transmission locking down....

553 Views 5 Replies 4 Participants Last post by Ravan17, Sep 10, 2007

kmn5

Discussion Starter · Sep 9, 2007 (Edited)

I have a question regarding leaving the car in gear when parked.
I posted in the general supra forums, cause I think all manuals should be the same (in principal at least)

But I think I might find some people more technically knowledgable about the W58 here.....

when I have the car on a hill (forward sloping down; front of car is lowe/rear of car is higher)
and I put the gear in Reverse, the car does not roll forward,
just curious about what's "locking" it in place since my rear diff is open, shouldn't the car still roll forward???

I used to be able to do the opposite on a forward sloping up hill and putting the gear in 1st, and kept it form rolling back.
Can any anyone else confirm this works for you???

but when I tried today, it failed to "lock" the wheels down.

My car was towed today like 50 feet by the nypd. Not sure if they towed it from the front or rear. But at the time my shifter was in Reverse; as I was on a foward downslope.....
When I tired to put it in 1st while parked on a hill later on in the day, the car still rolled backwards instead of "locking" down.....
wondering if they messed something up.....
Drove the car today ~50 miles and it seemed fine in all other respects

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Kurt

· #2 · Sep 9, 2007

One of your cylinders is on the compression stroke and the pressure is keeping the car from moving. Whether you put it in 1st or reverse, the effect will be the same. In 5th, the gearing will multiply the torque to the engine and it will probably slowly roll down hill.

The real question is, why aren't you using your park brake!!!??? haha

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Ravan17

· #3 · Sep 9, 2007 (Edited)

here is the deal...... first of all you will never "LOCK" your wheels in place by leaving it in gear.

second of all it shouldnt matter if its in reverse or first gear

what you do by leaving it in gear is make it hard for the car to move b/c with the engine in the off position the wheel have to rotate the mass of the tranny and the engine, and since the gearing is very high in first gear, its very hard to do, so you ahve more force holding the car in place then you do trying to move it.

now if you leave your car in 5th gear, it will be alot easier to move b/c of the lower gearing.

try putting your car on a flat surface and leaving it in each gear and try pushing it by hand, as you increase the gears (1, 2 ,3 , 4 ,5 ) it will gradually get easier and easier to push it, leaving it in reverse will only rotate the engine backwards if you are pushing the car forwards (make sense?)

when i park, i do both, leave it in 1st and the ebrake, the tranny parking technique is really good if you live far up north and have really cold days when you drive, b/c sometimes the ebrake cable can freeze up from the cold, and lock up your wheels untill it warms up, you can avoid this by simply parking in 1st gear

hope that helps

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dg_performance

· #4 · Sep 9, 2007

compression is still happening in the motor even if it is off!!!!
that is what kurt was saying above.... the motor is still going to have to be rotated against its own compression (on or off a motor has compression) which is what keeps the car from moving or makes it move in the first place. the gearing is kinda working like you say above but i dont feel like explaining the whole getting easier as gears go up thing.
it is more of engine compression with some help from the trans gearing actually "holding the car".

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kmn5

Discussion Starter · #5 · Sep 10, 2007

Thanks guys :bigthumb:

didn't realize the engine still has compression whgen off,
always figured one of the valves would lift or something like that

I only use the tranny to "lock down" the wheels on a steep hill, just in case the ebrake doesn't hold, I'm paranoid. (had seen a case where some lady's sentra rolled into an intersection, was not pretty)
anyways
Just wondering why it didn't work for me in 1st when I tried yesterday....I mean at least one of the cylinders should have been in a compression stroke, right?

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Ravan17

· #6 · Sep 10, 2007

well it depends on how steep of a hill it was, b/c like i said, your wheels arent exactly locked, they will still move, it will just take more force to move them

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