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  #1  
Old 10-24-2015, 09:16 PM
sixto's Avatar
smoke gets in your eyes
 
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stripped output shaft splines

I finally fashioned a tool out of a 1-1/4" socket (32mm works too) to remove the output flange and figure out why it spins free. I read about the nut coming loose ruining the splines but that's not the case here, at least it doesn't seem to be the case. it might have been a previous failure but I doubt it. The nut was on but good, no fore-aft play in the output flange. So, I removed the output flange and the tail housing. That plastic thing was loose but it's obvious where it fits. It snapped back into place. I thought about replacing parts but I put things back together for the night so as not to lose track of bits and pieces. Now the selector moves between P and R only. I guess I'm shopping for another transmission :/









Can I widen my search to include a 722.315 then swap in the .303 trigger wheel and tail housing?

Sixto
83 300SD

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  #2  
Old 10-24-2015, 09:55 PM
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Sorry to hear that the project just got delayed and more expensive. Hope you can find a new-to-you transmission. I'll ask my mechanic—he shares his shop with a transmission repair guy who might know of one. You need a 722.303? If you find one here I'll bring it down.
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  #3  
Old 10-24-2015, 11:46 PM
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That looks like the car was rolling when it was slammed into park..the splines on the output shaft look like they have some life in them..Maybe just another output flange??

You will need to open the pan and remove the valve body to get at the shift rod and see what is what with it..

Slamming it into park may have bent the rod
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1978 300SD 303400 miles
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  #4  
Old 10-25-2015, 12:33 AM
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I swapped a 303 tailcone onto a 315 transmission and you can indeed do this job successfully.

In my case, the 303 tailcone didn't completely cover that void where the lubrication tube for the speedo gear resides in the 315 body. I pinched-off and pushed in the tube and used JB weld to fill where the installed tailcone left that void.

But in your photos, you have a version of the 303 body that has the void but not the lube tube. Stretch's tear-down photos of his 303 also looked this way.

Therefore, your tailcone should fit without any modification, other than swapping the "spider". I swapped the entire parking cog with the attached spider rather than remove the speedo gear and install the spider.

After I had the car back on the road, I had an intermittent problem where the gear selector would not go into reverse or park without first turning-off the engine. This problem lasted for a few weeks and then went completely away. The transmission had sat for 6 years without use.

Of course, this is the opposite of your problem, but it may be related. The consensus was that the lockout mechanism that keeps you from shifting into reverse or park when the car is moving was malfunctioning. Probably a stuck valve related to the governor/secondary pump.

Now all is good.
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  #5  
Old 10-25-2015, 01:00 AM
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The selector was fine before I removed the tail housing so it's something I did or didn't do refitting the tail housing this evening.

Sixto
83 300SD
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  #6  
Old 10-25-2015, 07:34 AM
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Putting the car into park while rolling won't cause this type of damage, if anything it will snap off the parking pawl _after_ the car comes to a stop. When park is selected while rolling, the pawl will bounce off the parking gear until speeds are low enough that it finds a slot.

This is long term wear and it almost looks like there is a spacer missing ( governor gear ? ) in the stack up. I have seen situations where a nut or bolt was tight but it didn't compress the joint allowing things to move around.

As for the shifter not moving, the parking linkage / pawl assembly is likely not proper causing the park rod to jam.
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  #7  
Old 10-25-2015, 11:46 AM
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Going to rebuild my 722.315

Take a look at my tranny rebuild starting on page 10 shows the tail section being put back together ..It is not hard to take all this apart

You said earlier that the trans went out with a bang..Shifting it into park while it is rolling at any speed would put a tremendous strain on those splines..

The parking pawl is about 1/2 inch thick..same as the parking gear..The shaft that the pawl pivots on is pretty heavy too..The splines on the output shaft are pretty thin..
A sudden stop even at 3 mph could easily shear those splines off..
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  #8  
Old 10-25-2015, 01:45 PM
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No it won't shear the splines off if park was hit while moving. . . For the record, I base my words on 40 years of being in and around the car business / all sorts of machinery and seeing the results of someone hitting park at a walking speed.

As for my previous thought that a spacer was missing, I adjusted my screen and can see the governor drive gear is intact so the stack up was likely proper.

This is the result of long term wear called fretting, this is where two metal surfaces are slowly rubbing against each other causing them to wear. The metal generated during fretting is a fine powder that, given the location on the transmission, slowly made it's way into the fluid. When fretting occurs in a dry system, you will see fine brown rust around the joint.

I see no evidence of slivers of the alleged single catastrophic failure that resulted in sheared splines, if the drive flange splines had failed at the root, there will be small loose triangular pieces of metal. The trans shaft still has somewhat of a spline profile and definitely has not failed at the root. All of this points towards a long term failure, or even a the drive flange wearing out in the past, a replacement installed on a worn trans shaft and the wear process continuing.

And. . . .why are the parking gear splines / trans shaft in that area still intact? Why are the trans splines still perfectly straight? If this was an over torque, the entire trans shaft will be twisted to some extent.

It is well documented on this list that drive flanges wear out the internal splines resulting in sudden loss of drive. Any bang noise could have come from the drive line suddenly becoming unloaded.
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  #9  
Old 10-25-2015, 04:49 PM
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Then why is it that my rebuilt transmission that had over 400k miles on it didn't have any of this fretting going on..Perfectly clean and sharp on the splines..??

That is a shear off..where the splines are located on the yoke and shaft, it is dry on the outside of the transmission..no fluid to wash away the fretting..And if it is a dry area, your fretting powder would be seen..it is not..

The top of the splines of the yoke are in the valleys of the yolk splines..

That parking pawl is like a pole vaulters pole..the direction of the shaft spinning, will cause that pawl to jam into the first slot it hits..Sort of like the action of a ratchet wrench..where it will jam the spinning one way and click ratchet the other..

Why are the splines on the output shaft still intact you ask..Simply a harder metal..The yoke being a softer metal..

If this fretting wears everything down with its powder, where is the wear down on the output shaft??..the output shaft looks in pretty good shape..

Installing a good yoke and figuring out the problem on the shifting arm and you should be good to go

The OP said the the nut was on hard..he had a difficult time getting it off because it was so tight..If it is so tight as he said, how can there be movement??
If the nut was loose..yea there would be movement

My transmission has over 400k miles on it ..why doesn't it have this problem??
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1983 300D 341270 miles
1980 300SD 320456 miles
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  #10  
Old 10-25-2015, 06:34 PM
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For whatever reasons that yoke has been exerting wear on that output shaft and visa-versa for a long time. If you look at the shaft splines you can see the spline profile has been worn on both sides of the spline teeth eventually leaving only a shortened triangle in the place that originally was a splined tooth wide enough that a flat once existed at its outermost OD. That flat is missing and the shaft splines are now peaked, thinner and shorter.
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  #11  
Old 10-25-2015, 07:00 PM
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Quote:
Originally Posted by TopKnot View Post
If you look at the shaft splines you can see the spline profile has been worn on both sides of the spline teeth eventually leaving only a shortened triangle in the place that originally was a splined tooth wide enough that a flat once existed at its outermost OD. That flat is missing and the shaft splines are now peaked, thinner and shorter.
You are right..here is a picture of my tranny during the complete tear down..

The splines are flat on top..this is 400k plus miles on it..Why didn't mine do this wear problem??
Attached Thumbnails
stripped output shaft splines-aaaaa.jpg  
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1978 300SD 303400 miles
1983 300D 341270 miles
1980 300SD 320456 miles
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  #12  
Old 10-25-2015, 07:42 PM
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I looked at your thread and it's pictures in your post #146 where the splines on your shaft are perfect.

can't comment about why something like this didn't happen to you, but this instance could be due to someone being in that tranny previously or it could be something as simple as poor quality control somewhere in the supply chain or the assembly line.

My point was it's obvious that there is extreme wear on both the shaft and the yoke, extremely unlikely that would have occurred over a short time to end up looking like it does.

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