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Unimog 404, landrover 130
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Discussion Starter #1
Hi,
I have a '63 unimog 404, which is stuck in top (6th) gear. Of course I discovered this when driving through a toll tunnel under a local fjord and had to suffer the embarrassment of a tow back out again. The tunnel operators thought it was hilarious!
No nasty noises when it happened, and it was still possible to drive in 6th back home. basic checks seem ok. Transmission was not hot. Oil levels seem ok, and nothing leaking out, just a stuck lever. I have tried 'encouraging' the lever by hand, but I am wary or damaging the selector mechanism.
Anyone got any ideas where to start, or seen anything similar? As usual, getting to the top of the gearbox is a bit difficult, as a previous owner has done some unhelpful mods to the cab making it complicated to remove/tip it forward. Before I start the heavy engineering I though I would try and get some feel for the possible problem location in the box.

Many thanks
Richard
 

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1981 u1300L, 1998 s280
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2,113 Posts
Try taking the top off the box (yes I have read your bit about PO!) You don't need to touch the tab really to take the selector mechanism off.

If you just want a peek in the box, you can also take off the pto cover if you don't have a pto fitted.
 

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85' U1300L Holset Turbo VA A/C, 66' Propane 404.1 rock mog, 1975 416 Doka, G500, Volvo C303
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Have you owned the truck for sometime, or is this a new purchase.

I would suggest jacking up the rear and have someone spin the back tires while you give the shifter a bit of a slap back to 5th.

Otherwise I know its not uncommon to bend a shift fork inside the tranny. But I am not aware of the failure modes for this and if getting stuck in 6th is a common problem.
 

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1978 416.115
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1,035 Posts
There are brass synchros in mog transmissions, sounds like yours might be stuck.

Like DX said, take the top off and try to shift it and see where it's hanging.

I think Scott at EI posted a video one time showing where the synchros are.

Trust me, you'll be able to tell the difference in color, ie brass synchros are brass colored, and the other gears are steel.

Typically they get "stuck" if it's been sitting a long time. I don't know if they're used when shifting down or up from 3-6 though, someone else might know though.
 

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Unimogs
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860 Posts
Assuming he was driving when this occurred it is unlikely it is a frozen synchro. I would be more apt to be looking at shift plate problems including potential gearshift issues. If it was at temp I would be looking at the bronze bushing failures, but it sounds like this happened with a cold transmission which partially rules that out.....

Additional option is to verify the main shaft has not moved. It is held in place with a bolt to the rear flange/housing and I have seen this sheer which can allow the entire mainshaft to shift forward "jamming" the synchro.

You tube vid of a frozen synchro on the input shaft.
Not likely the case here.

Cheers,

Scott
 

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Unimog 404, landrover 130
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Discussion Starter #6
Have you owned the truck for sometime, or is this a new purchase.
Hi, and many thanks for the help so far, plenty to try and look at/try as soon as poss.
I have had the truck for around 2 years now. I have not taken it on too many long journeys, but it probably gets 10-20 outings/year. I am slowly transforming it into a sort of travelling mountain hut, and trying to keep it all running well. Considering it is older than me, and has had several careless owners I am very impressed with its mech condition (bodywork is another story). Mind you I am more used to owning landrovers, which never really get better than 80% working..

I would suggest jacking up the rear and have someone spin the back tires while you give the shifter a bit of a slap back to 5th.
Ok, this sounds like an easy one to try. On the drive back in 6th I did try letting the transmission drive the box by engine braking on some gentle downhill slopes, in case this helped. What is the thinking behind this trick?

Otherwise I know its not uncommon to bend a shift fork inside the tranny. But I am not aware of the failure modes for this and if getting stuck in 6th is a common problem.
Yup, I was wondering about the forks, although I would like to think I was pretty gentle on the shifter. Another comment was regarding the shift plate. The gear lever (shifter) is surprisingly rigid in its current stuck position, which tempts me to think that the problem is somewhere high up in the selector, otherwise I would expect to feel more play in the linkages (or the gearbox is in much better condition that I would expect!). I need to try find some drawings of the gearbox to get a feeling for what is where.
I think I will try and remove the selector and see if I have enough space above it to lift it free, or at least see if this changes anything. The PTO is a possible, although I have a PTO-driven winch, so it is a bit more work.. As far as the synchros go, I would expect the box to be up to running temp when it stuck, as I had been driving for ~20 mins when I tried to shift, and I think 10 mins of this would have been in 6th.

Many thanks again for the help, hopefully the weather will let me spend some time under the box tomorrow..

Richard
 

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2015 Rubicon Unlimited (Let the shame be upon me!)
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'88 U-1300L, '70 406, '78 406, '78 416 project, '82 406, '57 404, '65 404, '70 404, '68 Haflinger.
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You made one comment that could be important:

..chop....The gear lever (shifter) is surprisingly rigid in its current stuck position, which tempts me to think that the problem is somewhere high up in the selector, otherwise I would expect to feel more play in the linkages (or the gearbox is in much better condition that I would expect!). ...
Richard
The long 'snout' on top of the transmission has a shaft that moves forward and rearward. If the rear end of that housing gets water in it it's possible for the shaft (part of shift linkage) to get stuck in the rearward position. I've had a 406 do that.

The shaft could just as easily stick in 4th, too, but mine stuck in 6th. The solution is to get some lubricant into that area. I really can't remember how a 404 tranny is assembled but on the 406 there are 3 bolts that take off a cover/cap. Clean it out, grease, and maybe that'll fix it.

Bob
 
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