GMG, Unimog, County and other lesser-known all-wheel drive off-road tools

[25.4_mechanic]

The today-i-aquired thread briefly featured my GMG_2.5, which attracted interest.

Some also wanted to see more of our Unimog and I myself, for example, would like to know more about Country and other equipment I may never have heard of.

Basic Formula: Four driven wheels of equal size. (2, 3, 6, 8-wheeler welcome )


Let's start with the GMG_2.5 "All-terrain multi-purpose device" ("Geländegängiges Mehrzweck Gerät 2,5t"):

In the mid-1980s, it became increasingly clear to those responsible that the "GMG 2_70 field handling equipment" used by the "National People's Army" in the GDR since 1966 was inadequate in all respects.

The GMG_2_70:

The GMG_2_70 was mainly made from parts of the GDR's medium-sized truck, the "Robur", and was actually a mere stopgap from the very beginning.


The military derived the requirements specification for the successor from the shortcomings of the GMG_2_70; the list of requirements may not be complete:

- Heavy terrain capability,
- tyre pressure control system operable from the driver's seat at all times,
- climbing capability >=55%,
- high articulation of the axles to each other,
- self-propelled marching with the convoy (Vmax>=60km(h),
- marching regime and fine regime (mech. and hyd.-drive),
- loading and unloading of trucks and trailers from one side completely possible,
- high manoeuvrability (all-wheel steering),
- wading ability (overpressure system for all axles, gearboxes and differentials),
- long fatigue-free work possible (ergonomics),
- soldier-safe!,
- 2.5t stacking ability close and still 1.2t 2m in front of the vehicle,
- it had to be possible to pick up and set down load from/on inclined terrain,
- self-levelling of the load in a set frame,
- light recovery and self-recovery (winch 2.5t in the rear),
- towing capacity 8t with single-line air brake system,
- .....

With the GMG_2.5, everything was built from components of the large GDR trucks, the W50LA/A, except for the winch in the rear, which was still from the Robur.

First the main systems of the GMG_2.5

The engine [M] is a three-cylinder diesel engine with 62kW at 2200rpm from 4920cc.
Combustion chambers relocated into the piston crown (MAN patent, actually paid for and legally used).
The engine sits high in the rear and is modified for safe oil supply on gradients up to 55%, power output to the front.

Sitting in front of the engine, a pedal-operated clutch drives a "heavy power take-off" or "heavy secondary drive", which here acts as a "pump transfer gearbox" [PVG], and where the five small hydraulic pumps sit that are needed for most functions.

I'll take a break - please let me know if you want to know in such detail. Thank you.


Have a nice evening,


Carsten

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[500e]

Interesting machine

 

[25.4_mechanic]

Interesting machine

Yes, that's right - but would it have been the export hit in the East?!?
I have my doubts, perhaps too much intent, too complicated ....

We will never know.

Are details wanted or "pictures only" and "that'll do"?


Carsten

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[Mick Annick]

The details are interesting too!

 

[Newlands]

I’d like a drive in that GMG 2.5. In fact, if I won the lottery I think I’d have to buy one.

 

[25.4_mechanic]

I’d like a drive in that GMG 2.5.

That could be arranged ... on the continent!

In fact, if I won the lottery I think I’d have to buy one.

Firstly: little hope.
Secondly: do you already know enough about the thing to want that (or are you as crazy as me?)?



Carsten

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[Rannsachair]

Do you know who made the hydraulic pump and motor?

I recall visiting Hydraulik Norde in Parchim in the early/mid 90's, I was impressed by their machinery: high qulity machine tools and measuring kit. I was working for Eaton Hydraulics and we were considering buying them, think Danfoss bought them in the end.

The factory looked very Eastern Bloc:

 

[Nomad]

At least 2 folk on here I know like UMM (Portuguese designed, made in France & Portugal). links :
Owners club https://www.umm-world.com/
Wikipedia https://en.wikipedia.org/wiki/UMM_4x4
For sale (plenty of choice - in Portugal) https://www.olx.pt/d/carros-motos-e-barcos/q-umm/

 

[25.4_mechanic]

At least 2 folk on here I know like UMM (Portuguese designed, made in France & Portugal). links :
Owners club https://www.umm-world.com/
Wikipedia https://en.wikipedia.org/wiki/UMM_4x4
For sale (plenty of choice - in Portugal) https://www.olx.pt/d/carros-motos-e-barcos/q-umm/

Thank you!

Have to read about it .... but first reaction: I want one

EDIT: Uuuppps, watched again: for good ones we are near the lower G-Wagon region .... I have to look harder

 

[25.4_mechanic]

Do you know who made the hydraulic pump and motor?

I recall visiting Hydraulik Norde in Parchim in the early/mid 90's, I was impressed by their machinery: high qulity machine tools and measuring kit. I was working for Eaton Hydraulics and we were considering buying them, think Danfoss bought them in the end.

The factory looked very Eastern Bloc:

Oh yes, that looks eastern block - from 1955 to 1985, no real clue from when that pic stems, all the same ....

Have to have a look, either I find it on photographs here or we have to wait, the machine is 700km up north ...

... not far from

Hydraulik Nord

... they survived: https://hn-group.com/en/

The cream of the crop has found buyers - either to make money with the knowledge or to kill off unwelcome competition - the workforce-people have rarely been that lucky ....

Thank you, great pic ... and it seems I've found a hyd-guy to ask questions ...


Carsten

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[500e]

The UMM was an OK machine all steel construction 2mm, Dana axles with hub locks on front, rear had lsd on the Transcat. Peugeot motor and early ones had Boeg Warner gbox if I remember correctly later ones ZF and chain drive to xfer box, cart springs
The Altair was a later version slightly more sophisticated, both would put a LR to shame in mud with the hub locks and lsd as standard.
Poor importer and manufacturer back up

 

[Agroshield]

Thankyou for an interesting post and the diagrams are a bonus.

I believe the UK had a similar concept to the machine you show, the 'Eager Beaver':

Eager Beaver Air Portable Rough Terrain Fork Lift Truck

en.everybodywiki.com

Do you know of a manufacturer called 'Country'? Over here, we had 'County', who made/converted tractors (obligatory YT link:

).

 

[Robotstar5]

Thankyou for an interesting post and the diagrams are a bonus.

I believe the UK had a similar concept to the machine you show, the 'Eager Beaver':

Eager Beaver Air Portable Rough Terrain Fork Lift Truck

en.everybodywiki.com

Do you know of a manufacturer called 'Country'? Over here, we had 'County', who made/converted tractors (obligatory YT link:

).

Here you go...

 

[8ob]

Many moons ago the mechanical services company I worked for ran a forward control equal wheeled County, it was fitted with a huge Hiab and it towed a pipe trailer. Unstoppable would describe the thing, had lots of fun in that
It had steering of sorts but most of it was done on the brakes a bit like a bobcat. They used to be made about 200yards from where I lived as a kid.

A bit like this

 

[armalites]

When they were harvesting woodland at the farm my wife works at they were running a couple monster felling and forwarding machines which were probably £3-400K but they still had a County running too with a blade on the front and winch on the back. Chap said in this modern world there isn't much you can buy that will do the same job as the county given it's small footprint.

 

[25.4_mechanic]

( My bad: it's County not Country, sorry wrote it from memory and here you don't see them.)


Continuation about the main systems of the GMG_2,5:

After the pump transfer gearbox [PVG], the engine power goes into the change-over gearbox [UG], which also consists of a heavy power take-off like the [PVG].

This is where the changeover takes place between the mechanical regime for marching on the one hand and the hydraulic regime for loading and unloading on the other.

For marching, the engine power is fed - while maintaining the direction of rotation - into the change speed gearbox [WG], with its five forward gears and one reverse gear, which are shifted in the usual way by the driver.

Much more interesting is the other case and here the GMG_2.5 has one of its many unique selling points:


If the motor power is switched through the [UG] to the front, it drives a huge hydraulic pump [YP], which - controlled via a proportional/reversing valve - directly drives an equally huge hydraulic motor [YM].

The rotation of the hydraulic motor [YM] is transfered via the lowest shaft of the change-over gear [UG] - without connection to the other shafts! -

- into the change speed gearbox [WG] and from there into the transfer gearbox [VG].

In this hydraulic regime, the driver pre-selects a gear of the mechanical change speed gearbox.
Then he is able to control the direction and speed of the vehicle with the foot rocker alone -
- no clutch, no brake, ... a crazy feeling I can tell you!


Carsten

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[25.4_mechanic]

The Eager Beaver meant it had a much lower centre of gravity , Mk 1's didn't come with a cab , driving one in some serious foul weather gear, crash helmet and goggles was hell when it was minus 12 oC . Due to the light weight and small size it was air portable and parachutable.

I believe the UK had a similar concept to the machine you show, the 'Eager Beaver':

Eager Beaver Air Portable Rough Terrain Fork Lift Truck

en.everybodywiki.com

The "Eager Beaver" (nice name!) reminds me a bit of the pictures from the trial phase of GMG_2.5:

Note the head and facial hair of the time .... well, who else has such pictures of themselves lying around, deep in a drawer?

The GMG_2.5 is four times heavier and over all larger than the "Eager Beaver", so we are no longer talking about airlift by Andover, Argosy or C130 Hercules, but rather Antonov An-124 or An-225 (RIP).

And we'd best leave the parachute drop thing alone.

The comrades at that time - all of them certainly capable engineers and technicians - wanted to create the final, the ultimate field handling solution for the entire Eastern Bloc, soldier-safe even in the deepest Taiga ... in doing so, they - rather German - overshot the mark somewhat ...

And, although also designed for the military, the "Eager Beaver" was also developed and built under an economic aspects - the GMG_2.5 would have been far from affordable under market economy aspects.

In the pictures above and below, you can clearly see the rocker mechanism, which makes it possible to load and unload large lorries/trailers completely from one side.

Carsten

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[CompoSimmonite]

At least 2 folk on here I know like UMM (Portuguese designed, made in France & Portugal). links :
Owners club https://www.umm-world.com/
Wikipedia https://en.wikipedia.org/wiki/UMM_4x4
For sale (plenty of choice - in Portugal) https://www.olx.pt/d/carros-motos-e-barcos/q-umm/

View attachment 365342

I've got an UMM Transcat

 

[25.4_mechanic]

I've got an UMM Transcat

So, they have built LHD and RHD, so a certain number of units will have been produced...?

Tell me, how is the thing as a car and as an off-road vehicle? Thank you.


Carsten

--

 

[Mick Annick]

Many moons ago the mechanical services company I worked for ran a forward control equal wheeled County, it was fitted with a huge Hiab and it towed a pipe trailer. Unstoppable would describe the thing, had lots of fun in that
It had steering of sorts but most of it was done on the brakes a bit like a bobcat. They used to be made about 200yards from where I lived as a kid.

A bit like this

Fleet?