UPDATE--UP AND RUNNING-Transmission...

Discuss fixes, upgrades and modifications to your M37

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Cal_Gary
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UPDATE--UP AND RUNNING-Transmission...

Post by Cal_Gary »

Hi gang,
Been MIA lately, transmission quit shifting, is stuck in 2nd gear. Got a big snow storm for Christmas morning too so I've been moving snow and dragging a couple of folks out of snow banks with the Rubicon.

I had the top cover professionally rebuilt (wobbly retaining pin, remember?) as a precaution, the shift rails now work like new and the ball stud is seated and aligned with the shift rail components. When installed, the forward gear that the fork fits into appears to be stuck somehow-the shift stick won't move at all, left, right, or front and back. At present I have the top cover off and the case is still mounted in the truck.

Any ideas before I drop the tranny? I fear some small piece of metal is lodged in there somehow but I've never torn down a tranny so I'm not sure how best to proceed.
Thanks,
Gary
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Re: Deadlined-Transmission...

Post by just me »

You say you can't move the lever with the top OFF the transmission?
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Re: Deadlined-Transmission...

Post by just me »

With the top OFF, you should be able to slide the gears easily by hand in the transmission. Put transfer in 2wd high range. Jack the rear wheels off the ground and put on jack stands. There will be no load on the gears. You should be able to slide the 1st-2nd sliding gear with no effort between gears. With it in between gears the same for 3rd-4th except you will need a little more effort for the syncros.
You have to be absolutely certain that the gears are all in their neutral position (Reverse included) and the top in neutral when you mount it to the trans or the forks will not align and it will jam up.
If with the top off, you can not shift the lever, it is a problem in the top, (Lock out mechanism or detent poppets)
If you can't move the gears easily, it is a transmission problem. These are easy trannys to build, straightforward design. just need a couple of special tools, of course. I personally find the top to be way more fiddly than the trans itself.
"It may be ugly, but at least it is slow!"
Cal_Gary
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Re: Deadlined-Transmission...

Post by Cal_Gary »

Thanks guys,
I cannot slide the forward gear that is engaged by the shift fork, period, with the top cover OFF. The rear moves, along with the reverse lever.

I think I'm just going to drop the tranny out, pull the PTO then do a thorough inspection.

Puzzling for sure, as it was shifting just fine for roughly 1250 miles after it was rebuilt.
More to follow,
Gary
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Re: Deadlined-Transmission...

Post by ashyers »

Gary,
If I understand you the 1st/2nd sliding gear is jammed. It looks like it slides on splines on the main shaft, so not too much to go wrong there. Did the transmission stick while in use or sitting? Did you have any debris in the oil? Maybe the reverse idler or some of the pto items got free and bound things up. Was there any noise?

I'll likely be pulling my gearbox apart soon, it's on the list. Wish I could offer more help, it seems like a weird problem. The only way I can see the gear would stick on the splines is corrosion. If it isn't stuck on the splines it seems there must be something in the way in the bottom of the box out of sight.

I'm curious to hear what you find in there.

Andy
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Re: Deadlined-Transmission...

Post by just me »

Having had my fingers inside my trans before, I can only conjecture that a piece of something has gotten wedged in between the teeth of the sliding gear and the cluster. ( If you can't move the truck ) if the truck will drive in that gear but you can't shift it the only things I can think are you twisted the splined shaft. (Bloody unlikely) or the tiniest little bit of something got wedged into the spline between the shaft and the gear.
Getting it apart becomes "trickier" at this point.
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Re: Deadlined-Transmission...

Post by Cal_Gary »

Thank you guys,
I wonder if I lost a washer down into the gear lube when I pulled the top cover the first time? I didn't see any twisting of the main shaft, and the top cover shifts fine off of the transmission case. The oil is in excellent shape, no corrosion inside, and I ran a magnet probe through it to ensure there were no metal bits, washers, etc. and I found nothing amiss. It shifted fine after my field repair of the retaining pin, putting around 30 miles on the truck with no unusual noise (something I'm always listening for). It refused to shift later that evening when I fired it up to put it in the garage and I determined was/is stuck in 2nd gear.

Tomorrow will be decent, weather-wise so I will get my hands dirty either freeing up the gear set, or dropping the tranny altogether. I don't like having the M37 in a non-op state (since that's what it was in for the first 10 years I owned it)! We've got more snow on the way next week....
I appreciate all the advice!
More to follow,
Gary
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Re: Deadlined-Transmission...

Post by Cal_Gary »

Dropped the tranny out today, then drained the oil and removed the PTO. Nothing glaring that i can see; will obtain a rebuild manual then tear this rascal down. I've been wanting to learn how to tear down then reassemble the tranny anyway so this will be my opportunity to learn.

More to follow,
Gary
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Re: Deadlined-Transmission...

Post by ashyers »

Gary,
We have the transmission on the bench, so the race is on! Who will get the truck back on the road 1st? Gary the fearless moderator, snow shoveler, and guy with a busy schedule, or Andy and his bunch of high school kids who are VERY good at disassembly (assembly...Huh?), constantly distracted by cell phones, hormones, and, well, anything.

We should have the box cracked open tomorrow to see how things look inside. I don't expect issues, but I've learned these things will function when pretty beat up. I do have concerns about the infamous snap ring/spline failure. I'm sure it has not failed, but it may be on its way. The major issue leading to the removal was leaks.

Time for a few snow days Gary! Gear up and get it done! The gauntlet has been tossed :lol: !

Andy, herder of cats
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Re: Deadlined-Transmission...

Post by Cal_Gary »

Thanks for the motivation Andy but you will probably win. I had to move the latest snow storm off the driveway this afternoon, with 2 more storms due in the next 48 hours....
Gary
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Re: Deadlined-Transmission...

Post by ashyers »

Gary,
Those storms are over our heads now, you'll be busy, but don't give up hope! If this project goes like the transfer case it will take forever :roll: .
Be careful with your back, and I wish you dry snow!

Andy
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Re: Deadlined-Transmission...

Post by Elwood »

ashyers wrote:Gary,
We have the transmission on the bench, so the race is on! Who will get the truck back on the road 1st? Gary the fearless moderator, snow shoveler, and guy with a busy schedule, or Andy and his bunch of high school kids who are VERY good at disassembly (assembly...Huh?), constantly distracted by cell phones, hormones, and, well, anything.

We should have the box cracked open tomorrow to see how things look inside. I don't expect issues, but I've learned these things will function when pretty beat up. I do have concerns about the infamous snap ring/spline failure. I'm sure it has not failed, but it may be on its way. The major issue leading to the removal was leaks.

Time for a few snow days Gary! Gear up and get it done! The gauntlet has been tossed :lol: !

Andy, herder of cats
Andy, my NP420 seemed fairly normal before I removed and disassembled it. No jumping out of gear, no crunchy shifts, no grinding noises. When I got it apart, I discovered that one of the snap rings was in pieces at the bottom, chewed up, and the spline end of the mainshaft had been partially broken off. I don't know how much longer it would have run, or long it had been like that, but it didn't give much warning of problems.

Does your trans have a PTO? If not, you're going to have to give Gary some extra time in this wager. :wink:
“When a long train of abuses and usurpations, pursuing invariably the same Object evinces a design to reduce them under absolute Despotism, IT IS THEIR RIGHT, IT IS THEIR DUTY, TO THROW OFF SUCH GOVERNMENT...” -Declaration of Independence, 1776
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Re: Deadlined-Transmission...

Post by just me »

I'll be pulling mine in February. Early box, not 420. I expect to spend no more than two days on it and the PTO. It isn't remotely complicated. If I can do MGA, Jaguar, Mitsubishi 5 speeds and Clark and Fuller boxes, I can knock one of these out. (And I already have a brand spanking new top cover for it, so I don't have to mess with that.
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Re: Deadlined-Transmission...

Post by Cal_Gary »

Well we got another foot and a half today, on top of the foot and a half a couple of days ago, and another foot and a half coming in on Sunday. Yeah, I'm tired and sore this morning. I have trenches in the back yard so the dogs can do their stuff-thank goodness the snow blower works so well!
Gary
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Re: Deadlined-Transmission...

Post by ashyers »

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