Advice on play, chipped gears in M5OD-R1 rebuild (take 2)?

[lowspeedpursuit]

Noise continues with varying loudness. Worst noises have stabilized to heavy acceleration in 3rd, or decel in gear in 2nd. Here's my thought process: a Zumbrota reman 2.3L 4x4 M5OD is ~$1400 shipped on RockAuto, including $400 core. My junkyard charges $145 for a transmission. So, now I have a mileage-unknown, 2.3L 2wd M5OD out of a '97. Spins freely; some play in the input shaft.

I am going to take both transmissions apart, again. I am going to see if I somehow obviously smoked a bearing in my original, either from installer error or maybe building it too tight and burning it up. Then I'm going to compare all the parts I didn't replace: forks, synchro assemblies, gears, and the cases themselves, to see if anything from my original looks noticeably worse. I'm going to install the 4x4 mainshaft and tailhosing on the '97 case, with whatever parts look best between the two of them. If it works, great. If it doesn't, I set some money aside to buy a reman and send the trans full of worse-looking 2wd parts in as a core, saving myself $200+ in core charges.

 

[lowspeedpursuit]

Teardown is done. I have learned 2 lessons and not really discovered anything about why the trans still makes noise:

1: It's a lot easier to remove the rear main bearing with two opposed prybars than one. Like exponentially easier.

2: My fears about the countershaft bearings needing to "rock out" were correct. That thing was a bitch to remove, and since there's no clearance to pull the input/output shafts without dropping the countershaft out of its bearings, I couldn't even just abandon it in the old case. Learn from my mistake: never do or install anything to try and secure the countershaft bearings from spinning in their bores.

3: The original transmission looks and sounds pristine. No bearings are obviously loose, bound up, pitted, crunchy, or discolored. Nothing about the forks, synchro assemblies, needles, etc. looks any different between the two transmissions.

3a: Literally the only thing I have found making noise in there was the pivot arm that connects the shifter to the 5/R fork. It had enough play to rattle around pretty good in the old transmission, but was held relatively more tightly in place in the '97. That said, some of that was just disuse, because removing and reinstalling the '97 pivot loosened it up a bit. All of the parts involved measure basically the same; nothing in the old trans is worn.

All things considered, I still don't know what's wrong with the old transmission, and it's kind of pissing me off. While I was pulling the trans, I started the truck and revved it in various gears with the transfer case removed, definitively isolating the rattle to the trans. At some point, I'll fire the truck using an empty case--or more likely the bellhousing from my old automatic--to make sure the rattling isn't somehow coming from the clutch itself.

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These pictures are in honor of the guy on reddit last week who wanted a better understanding of the difference between output shafts. 2wd is on top, considerably longer, and ~1/4" thicker at the splines (28 vs. 25):

 

[Shran]

That's annoying. I sometimes wonder if noises and stuff like this are simply due to new parts meshing with old worn parts. Always makes me nervous to put a new countershaft in a trans full of old gears...for example.

I rebuilt a FM-145 for my wife's truck a while back and the trans I used had water in it... like a lot of water... and for quite a while. Gears had rust pits and crusty rust all over them and the bearings were all junk. I wire wheeled as much rust off as possible, cleaned everything really well and reassembled with new bearings and it works frickin perfectly. Other than a quiet "whump whump whump" noise in 1st gear at low speeds which I would attribute to half of that gear being in significantly better shape than the other half.... it pisses me off that it works great but my M5OD that has over a grand worth of new parts in it continues to fail.

 

[lowspeedpursuit]

I'm hesitant to even post this, because I don't want to jinx it, but I also hate leaving shit unfinished. So far today, the truck seems to be driving without incident. Well, the shifter makes a louder "snick" noise into some gears than it used to, but I can live with that.

Final assembly uses the '97 case, top cover, forks and synchro assemblies, 3rd and 4th synchro rings, all gears and forward needles, countershaft and its bearings. The input shaft, bearing, pocket, thrust, rear bearings, reverse needles, 1,2,5,R synchro rings were reused from the first rebuild attempt, so clearly none of those bearings were responsible for the noise. Fresh output shaft center bearing (these cost $40 local!). I also replaced the throwout and pilot bearings, even though they were relatively new. **** it.

ISB shim clearance calculated out the same, but I loosened it up from the .157 solid shim to a .155 stack made from the shim kit. Counter shim clearance calculated .002 looser, and I reused the .110 shim. So, I effectively loosened each front play by .002. I'm also running Dex/Merc again, whereas I had tried Mercon V after the first rebuild. I'm not sure if that makes a functional difference, but Mercon V smells like absolute dogshit, and you could sometimes smell it in the cab.

Ultimately, I'm still not competely sure what was wrong with the '95. Extremely close inspection of the components revealed maybe three points of interest:

Single chip on this gear, IIRC 2nd:



Noticeably worn dog teeth on this gear, IIRC 3rd ('95 vs. '97):



And finally, extensive chipping of the counter input gear:



It's extremely tempting to blame the noise on that last one, right? Except that I beat the absolute piss out of the counter right there in order to remove the locktited shafts from the '95 for the final time. I'm fairly confident most of that damage happened right then, but I guess I'll never know for sure.

 

[Jazzer]

You been through hell on this one, hope it stays quiet!

-Jazzer