M5OD has begun popping out of 1st and sometimes 2nd

[shran]

Posted this over on the Ranger Station too, maybe some others will see this here. I will preface this discussion by stating that I rebuilt the trans in question, I have successfully rebuilt several others and have had a bunch of them apart and am looking for some experienced guidance on how to proceed.

This is all in a 1992 Explorer and the goal was to get a trans with lower 1st, 2nd, 3rd gears. My build consisted of a 1994 4.0 M5OD case, 1988 2.3 tailshaft/1/2/3 gears, 1997 5th/reverse cluster, new input and countershafts to match the 2.3L components, a bearing and syncro kit obtained from Allstate Gear, and a top shifter housing from the 1988 2.3L trans.

I inspected everything as well as my fairly untrained eyes could throughout the build process and replaced anything that looked worn. Everything on the main shaft looked to be in good condition and the build process was pretty smooth. I used the shifter housing from the older trans because the shift forks were in good shape and it has the neutral switch, which my Explorer also has.

I put roughly 2000 miles on the trans with zero issues other than 4th gear being slightly hard to engage right out of the box, which I attributed to break-in and it has since been much better. However during my Utah trip last week, I was going up a small hill on a dirt road in 2nd gear, 2wd and it popped out of gear. I initially figured I was just lugging it too hard but the next day it happened again in 1st, 2wd. Frustrating. I wheeled all of Hell's Revenge and another ~500 miles of dirt and highway and had zero issues until a steep dirt road where it again popped out twice in 1st, 2wd. After that it has been much worse... even on the street pulling away from stop lights it will pop out of first. I will note that it has never happened in 4 Low (I'm assuming the gear reduction takes some load off whatever is happening in the trans.)

Looking for some guidance on what to look for - I will for sure check the 1/2 shift collar, IIRC that one is directional but I'm 99.99999% sure it's oriented correctly since I marked it as the donor was disassembled. 1/2 shift fork is a possibility but it looked fine, just some light scuffing was all. I read another thread that I can't find now where someone mentioned shimming the countershaft tighter fixed a similar issue. Seems to me that I had to shim it a hair loose.

Ideas? A worn shift fork would absolutely cause this but IF that ends up being the case, how did it happen? Difference in top cover between 1988 and 1994? Shift collar installed backwards although I think I did it right? Variations in the shift fork itself between years? Something else?

I need to pull it and tear it down I guess... I am gonna be very confused if the 1/2 fork is fine and the shift collar is oriented correctly. FWIW I changed the fluid about 400 miles in and saw nothing I would consider abnormal...

 

[JK080]

Popping out of gear in most cases is due to wear on the little teeth that the synchronizer collar indexes on the gear, so look for wear on the gear and collar teeth, they should be sharp and come to a point. If they are rounded off then you should replace the gear/collar.

 

[shran]

Popping out of gear in most cases is due to wear on the little teeth that the synchronizer collar indexes on the gear, so look for wear on the gear and collar teeth, they should be sharp and come to a point. If they are rounded off then you should replace the gear/collar.

Thank you. I'll report back when I've got it torn down.

 

[shran]

@JK080
I have this torn down finally and would like some opinions. Some things I noticed:

- both slider rings 1/2 and 3/4 are kinda "loose" and move a little in every direction even when they're locked into a gear. 3/4 is probably looser than 1/2. Normal?
- Those little teeth on the gears themselves have a bit of wear... some of the other transmissions I've torn down were significantly worse. Should I just replace them?
- Shift forks are fine. They have light polished areas where they contact the slider rings but no material missing.
- Also noticed that I have a little bit of play in my input shaft bearing. Was not there when I built the trans, either I did not shim it correctly or there is some wear.

Would the slider rings being as loose as they are, compounded with a bit of wear on the teeth cause this? I am real tempted to just order new 1/2 and 3/4 clusters at this point...

See video:

 

[JK080]

I think the looseness that you are showing seems typical to me, I would not think this is the issue and the teeth on the gears dont look bad enough to cause it to jump out of gear, not sure what's going on based on anything I see so far.

Definitely look at the endplay, maybe something is off causing the shafts to float around just enough to pull it out of gear. I would take it back apart and double check everything like the rear bearing retainer plate and the bearing between the input and output shaft.

I have had shifters hit the floor board and cause them to be knocked out of gear, especially if there has been a body lift installed, or weak mounts, maybe hard to see with the boot installed.

The M50D is also known for shifter issues, not only are the shifter bushings and metal covers and pins a issue the housing can wear too.

 

[shran]

I think the looseness that you are showing seems typical to me, I would not think this is the issue and the teeth on the gears dont look bad enough to cause it to jump out of gear, not sure what's going on based on anything I see so far.

Definitely look at the endplay, maybe something is off causing the shafts to float around just enough to pull it out of gear. I would take it back apart and double check everything like the rear bearing retainer plate and the bearing between the input and output shaft.

I have had shifters hit the floor board and cause them to be knocked out of gear, especially if there has been a body lift installed, or weak mounts, maybe hard to see with the boot installed.

The M50D is also known for shifter issues, not only are the shifter bushings and metal covers and pins a issue the housing can wear too.

10-4... shifter bushings, pins etc are new, shifter seemed really tight, almost stiff, especially when warm. No body lift, just stock height there. Trans mount looked OK but I will check that again, may just replace it anyway.

As far as endplay goes... where and how do I measure that? I apologize for the noob question, I'm assuming you're referring to the main shaft assembly moving forward and backward in relation to the trans case itself? That is set by the input shaft bearing shims, correct?

With the tailhousing removed I do have a bit of movement in every direction at the middle main shaft bearing (at the rear bearing retainer.) Not very much, but noticeable. I don't know if that's normal and caused by the rear bearing not being supported by the tailhousing though.

 

[JK080]

From what I found Ford says .002 to .006 for the input shaft and .006 to .010 for the counter shaft.

I would only be worried about the movement of the main shaft in a forward and back motion with the tail housing removed.

 

[shran]

Gotcha. I looked at that tonight, it didn't really have much if any play front to back. Found some other interesting things though, copypasta from my post on TRS:

I got this thing torn down the rest of the way tonight. I found one huge, glaring problem - the main shaft center bearing race was crooked inside its pocket and inside the rear bearing retainer. It was worn really bad - visibly so - I measured that it was 0.245" deep on one spot and 0.272" on another. So that needs fixed for sure... I don't know if it was like that before the rebuild and I missed it, or if something else is going on. The fluid was full of ground up aluminum particles, that bearing is thrashed, the input shaft bearing is junk. I don't think the bearing itself was to blame, it was seated flush on the main shaft.

Could that cause or at least contribute to my popping out of gear issue?

I would think that the race should be somewhat loose-ish inside its pocket... correct? I can slip it in and out like I can with the input shaft race... it's not super sloppy, I'm just not sure why it would have spun inside the bearing retainer, and spun crooked for that matter.

Guess what I'm getting at is, like to just rule out a junk case. I have another one I could probably put these guts into but it's still a functional spare trans so I don't know if I want to give that up.

First gear looks OK, the hubs look OK, sliders both have a bit of wear so I will just replace those. 2nd gear looks a hair worn too, a few teeth are a little rounded off but nothing like your pics, just the very tip is worn. 3rd gear looks good, input/4th still looks new.