How to determine the shifting schedule of automatic gearbox?

[ForestGump]

Can anybody give me a detailed description on how to determine the gear shifting schedule? Also, what causes the difference between upshift and downshift curves(they obviously don't follow the identical locus)?

 

[GregLocock]

Last bit first, no they don't. At all.

I'm only familiar with one brand. The basic shcedule is set by road speed and MAP, so you need a tacho or a speedo, and a vac gauge. There may be some advantage in a throttle position sensor.

Drive at constant MAP (say -40 kPa), plotting the upshift speeds. Do the same for -20 kpA, and for 0 kPA, trying to stay out of kickdown. Then try full throttle.

The best bet is to log rpm vs speed, which allows you to pick the upshift speeds exactly.

Then, on downshifts do the same. I haven't done this part, and don't know how succesful you are likely to be.

In reality the whole thing is set by a series of lookup tables inside the trans computer (which is often a part of the EEC), it is optimised for many different aspects of the performance of the car.






Cheers

Greg Locock

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