1993 camrys RPM's inconsistent in overdrive?

tman · 19 Jul 2010, 03:57 am

Hi, I have a 1993 camry. When I am driving on the highway, especially up a hill, I try to limit the amount of gas I give the car to prevent it from shifting out of overdrive and into 3rd gear to save gas. However, it seems that the car will do a very small downshift while in overdrive, without shifting into 3rd gear. RPM's only rise about by about 500. What exactly is happening here? I don't think it is a real problem, as it does give the car slightly more power. But it doesn't make sense to me. It seems like a car with 4 gears should only have the option to make 4 shifts.

Thanks!

xyz87 · 19 Jul 2010, 04:03 am

only use over-drive. Without over-drive you maybe stressing the transmission and the ride won't be smooth at all. The idea of saving gas by turning off over-drive is ridiculous. It doesn't do anything to save.

wondering · 19 Jul 2010, 04:10 am

It is the torque converter clutch (TCC) unlocking. When steady state cruising the clutch engages or locks so that there is no energy wasting slip between the engine and transmission. When you go up a hill the TCC unlocks which allows:

The engine RPM to increase slightly so it can produce more horsepower.

The torque converter to do its job of multiplying the now greater engine torque to help the car climb the hill.

So say the engine RPM goes from 1500 to 2000 RPM which is a .75:1 ratio the torque would be multiplied by slightly less than the same ratio due to the losses. So if the engine output torque is 30 ft-lbs the torque into the transmission would be a little bit less than 40 ft-lbs.

1993 camrys RPM's inconsistent in overdrive?

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