727 deference between D and 1 from a stop

[68 Sport Satellite]

Start in first to get the tires spinning and shift to 2 without lifting, and finish your burnout.

and this applies for regular forward valve bodies also, correct?

Sorry OP to go a bit off topic here, but it's somewhat relevant.

 

[toolmanmike]

and this applies for regular forward valve bodies also, correct?

Sorry OP to go a bit off topic here, but it's somewhat relevant.

Yes. Don't stay in 1st with a Torqueflite. Manual low to second during the tire spin. The big horsepower guys start in second.

 

[toolmanmike]

and this applies for regular forward valve bodies also, correct?

Sorry OP to go a bit off topic here, but it's somewhat relevant.

1-2 that quick. You can hear the engine pull down.

 

[Photon440]

1-2 that quick. You can hear the engine pull down.

Well, it sounds more electric in that video.

 

[toolmanmike]

Tom in the Duster starts in second. Near 900 horse and a manual valve body (of course)

 

[RemCharger]

The big horsepower guys start in second.

But again, for the regular folks reading, starting in second is for manual shift valvebodies .

 

[toolmanmike]

But again, for the regular folks reading, starting in second is for manual shift valvebodies .

Yes.

 

[451Mopar]

Sort of related, always stop the car with the brakes before shifting from forward to reverse, and reverse to forward.

 

[Photon440]

Sort of related, always stop the car with the brakes before shifting from forward to reverse, and reverse to forward.

Well, you're no fun.

 

[dvw]

Ok this explains there is a mechanical difference/behavior between starting in D and 1, and answers my question. I think I will have to better understand automatic trans to really get it.

So the gear ratio is the same, but 1st allows for more slipping, which allows more RPM and more torque?

Is this typical of more automatics of the time?

I don't think you understand. 1st gear is provided when the forward clutch (rear location in the trans) is applied and the rear drum is held. In manual low the rear drum is held with the low roller clutch and the rear band. In the D selection the rear drum is held by the low roller clutch alone. Either way the components that hold the rear drum in 1st gear are both doing the same job. There is no difference in slip. The difference occurs on the 1/2 shift. To complete a 1/2 shift the intermediate band is applied stopping the high/reverse drum. The forward clutch is still applied. This creates 2nd gear. In the D selection when the intermediate band applies the rear drum is allowed to rotate as the low roller clutch only holds it in one direction only. In posistion 2, the rear band needs to release as the intermediate band applies. The low roller still overruns the same. So the only difference between the two selections is that the rear band has to release the drum if it's in selection 2. Either way the low low roller always hold the drum in one direction. So there is no "Slip" difference.
Doug

 

[BSB67]

I don't think you understand. 1st gear is provided when the forward clutch (rear location in the trans) is applied and the rear drum is held. In manual low the rear drum is held with the low roller clutch and the rear band. In the D selection the rear drum is held by the low roller clutch alone. Either way the components that hold the rear drum in 1st gear are both doing the same job. There is no difference in slip. The difference occurs on the 1/2 shift. To complete a 1/2 shift the intermediate band is applied stopping the high/reverse drum. The forward clutch is still applied. This creates 2nd gear. In the D selection when the intermediate band applies the rear drum is allowed to rotate as the low roller clutch only holds it in one direction only. In posistion 2, the rear band needs to release as the intermediate band applies. The low roller still overruns the same. So the only difference between the two selections is that the rear band has to release the drum if it's in selection 2. Either way the low low roller always hold the drum in one direction. So there is no "Slip" difference.
Doug

Doug - in a typical street deal, is the 1-2 shift cleaner/faster in “D” because there is only one action - applying the intermediate band, verses the two “simultaneous” actions of both applying and releasing the intermediate and rear bands?

 

[AR67GTX]

I’m always amazed that I managed to do a complete rebuild my 727 successfully, but I continue to have the shallowest understanding of how the damn thing actually works. Good step by step instructions I guess.

 

[dvw]

Doug - in a typical street deal, is the 1-2 shift cleaner/faster in “D” because there is only one action - applying the intermediate band, verses the two “simultaneous” actions of both applying and releasing the intermediate and rear bands?

Yes it is. Thats why many race valve bodies don't have low band apply. The 1/2 shift is seemless. It's either in 1st or in 2nd. There can't be any overlap like during the 2/3 shift.
Doug

 

[BSB67]

Yes it is. Thats why many race valve bodies don't have low band apply. The 1/2 shift is seemless. It's either in 1st or in 2nd. There can't be any overlap like during the 2/3 shift.
Doug

I don’t remember, do you use LBA in your race car?

 

[dvw]

I don’t remember, do you use LBA in your race car?

The racecar does not use LBA. I do have one in my street car as it doesn't have a shield.
Doug

 

[451Mopar]

Well, you're no fun.

My days of neutral drops, and throwing the car in reverse at 50 MPH are over. Broke too many transmissions when I was a teenager.

 

[BSB67]

To recap to the OPs original question:

The car will accelerate exactly the same in D-1st as it will in manual-1st, up to the shift point. Or, said differently, they will accelerate the same while in 1st gear.

A lot of other good info too.