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HYDROSTATIC DRIVE QUESTIONS

17664 Views 41 Replies 14 Participants Last post by  TRUKTOR
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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1976 406
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604 Posts
Paul,

I am very intrigued in the hydrostatic system you describe for a 406/416 and am curious if that is the way they came from the factory. Do you know if it is? In the statement you made above

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?
how does the bottom PTO power the drive train (wheels)? Isn't it separate from the transmission for the wheels just like the side mount PTO unit is?

TIA,
Blane
 

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1975 Case 406 Unimog
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164 Posts
Blane,

I agree that it's pretty thought provoking. Yes, from the manual it looks like this was an available option from the factory. I'll have to look again at the manual, but it looks like the hydrostatic option included its own bolt-on bottom PTO with gears that engage the input shaft of the tranny. It seems to me that it couldn't work with the standard bottom pto.

Paul,
I am very intrigued in the hydrostatic system you describe for a 406/416 and am curious if that is the way they came from the factory. Do you know if it is? In the statement you made above



how does the bottom PTO power the drive train (wheels)? Isn't it separate from the transmission for the wheels just like the side mount PTO unit is?

TIA,
Blane
 

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mogless, except for my friends MB4-94. And a bunch of other diesel junk.
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2,513 Posts
For what it's worth,
The one mog I've looked over that had the hydrostatic option worked as follows
There was a cascade box mounted pto that ran a pump, the pump fed a hydraulic drive that was bolted in place of the standard pto. It essentially runs the trans off of a hydraulic motor, as if you had a separate engine to power the mog through the pto shaft. Neat, but complicated.
 

· Unimog Moderator
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13,988 Posts
There was some talk (here or the mailing list..can't remember) if it would be possible to put a forklift or similar electric motor onto the PTO, and a box full-o-batteries, and have sort of a hybrid mog, if you had a powerful enough electric motor that could be great for crawling, as they produce all available torque at 1 or full rpm
 

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1976 406
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604 Posts
Does anybody on this list have an hydrostatic drive setup on their 406 or 416 truck?

BWSwede
 

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MERZ-1997-U-1350 LM Belgian Troop truck 366A-fast. axles-Binz Engine 220 HP HP upgrade in Nederlands
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698 Posts
That truck probably has no rear coils and is solid axle attachment with chain limiters to prevent excess axle travel!! Not conducive to 4 wheeling. But could retrofitted with standard coil suspension SN shocks.
 

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FLU 419.101 (2), FLU 419.102, Flu 419.103 (2), 406.121
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388 Posts
Pages 23, 24 and 25 in the 406 owners manual covers operation, what were you looking for?
Not to be a complete smartass, but one thing I'm looking for is levers.
There's the regular shifter, the high range/low range/reverse lever, and one for the front hydraulics. That's it. Not even a PTO lever.

It sounds like the rear hydraulics are always on, which makes sense since there's no lever, but that doesn't seem quite right.

Not wanting to destroy anything, I'm trying to learn how it's all supposed to work before putting it to the test.
Also, it looks/sounds like the injectors leave a bit to be desired so I want to get the engine running right before digging into the hydraulics.
Either way, any and all information is welcomed and appreciated.
 

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FLU 419.101 (2), FLU 419.102, Flu 419.103 (2), 406.121
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388 Posts
That truck probably has no rear coils and is solid axle attachment with chain limiters to prevent excess axle travel!! Not conducive to 4 wheeling. But could retrofitted with standard coil suspension SN shocks.
tlane, if you're referring to the one with the hydraulic drive I posted the photo of, it does have the normal rear suspension. But it can be manually locked.
 

· Registered
MERZ-1997-U-1350 LM Belgian Troop truck 366A-fast. axles-Binz Engine 220 HP HP upgrade in Nederlands
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698 Posts
No I was referring to the old post by John about the crab steer Snow Cutter-- the old post. I saw the date on the post after the fact.
 

· Registered
1984 U1200AG (soon a hydrostat and rotzler teibmatic winch)
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548 Posts
I have a 66-page service manual for it, in english, with lots of fold-out diagrams. I can stick it in the mail if you want to take a gander at it.

Do you still have that manual? I am going to install on on my 1200, it does not really look to bad to do. I would love to have a look at that manual!
 

· Unimog Moderator
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Do you still have that manual? I am going to install on on my 1200, it does not really look to bad to do. I would love to have a look at that manual!
If it's for snow pushing be careful, fellow up here has a U2100 w/hydrostatic and has turfed several drive units, really good for snow blowing, not so much for pushing.
 

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1984 U1200AG (soon a hydrostat and rotzler teibmatic winch)
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548 Posts
Trev, interesting...the manual even calls out using a plow and says max speed plowing is 25km/hr. I am going to use it for snow-blowing anyway which it should be really good at as you said.

The hydraulic pump and motor do not look that big compared to the size of the truck, say vs the hydrostat in my 30hp tractor or my 110hp forklift. Yet the manual also mentions a front loader with the hydrostat.

There is a temp sensor that must be respected (a light comes on when the oil is 90C), I wonder if the fellow with the U2100 has a bad temp sensor and is overheating them. Really seems strange that he is having that issue.
 

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1250v
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Are there more than one size hydrostatic drive for these trucks? 200 plus horsepower is definitely going to put more stress on the hydrostatic setup than 150hp will. I'm also surprised the warning light is at 90c. The equipment and oil we run warns about damage to hydraulic components over 80c.
 

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1984 U1200AG (soon a hydrostat and rotzler teibmatic winch)
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548 Posts
I agree, 90C seems high it is what the owners manual says, I will look a the repair manual and see if it is different.

Pump and motor sizes are different like you were thinking, it looks like everything else is the same. In other words putting the bigger pump/motor just adds weight and cost but from a fitment perspective it looks the same to me so far.
 

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1984 U1200AG (soon a hydrostat and rotzler teibmatic winch)
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548 Posts
Trev and Ben got me thinking, thanks gents. As a result of your questions and concerns I think I have a better understanding of the limits of this system.

I converted the specs in the manual to GPM and PSI so I could better understand what I am looking at:
The pressures are the same for both versions of the hydrostat I have in my manual, the small hydrostat goes in the U1000, U1200, U1250 and U1250L the larger hysdrostat goes in the U1300 and U1500. I am sure there are other versions but those are the only ones listed in my maintenance manual.

The pressures are: (same for both units)
Max: 7100psi
Max operating: 6100psi
Working: 3620psi

The smaller hydrostat fluid flows are:
Pump 40GPM at 3000RPM [email protected] max flow rate
Motor “absorption volume” 53GPM at 4000RPM [email protected] max flow rate

The larger hydrostat fluid flows are:
Pump 56GPM at 3000RPM [email protected] max flow rate
Motor “absorption volume” 73GPM at 3700RPM [email protected] max flow rate

The 90C temp sensor is in the bottom of the reservoir, I think I will add a gauge to mine. To your point Ben that just seems crazy hot, the fluid called for is SAE HLP/HLP D46. The Mobil version of that oil is 250$ for 5 gallons…and has a max operating temperature of 150C. Maybe I should run the oil cooler into the cab for winter ops…. 😊 …I would roast myself out of the cab….

I am pretty sure I am getting is the larger one, since I have a U1200 the smaller one would work as well. The unit I am getting was listed as being able to go into any truck from U1000 to U2400, I will verify but that should mean it is the heavier duty unit. I need to know what it came out of specifically anyway in case I need any parts later.

Trev, I am very interested to know what component is failing on the unit you mentioned, pump, motor or something else.

I am not installing this thing until the spring so I have lots of time to get smart on it.
 
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