Shift points on an automatic three speed

[Rusty Davenport]

As I approach the world of three speed transmissions for the first time----I am curious about the shift points-------everybody has two different shift points in their control box------why the two different shift points ??????-----four speed manual guys never worry about that, they shift in the same place (at least they used to in the old days when real race cars had clutches )..........what is the deal here on two different shift points ????? Please, no comment from those who remember my four speed driving days.

[bobby]

I have often wondered that same thing. Seems like if you have two different shift points, that's something else that you have to remember. Oh yea, I manually shift my car.

[George Mirza]

There are a few reasons for different shift points. One is you only have 3 gears, and depending on the gear ratios the motor will drop out of the power band. Good example is a car with a low first gear will pull good through the 1-2 shift but lay over when you put it into 3rd. So you may have to turn it up a few hundred rpms to stay in the power on the 2-3 shift. I've heard some big block cars love to be short shifted on the 1-2 shift. Every car and combo is different and you just have to get out and test and see what works best.

George Mirza

[Todd Geisler]

Sometimes the automatic trans (manual VB in mine) will have a delay from when the shifter is moved till the trans actually makes the shift. You then have to shift earlier to have the shift wind up where you wanted. With my th400, there's about a 400 to 600 rpm delay in the 1-2 shift and maybe only a 100-200 rpm delay on the 2-3 shift.

Also, the rpm rate of accelleration is much quicker in 1st gear, so the shift comes pretty quick compared to down track when the engine isn't accellerating as quickly making the 2nd gear pull.

[bobby]

Originally Posted by Todd Geisler

Sometimes the automatic trans (manual VB in mine) will have a delay from when the shifter is moved till the trans actually makes the shift. You then have to shift earlier to have the shift wind up where you wanted. With my th400, there's about a 400 to 600 rpm delay in the 1-2 shift and maybe only a 100-200 rpm delay on the 2-3 shift.

Also, the rpm rate of accelleration is much quicker in 1st gear, so the shift comes pretty quick compared to down track when the engine isn't accellerating as quickly making the 2nd gear pull.

WOW, that's a lot of delay from one to two. Mine is only 200 in both gears.

[mrolds]

Originally Posted by Todd Geisler

Sometimes the automatic trans (manual VB in mine) will have a delay from when the shifter is moved till the trans actually makes the shift. You then have to shift earlier to have the shift wind up where you wanted. With my th400, there's about a 400 to 600 rpm delay in the 1-2 shift and maybe only a 100-200 rpm delay on the 2-3 shift.

Also, the rpm rate of accelleration is much quicker in 1st gear, so the shift comes pretty quick compared to down track when the engine isn't accellerating as quickly making the 2nd gear pull.

I've had the same experience on both counts. I have the shift light set at 5750 & still occasionally hit the rev limiter (set at 6200) on the 1-2 shift if I'm not quick enough. this was on two different brand transbrakes .

[Todd Geisler]

Originally Posted by bobby

WOW, that's a lot of delay from one to two. Mine is only 200 in both gears.

Are you sure? I use a data logger to verify the actual shift rpm.

[gymracer01]

I have played around with this and also use a logger to verify what is happening. My Buick likes a little (200rpm) early shift 1-2 than 2-3. My low compression stock head engine, could not be shifter too early really 1-2. I actually picked up a .1 one day at Bowling Green trying to slow it down by shifting early. Just have to learn your car.
Jim Netherland
2007 NMCA Nostalgia Super Stock World Champion
B/NSS 67 GS 400

[bobby]

Originally Posted by Todd Geisler

Are you sure? I use a data logger to verify the actual shift rpm.

It's a footbrake car, no-electronics. during timetrials, I actually watch the tach, ( who's watching the track?)sure I understand that it may seem like it's only 200, maybe more like 400. Maybe I am shifting sooner than I think? Wish I could afford a data logger, but with diesel prices as they are, I would have to not race for a year to be able to buy one, LOL.

[gymracer01]

Bobby, an Autometer Ultimate II Tach with the driveshaft sensor will get you what you need.
JIm N.