since 1946
Design by DmdB

The factory of Zbrojovka company, in the Moravian town Brno (say: Bruno), Czech republic, has a long history as a metal foundry since 1864. In the second world war this factory was a forced dependant of the German company "Flugzeugwerke Ostmark", or "Airplane works Ostmark", what used the Zbrojovka plant in the Brno district Vankova for the production of airplane engines and components. Most of the factory's facilities were damaged by Allied bombs during the war. Directly after WW II, the development of a prototype of the Zetor 25 started. The engineers were from the former Zbrojovka car plant. This design team was under supervisory of engineer F. Musil.


model 25

The 25 was a modern Diesel tractor, developed in the years 1945 - 1948. The engine was a two cylinder four stroke engine with 105 mm bore and 120 mm stroke. It had indirect fuel injection, with mechanical dispensers instead of commonly used compressed air dispension or hotbulbs.
This Diesel was a good engine, that was most competitors ahead in technique and lifespan. The design style was classic, but modern technology and constructions were used.

compare the front axle of the 25 (straight, like a truck axle) and the axle of the later built 25 A (portal)

The transmission was equipped with 6 forward and 2 reverse speeds, divided into two groups.The PTO shaft made 540 rpm conform the European standard. The belt pulley, used to drive things like a threshing machine or a sawmill, was mounted on the same shaft as the PTO, using a bevel gear. These tractors had also independent steering brakes to decrease turning radius. Other standard equipment was a differential lock, a mechanism that is very useful, but was not seen on most tractors of that time. Most of these tractors had a mechanical hitch.


model 15

In 1947, a one cylinder model came from Brno. It was targeted as a more affordable alternative for the 25 two cylinder, with 15 hp. It had 120 mm bore and 140 mm stroke, that was also using the four stroke Diesel proces. The transmision had 5 speeds forward and 1 reverse. It was probably a predecessor of the transmission of the Super series, they had the same belt pulley drive.
This model was quite old-fashioned compared with the 25. It had to start using a decompressor, and a glow fuse. This is probably the rarest Zetor there is, only 1800 were built.

The major design of both engines was probably a joint-engineering project with Tatra, what was developing air cooled engines with identical bore and stroke. The cylinder liners of the two cylinder were replacable with those of the early Tatra engines.

Worth noticing is that the top speed of the 25 was about 30% higher than usual in the 40's and 50's. The transmission of the 15 had lower speeds, it had smaller tires and a lower engine speed of 1500 rpm. (see table below)


model 25 A

In 1948, the 25 was succeeded by the model 25 A. The tractor was updated in many details, for example: the metal pan seat was replaced by a leather seat, the front of the bonnet was redesigned, the brake pedals and gas throttle were placed more ergonomic, and the side exhaust was now mounted upright, to prevent setting your hay on fire.

Also the durability, mostly of the transmission, was improved by adding 76 kg of material to crucial parts of the construction. The front axle was a new gate formed one, what increased the ground clearance with about 10 centimeters.

a Zetor 25 A

Anyway, The A-model (All-round) was still not very suitable for row crops, its ground clearance was too small. The A model had a low center of gravity, so that the tractor would be more stabile on hill slopes. This made it suitable for the cattle farmers, that used it just for towing and mowing in the Czech mountains. The model A had a hydraulic hitch as option.

  
The halftrack 25 A 'polopasovy'
 
Another factory installed modification for the 25 A was the half-track. A belt was running over the rear wheels and a supplementary axle, stretched by springs. The belt was built up from two cables, with iron beams between them.
 
The tractor had a steered front axle, but the independent foot brakes were needed to turn tight. The advantages of the halftracks are best used in mud, snow and forest.

model 25 K

At the same time, another model was introduced as a row crop, model 25 K. It had much bigger rear wheels, and a higher front axle. Longer turning columns of the front axle gave it about 19 centimeters (7.5") more ground clearance. A hydraulic hitch was standard.

The transmission of the K had a closer gear ratio spacing, for better performance in the field. It had 4 gears in the important field speed range of 4 to 12 km/h. The closer gear ratio spacing also resulted in a lower top speed of 20.3 km/h.

The model K (Kultivaci, cultivating) was targeted to the crop farmers on flat land, what would use the tractor for tillage, and row crop care. For row crop use, tires of size 9x36 were used (blue tractor). When it was used for tillage, the K came with 13x28 tires. (brown tractor). The differential lock was an advantage for tillage, the independent brakes were advantageous in row crop.


Prototypes based on the T25 series

The Zbrojovka engineers developed several prototypes (partly) based on the 15, 25 and Super models. The most interesting ones are not serial produced, but they were design studies for the later Unified Range 1, one of the most modern tractor series of its time.

Zetor T18 
A one cylinder tractor for row crop care. It was designed to carry equipment like sprayers and hoes
Zetor 18
A small one cylinder crawler tractor, what can be seen as the predecessor of the UR1 series.
Zetor 26
had a two cylinder engine with enlarged stroke. It was produced in around 1955. The engine had a bore/stroke of 105x130 mm and a displacement of 2251cc. It's power was 28 hp at 1600 rpm.
Zetor 30
was ready for serial production in 1949. This tractor was the same as the 25, except the cylinder heads. The Zetor 30 was one of the world's first tractors with direct Diesel injection. It was promptly awarded on the Prague Agricultural show with a gold medal. However, the Communist Central Office decided that the 30 would not be serial produced, they decided that a tractor with higher power should be developed...(subject changes not to politics here)
A three cylinder tractor
also appeared in this era. The engine was a combination of one and a half T25 engines. It's power was 29 hp at 1400 rpm.


Specifications of the Zetor T series

model

15

25/25 A

25 K

production

 1947-1949 

 1946-1948/ 
1961

1948-1961

type of engine

4 stroke OHV, indirect injected Diesel,
water cooled

No. of cylinders

1

2

bore x stroke (mm)

120 x 140

105 x 120

displacement (CC)

1583

2078

power (hp)

15

25

at rpm

1500

1800

    transmission speeds   1 
(km/h)   2 




reverse  low  
high 

3.9
5.6
8.2
13
22.3
-
2.8
-

3.4
5.2
7.8
13
20
32
2.3
9.0

4.3
5.6
7.2
11.9
15.6
20.3
3.0
7.7

PTO

dependent 540 rpm

belt pulley

yes

hydraulic hitch

option

standard

tires          front 
         rear 

5.50 x 16
9 x 24

5.50 x 16
11.25 x 24

5.50 x 16
 9x 36/13x 28

trackwidth (cm)  front 
rear 

127-145
127-145

120-150
120-150

122-154
115-146

wheelbase (cm)

156

190

weight (kg)

1400

1750/1826

1955

The 25 A and K production stopped in 1961, when a total of 158.570 units were built of the 25. Thousands of them are still running, or even in use on farms, at most in Scandinavia. The 25 two cylinder engine is the grandfather of the nowadays range 2, 3 and 4 engines, so its 'spirit' lives on.


Super 35 - Super 50

ZETOR came with their first four cylinder tractor in 1955, called the Super 35. Its engine was a direct clone of the one of the 25, and was used in the models 35 super, and Super P.

The updated Super 35 was called Super 50, introduced in 1960. It had a power output of 50 hp, also at 1500 rpm. The transmission was in the same style as the one of the model 15, the place of the belt pulley, and the number and gear ratios were similar. The 5 speed had a solid and simple construction.

the super 50

The Super series had also some nice standard features, such as an independently leaf sprung front axle, differential lock, air compressor, and an engine oil cooler. This cooler was an advantage for stationary work, such as driving a threshing machine on the belt pulley. Optional was a drivers cab with heater.


the Super P

The 42 hp engine was also used in a tracked tractor, the Super P. Its weight was 4200 kg, what means a specific weight of 100 kg per HP.
The transmission had other gear ratios than the wheeled super, it was made for heavy haulage at between 3 and 7 km per hour. Its maximum speed was 15 kph. The folder speaks of a fuel use of 17.5 litre per Hectare, or 9 litre of Diesel per hour at a ploughing depth of 30 cm.
The demand for tracked tractors in the fifties consisted from the lack of hitch-hydraulic weight transfer systems and the slow development of good tractor tires.

front of the original folder

A winch was an option when it was used in forestry to haul trees trough the woods.The agricultural versions had standard a hydraulic hitch. It was also used with optional dozer blade for landscaping and earthmoving, and for the deep tillage what land reclaim projects demanded. 

the Super P at forest
"Tough guy..."


specifications of the Zetor Super

model

35 Super

50 Super

Super P

production

1955-1960

1960-1968

1956-1958

type of engine

4 stroke OHV Diesel, indirect
injected, water cooled

No. of cylinders

4

bore x stroke (mm)

105 x 120

displacement (CC)

4,156

Power HP

42

50

42

at rpm

1500

transmission speeds 1 
(km/h) 2 



3.92
5.15
7.42
12
24
?

2.4
3.14
4.5
7.3
14.6
2.4

PTO

dependent 540 rpm

belt pulley

yes

hydraulic hitch

yes

trackwidth

120-150

173

Tires       front 
rear 

6.00 x 20
13 x 28

tracks

weight (kg)

2550

4200

A local agricultural contractor had two Zetor 50 Supers in the fifties. These tractors left quite an impression on the people of that time. My neighbour remembers them as "two of those real huge Zetors pulling the manure spreaders" These tractors were extremely tough pullers, because of the low engine speed and big displacement. Only the real hog could wreck these solid machines without a sledge hammer.

The Supers are built from 1955. The Super 35 was succeeded in 1960 by the Super 50, which was produced to 1968. It was sold as affordable alternative for the UR 1 type 4011, which was more productive and economic in use. From 1955 to 1968, 106.881 tractors were made in the Super series.

DmdB 2001