FLU Transmission

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patrol578

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Howdy folks.

In the interest of providing some passive moderation to the FLU419 discussions here, I'd like to start a thread on SEE transmission specifics, and trans issues owners may have had. Hopefully we can start divvying up the various systems into their own threads, rather than just dumping it all in the SEE Owners Forum thread (I admit to being just as guilty as anyone). Up to this time, I have found a good bit of transmission information here at Steel Soldiers, but it is scattered among ambiguous threads with names like "My SEE Won't Move, HELP," as well as the ungainly Owners Forum (was it Peakbagger that called it monstrous a while back?).

So, without further yakking, here is my first contribution, an annotated image taken from above the trans with the top cover removed. It is courtesy of choprboy over on Benzword. I have literally spent days poring over the Army TMs trying to figure out how it all goes together and works. Choprboy's picture helped me understand it all in just a few minutes.

IMG_2691s_annotated.JPG.jpg

Left is the front of the truck, right is rear, top is passenger side, bottom is driver's. Here's how the power flows:

Power comes in from the airshift cascade gearbox via the Input Shaft. In LOW (forward) RANGE and REVERSE, it follows the blue line, spinning the Reduction Shaft.

The Reduction Shaft turns the Main Shaft or the Counter Shaft (depending on the position of the Forward/Reverse collar). In LOW it spins the Main Shaft via the 3rd gear. The Main Shaft then spins the Counter Shaft (in gears 1, 2 and 3, but not 4th). The Counter Shaft turns that giant gear on the far right which is fixed to the Output Shaft. But in REVERSE the Reduction Shaft turns the 2nd gear cog riding on (but not fixed to) the Counter Shaft. That 2nd gear cog then turns the Main Shaft and power runs through gears 1/3/4 as normal. When in 2nd gear, the gear cog is then fixed to the Counter Shaft and spins the Output Shaft directly (without going through the Main Shaft).

The Output Shaft is connected to the rear prop shaft by a flange. The front prop shaft is driven by spur gears which take power from that giant gear on the Output shaft. The first of these is just visible at the very bottom right of the image.

In HIGH RANGE (II on the shuttle lever) the High Range collar couples the Input Shaft to the Main Shaft and power follows the green line. The Forward/Reverse collar on the Reduction Shaft remains in Neutral.

In 4th gear (regardless of shuttle lever position), the 4th gear collar couples the Main Shaft to the Output Shaft. So in II/4th, the Output Shaft is directly driven at the same RPM as the Input Shaft brings into the gearbox. Although it looks like the Input, Main and Output shafts are all one and the same, they actually spin independently of each other unless the High Range or 4th Gear collars are engaged.


My next post will be a similar one about the workings of the shifting mechanisms found on the underside of the transmission top cover. If I have made any mistakes on the above, PLEASE call me out so that I can make the correction. Choprboy, if you are lurking here, feel free to correct me on B-world if I've screwed anything up, and big thanks for the annotated picture!

Hope this helps,

Patrol578
 
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patrol578

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Steel Soldiers Supporter
Ok, now to round 2. Let's talk about the basics of the mechanism which translates the motions of the shift levers in the cab to actual movements of those shift collars. The image below is of the underside of the transmission cover. I think it is much easier to understand when looking at it as an assembly than squinting at the Army's -24P manual for hours. Once again, left is the front of the vehicle, right is rear, but this time top is the DRIVER'S side and bottom is PASSENGER'S.

Imagine the SEE transmission is your favorite beverage cooler. The side of the cooler's lid which opens faces you; the side with the hinge faces away. When you open it, you see the underside of the lid. So assuming you are standing on the driver's side of the vehicle (just like in the last post), if you were to open the top cover of the transmission like the lid of your cooler this is what you would see:

20200112_150707 Anno1.jpg

You see four rods which slide front/rear as determined by the movement of the gear levers in the cab. Attached to these rods are two obvious shift forks (two prongs) and three bell cranks (two at the bottom, like single-prong forks, one very long one at the upper right). I don't know why they are called "bell cranks" but that is what the parts manual says.

The top two rods (driver's side) are actuated by the shuttle shift lever (II/I/Rev) while the bottom two (passenger side) respond to the main gear shift lever (gears 1/2/3/4). Some people are better with pictures than words, so here you go:

20200112_150707 Annotated.jpg

In greater detail, Rod #1 handles Low range and reverse (I/Rev). Rod #2 is for High range (II) only. Rod #3 is for 3rd and 4th gear, and Rod #4 is 1st and 2nd.

Stay tuned. More specifics on how they move and other details to come.
 
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Hawaiimoger

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Aloha! This is Awesome! Thank you for braking this down!
I just bought my my first unimog flu419 last Friday! I've been dreaming of owning one since I was a kid. Super stoked!
But I was a little bumbed as I drove it home, because it would shift smoothly in and out of all gears but 3rd. It would grind into 3rd. And At first I thought it was just me not pushing the clutch in far enough, but no matter how fast or slow I would try to shift it to 3rd, it would always grind. So I would just skip 3rd and go straight to 4th. Has anyone else had this problem? What is the solution? Hope I don't need to tare apart the tranny.
Once it's in 3rd it drives fine, and shifts out of third fine without grinding.
Your experience and knowledge will be greatly appreciated! Thank you!
 

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patrol578

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Steel Soldiers Supporter
Congrats Hawaiimoger, and welcome to the sickness.

As far as shifting issues go, I encourage you to search the Unimog threads here on SteelSoldiers. Shifting issues seem to be common and there has been lots of discussion on them. In a nutshell, check that your trans fluid is at the correct level. There are many accounts of low fluid making Unimog shifting more difficult. The second thing to check/replace are the plastic shift bushings. This is a reasonable fix even for relatively inexperienced mechanics. After that it gets more complicated. Search the threads and read the Army's Technical Manuals; that's the best way to learn how to take care of your SEE.

Good luck!
 

The FLU farm

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And At first I thought it was just me not pushing the clutch in far enough, but no matter how fast or slow I would try to shift it to 3rd, it would always grind.
Welcome, Hawaiimoger!

Don't get me wrong, but if you shift correctly there should be any grinding...even without using the clutch and with a non-synchro trans.
Spend some more time behind the wheel of your SEE and that issue (synchros?) may not be an issue at all.
 

joeblack5

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I like to continue this thread as the flu owner thread is very hard to follow.

So today I took a look inside the transmission of the broken flu419.

I expected the shift collar from forward reverse to be stuck ..but it is not.. The shiftcollar from 4th gear is free and moveable but does not engage..even if slid over..synchro moves freely and rotates forward an backward in its slot. But no engagement when the collar is slid over.

The the collar from hi low range is discolored. Nevertheless the synchro is loose from the collar but does not rotate forward and backward.

I turned the input shaft with the starter motor and it seemed that the high range was enabled so I expected that the roller bearing inside had seized up . in an attempt to brake that free I engaged the forward ( low)/ reverse collar and to my surprise the high range was not seized up. .

Better watching showed that the whole main shaft has slid towards the engine by about 3/16 to 1/4 " judging by the misalignment of the 3 rd..2nd...1 st.. Gear .

The main shaft cannot move axially and his hard to turn with the clutch depressed.

The space at the 4th collar seems a little large.

Now where it gets weirder is that these gears are not straight so an axial force is exerted but the bearings holding are rollers. ???

Can the output shaft have pushed the whole assembly forward?

The PO mentioned that the rear wheel drive stopped engaging and he drove only on the front wheel by engaging 4*4.

Attached some pics

Please advise

Johan

IMG_20200513_162037_999.jpgIMG_20200513_161702_253.jpgIMG_20200513_161653_146.jpgIMG_20200513_161642_789.jpg
 

Speedwoble

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Have fun. Scott at EI referred me to a retired Unimog mechanic, Tony ? in his area a few years back. I give him a call about some work on a 1300 and he mentioned that he was previously a Case MB94 mechanic and was there during the trials for the SEE. He spent his subsequent career teaching military mechanics on servicing the SEE. He mentioned he did a lot of transmission rebuilds as his comment was that many folks shifted far too quickly. When the SEE went away he retired but as of few years ago he was still doing Unimog work. He does not work for free but could be a resource on the wrong side of the country.

No doubt there are a few dead SEEs around with good transmissions, its just finding them as I expect the owners are embarrassed that they gave up trying to get them running and would rather let them rot then admit it. Von may have a handle on one https://vonsmog.com/unimog_used_parts.html. Might be cheaper than buying parts.
 

Ferretboy

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Im not an expert...and i dont know if your gear box has a bottom plate or pan that you can remove...but i would be looking for parts and pieces of some spacers or shims down in the bottom of the case that failed.....
 

Ferretboy

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Also be looking for c-clips or snap rings that have come out of place......im not sure how your gear box is constructed but many use these to hold gears and bearings in place....either way the box probly has to be removed to repair...
 

Ferretboy

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Just remember boys and girls..anything can be repaired....just put your mind to it....dont be afraid to rip into it...but a manual helps...best to ya..
 
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