M37 Transmission Discovery

Discuss fixes, upgrades and modifications to your M37

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keyslammer
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M37 Transmission Discovery

Post by keyslammer »

Guys,
I am replacing the fluid in my M37 tranny for the first time since purchasing it and I always check inside and feel around for chunks. I discovered a one inch long chunk of a copper shaft (see photo). It does not look like a tranny part. Looks more like someone used a copper drift as a lever and busted off the end. Can someone familiar with the innards tell me if this is anything to worry about?

Keyslammer

Update: NOT copper, steel...and 0.312" diameter about 1.2" long
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broken synchro pin.jpg
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Last edited by keyslammer on Mon Mar 19, 2018 8:50 am, edited 2 times in total.
Elwood
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Re: M37 Transmission Discovery

Post by Elwood »

Finding a piece of metal like that in the bottom of a transmission would make me concerned. When was the last time the trans lube was drained? Have you noticed any issues, noises, etc. with the transmission? At a minimum, I'd want to remove the top cover (the shifting assembly) and have a look at all of the gear teeth.

Which transmission are you running: 88950, NP420, or Canadian? Does it have a PTO attached?

Are you sure the mystery piece is made of copper?

Both ends of the mystery object look like they've been chamfered, which would suggest it was not broken off of a longer piece.

About the only thing I can think of that's close to the shape and size would be the gear shift rail interlock pin 7373633.
“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
rickf
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Re: M37 Transmission Discovery

Post by rickf »

That does not look like copper, copper would not normally stress crack like that where it bent. That looks like steel and steel that had some serious force on it. You need to sand a portion of it and also use a magnet to see exactly what it is to get a better idea of where it might have come from.
1953 M37
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Marmalute
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Re: M37 Transmission Discovery

Post by Marmalute »

Pin 7373633 is only 0.185 x 0.525 long, looks bigger than that to me. But could it e 7373634 (plunger reverse shifter shaft)? How does your shifter feel going into reverse gate? Can you measure the diameter? It looks like 0.375 to me but hard to say. There aren’t many things in those gear boxes that look like that. Any issues with the way the transmission works?
Keep us posted...
Doug
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Re: M37 Transmission Discovery

Post by Elwood »

Marmalute wrote:Pin 7373633 is only 0.185 x 0.525 long, looks bigger than that to me. But could it e 7373634 (plunger reverse shifter shaft)? How does your shifter feel going into reverse gate? Can you measure the diameter? It looks like 0.375 to me but hard to say. There aren’t many things in those gear boxes that look like that. Any issues with the way the transmission works?
Keep us posted...
Doug
I wondered if the interlock pin was too small, but I didn't see any evidence of the C-clip groove to suggest it might be the reverse plunger shaft.

Another possibility would be one of the pins NP-88477 from one of the synchronizer stop rings.

Image
“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: M37 Transmission Discovery

Post by ashyers »

I'm betting Elwood is right. That was what popped into my head when I saw the initial photo. Looks like time for a tear down :(
Marmalute
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Re: M37 Transmission Discovery

Post by Marmalute »

Yup, that sure looks like it. Has anyone seen these shear before?
Looks like it could be time to dive into that transmission.
And as was said before, you might be able to learn a bit more by popping the top off the box. Ultimately they are pretty straightforward to remove and replace.
Best of luck with it!
Doug
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Re: M37 Transmission Discovery

Post by Elwood »

I've never seen a synchronizer stop ring pin shear before, but I suppose if someone put too much pressure trying to shift, or was leaning on the shifter cane all the time, it might fatigue one of the pins where it narrows down.

Keyslammer, removing the top cover is fairly simple, and worth doing. The transmission does not need to be removed from the truck. Shift the transmission into neutral, remove the shifter cane from the transmission top cover shifter shaft stub, pull the floor pan from the cab, then you can remove the six machine screws that hold the cover to the transmission case - note which screws go where, as they are not the same length, and two of them should be special shouldered screws that align the cover to the case. Be careful not to move the shift rails and forks or the transmission gearing out of neutral, otherwise you'll have a more difficult job putting the cover back on the trans.

Once you remove the cover, you should see something like this. The synchronizer pins are circled in red towards the right. There should be six (6) of them total, and you'll have to rotate the output flange to turn the synchronizer assembly and verify that all six are there...or not there. :shock:

Image
“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
MSeriesRebuild
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Re: M37 Transmission Discovery

Post by MSeriesRebuild »

Can't recall ever seeing one sheared off, but have seen MANY that were loose where they are braded into the stop ring and could have easily become dislodged from it.
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keyslammer
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Re: M37 Transmission Discovery

Post by keyslammer »

Ok...I think I was blindly hoping it was a copper or bronze piece left behind when tapping something into place. I had to go out to the garage and get my Magnetic pick-up. Sure enough, this is American steel. I think you nailed it...it looks like the synchro pin you have a photo of. This is 0.312” in diameter and 1.13” long. I am guessing the color is from its extended time in the gear oil (sulphur). The photo doesn’t show the color well but it is identical to the patina on my 50-yr old brass drift set.

So, I’ve not noticed ANY odd shifting or synch issues between 2nd and 3rd. Tranny runs smooth with no noticeable hitches. There are no other “tooth” or gear pieces at the bottom of the tranny. Clearly, you have had more gear-time than I have, so this now becomes a question of whether this is a serious problem (gears coming apart, shattered case, etc)...or merely a note for what I will need to do “when I get around to it”.

This synchro pin shows where it got “bent” against another face (photo attached).

Thanks for the feedback. I am hoping to get through the summer without rebuilding my tranny.

Keyslammer
Attachments
broken synchro pin.jpg
broken synchro pin.jpg (30.04 KiB) Viewed 2166 times
Last edited by keyslammer on Mon Mar 19, 2018 8:49 am, edited 1 time in total.
Elwood
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Re: M37 Transmission Discovery

Post by Elwood »

keyslammer wrote:Ok...I think I was blindly hoping it was a copper or bronze piece left behind when tapping something into place. I had to go out to the garage and get my Magnetic pick-up. Sure enough, this is American steel. I think you nailed it...it looks like the synchro pin you have a photo of. This is 0.312” in diameter and 1.13” long. I am guessing the color is from its extended time in the gear oil (sulphur). The photo doesn’t show the color well but it is identical to the patina on my 50-yr old brass drift set.

So, I’ve not noticed ANY odd shifting or synch issues between 2nd and 3rd. Tranny runs smooth with no noticeable hitches. There are no other “tooth” or gear pieces at the bottom of the tranny. Clearly, you have had more gear-time than I have, so this now becomes a question of whether this is a serious problem (gears coming apart, shattered case, etc)...or merely a note for what I will need to do “when I get around to it”.

This synchro pin shows where it got “bent” against another face (photo attached).
The damage to that synchro pin (or whatever it is) had to be caused by it being crunched between moving parts, which in a transmission means gears. I'd be surprised if, given the amount of damage it sustained and being steel, that it didn't damage any gears.

When I pulled apart the NP420 from my truck, I found plenty of wear and a broken tooth on 3rd gear. But the transmission shifted okay, and seemed to run fine. With a missing tooth, however, the adjacent gear teeth are loaded more than normal, and could fail, too. What I'm saying is that accumulated wear and damage can (will?) cause a larger failure some day.

Some of the parts for these NP420 transmissions are still available, and some aren't. Main drive gears (the input gear and shaft from the clutch) are getting really hard to find. If you end up damaging that, what might have been a relatively cheap and simple fix just got a lot more expensive.

The synchro assembly, fortunately, is the same part number as the one used in the later NP435, except that the assemblies available now are "bonded", which means that the six pins are permanently attached to the rings on both ends and the assembly cannot be separated. Possibly a design change caused by pin failures such as you may have experienced, or the looseness that Charles described above.

Here's what the original synchro design looks like disassembled:

Image

Note that the rings (items 3) have three pins each, which are end riveted from the backside (not visible), and the free ends of the pins just slide and bang against the round bosses on the other ring. The bonded synchro assembly (below) cannot be taken apart like the one above, because the pins are attached at both ends.

Image
“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
keyslammer
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Re: M37 Transmission Discovery

Post by keyslammer »

All Technical support posts should be measured by this one. Given the limited information available, not only have the replies likely identified the piece, but Elwood has provided detailed photographic evidence along with a description of the damaged part (to be confirmed) and the alternatives available as a means of repair. I have to believe some of the best mechanics are to be found on this site.

I’m guessing my synchro is bouncing around with no more than two pins. The remaining pins are likely dangerously loose (expletive, expletive)...just when I thought I had it ready for the road again (all brake parts replaced, wheel bearings and seals done, valves gapped, carb rebuilt). Time for some TLC...keep the advice flowing, I appreciate all the encouragement.

Top notch post Elwood!

Keyslammer
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60B90036-B145-4F53-8E4D-959C3213F769.jpeg
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keyslammer
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Re: M37 Transmission Discovery

Post by keyslammer »

Elwood,
I've found a synchro for the NP435, but don't have a p/n reference to validate this against what I have in the NP420. This is the p/n, and it looks like this was used on early Ford trannys (?):

Ford NP435 3-4 Synchro Assembly, part number: D4HZ7124A

This looks like a better route to go than the older version of the synchro if it is a drop-in. Considering this project, I think I may purchase a rebuilt tranny...swap mine out...then rebuild mine over time. That will keep me on the road and give me time to ignore yet another project. I appreciate your insight and direction on the TM's too. It will be interesting to see what I find inside the case.

I am glad I checked inside the case when I drained the tranny oil...never know what you're gonna find in there...of course I might have driven the truck the rest of my life in blissful ignorance too...

Keyslammer
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Synchronizer.jpg
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MSeriesRebuild
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Re: M37 Transmission Discovery

Post by MSeriesRebuild »

There is 2 nylon inserts (placed in the ends of the fork that engage the synchronizer slider of this unit). If yours are worn or broken which likely they are if there is synchro damage, you will also need to replace them or you will have massive loose motion in the shifter assembly.
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Re: M37 Transmission Discovery

Post by Elwood »

keyslammer wrote:Elwood,
I've found a synchro for the NP435, but don't have a p/n reference to validate this against what I have in the NP420. This is the p/n, and it looks like this was used on early Ford trannys (?):

Ford NP435 3-4 Synchro Assembly, part number: D4HZ7124A

This looks like a better route to go than the older version of the synchro if it is a drop-in.
There are some differences in the version of the NP435 made for Ford such as input gear shaft diameter and bearing design, but I don't know Ford stuff well enough to say if that synchro assembly will work, sorry. Nor do I have a cross reference for Ford parts to know if that p/n is correct.

I purchased some transmission parts as a lot once, including an NOS synchro assembly that was supposedly for the M37 NP420, only to discover after I had installed it that the thickness of the synchro assembly was not correct, and I couldn't get the shim adjustment to set up correctly. So I had to remove the main shaft and input gear again, and order a correct synchro assembly. I still haven't figured out what that odd synchro goes to.
Considering this project, I think I may purchase a rebuilt tranny...swap mine out...then rebuild mine over time. That will keep me on the road and give me time to ignore yet another project. I appreciate your insight and direction on the TM's too. It will be interesting to see what I find inside the case.
Good plan, but if you're buying a rebuilt trans, get it from someone who knows these transmissions, does quality work, and stands behind the product. With a closed case, there's too much opportunity to use inferior parts or skip over some of the time-consuming steps such as shim set up, knowing that the end user will not know the difference until too late down the road. If I didn't do my own transmission work, I wouldn't hesitate to buy one from Charles at M Series Rebuild.

Charles' comment about the nylon inserts (NP p/n 93549) on the 3rd and direct drive shift fork has certainly been my experience, too. I think I've found maybe one intact nylon insert, the rest have just disappeared, likely ground up by the gears and drained out during the next lube change. The odd thing is that these inserts don't appear in the ORD 9 SNL parts listing or in the later NP420 manual, so maybe they were a mid-production change by New Process Gear - if your 3rd and direct shift fork has small horizontal cuts in the fork ends, and the vertical cuts of the fork ends seem oversize for the thickness of the synchro sliding clutch, then you're missing the nylon inserts. I think VPW sells them, but you can also get them (and NP435 parts) from places like Novak Conversions: https://www.novak-adapt.com/catalog/tra ... 435-parts/

Please let us know what you find when you open up the transmission.
“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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