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U1450L DOKA
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Discussion Starter · #1 ·
OK, I am looking for some help on the nature of the Hydrostatic Drive on the SBU
Series. On the Snow Cutter I looked at yesterday, it was equipped with a drive as pictured in the photos of the Trans on the pallet. The instructions for using the drive are as shown. I suppose the Instructions on the red engraved plate echo the same instructions in German
which are under it.

I couldn't get the truck to do anything other than what you'd expect of a UNIMOG. Admittedly, I only moved it a few feet forward and a few feet back, but the Manual trans
worked as normal, the working gears also, but I could not get the thing to act as if there
was a HYDRO-anything, despite the position of the lever, etc.



I know some of you can explain it all to me. Thanks.
 

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Non MB 1975 Volvo C304, 1958 Kramer U540, 1959 unimog Westfalia 411
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I have a friend who Knows them well. There are a lot of controls in the rear doghouse. my friend is case trained mog mechanic who went to all kinds of remote places up here servicing units he calls the unit your showing a t3 or ts3 maybe. He told me a outfit got a unit like your pics and went off with a torch removing the blower unit and power pack and left quite a mess for him to clean up. heres a pic of a case unit MB4/94 cutting through a berm left by D7 this is early 80's Hatcher Pass to the gold mines. So Am I restrictedf from multiple pics? if I post another it replaces the first. Oh I am way off no help.
 

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"Countershaft used for subsequent equipment with hydrostatic drive"

I have no idea what that means. :confused:

It also lists a Converter Lock-Up Coupling, and an automatic transmission (which then says SEE SPECIAL VERSION (SA) INDEX) I haven't figured out how to search that yet
 

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G500, Unimog 2450, Pinzgauer 712M
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Is that the legendary TwinDisk?
No, but some similarities in function. The hydrostat bolts onto the back of a standard manual transmission, and allows independent PTO and driving speeds up to 20km/h in gears 1-4. The TwinDisc completely replaces the manual transmission with a fully automatic transmission and torque converter, and it has the same ability to deliver independent PTO and driving speed. But it will go up to 85mph. I have the manual for the TwinDisc if anyone is interested. (also have a U2450 with one installed, plus a spare one)
 

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G500, Unimog 2450, Pinzgauer 712M
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looking through the manual, there are detailed instructions on how to get it going. There should be a switch on the dashboard to turn it on, and that should light up when it is operating. The switch should be installed to the left of the red hazard light switch. Switch it on only when the hand lever is in the center position and the clutch is disengaged. Then pushing the hand lever should make the vehicle move. You can move the hand lever back to go in reverse. Only change gear, stop, or brake when the hand lever is in the off (center) position. When unit is off, truck drives like normal manual transmission.

That's the executive summary. 65 more pages available. Do you want it mailed to Montana?
 

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1975 Case 406 Unimog
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That's very interesting! I remember seeing a few pages in the 406 shop manual about hydrostatic drive but didn't pay any attention to it. I never understood why a hydraulic *motor* would be connected to the bottom PTO instead of a pump. What it *looks* like they've implemented in the 406 is a similar function if I understand it correctly. Here's how things seem to function if I can detect what's going on from the photos in the manual. First, there is a variable displacement hydrostatic piston pump that looks like it's driven by the rear PTO output - engage the pto and you drive the pump. Next, there's a hydraulic piston MOTOR attached to the bottom PTO where the optional backhoe PUMP is normally installed. So it appears that they're using one PTO out put to drive a pump which powers a motor as input to another PTO to drive the transmission instead of the engine. This way you could have infinitely variable vehicle (low) speed at constant engine speed. Any thoughts? Am I out in the weeds on this?

It looks like you've got a similar system in essence in the 424 with both a hydrostatic variable piston pump and piston motor shown in the picture. I'm not familiar enough with the SBU transmissions to tell what these might be connected to however.
 

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230G, U1200 Ag, 1017A, lots of MB cars, Volvo c303, 416 raildoka, LR D110 TDi
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John,

Like w5yk said, there is an engagement switch somewhere. The hydrostat operates similarily to how the high-speed trans mount PTO would, sometimes the switch for it is on the dash next to the speedometer, and on the very early units it is on the shift plate. The switch is square with a big "H" on it and it pushes down. The hydrostat bypasses the forward/reverse selection of the trans and the pump for the system is driven off of the input shaft of the trans where it would have run into the high speed pto, if there had been one, and the f/r lever must be in neutral. The drive motor plugs into the back of the main gear set and drives the 1-4 sector of the trans. To get the truck to move with the hydrostat, the long and short of it is 1. push in the clutch, 2. put the f/r lever in neutral, 3. put the main trans lever in 1-4, 4. push the hydrostat button and observe the light on the dash lighting up, 5. let out on the clutch, and 6. use the hydrostat lever on the dash to move forward and reverse (the clutch does not need to be used after this point, except to switch back to the main transmission). I'm sure that is clear as mud, but at any rate that might help clear it up.

Cheers,
Ben
 

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U1450L DOKA
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Discussion Starter · #11 · (Edited)
Gentlemen, thanks for the answers. The picture is becoming clearer,much clearer than mud.
We were planning on driving back out there again, so I'll probably have another go at it.

I....um...., noticed a button on the dash that is probably the missing link-at least a button
I failed to push, which was probably the difference. Maybe I was breathing the Automatic Ether or something. The Hydro Control Lever was DEAD, as in, it had no resistance like it controlled anything or was connected to anything, but I'd expect that would be different once the system was on and charged.

So, I get the concept, and you "drive" the truck via the Hydro Control Lever, which
on this truck is on the shift plate, but is often mounted up , off of the dash. So, depending on the speed you'll need, you choose a gear 1 through 4. (Can you be in the working gear range and use 1-4 ? I'd guess yes...) No Clutch, OK, understood. F/R in Neutral, OK.
And forward/reverse is determined by the Hydro Lever. What about speed ? Do
you use the "accelerator" pedal for speed, or is that also determined by the position of
the Hydro Control lever ? I'd guess pedal...but there is a range of movement on the lever
that might account for speed as well.

OK, so let's say I get it working and can move the truck with it. What are the advantages/
disadvantages to having a truck so equipped ? I understand that the Zweiweig Rail trucks
are often equipped with the system, and then you have this Snow Cutter. Is it all
about controlling slow speed work, or is it a way to put maximum power down gradually while taking it easy on the driveline ? Or something else ?

One disadvantage I see, if the truck were to be converted to "normal" recreational use,
would be the added complexity of carrying a system that you may never use. Or would
you ? Hypothetically, If you were to take this truck, after it shed all of the Snow Cutter equipment, to Moab, let's say, would you find a use for the Hydrostatic drive in that situation ?

Thanks for all the help, I appreciate it.Thanks for the generous offer of shipping the Manual for a look-see, w5yk, but I think it is a bit early for me to get too deep. It is an interesting
bit of UNIMOG equipment that I had never paid any attention to, so it is good to figure
it out, whether I'd ever really have to live with it or not.

A truck and a hobby all in one, it seems.

OOPS : The lower-left photo is Not supposed to be here-it does not show a Hydro static drive system.
 

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G500, Unimog 2450, Pinzgauer 712M
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. What about speed ? Do
you use the "accelerator" pedal for speed, or is that also determined by the position of
the Hydro Control lever ? I'd guess pedal...but there is a range of movement on the lever
that might account for speed as well.
I think the idea is to set the engine speed at a fixed value, say 2,000 rpm, using the standard engine hand throttle (ie the one beside the throttle pedal). So now your side-cutter or whatever is purring along taking most of the engine power, at a fixed RPM. Then you use the hydrostat lever only to control the speed of the vehicle.

This is a big advantage over the normal transmission, where if you change the vehicle speed, the PTO speed is going to change as well.

A lot of tractors work like that too.
 

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One disadvantage I see, if the truck were to be converted to "normal" recreational use,
would be the added complexity of carrying a system that you may never use. Or would
you ? Hypothetically, If you were to take this truck, after it shed all of the Snow Cutter equipment, to Moab, let's say, would you find a use for the Hydrostatic drive in that situation ?
I don't think it is of any use for rock crawling. It will get too hot if there is any resistance to the vehicle movement. You can still stall it, and if you do that you have to wait 3 minutes for cool down according to the book. The book also says you can damage it descending a hill due to the wheels over-revving the motor.

Might be useful in a slow-tractor race.
 

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Truktor, slightly off-topic, but in the first photo above, there is big honkin' shaft sticking out of the dashboard right where the 4WD knob needs to swing. Any ideas?
 

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U1450L DOKA
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Discussion Starter · #16 · (Edited)
YES, that bit of Jethro Engineering was apparently installed to PREVENT the use of the
lockers....Why, I could only guess.

A short wheel base, rear-steer UNIMOG with LARGE running gear, a Very Large Cummins
in back, and Tons of braces, drive shafts, Gearboxes and so on ....and a bonus :a muffler full of water...

And they don't want to be able to LOCK it up ?

There is a sticker that says not to use the rear steer over 15 MPH (Chickens...), but why they would eliminate the Diff Locks is baffling to me.

I'm not going to purchase this truck in any event, but a buddy of mine is all hot to trot, and I am doing my duty and leading him astray and down the path to UNIMOG ownership.

This might be a tough truck to start with, but he IS a tinkerer, and there is lots to
screw around with on this beast. I was trying to point him towards a U1300L, but he seems
to be vectored in on this thing.

There are a LOT of things on this truck that still need to be tested on the GO/NO GO
list before a price can be discussed with any reason...

This truck has no Mechanical PTO on it, nor does it have the AUX (belt driven) air Compressor or the standard Hydraulic pump (engine driven ), which is not to say it does not have gobs of stuff running all over it.
 

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They must have had a bad experience busting an axle at one time, shouldn't be that big on an issue to train the user...but...

When I was looking at buying that truck when it was first at auction, I contacted a few oil field company's that my friends work for, about that rear Cummins, they all were very interested in it, as it's the same model used in some very large genset's, so your buddy might be able to recoup some of the purchase price if its in good working order.

Even still that's a HUGE undertaking to get it to offroad state, me thinks he'd be better off with an AG spec and convert it to 4ws, or find a 4ws mog in Europe (I still want one of those damn French short fire doka's with 4ws....) and bring it over.

Unless the price is really good, and its nice to see it in person, gets a guy excited.
 

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the biggest reason for the hydrostat is to change directions without using the clutch and little to no brakes, as in snow removal operations, loader operations, ect. It could also be nice for rock crawling type operations, as the speed can be varied infinately between zero and the max speed of the selected gear and you can actually stop the movement of the vehicle without the brakes, the "neutral" location of the hydro lever will essentially stop the truck if you get used to it. The only issue would be overheating, but if it can be used in conjunction with the working and crawler gears (I have only driven two with the hydrostat, and that was just to see if it worked correctly), then it would be much less apt to have heating problems. I have had a couple 50-60hp farm tractors with hydrostat transmissions, and you could be driving full speed forward and throw the lever in reverse and spin the tires backwards... but that is not good on the drivetrain (but I was younger and dumber at the time ;-)).

Cheers,
Ben
 

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Discussion Starter · #19 ·
Thanks guys, I appreciate the help. I realize that IF I had taken more time while on site
and carefully read the RED plaque, I should have been able to pass the Jethro Test and get the Hydro Drive fired up. It was all there in Red and White. There
was a lot going on, my buddy was frequently asking "what is this thing ? Does your truck have one like this ?" etc...In Short, I flunked the Jethro Test. The shame of it all. I'll try for a do-over.

It is a very thickly packed chassis- all sorts of plumbing going on , as well as all the Snow Cutter equipment, sub frame and bracing and the rather low hanging auxiliary drive shaft. A lot to be crammed into the regular, short wheelbase. Physically, I'm not really ready to be squirming around on my back looking at trucks, a fact my body was happy to make me aware of both at the time and later.

Trev, thanks for the tip on the Genset Power plant. I'll pass it along.
 

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Vehicle: 1397 Portative Organ Normally Aspirated....U411, U2450,463 300GD
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I have always been interested in the hydrostat for loader and snow work....but retrofitting one was a bit daunting i.e. all the fiddly bits. The rail units used a diifferent setup (torque converter) as I recall. If anyone out there has ever retrofitted one on an SBU I might still be interested. And I forget if you get to keep full pto and working gear crawler groups. That hydrostat with the 4 wheel steer would make it a cool unit. And I am saying this after pushing snow for 9 hours...bloody March 23 snowfall..12 centimeters....grumble.
 
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