727 deference between D and 1 from a stop

[subforry]

Hi all,

This has been on my mind for awhile. My '66 Charger has 440 with 727 that might have had some performance work done on it - who knows. If I stomp on the gas in D/3, tires squeal as the the car quickly moves out. If I put the car in 1, stomp on the gas, it will spin the tires until I - pick one (chicken out, let up, or shift).

So why is it different? The trans is starting in 1st either way. Is there some trans/torque converter magic going on here?

Thanks.

 

[pnora]

Hi all,

This has been on my mind for awhile. My '66 Charger has 440 with 727 that might have had some performance work done on it - who knows. If I stomp on the gas in D/3, tires squeal as the the car quickly moves out. If I put the car in 1, stomp on the gas, it will spin the tires until I - pick one (chicken out, let up, or shift).

So why is it different? The trans is starting in 1st either way. Is there some trans/torque converter magic going on here?

Thanks.

They both start out the same. When you are in drive its allowing it to shift to 2nd with the wheel speed.

 

[BSB67]

They both start out the same. When you are in drive its allowing it to shift to 2nd with the wheel speed.

This. Its automatically upshifting from 1st to 2nd when in D and dragging the motor down.

You can reprogram the auto up-shift rpm.

 

[Photon440]

Starting in D engages the rear clutch. Starting in 1 engages the rear clutch AND the low/reverse band. Maybe you have a bit of slip in the rear clutch?

 

[R413]

Yes the whole thing is magic!

Manual low engages the rear clutch and low reverse band. Partial hold on overrunning clutch.

In drive first gear uses the rear clutch and the overrunning clutch

The front clutch is only engaged in third gear and reverse.

 

[BSB67]

Sure , but probably should not confuse the OP with the details that are not in response to the symptom that he is describing.

 

[Geoff 2]

subforry,
So, what exactly is different between the two scenarios? Wheels spin with each scenario?

 

[Photon440]

Sure , but probably should not confuse the OP with the details that are not in response to the symptom that he is describing.

He specifically asked about differences between 'D' and '1'.

 

[451Mopar]

"1" manual low applies the rear band and sprag, and also ignores the governor pressure so the trans won't shift to second until the selector is moved to second or drive.
"D" drive does not apply the rear band, and is harder on the sprag, but the transmission will try to automatically upshift when the governor pressure increases from the output / driveshaft speed

 

[68 Sport Satellite]

Any difference between the 2 for quickness of launch out of the hole from a dead stop with something like 1/2 throttle application? When comparing in my car, since the Low/Rev band is applied you can tell it feels tighter. With heavy throttle this can feel snappier, but with lighter throttle it feels like the motor bogs a bit compared to the same in Drive. This is all before a 1-2 shift has occurred. I might not be describing this correctly...

I know the OP didn't ask about drag racing, but I've often wondered if all else was equal, which would yield the quicker time? I barely know anything, but I would suspect from my little experience it could be about the same, but with an experienced driver, the edge may go to starting in 1 and manually shifting, as long as you don't shift too soon and hit the shifts cleanly.

 

[451Mopar]

The low band apply should not make a difference when starting off, but might change the 1-2 shift timing

 

[OneWheelPeel]

Aren’t burnouts more dangerous for the tranny in one scenario vs the other for the 727 and the 904?

 

[451Mopar]

Aren’t burnouts more dangerous for the tranny in one scenario vs the other for the 727 and the 904?

Yes, but some confusion because of the old reverse manual body instructions saying not to do burnouts in first, and use second gear, but that only applies to aftermarket manual valve bodies. starting in second gear in a normal forward body valve body is the same as in drive where you start in first with only the sprag to hold the drum. Use "1" manual low on a regular valve body to start a burn out so the low band is applied, and then shift into second gear.

 

[OneWheelPeel]

Yes, but some confusion because of the old reverse manual body instructions saying not to do burnouts in first, and use second gear, but that only applies to aftermarket manual valve bodies. starting in second gear in a normal forward body valve body is the same as in drive where you start in first with only the sprag to hold the drum. Use "1" manual low on a regular valve body to start a burn out so the low band is applied, and then shift into second gear.

Ok thanks, always kind of wonder if I’d grenade my stock tranny trying that, especially because of the confusion you mentioned.

 

[BSB67]

He specifically asked about differences between 'D' and '1'.

So, in the full context of everything the OP wrote in his post, you think this is what he is asking. Interesting.

 

[toolmanmike]

Aren’t burnouts more dangerous for the tranny in one scenario vs the other for the 727 and the 904?

Yes, if you do a high rpm burnout in manual low and back off the gas without shifting, you can take the sprag out and do some damage if not destroy the transmission.

 

[toolmanmike]

Yes, but some confusion because of the old reverse manual body instructions saying not to do burnouts in first, and use second gear, but that only applies to aftermarket manual valve bodies. starting in second gear in a normal forward body valve body is the same as in drive where you start in first with only the sprag to hold the drum. Use "1" manual low on a regular valve body to start a burn out so the low band is applied, and then shift into second gear.

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

 

[subforry]

Yes the whole thing is magic!

Manual low engages the rear clutch and low reverse band. Partial hold on overrunning clutch.

In drive first gear uses the rear clutch and the overrunning clutch

The front clutch is only engaged in third gear and reverse.

View attachment 1813189

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?

 

[R413]

How many burnouts have you been doing in drive verses manual low? The low reverse bamd is holding in manual low. That's the preferred operation of low on manual valve bodies, "low band apply" Maybe your sprague is damaged?

The car should do the same burnout had have the same power to the rear tires if everything is working correctly.

I had a broken sprague and didn't know it way back years ago. Took trans in and sprague was bad. Don't remember what the trans was doing but it wasn't right and shop said rebuild it.

 

[RemCharger]

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?

Well not quite. The gear ratio is the same, rpm the same, slippage the same.. ( none) .. but the difference is the torque holding capabilities. If you easily drive off in drive, the sprag is capable of holding. The manual low and use of the rear band, is there for high torque capability. ( towing, launching hard etc)