My second M715 build. What was I thinking?

[67smith]

The shafts are split right behind 4th gear(small gear at front of transmission, 1st is the large gear at the back still internal to the case)

Basic principal is a sliding collar that is splined directly to the shafts, the gears themselves aren't directly connected to the output shaft. There should be a clear space between syncros and collar.

When in 4th the power comes from the input directly out the output shaft, all other gears go through the counter shaft.

If you slide the collars back and forth, you "should" be able to spin the gears and the input should not move with the output. That should narrow the inspection down to a certain area.


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[67smith]

I mispoke, and edit is too long gone. Reverse is the last large gear internal to the main case,

gear as ordered front to back- 4th, 3rd, 2nd, 1st, reverse, 5th is contained in the rear housing. fifth has its shift collar on the counter-shaft unlike all the other gears. so the fifth attached to the output is fixed, unlike all the other gears. fifth on the countershaft is "free-spinning" unlike the other gears.

[jeeper]

Thanks for that.

So in 4th gear then the shift collars would all need to be engaged to lock the input and output together directly without power going through the counter shaft? It looks like 4th gear also powers the counter shaft continuously. It must also be the gear attached to the input shaft?

[67smith]

Thanks for that.

So in 4th gear then the shift collars would all need to be engaged to lock the input and output together directly without power going through the counter shaft? It looks like 4th gear also powers the counter shaft continuously. It must also be the gear attached to the input shaft?

Yes, 4th gear shift collar will connect input to output, and it also drives the countershaft. ..so technically speaking there is no real 4th" gear"

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[Von]

Wow. Looking at the exploded view... Nuthin like my T10.….
At least it appears to use all bearing assembles and not loose needle bearings like mine.

Have you determined that it is stuck in 5th? That would narrow down where the problem is. I keep thinking, whichever gear it's stuck in, the syncro ring is stuck. On the gear or on a dog in the slider. ... But I'm used to my antique trans.

Does it spin okay by hand... in whatever gear it's in? Doesn't appear to be any obvious signs of destruction in there.

Man, wish you were local. I just wanna dig into that thing...

[jeeper]

It turns somewhat easily by hand. There is some minor damage on the surface of a few teeth on 4th gear but it seems minor to me.

After I looked closer I didn't see how it could be stuck in 5th gear. When I turn the input shaft the output shaft seems to turn 1:1.

I didn't get much time today but I did get the gear off the counter shaft for 5th gear. It definitely is not stuck in 5th gear. The 1:1 ratio of the shafts suggests it's stuck in 4th gear to me.

I hope to get time tomorrow to tear into this more. I don't have some of the tools suggested by the manual I found for this transmission.

[jeeper]

https://youtu.be/3nkb91WVGTM




I didn't have to get far to discover what allows the input shaft and output shaft to spin freely and independently. It seems the main shaft bearing retainer plate is too tight?

Sorry for the shaky video. It is a bit hard to see but at the beginning of the video I am spinning the output shaft and the input shaft is not moving.

[Von]

Looking at the manual (great manual by the way!) You should be able to front bearing retainer off then pull the input shaft out to see if there's anything wonky there.

[jeeper]

I think I'm starting to understand the internals of this transmission after studying it for a while. I can see there is a shim between the plate and the bearing that needs to be removed. I should just go buy the needed puller to remove 5th gear but am implementing a hack instead.

I ended up adding a sheet metal shim between the plate and the transmission case. I realize this is a shade tree fix but it is only temporary.

My plan is to run this the way it is to get the kinks out of the rest of the truck. I'm hoping this hack will allow me to run the truck this summer and I can do a full transmission rebuild next winter.

I'm feeling more confident about my ability to rebuild this transmission myself now that I've been forced to learn about it a little more. I will need to buy another puller to get some of the bearings and gears off but that shouldn't be a show stopper.

[Von]

I realize this is a shade tree fix but it is only temporary.

LOL, I don't have the gall to rag on anyone's shade tree work.. not with some of the silly crap I've done.

Well at least you got it usable again. That was a used trans wasn't it? Not a recent rebuild?
Gotta be something buggered up betwixt the two shafts to make it bind up, pocket bearing or something.

Rebuilding a manual trans isn't as hard as I thought it would be. They look intimidating scattered all over a work bench but if you take your time, stay semi organized and keep a diagram handy it'll be fine.
The right tools make all the difference too.

A GOOD pair of snap ring pliers... I didn't need the pullers shown in the manual you posted earlier for my 4 speed. I think those are the only pullers I don't own... a big bearing separator and 20 ton shop press was all I needed. except for the speedo gear. I could have used the shop press for that but it would have been.. awkward.
So I got to break out this ridiculous 20 ton 3 jaw puller... I got a good deal on it and have never used it before. It took longer to assemble the silly thing than it did to pull the gear off.