In my never ending quest for random knowledge...
#1
Lexus Test Driver
Thread Starter
In my never ending quest for random knowledge...
What keeps my car from rolling backwards on a hill when I am D? I have been in many cars where the car will roll backwards when on a steep hill even when the car is D. My 1994 Lexus SC doesn't roll backwards ever on a hill when I'm in D, despite the grade of the hill. What is the reason mechanically? Is the differential the cause for this, or is it the use of a one way clutch?
#3
Lexus Test Driver
Thread Starter
Originally Posted by magneto112
Idle speed?? The fact that your car moves forward as soon as you let go of the brake??
#4
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iTrader: (4)
even my 92 camry, when it's on a not-so-steep incline, it doesn't roll back. just imagine when you are on a flat surface, if you don't hold your brake the car will roll forward right? you can think of that opposing the downhill down in "holding" your car's position.
#5
Lexus Test Driver
Thread Starter
Originally Posted by rominl
even my 92 camry, when it's on a not-so-steep incline, it doesn't roll back. just imagine when you are on a flat surface, if you don't hold your brake the car will roll forward right? you can think of that opposing the downhill down in "holding" your car's position.
ok I can understand that......but then why do some cars still end up having to be held when on an incline? Is it just poor quality in parts? Usually they are the cheaper cars that will roll backwards even when in D. My friend has a Cavalier, rolls back everytime. Another friend of mine has an automatic 94 Integra, rolls back every time.
#6
Lexus Fanatic
Several factors affect this besides those already discussed.....torque converter stall speed, type and viscosity of transmission fluid, transmission fluid temperature ( cold fluid has more drag than hot fluid ) , amount of brake pressure, type and efficiency of brake linings, transmission gear ratios in first and reverse ( you may have the lever in " D " but at a dead stop, in gear, the transmission itself will actually be in first ). Additional factors are vehicle weight and weight distribution, the torque curve of the engine ( especially at idle ) and the fact that some newer vehicles have " grade logic " sensors in the transmissions that can determine if the car is nose-up or nose-down and not only adjust the transmission's shift and gear-hold characteristics but also adjust the idle speed accordingly.
#7
Lexus Test Driver
Thread Starter
Originally Posted by mmarshall
Several factors affect this besides those already discussed.....torque converter stall speed, type and viscosity of transmission fluid, transmission fluid temperature ( cold fluid has more drag than hot fluid ) , amount of brake pressure, type and efficiency of brake linings, transmission gear ratios in first and reverse ( you may have the lever in " D " but at a dead stop, in gear, the transmission itself will actually be in first ). Additional factors are vehicle weight and weight distribution, the torque curve of the engine ( especially at idle ) and the fact that some newer vehicles have " grade logic " sensors in the transmissions that can determine if the car is nose-up or nose-down and not only adjust the transmission's shift and gear-hold characteristics but also adjust the idle speed accordingly.
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#10
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iTrader: (4)
Originally Posted by NYLexSC
ok I can understand that......but then why do some cars still end up having to be held when on an incline? Is it just poor quality in parts? Usually they are the cheaper cars that will roll backwards even when in D. My friend has a Cavalier, rolls back everytime. Another friend of mine has an automatic 94 Integra, rolls back every time.
#12
Lexus Fanatic
Originally Posted by NYLexSC
Didn't know it was that complex! Thanks for the insight mmarshall, I'm gonna do some googling to satisfy my interest now
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