. if you don't know what you're talking about, STFU.
it's perfectly normal. I work on 4-5 cars a day and see it in probaly 75% of the manual tranny cars, as I have a pretty steep drive.
thus, I just keep a few wheel chocks laying around the driveway. pull up, stick in gear, shut off engine, SLOWLY let off brake to let car settle, jump out and stick wheel chock behind car. much safer than relying on the engine to hold it in place and it doesn't warp rotors like yanking the parking brake with hot discs. ouch.
it's perfectly normal. I work on 4-5 cars a day and see it in probaly 75% of the manual tranny cars, as I have a pretty steep drive.
thus, I just keep a few wheel chocks laying around the driveway. pull up, stick in gear, shut off engine, SLOWLY let off brake to let car settle, jump out and stick wheel chock behind car. much safer than relying on the engine to hold it in place and it doesn't warp rotors like yanking the parking brake with hot discs. ouch.
09-04-2005, 11:15 PM
#24
Originally Posted by chr0nos
what if you leave it in 4th gear? that's what i ususally do+ e brake. i have had some work done on my car, and after picking it up, the dealer always left it in 4th. would the gear resistance be higher or lower in 4th gear?
09-04-2005, 11:16 PM
#25
Originally Posted by SEmy2K2go
Why would you put the tranny under that stress, even if it is a slight incline? Just use the e-brake.
09-05-2005, 07:22 AM
#28
depends on which way the car is facing.
remember, the last thing you want to do is make the engine turn backwards. that screws with cams/valves, timing chains, oil pump, etc. not cool.
if the front is facing downhill, stick it in 1st so *if* it rolls, the engine will roll normal direction.
if the car is pointed uphill, put it in reverse.
As far as gearing, 1st and reverse are very close in overall drive ratio. depending on the tranny, 1st is either slightly shorter or taller than reverse. so it's a wash as to which one has the strongest holding power.
remember, the last thing you want to do is make the engine turn backwards. that screws with cams/valves, timing chains, oil pump, etc. not cool.
if the front is facing downhill, stick it in 1st so *if* it rolls, the engine will roll normal direction.
if the car is pointed uphill, put it in reverse.
As far as gearing, 1st and reverse are very close in overall drive ratio. depending on the tranny, 1st is either slightly shorter or taller than reverse. so it's a wash as to which one has the strongest holding power.
09-05-2005, 12:17 PM
#30
certain parts don't like to go backwards. it puts stresses on stuff that aren't usually stressed. If you look in the FSM on the timing chains and other stuff like that, it mentions specifically (several times) that you should NOT turn the engine backwards.
the actual problems that can occur by it? I dunno- but if the FSM says not to, the outcome can't be good.
the actual problems that can occur by it? I dunno- but if the FSM says not to, the outcome can't be good.
09-05-2005, 05:19 PM
#31
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oil pump losing its prime, timing chain slack on the wrong side, if the key were on, the engine might try to fire, which im a bit curious about myself...
probably nothing major, at least after only one or two times of it happening. i wouldnt make a habit of it.
probably nothing major, at least after only one or two times of it happening. i wouldnt make a habit of it.
09-05-2005, 10:29 PM
#33
Generally I'd say yeah, just use the parking brake and leave it in neutral, but Matt has a good point that if the brakes are very hot, you're going to mess up your rear rotors if you do it repeatedly. In that case park in gear with no brake unless you're on a serious hill.
09-06-2005, 06:02 PM
#35
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Originally Posted by Matt93SE
depends on which way the car is facing.
remember, the last thing you want to do is make the engine turn backwards. that screws with cams/valves, timing chains, oil pump, etc. not cool.
if the front is facing downhill, stick it in 1st so *if* it rolls, the engine will roll normal direction.
if the car is pointed uphill, put it in reverse.
As far as gearing, 1st and reverse are very close in overall drive ratio. depending on the tranny, 1st is either slightly shorter or taller than reverse. so it's a wash as to which one has the strongest holding power.
remember, the last thing you want to do is make the engine turn backwards. that screws with cams/valves, timing chains, oil pump, etc. not cool.
if the front is facing downhill, stick it in 1st so *if* it rolls, the engine will roll normal direction.
if the car is pointed uphill, put it in reverse.
As far as gearing, 1st and reverse are very close in overall drive ratio. depending on the tranny, 1st is either slightly shorter or taller than reverse. so it's a wash as to which one has the strongest holding power.
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