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1986 Unimog U1700L (435 series)
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Discussion Starter #1
Hello everyone,

Today I drained the transmission oil for the first time. Good news, oil looked ok. Bad news a broken metal cast piece fell out. I fished around inside with my finger could feel no other bits. Some swarf on magnetic plug, as per photo.
I though I was worried before, now I'm worried. The broken part came out the passenger side rear most drain.
Does anyone recognise what it broke off, and if I can likely get the broken item PICT1049.JPG PICT1048.JPG PICT1047.JPG PICT1046.JPG replaced without removing gear box. I could try for another gearbox (a used one for parts) at auction, but its a lot of money, and condition is unknown.
 

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1986 Unimog U1700L (435 series)
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314 Posts
Discussion Starter #3
Hi Chas. Thanks for that.

I'm guessing one of the gears may not select. I suppose I'll find out when I get it back on the road. Or maybe one side of the fork is doing all the heavy lifting (so to speak).

Do you happen to know if this is the sort of thing that can be fixed by accessing the large forward plate, or if the whole box has to come out?
 

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1989 W124 260E
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Jason this part might be from some older repair ,So dont jump at removing the box just yet . I would put everything back fill it up with oil ,,and run the car .Then if problems arise,, then you will know the reason of the problem and then do the repair
 

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1986 Unimog U1700L (435 series)
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Discussion Starter #5
Hi plinker17722. I had a look at pictures of selector forks and could not see any with the same profile.
Some one else has mentioned that its from the box casting itself.
What ever it is, I was able to drive the vehicle ok using gears 4 to 8 (and reverse). When its back on the road, i'll try the other lower gears. You might be right, could be a part from a previous repair that they missed seeing. I'm going to drain the PTO box next then the diffs.
 

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1987 1300L
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Hi Jason. I'll try to post a couple of pictures of my U1300L transmission when I had it out 16 years ago. Sorry, but I don't have a pictue of the front (planetary) part of the transmission opened up. I don't think you can do any work on the tranny by removing plates. From what I remember, the entire transmission unplugs from the transfer case and then you pull the planetary cage out of the front portion and remove bolts from the inside and outside to remove the rear case from covering the main part transmission. Possibly the pictures can help you determine where the piece came from. It kind of looks like part of the case casting to me.
 

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1986 Unimog U1700L (435 series)
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Discussion Starter #7
Thanks burgy. All too hard to guess. I'll just have to drive it and find out what does not work. Hope I don't get a catastrophic failure one day somewhere in whoop whoop (the back of Burk) :-(
 

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1988 U1300L RW1 Working gears Mogauspuf Dual Tanks Other Goodies 91 F250 HD 4x4
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Thanks burgy. All too hard to guess. I'll just have to drive it and find out what does not work. Hope I don't get a catastrophic failure one day somewhere in whoop whoop (the back of Burk) :-(
Jason, guessing is not that hard; it is the knowing that bedevils. I marked up burgy's second photo. Mere speculation of course, but sure looks like it could be a possibility, as the source of the fragment. End of a cast portion, machined to receive a larger disc and smaller dowel or rod. Not too hard to envision how a dweb mechanic could have fouled the alignment or insertion, and the dowel pressured the end of the casting. If all this is so, then there is the possibility that the error/ fracture was not realized, and the dowel not recovered. You might try with a magnet or borescope, just as a way to drive yourself bonkers. Also possible that the fracture was loud and noticed, and the tranny pulled apart, and the dowel, at least, was recovered. Or maybe the dowel poured out in a previous lube change.

Quick edit: Looking again from a global perspective (not implying stateside, mind you), I think the dowel would remain captive, if only the bit you recovered was broken off; there would appear to be more than a 180 degree wrap of the dowel still intact, no sideways exit permitted. Hope is (NOT) a plan, you know.

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1987 1300L
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Good eye Photobldr. I had looked at that area too, but at first thought the machined section looked too thick. Looking at Jason's pictures again, it seems that tip of the casting you point out may be precisely where the broken piece originated. That would also be in keeping with the double machined step in the broken piece, the bottom being where the planetary housing rested. The smooth surface of the bored part of the broken piece would also suggest that it was related to that locator pin in the area you point out, as I don't think there are any assembly dowels in the outer case that could match that piece. Maybe the corner of that casting was hit hard enough in assembly/disassembly that it cracked and only broke apart under virbration or load once assembled and put back into service. I also agree with your edit, that the locating pin may have remained in placed after the corner of the casting broke off. If this is indeed where the broken piece came from, I can't see there being any further problems, as long as the locator pin doesn't fall out too and become shrapnel. The case would certainly be just as strong and servicable, even witihout that broken piece and one locator pin.
 

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1986 Unimog U1700L (435 series)
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Discussion Starter #10
Thank you Photobldr and burgy and everyone else who helped. I am very much grateful for the effort and information. People like me would have no chance, if experts did not take the time to pass on their experience.
This does indeed make sense and looks just like the item. Its also located in the same spot where if it broke off, it would end up in the cavity with the same drain plug that the part came out. I now have confidence that the box is unlikely to self destruct on me.
 

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1987 1300L
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Glad you have some peace of mind Jason. To take it one step further, maybe you could use something like a flashlight/dental mirror combo or one of those cheap laptop attachable bore scopes to actually look up into the suspect area from the drain plug hole for confirmation. They are pretty close together. I'm also pretty sure that if that pin were to ever dislodge and fall out too, it would simply drop down into the area of the drain plug until the next time you dropped the oil. It is heavy enough that I don;t think it would bounce up into the gears in that heavy oil environment and the transmission oil pump has a screen on the bottom to prevent anything that large from being sucked up by the oil system.
 

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1986 Unimog U1700L (435 series)
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Discussion Starter #12
Yes, a good idea. I will try to find an affordable camera (should have bought the Aldi one). At least I should be able to see it its even still there. I have also installed the strongest magnetic plugs available, into the fill and drain holes. The magnetic plug might capture the item.
 

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250GD Wolf
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I bought a nice little borescope from Amazon that plugs into my phone, for around $30 it's sure handy. If you've ever wondered what the bore of a Mauser Mod 71 looks like after neglect, here it is:


The nice thing about it is it has an adjustable LED light, magnetic end, and you use your phone as the viewing screen. New one's are even wireless so you don't need to worry about what plug (USB micro, mini, USB C, lightning port..ect) your phone has.
 

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1986 Unimog U1700L (435 series)
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Discussion Starter #14
Purchased a camera. Could not get it to work on tablets or phones, but it did work on my desktop PC. Lugged the PC outside and managed to get some shots. It is exactly as shown circled by Photobldr. Sorry about the blury snapshops of the video (I don't have fancy software to capture properly). 1st pic shows pin, 2nd pic shows some overhang of the casting retaining the pin.Thanks again everyone for your guidance.
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U1000Ag
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Well done Jason (y)
Now you just need to determine if there is a functional/reliability issue and whether you can leave it be.
 

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1986 Unimog U1700L (435 series)
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Discussion Starter #16
Hi Krietpiel, Thanks. I am now comfortable to leave it as it is.
Regards
Jason
 

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1987 1300L
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Great picture Jason. As is shown, it basically confirms exactly what we were thinking earlier and should give you the peace of mind that was still a bit fleeting without the photo confirmation. I agree that it should be fine as it is, as there should be no extra strain or movement in that area once assembled. Something I would do though, if you ever had reason to take the transmiission apart in the future, is to simply leave that specific locating/anti-torque pin out totally upon reassembly. It is not really needed,with all the other pins in place and would eliminate any chance of more damage occuring on reassembly, which could cause the pin to become dislodged and act as shrapnel. The transmission case itself should be fine to use again. Nice job.
 
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