727 Big Block not engaging momentarily????

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BadBee

BadBee

'69 Dart 440/6/4 speed
Joined
Aug 16, 2015
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Hello ALL!!!
Here's the issue, '69 Dart BB /440. Start her up let her warm up, Sometimes not ALL the time, She will act like she's in NEUTRAL or PARK WHEN IN DRIVE or LOW GEAR??
(MILD SHIFT KIT- HURST HIS/HERS DUAL GATE SHIFTER) I usually shift it all the time,
Then after a while its fine! FLUID IS FINE ( COLD/HOT neutral,park) I just need her to last till
4 Speed goes back in but don't wanna BURN IT!!
I WAS THINKING FRONT PUMP??? only 5-6 K SINCE REBUILD!!!
A THANK YOU IN ADVACE AND HAPPY ST. PADDYS DAY TO ALL!!!! EVEN IF YOUR NOT IRISH
OR IRISH DESCENT!!
Thanks,
Mitch
 
Sounds like a classic sign of "morning sickness" as when the rubber seals are starting to harden up they take a bit to warm up enough to flare back out and seal.

1. Is it worse, or take longer to engage in the morning when cold and hasn't warmed up yet?

2. Does it engage if you rev it up a little?

3. Does it seem completely normal for the rest of the time you drive after it does this?
 
Seems normal after its driven, just does it when it's cold, seals seem to make sense,??
 
Could it be the converter draining down? Try letting it idle in neutral to get full flow before pulling into gear.
 
BadBee said:
Seems normal after its driven, just does it when it's cold, seals seem to make sense,??
Click to expand...

That's what it is then.
A converter drainback problem goes away in a few seconds weather it's cold or warm does not matter.
Hardening rubber parts work great warm but not cold.
Basically they call it "a soft parts rebuild" meaning nothing broken, just needs it's rubber parts replaced mostly.

That said, I wouldn't even think to do something about it without planning on new clutches and a front band at the very least. (well, front and rear seals also of course)

Sounds like that 4 speed may happen sooner, but the automatic could do what it's doing for a long time before it actually quits engaging completely.
 
Keep in mind that while the Forward-clutch (rear clutch) is slipping.......................
But then if the L/R band has run or is running out of servo apply that could do it.
Next time the tranny is cold, start it up in park, and then as soon as the engine will allow, shift it into reverse. If it bangs in; the following parts are working just fine; TC,pump,hi-drum and L/R band. That just leaves the forward clutch, and the KD band. And since nobody I know starts in manual second, it really just leaves the F-clutch.
But;
If it has a slight delay while the TC is filling and then, in a second or two, bangs in, then the TC is draining;no biggie. But if it acts the same as in manual low, that points to a L/R band adjustment. If after the band is known to be adjusted right, then by process of elimination, the Fclutch is Fubarred.
Or will be soon.
 
Assuming the rubber is not sealing when cold the trans doesn't slip, it just doesn't engage at all until the lip seal flares to the drum and then it applies fairly normally.
This is why they can run for quite some time in this condition.

Of course the little diagnostic questions and answers should tell us more.
I didn't get the answer about revving it a little and see if it engages when it refuses to move.



AJ/FormS said:
Keep in mind that while the Forward-clutch (rear clutch) is slipping.......................
But then if the L/R band has run or is running out of servo apply that could do it.
Next time the tranny is cold, start it up in park, and then as soon as the engine will allow, shift it into reverse. If it bangs in; the following parts are working just fine; TC,pump,hi-drum and L/R band. That just leaves the forward clutch, and the KD band. And since nobody I know starts in manual second, it really just leaves the F-clutch.
But;
If it has a slight delay while the TC is filling and then, in a second or two, bangs in, then the TC is draining;no biggie. But if it acts the same as in manual low, that points to a L/R band adjustment. If after the band is known to be adjusted right, then by process of elimination, the Fclutch is Fubarred.
Or will be soon.
Click to expand...
 
blown71duster said:
I would find it hard to believe a trans with a few thousand miles would have hardened seals.

Just sounds like the converter is draining down and with no flow in park would cause a delay in engaging.

http://www.forbbodiesonly.com/moparforum/showthread.php?45889-727-torque-converter-drain-back
Click to expand...

Could even depend on the age of the parts before they went into the trans, but anything is possible.

That would be fairly easy to diagnose.
Start it and put it in neutral when cold and give it a couple of seconds and put it in gear.
If it then moves when dead cold it is probably drain back.
If not, rubber.
Either one would be a fairly easy fix, if he wanted to fix it instead of replacing it with a 4 speed.

My point to the OP was it'll probably last awhile even though it does what it does.
 
Thanks for the input guys, ill go to the garage on Tuesday as we are getting hit with
More snow here in the northeast,Trailbeast I bought this machine off a guy who had
it in the garage for 25 years so yes I would say rubber seals are old,I'll be dropping
the granny in may if she lasts to do the convert back to the original 4speed as I wanna take it to Carlisle in July I'll post what happens Tuesday night
Thank you All!!!
 
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