727 - Driveshaft Jammed All The Way In

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Sleddogg

Sleddogg

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1972 Duster Twister / 318 / 727 / 7.25 axle

Greetings -

I'm finally getting around to getting my 8 3/4 swapped into my Duster (as an upgrade and to address weird drivetrain noise that I 'thought' was a pinion bearing) Today I crawled under and started removing the driveshaft and realized....no movement forward after pulling the u-joint straps. I got around to shining a light on the tail shaft and there is NO silver showing on the slip joint. It is jammed up in the trans and bottomed out - rear axle is at full droop at this point so we should be seeing something.

I know (well, my gut says - no fender tag) this car did not come with a 727 and likely born with a 904. Also, seems like I remember a 727 has a 3" longer tail shaft housing than the 904 as well. So, I am thinking that whoever monkeyed this transmission in the car never shortened the driveshaft and just caveman'd it all together. I was able to get the shaft out after basically destroying the u-joint.

So, I guess the question is - how much damage can I expect to the transmission with that driveshaft being bottomed out for so long. I don't know how long this trans has been installed like this. I've driven the car very little in the 9 months I have had it as I have been working on it.

Thanks in advance!
 
Did you swap in a 8 3/4 Where a 7 1/4 was?

If so the CL of axle to CL of pinion u joint is about 2 inches longer on the 8 3/4

That would account for the bottomed out slip yoke
 
Nope - haven't installed the 8 3/4 yet. This is with the 7.25 still installed - the only thing I have done is remove the driveshaft so far.

Sorry if that was unclear :)

Thanks!
 
Crazy thing is, when the axle is lowered, it does the opposite of what you want. Raise the axle, see if you get clearance...
 
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Hi Mopar Tim - thanks for the feedback. Even with the currently installed axle jacked up and not hanging, the driveshaft is fully seated in the transmission (bottomed out) and there is about 1/4" stopping the ujoint from going into the pinion yoke.

Just to clarify -I'm not trying to assemble this, I am tearing it all down for the swap (my first post may have been confusing, and for that I apologize). This is how the car came to me. My main concern is if there is any damage, I need to be looking for with the transmission with that input shaft being bottomed out for however long it has been before I got the car.

Thank you everyone
 
Sleddogg said:
Hi Mopar Tim - thanks for the feedback. Even with the currently installed axle jacked up and not hanging, the driveshaft is fully seated in the transmission (bottomed out) and there is about 1/4" stopping the ujoint from going into the pinion yoke.

Just to clarify -I'm not trying to assemble this, I am tearing it all down for the swap (my first post may have been confusing, and for that I apologize). This is how the car came to me. My main concern is if there is any damage, I need to be looking for with the transmission with that input shaft being bottomed out for however long it has been before I got the car.

Thank you everyone
Click to expand...
At this point, I would remove the u bolts, and move the axle back, remove the drive shaft, then figure out the correct length needed...
 
As for damage.

You mentioned that you had to destroy a u joint to get the slip yoke out.

Was this to get the drive shaft out of the rear pinion with no distance to push it into the transmission?


Which leads me to believe you got the slip yoke out.

Pull the seal off the end of the transmission and post some photos of the yoke and the end of the transmission.
 
Dana67Dart said:
As for damage.

You mentioned that you had to destroy a u joint to get the slip yoke out.

Was this to get the drive shaft out of the rear pinion with no distance to push it into the transmission?


Which leads me to believe you got the slip yoke out.

Pull the seal off the end of the transmission and post some photos of the yoke and the end of the transmission.
Click to expand...
Caps were damaged on the rear joint upon disassembly - but they were getting tossed anyway.

Yes, that was due to not having any distance to push the driveshaft in like I normally would.


I'll pull the seal and get the slip joint pictures posted here in a bit.

Thanks
 
Photos are attached - we have some other issues though (and why wouldn't there be lol)

Lots of rust on slip joint and if you look closely enough, we have some strawberry milkshake in the trans....interestingly enough what's in the pan looks OK. But it's definitely seen some water at some point.

Also looks like that drive shaft has kissed the tunnel at one point as well

IMG_1007.jpg


IMG_1008.jpg


IMG_1009.jpg


IMG_1010.jpg


IMG_1011.jpg


IMG_1012.jpg
 
You won’t like my answer, but it is what I would do in this situation.
Remove the trans. Check engine crankshaft end play, to be sure it’s not excessive from possibly getting shoved forward.
Remove converter from trans and check trans input shaft end play to get an idea if there is any damage internally.
Disassemble the trans for proper inspection of thrust bushings, and really everything. If all ok, reassemble with a minimum of new seal kit. Frictions and steels too if any signs of excessive wear or heat.
Now complete the rear end install with a new driveshaft and new slip yoke.

There is a chance it will be ok, so you could do the rear end and new driveshaft and slip yoke only. If the trans goes later on, the only extra work is removing the driveshaft again, after towing it home.
 
I think the internal rust on the slip yoke is an indicator of bad things inside the transmission.

The missing undercoat near the trans end might be from a trans swap. Don't think the drive shaft could have done that unless the previous trans tail shaft exploded.


You could wire wheel the rusty end and then insert it into the trans and check for play.

My guess is the bushing has been damaged from it's removal.
Might not be terminal.

Is this dirt or a crack.
Screenshot_20230225-180620.png



Is the trans /engine rotated?

Screenshot_20230225-180848.png
 
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Rear bushing is likely fine. You can see in the photos the slip yoke has a dirty area where the seal never rode against. So the output shaft was bottomed out inside the slip yoke, away from the rear bushing.

Editing to add, there is a chance the trans was fine and the previous owner just put an ugly slip yoke in there with a driveshaft that was too long. So the rust and dirty fluid in the rear did not get anywhere else. But chances always bite me in the ***.
 
Bobzilla said:
You won’t like my answer, but it is what I would do in this situation.
Remove the trans. Check engine crankshaft end play, to be sure it’s not excessive from possibly getting shoved forward.
Remove converter from trans and check trans input shaft end play to get an idea if there is any damage internally.
Disassemble the trans for proper inspection of thrust bushings, and really everything. If all ok, reassemble with a minimum of new seal kit. Frictions and steels too if any signs of excessive wear or heat.
Now complete the rear end install with a new driveshaft and new slip yoke.

There is a chance it will be ok, so you could do the rear end and new driveshaft and slip yoke only. If the trans goes later on, the only extra work is removing the driveshaft again, after towing it home.
Click to expand...
Hey Bobzilla-

No hate for your answer at all. I appreciate it. Ive pretty much resigned myself to pulling this transmission and have it gone through. The PO claimed it was rebuilt but if the same folks that jammed that driveshaft in without shortening it were the ones who built it, I’m certain I want to start fresh.

Its a project so no rush

thanks!
 
It makes one to wonder how they got the shaft installed in the first place. I don't even like to use a big screwdriver to pry a shaft over and into the yolk as I believe thats to danged tight. And it is. The slip joint is for slipping under dynamics and some extra. Plus expansion characteristics from heat.
 
cryplydog said:
It makes one to wonder how they got the shaft installed in the first place
Click to expand...

  1. The position of the rear yoke 12:00 or 3:00 might make a difference
  2. They might have loosened the axle u bolts to gain clearance
  3. The axle and springs supporting the weight of the car might have pushed the housing back enough to install.
It might be that the drive shaft is only a bit too long and under normal driving conditions (axle not dropping) the shaft fits and works fine.


If I interpreted your posts you did not have problems getting the slip yoke out of the trans once you got the rear u joint out of the rear yoke.

If the trans pan and fluid was clear, maybe the tail shaft seal had a leak, or was installed in the incorrect position and allowed water to enter the slip yoke area. I don't recall if the hole should face 12:00, 3:00 or 6:00

Screenshot_20230225-185057.png
 
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The best thing to do would be to measure for the correct driveline length after your new differential has been installed.
 
Get the drive shaft the correct length FIRST and then start your diagnosis.
 
Guys, I REALLY appreciate all the feedback-


1) I've been planning this swap for some time now - rebuilding the axle, purchasing new left springs etc. Part of the plan all along has been to measure for and have a correct length driveshaft built or have this one cut down and balanced, as I know that the 8 3/4 will require a shorter driveshaft. I have a local shop that is going to do that for me when ready.

2) My discovery of the slip yoke being bottomed (or close to it) out at full droop, full compression and ride height (after Mopar Tim's suggestion) led me to question whether or not some internal damage to the transmission could have taken place. It is my understanding that (and please correct me if I am wrong) that there is an overall length difference between a 904 and a 727 (Approx 3" if memory serves) - I am relatively certain this car came from the factory with a 904 which could explain why - this shaft is too long now and bottoming the slip yoke - However, when I got this car it DID have incorrect motor mounts installed - I have since installed the correct mounts and biscuits and replaced the transmission mount- perhaps that moved the motor back to its rightful place putting that pressure on the driveshaft.

3) As far as the current transmission - if I keep the 727, it will come out and be rebuilt. The presence of water in the fluid in the tail shaft housing doesn't bode well, and I can't trust that someone down the line just didn't do a quick pan drop and fluid change after having a trans cooler fail or something.

All in all - I have a pretty clear path moving forward. I appreciate the insight and hope that all have a great day.

Thanks

Edited to clarify that slip yoke was bottomed or very close to being bottomed
 
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Dana67Dart said:
I think the internal rust on the slip yoke is an indicator of bad things inside the transmission.

The missing undercoat near the trans end might be from a trans swap. Don't think the drive shaft could have done that unless the previous trans tail shaft exploded.


You could wire wheel the rusty end and then insert it into the trans and check for play.

My guess is the bushing has been damaged from it's removal.
Might not be terminal.

Is this dirt or a crack.
View attachment 1716055794


Is the trans /engine rotated?

View attachment 1716055796
Click to expand...
Sorry for the delay - the circled area is dirt

The transmission and motor sit level. That casting on the tail shaft housing above the red lines is not symmetrical for some reason.
 
Your plan , moving forward is excellent and I know you will be satisfied with te results :thumbsup:
 
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