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1250v
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273 Posts
Discussion Starter #1
My mog left me stranded beside the road, waiting for the truck to come get me now.

It won't stay in forward or reverse, it doesn't move the shifter in the truck. When I do move the shifter between forward and reverse it doesn't change the grinding noise I hear when I try moving the truck.

I can reach in and move the forward reverse shifter on the top of the transmission, and I can pick it straight up about 1/2"

Im guessing something has disconnected the shift fork from the shifter.

Does anyone know if you can get access to that linkage without pulling the transmission off the transfer case?

Ben
 

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U1450L DOKA
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10,468 Posts
I’m sorry to hear about your misfortune.

I’ve never had the transmission apart, but from looking at some photos, I think you’ll
Probably have to pull it.

Although the Forward / Reverse collar lives in the top chamber, above the main shaft,
It is ensconced in the rearmost housing of the transmission assembly, and there isn’t any access to that area unless the housing is split, from what I can see.

There is a rear cap, but don’t think that will expose anything except the back end of the shaft and the bearing.

I think you’d want this thing on the bench for repair. I hope I’m wrong, but I don’t think having the transmission case split and working on it under the truck is a good idea,
If it is even possible.
Here are some photos. You can see that the red part is the forward case, and then the black one is the rear case, where the F/R
Assembly resides.
The cutaway shows the mechanism a little bit.
CA043D94-91A6-48F0-A807-8473E4898A0D.jpeg
E370660A-996A-4AA5-921F-5706C55DFDF9.jpeg
14D774F3-E07A-41BD-BC0E-4B78BF92E6F9.jpeg
EBADFC2D-6A45-45D7-BF02-393381B5E89F.jpeg
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FFCD9102-452F-40CE-8A82-4265DEB8D9DA.jpeg
47899E90-BBCE-4E09-95B4-A100BA90228D.jpeg
1F69DEB5-F20D-433C-9988-359FABE6CE84.jpeg
7095B922-4F36-46E0-968F-976C62063502.jpeg
 

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'91 U1250 '02 U500NA
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3,616 Posts
It sounds to me like range change is failing.
It has happen to me on my U1250 a few weeks before the range change shifter broke off completely.
You can probably use a long bar and push the R/C lever from passenger side under the box bed towards the front to engage the gear.
I might be wrong but it sounds too familiar to me.
 

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1250v
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Discussion Starter #4
Thanks for the pictures, that helps a lot, it looks like i might be able to see whats going on if I take the shift plate off the side of the transmission. Before I gave up and called the truck driver I moved both the high low shifter and the forward reverse shifter with a bar and got them to travel full stroke, but it didn't change what the transmission was doing.

We just pushed it into the shop, and I went to throw it in gear so we could listen to the sound it was making, and its in gear now. I could have driven it in. The only thing that seems out of place is the the forward reverse shifter shaft coming up out of the transmission is leaking oil around it, and I can pull it up out of the transmission .5" and push it back in again.
 

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U1450L DOKA
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Yes, I think that shift plate might be a good window to see what has happened in there-
It certainly is a good place for a borescope to enter and poke around.
Unfortunately, the only photo I found of looking into that opening favors the lower end of it.
DC503906-5D15-408D-AF68-B5227693E0B5.jpeg
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776C27F9-FEA7-409A-8E15-2D34546D6AEF.jpeg
BC0A2223-3547-46FA-96AB-B17C50C7D0B9.jpeg
 

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1250v
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Discussion Starter #6
I ordered a bore scope. I will pull the shift cover off and see whats going on in there. Its kind of annoying that its fixed itself, it would be easier to track down the problem if it was still happening.

Thanks for all the help and clues for where to look

Ben
 

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Ex ADF 1987 U1700L Crane, 1987 U1700 with winch and a parts truck 1987 U1700L with winch
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You can see the forward reverse select in this cut away. There is a roll pin that locks the fwd/rev lever onto the selector finger, you access the roll pin through the gear selector housing.
 

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Discussion Starter #9
Those are really helpful pictures, thank you. It would be nice if it was something as easy as a roll pin!

Ben
 

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Discussion Starter #11
Thats what im worried I will find. Did you replace the transmission or just the bad parts?

I'm working on Christmas presents this week, I cant even take time to drain the oil to see if there is a bunch of metal laying in the bottom. That can be a good Saturday project!
 

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That is a nice cutaway unit - it is opened up enough to actually see things.

Chas, is there a reason that happened, or did it just fail ? Something like not being fully engaged in F or R, or some other situation?
 

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And, to follow up, was it able to be repaired without splitting the cases, while in the truck, or was it the whole R & R drill ?
 

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Discussion Starter #15
These look really easy to work on when they are sitting on a bench!

Thats a great picture, thank you for keeping such an amazing collection, and having the time to share with all of us when we need help.

Ben
 

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1991 1250L Doka Unimog, 2002 ML320
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Truktor I had a "noise" that folks said was just the mog tranny "marbles in a can". I had it from the first drive from Montana. Push in the clutch and magically went away. Got worse one Christmas day, 100k kilometers later, going to Pismo pulling the toyhauler. Stopped on beautiful I5. Wrecker with slide bed's winch didn't have the power to pull the mog and 10k trailer up so.....I put it in gear and drove up. Bearing on the idler shaft gave up the ghost and ate the gear. Removed the tranny but left the torque tube case in vehicle. Had to order bearings, gears oil pump ect....Thanks Scott at E.I. again. Mario put the tranny together and I installed it. Thanks again to Charlie for his kindness and shop. I had been paying $12 per year for towing.....$2600 bill to get me to even more beautiful Kettleman City.
I still have ptsd from all of that.
Chas
 

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Wow ! a reminder to us all to check that magnetic drain plug regularly. Should a bearing go, hopefully you would see that before the gears get eaten........Still a lot of work even to replace a bearing, but still...
 

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If I can pull a photo that helps, I’m glad to do it, when it works.

Otherwise, posting stuff for entertainment,
Intrigue, and nonsense maybe.

It’s luck if a photo explains something in a way that actually leads to solving a problem,
But it is always worth a try, I reckon.
 

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1991 1250L Doka Unimog, 2002 ML320
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Krietpeil, I had changed the fluid over, if memory serves...., and the magnets showed nothing at all, never did. The noise got louder on that trip. I have gone back to Royal Purple, but, doubt the other lube was the cause. I also remember the shift to 5 was better when the tranny took a dump.....hahahaha
Chas
 

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Discussion Starter #20
I had some time to start diving into the transmission, I found a problem, but im not sure its the one I'm looking for.

I removed the shift cover and found the roll pin that holds the forward reverse shifter fork to the shaft. It looked fine. When I pulled the shifter up on the top of the case the shift fork and shaft move up and down .5" I'm wondering if I'm missing the brass block that attaches to the shift fork on the top side of the fork. The one on the bottom I can see, and its sitting just about out of the groove.

Im going to drain the oil Monday and see if I can get a camera up in to look at the high low shift mechanism.

All the gears and synchronizers that I could see looking through the shift cover looked good, I didnt see and teeth broken or worn
 
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