727 transmission dilemma.

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Infiniti Dave

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Just completed a 727 Torqueflite overhaul with a few mods from a TCI kit. It's been 40 some years since I've had one of these apart ,but most of it came back. Upon completion including "air checking" all seemed well. The problem began when I slipped a spare slip yoke into the extension housing and realized that it will turn only one direction in neutral , but not the other. Disassembly for a second inspection found no apparent problems. Ant thoughts will be greatly appreciated !
 
Infiniti Dave said:
Just completed a 727 Torqueflite overhaul with a few mods from a TCI kit. It's been 40 some years since I've had one of these apart ,but most of it came back. Upon completion including "air checking" all seemed well. The problem began when I slipped a spare slip yoke into the extension housing and realized that it will turn only one direction in neutral , but not the other. Disassembly for a second inspection found no apparent problems. Ant thoughts will be greatly appreciated !
Click to expand...
The overrunning clutch prevents it from turning the other way. Perfectly normal!
 
I thought the same thing until I opened it up again and discovered that the condition went away when the clutches were removed. My next thought was that a clutch was stuck for some reason , but not so. It seems that the overrunning clutch is part of the driven components and splined to the planetary. It doesn't appear to be in play until the components in front of the output shaft (ahead of the snap ring) are installed.
 
Infiniti Dave said:
I thought the same thing until I opened it up again and discovered that the condition went away when the clutches were removed. My next thought was that a clutch was stuck for some reason , but not so. It seems that the overrunning clutch is part of the driven components and splined to the planetary. It doesn't appear to be in play until the components in front of the output shaft (ahead of the snap ring) are installed.
Click to expand...

That is because of trying to turn it through backwards gear reduction.
Perfectly normal.
 
I hear you.
As others have said, rotating the output in opposite direction is always more difficult, We all understand that; but that's not your problem.
Here are some possibilities;

1) If the trans is standing on it's face for this test;
gravity will be enough to cause all the clutches to fall together, and when they do, there is enough resistance to turning, to cause concern. This is especially true if the trans has been sitting this way for an extended period of time, which seems to cause the oil to be squeezed out.
But as soon as the trans is horizontal again, the clutches separate, and most of the resistance usually goes away.
2) bands too tight.
IDK how or why this is, but it has always seemed to me, that the L/R band in reverse direction is sortof self energizing. and I think the flex-band is worse for this. The KD band seems less sensitive. Plus when the trans is on it's face, the bands fall down a bit and rub on their respective drums, adding their bit of resistance to the clutches.
3) If when installing the front clutch onto the rear clutch, or
when installing the front end into the case,
one of the clutches fails to engage the splines of it's partner, then friction is greatly increased. and if you assemble it this way, it will bind up, but usually in both directions. IMO, this is not your issue.
4) But, if during assembly somehow a thrust washer to a planetary comes out of place, or is installed in the wrong anchor holes, then the geartrain will seem normal, until you load the front end, and snug it down; that action will crush the tangs on the washer, jamming it up. Depending on your endplays, this could produce a varying amount of preload, in addition to the normal one-way resistance.
The washer out-of-place thing should be discovered while checking the geartrain endplay, prior to loading the front end.
5) And finally, IIRC the sprague race has a lead-in chamfer on one side, that needs to go against the support. It's been well over 20 years since I last assembled one of those. So my question is this, what if it's in backwards? I mean, this will not affect the operation of the sprague, but if it was possible, and I don't know that it is, that the race does not seat, then the entire geartrain would be moved forward. If this was to occur, it might make installing the snapring difficult, not to forget the governor cross-pin. Now; I'm not saying the is your issue nor if it's even possible; I just remember the chamfer. So, if you cannot find an issue elsewhere, I guess a quick peek would be prudent.

IDK which....... if any ....... of these possibilities is your issue; but I've been tripped up a time or two by these kinds of things.

But as mentioned, once the trans is horizontal, a modest amount of resistance to rotation in the reverse direction is normal.

Good luck
 
Last edited:
Thank you for your experienced advice. I wonder though if we had clearance issues with the overrunning clutch or with a planetary thrust washer installed , both possibilities , would the snap ring at the end of the output shaft seat in the groove ? Also the end play of the input shaft after assembly seems normal.
 
Infiniti Dave said:
Oh;I forgot to mention the transmission assembly is horizontal on the bench.
Click to expand...
and was at the time of testing?
If the trans was mine, and already or still, on the bench, I'd be taking it apart. But if it was mine, I'm reasonably confident that it wouldda never come to this.
But since I'm not there to judge the turning effort,
which to me; "it will turn only one direction in neutral" seems excessive,
I can't recommend that YOU take YOURS apart. Like those before me have agreed upon, and your inspection showed, it could be and/or probably is, normal.

But just to reiterate in stronger words;
I have never had a TF that would not turn at all, in reverse rotation.
Well unless it was in Park, lol; but then, it wouldn't turn at all, lol.
 
AJ/FormS said:
and was at the time of testing?
If the trans was mine, and already or still, on the bench, I'd be taking it apart. But if it was mine, I'm reasonably confident that it wouldda never come to this.
But since I'm not there to judge the turning effort,
which to me; "it will turn only one direction in neutral" seems excessive,
I can't recommend that YOU take YOURS apart. Like those before me have agreed upon, and your inspection showed, it could be and/or probably is, normal.

But just to reiterate in stronger words;
I have never had a TF that would not turn at all, in reverse rotation.
Well unless it was in Park, lol; but then, it wouldn't turn at all, lol.
Click to expand...

I have always had to use pliers or channel locks to turn that way.
If in the car with wheels off the ground it can be turned with the drive shaft, but it still ain’t easy.
 
AJ/FormS said:
I hear you.
As others have said, rotating the output in opposite direction is always more difficult, We all understand that; but that's not your problem.
Here are some possibilities;

1) If the trans is standing on it's face for this test;
gravity will be enough to cause all the clutches to fall together, and when they do, there is enough resistance to turning, to cause concern. This is especially true if the trans has been sitting this way for an extended period of time, which seems to cause the oil to be squeezed out.
But as soon as the trans is horizontal again, the clutches separate, and most of the resistance usually goes away.
2) bands too tight.
IDK how or why this is, but it has always seemed to me, that the L/R band in reverse direction is sortof self energizing. and I think the flex-band is worse for this. The KD band seems less sensitive. Plus when the trans is on it's face, the bands fall down a bit and rub on their respective drums, adding their bit of resistance to the clutches.
3) If when installing the front clutch onto the rear clutch, or
when installing the front end into the case,
one of the clutches fails to engage the splines of it's partner, then friction is greatly increased. and if you assemble it this way, it will bind up, but usually in both directions. IMO, this is not your issue.
4) But, if during assembly somehow a thrust washer to a planetary comes out of place, or is installed in the wrong anchor holes, then the geartrain will seem normal, until you load the front end, and snug it down; that action will crush the tangs on the washer, jamming it up. Depending on your endplays, this could produce a varying amount of preload, in addition to the normal one-way resistance.
The washer out-of-place thing should be discovered while checking the geartrain endplay, prior to loading the front end.
5) And finally, IIRC the sprague race has a lead-in chamfer on one side, that needs to go against the support. It's been well over 20 years since I last assembled one of those. So my question is this, what if it's in backwards? I mean, this will not affect the operation of the sprague, but if it was possible, and I don't know that it is, that the race does not seat, then the entire geartrain would be moved forward. If this was to occur, it might make installing the snapring difficult, not to forget the governor cross-pin. Now; I'm not saying the is your issue nor if it's even possible; I just remember the chamfer. So, if you cannot find an issue elsewhere, I guess a quick peek would be prudent.

IDK which....... if any ....... of these possibilities is your issue; but I've been tripped up a time or two by these kinds of things.

But as mentioned, once the trans is horizontal, a modest amount of resistance to rotation in the reverse direction is normal.

Good luck
Click to expand...
<rolls eyes>
 
Infiniti Dave said:
Thank you for your experienced advice. I wonder though if we had clearance issues with the overrunning clutch or with a planetary thrust washer installed , both possibilities , would the snap ring at the end of the output shaft seat in the groove ? Also the end play of the input shaft after assembly seems normal.
Click to expand...

Yes, if you have a thrust washer out of place, or a seating issue with the sprag inner race , the snap ring on the output shaft would not seat into the groove.
 
Sorta thought that was the case. The back half has all gone back together clean and the snap ring is seated in the groove. I think this back end is okay, but I appreciate your thoughts and attention. Gonna complete the reassembly and hope something positive happens ! Thank you again.
 
Thank you to everyone who shared their experience and expertise. I still can't explain what happened , but upon the second assembly all seems functional. Content with final and not ready to ask a lot of unanswerable questions. Just accept my sincere thanks for every ones input.
 
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