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No coast on cast iron Torqueflite?
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LostDeere59
Posted 2018-05-10 10:22 PM (#563124)
Subject: No coast on cast iron Torqueflite?



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This may be a silly question to those of you with more experience than I with the older drivelines . . .

My 60 Desoto is a 361/3 speed iron Torquflite car. Ever since I first road tested it prior to purchase I noticed that the transmission does not allow the car to "coast" in any gear - even 3rd.

No matter the conditions there is always some degree of engine braking taking place.

I know that often the early versions of automatic transmissions have what seem to be odd functionalities, so I don't know if this is a normal condition, or an indication of something wrong in the trans.

Any thoughts?

Thanks


Gregg
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di_ch_NY56
Posted 2018-05-11 3:03 AM (#563125 - in reply to #563124)
Subject: RE: No coast on cast iron Torqueflite?



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Hi Gregg

That‘s normal. When you keep the speed, you hold your foot on the throttle pedal. As soon as you lift it, the engine goes to the idle. Then the engine brakes when the engine is above the idle speed. It‘s a normal behavior on every „old“ automatic transmission as on every manual trans, except you press the neutral button at the gear selector or lift the clutch at a manual trans.

Only in some very modern roller coasters the electronic switches into a neutral position to save gas (hypothetical lower gas consumption or higher mpg at the test stand). For these roller coasters you have to apply the brakes more often...

Happy Restoring!

Dieter

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1960fury
Posted 2018-05-11 7:49 AM (#563129 - in reply to #563124)
Subject: Re: No coast on cast iron Torqueflite?



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so new automatics let the car freewheeling when you take the foot off the gas pedal? i do not think so.
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di_ch_NY56
Posted 2018-05-11 10:29 AM (#563138 - in reply to #563129)
Subject: Re: No coast on cast iron Torqueflite?



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1960fury - 2018-05-10 1:49 PM so new automatics let the car freewheeling when you take the foot off the gas pedal? i do not think so.

How it behaves at a very contenporary torque converter automatic (e.g. ZF 8 or 9 speed) I don't know - never ever driven one. But VW DSG (double clutch gear box) and manual trans at the Golf 7 will go to neutral when you coast (released the foot from the accelerator pedal)...

Happy Restoring!

Dieter

BTW: you'll notice almost no engine brake power (at 50 km/h - 30 mph) when the choke is active and the idle speed at the choke idle speed.

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57chizler
Posted 2018-05-11 12:02 PM (#563145 - in reply to #563138)
Subject: Re: No coast on cast iron Torqueflite?



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I don't believe there's any "freewheeling" in modern automatics but a lot of them do unlock the torque converter during deceleration which gives the effect of less engine braking.

In the case of the Torqueflite, there is freewheeling in one gear, breakaway first. If you accelerate from a stop in Drive and throttle back, there is no coast braking but it's hard to detect because the trans will usually upshift to 2nd when the throttle is raised and there is coast braking in 2nd.
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LostDeere59
Posted 2018-05-11 12:14 PM (#563147 - in reply to #563124)
Subject: RE: No coast on cast iron Torqueflite?



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Hmmmm . . . seems I've opened a can of worms.

Let me start by clarifying my concern. I'm talking about a significant amount of engine braking caused by back-drive through the transmission. The trans in my car upshifts very quickly, getting into 3rd gear at fairly low road speeds. I also have virtually no kick-down actuation, unless you really, really mash it. I suspect that may be due to worn/misadjusted linkage between the pedal/carb/trans.

That issue aside, when the accelerator pedal is released the car does not "coast" - it behaves the same as a manual transmission in high gear.

I know from education and experience that later "standard" aluminum case Torqueflites - both the 727 and 904 variants (and all other automatics of the same period) don't do that - when in high gear and with no accelerator input the transmission overruns, usually as a function of an overrunning or sprag clutch on the high gear drum. This is not the same as freewheeling or being in neutral because when power is applied to the transmission input the roller clutch lock up and power is again sent to the rear wheels.

My concern is that if my older iron case TF is supposed to function the same way, and isn't, that I may have a seized roller clutch, or hung/mis-adjusted band (which may be covering for a blown overrunning clutch). Obviously if the functionality is different, and the older iron TF doesn't coast, then I have no issue beyond adjusting the linkage.

And regarding "modern" transmissions - one of the significant changes in transmission function in recent years has been the replacement of mechanical governing with electronic shift control. This allows more precise, and varied, shift points. Another function that older "traditional" transmissions don't have is electronic control of the line pressure. In modern transmissions the line pressure is often reduced, or even dropped to zero, to reduce driveline drag and improve fuel consumption. So yes, when under light load coast conditions the trans may effectively be freewheeling, although the clutches are still electrically engaged awaiting line pressure to apply. Another scenario is stoplights - the line pressure is dumped essentially putting the trans in neutral, allowing reduced idle speed and engine load - less fuel. Of course the newest systems simply shut the engine off until the brake pedal is released . . .


Gregg
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1960fury
Posted 2018-05-11 2:23 PM (#563160 - in reply to #563138)
Subject: Re: No coast on cast iron Torqueflite?



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di_ch_NY56 - 2018-05-11 10:29 AM

VW DSG (double clutch gear box) and manual trans at the Golf 7 will go to neutral when you coast (released the foot from the accelerator pedal)...

_____

I do not THINK so. Modern cars do not burn fuel when you let them coast in gear but they do of course when you let them idle, so this would be a waste of fuel and also engine braking is sometimes needed.

Edited by 1960fury 2018-05-11 2:25 PM
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di_ch_NY56
Posted 2018-05-11 2:33 PM (#563161 - in reply to #563124)
Subject: RE: No coast on cast iron Torqueflite?



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Hi Gregg

I enclosed the chart out of the 1960 FSM, Chapter 21. Of course the iron hog (iron case torqueflite) has an overrunning clutch as the newer aluminum torqueflite. Personally I don't think the overrunning clutch could overheat. But what I have seen is an overrunning clutch with slashed rollers due to rust in the transmission caused by a leak in the radiator (/w integrated trans oil cooler). The trouble chart at the FSM addresses many malfunctionality.
Good Luck
Dieter





(Clutch engagement and Band Application Chart 1960 FSM.jpg)



Attachments
----------------
Attachments Clutch engagement and Band Application Chart 1960 FSM.jpg (152KB - 5 downloads)
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1960fury
Posted 2018-05-11 4:53 PM (#563175 - in reply to #563124)
Subject: Re: No coast on cast iron Torqueflite?



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Okay, I googled that. It seems that SOME newer VW automatics (couldn't find any other make, so it seems its again german smart ass technology) can be adjusted to be automatically freewheeling when coasting but this subject seems to be highly controversal as, as I said, when the (new) car is coasting in gear, it doesn't use any fuel but it does when freewheeling (idling) and of course every automatic can be shifted to neutral manually. Most owners seem to dislike the VW freewheeling option and to me it makes no sense whatsoever.

Edited by 1960fury 2018-05-11 4:59 PM
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57chizler
Posted 2018-05-12 12:47 PM (#563233 - in reply to #563147)
Subject: RE: No coast on cast iron Torqueflite?



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LostDeere59 - 2018-05-11 9:14 AM
I know from education and experience that later "standard" aluminum case Torqueflites - both the 727 and 904 variants (and all other automatics of the same period) don't do that - when in high gear and with no accelerator input the transmission overruns, usually as a function of an overrunning or sprag clutch on the high gear drum.


Not so; as I explained in my previous reply, the only time there is an overrunning function is in 1st gear in Drive. The overrunning clutch is in the rear of the case, not in any drum.

In high gear, when decelerating, the transmission is straight through engaged i.e. the input shaft is locked to the output shaft by engaged clutches. On deceleration the only thing affecting engine braking is the normal slippage in a non-lockup converter. With a lockup converter that doesn't disengage on deceleration engine braking is the same as a standard trans.
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57chizler
Posted 2018-05-13 4:15 PM (#563305 - in reply to #563175)
Subject: Re: No coast on cast iron Torqueflite?



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1960fury - 2018-05-11 1:53 PM

and of course every automatic can be shifted to neutral manually.


Illegal while moving in many parts of the U.S.
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LostDeere59
Posted 2018-05-13 5:52 PM (#563311 - in reply to #563233)
Subject: RE: No coast on cast iron Torqueflite?



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57chizler - 2018-05-12 12:47 PM

LostDeere59 - 2018-05-11 9:14 AM
I know from education and experience that later "standard" aluminum case Torqueflites - both the 727 and 904 variants (and all other automatics of the same period) don't do that - when in high gear and with no accelerator input the transmission overruns, usually as a function of an overrunning or sprag clutch on the high gear drum.


Not so; as I explained in my previous reply, the only time there is an overrunning function is in 1st gear in Drive. The overrunning clutch is in the rear of the case, not in any drum.

In high gear, when decelerating, the transmission is straight through engaged i.e. the input shaft is locked to the output shaft by engaged clutches. On deceleration the only thing affecting engine braking is the normal slippage in a non-lockup converter. With a lockup converter that doesn't disengage on deceleration engine braking is the same as a standard trans.



It would appear I have been schooled . . .again.

I spent some time looking around online and it seems my recollection is incorrect. However, that just leads to a slightly different version of the same question . . .

I spent plenty of time driving all kinds of automatic equipped cars from the 60's through current products. None of them exhibited the degree of engine braking my Desoto has. I'm talking any Chrysler/Ford/GM product from 1964 through the mid 80's. In high gear with no accelerator input those cars coast - yes there may be engine braking, but it is minimal, not enough to cause the typical exhaust noise, or even appreciably slow the vehicle.

But as I said above, the Desoto feels just like a manual trans - substantial deceleration, burbley exhaust, the whole deal. So based on the power flow through the trans, this must be something to do with the torque converter design. All things considered I wouldn't be surprised if the behavior is normal, I'm just looking for someone to confirm that the difference I feel isn't something broken . . .


Gregg
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1960fury
Posted 2018-05-13 6:51 PM (#563312 - in reply to #563305)
Subject: Re: No coast on cast iron Torqueflite?



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57chizler - 2018-05-13 4:15 PM

1960fury - 2018-05-11 1:53 PM

and of course every automatic can be shifted to neutral manually.


Illegal while moving in many parts of the U.S.


So the VW crap is illegal in some parts of the US?
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LostDeere59
Posted 2018-05-14 9:58 AM (#563342 - in reply to #563312)
Subject: Re: No coast on cast iron Torqueflite?



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1960fury - 2018-05-13 6:51 PM

57chizler - 2018-05-13 4:15 PM

1960fury - 2018-05-11 1:53 PM

and of course every automatic can be shifted to neutral manually.


Illegal while moving in many parts of the U.S.


So the VW crap is illegal in some parts of the US? :laugh:


No - because it is part of the normal functionality of the system, not a driver input.

Anyone with any thoughts on my updated question?


Gregg
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57chizler
Posted 2018-05-14 2:59 PM (#563366 - in reply to #563311)
Subject: RE: No coast on cast iron Torqueflite?



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LostDeere59 - 2018-05-13 2:52 PM
But as I said above, the Desoto feels just like a manual trans - substantial deceleration, burbley exhaust, the whole deal. So based on the power flow through the trans, this must be something to do with the torque converter design.


Plus the weight of the car and its axle ratio. Cars with higher numeric axle ratios (3.54-3.31) will experience more engine braking than cars with lower numeric ratios (2.93-2.76). Ditto for weight (inertia).
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LostDeere59
Posted 2018-05-15 11:11 AM (#563431 - in reply to #563366)
Subject: RE: No coast on cast iron Torqueflite?



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So it sounds like I may well be concerned about nothing.

I'll have to look into the rear axle ratio - I've also noticed that she doesn't seem to have very long legs, as they say, but I assumed it was just by comparison to my daily driver which has OD and a lock-up converter. Perhaps the answer to both of those observations is in the rear.

Thank you for the information sir - I appreciate the help.

Gregg
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