Z4p / Z4t – Info (Late Build)


Z4p late Head

Diesel replaces Electric and Steam in Östergötland

In January 1955 the SJ Operational Services Bureau of Mechanical Technology Agency identified the requirement for an additional 10 Z4p multiple operation locomotives to supplement demand as a result of the transition from electric traction on the narrow gauge lines west of Linkoping

By 1956, the Railway Board had decided that all electric lines Linkoping Vadstena, Fornåsa-Motala and Klockrike-Borensberg were to be phased out by the start of the Summer timetable. New diesel locomotives were also required for freight traffic upon the withdrawl of steam locos in operation on the Kimstad-Skärblacka route.

Tender Enquiry and order

During July 1955 the Machine Technology Agency had granted permission for request for tenders to be sent out to potential suppliers – Kalmar Workshop, Kockums of Malmö and ASJ in Falun. The specification was for the construction of ten railway locomotives of a Z4p type for 891mm gauge. SJ provided as part of the tender packs drawings for chassis framework and mechanics for the locos based on the Kalmar Workshop design which had previously supplied SJ with similar locomotives. The superstructure was to be fabricated by the builder and at no cost, SJ would supply the Hydraulic gearboxes, transmission and brake components.

By August 1955 the tenders quotes were received from all the proposed builders – ASJ Falun tender had the lowest price of 74,000SEK per loco with delivery 10-14 months after order. Kockums provided the most expensive quote of 79,150SEK per loco and delivery would take place during the period September-November 1956. Kalmar Workshop’s tender was received at 75,600SEK per loco and was thus slightly more expensive than ASJ Falun,although delivery from Kalmar would not commence for another 5-9 months after ordering.

SJ chose to opt for the Kalmar Workshop tender, citing the advantageous delivery times. The orders were completed by the end of September 1955 and in November exchanged contracts for Z4p locos ‘387-396’.

Diesel replacing steam in Småland

During October 1955 the SJ traffic inspector announced that the local freight services between Vetlanda Sävsjö-Målilla-Vetlandan would no longer be steam operated and would be replaced by Diesel traction. An assessment of services demonstrated that smaller lighter locos would be capable of hauling the services. Meanwhile it was suggested that the steam traction on the Gårdveda-Målilla route would be withdrawn.  Following an inquiry it was proposed by the district manager in Borås that 3 of the newly ordered lokomotorerna would be assigned to a district executive for use elsewhere.

Alternatively, the order of Kalmar workshop would be increased.

The Operational Service Agency identified that traffic between Vetlanda and Sävsjö was of such that multiple interconnected locomotives would be required for freight train operation. Routes between Vetlanda and Farmveda were minor and usually headed by a single locomotive. A result of this ensured that one locomotive could remain in Vetlanda for use on shunting activities.  As a result the annual operating cost reduction was estimated at 140,000SEK.

Extended order

Following a telephone inquiry by the Machine Technology Agency,  Kalmar workshops offered an additional 5 locomotives at the cost of 74,000SEK each.   Final delivery would take place before the middle of September 1956. The additional locomotives would receive numbers 407-411. To ensure a contiguous number series were the numbers of the 10 previously ordered locomotives were changed from 387-396 to 397-406.

Transmissions from tanks

In accordance with the quotation conditions, SJ would provide among other items Atlas hydraulic gearboxes type DF 1.0. These transmissions were purchased from the Swedish Army and were originally destined for use in M40 and M42-TH artillery vehicles.  Before being fitted by the Kalmar workshop each gearbox was refurbished and remodelled by Atlas.


The delivery was completed in the agreed time between February and September 1956. In February 1956, Operation Service Agency decided how the 15 new locomotive engines would be distributed. The decision was based on the preferences that during 1954 and 1955 submitted by districts.

Z4p 397-401

Z4p 397-401 was delivered to 27 machine section in Småland. Three were intended for the train services between Sävsjö-Vetlanda Gårdveda, one being used for switching in Växjö and the remainder would be held in reserve.

397-399 were originally used initially for running various tests.

In April 1956 it was decided that they be lent to the 37 operating section. There was a significant need for traction on Gotland as a result of transport from the Stånga gravel pit to support the construction of Visby Airport.   Locomotives would have returned to 27 machine section in June but was retained on Gotland during the summer. By September their future had been determined and that they would be transferred to the operating section 37 for further use on the island.

400-401 was placed in Vetlanda and intended for freight service between Sävsjö-Vetlanda Gårdveda. Both locomotives were retained in Vetlanda during their working lives.

Z4p 402-411

Z4p 402-411 were delivered to two machine section in Östergötland. Five were intended to replace older locos, three for train services between Skärblacka-Kimstad and one for switching in Finspång. The remainder would be held in reserve.

402-406 was placed in Linköping for use in freight trains on the lines west of Linköping and for freight trains between Linkoping Kimstad.

407-411 were placed at Norrköping. 409 was loaned to 5 hardware section in Västergötland the first few months after delivery. The use on freight trains between Skärblacka-Kimstad did not occur due to staff  objections.

By 1957, Tp locos were now in traffic and heading the Skärblacka-Kimstad services. The new Z4p locomotives were re assigned for use on the freight Norrköping-Arkösund/Valdemarsvik workings. The surplus locos r 410-411 were relocated to 5 machine section in exchange for two Z4p that lacked the necessary equipment to run in multiple.

Problems with the drive chains

During the first months of Östergötland opperation a number of problems had already occurred with the loco drive chains. The Mechanical Engineer in Norrköping reported in september 1956 to Machine Technology Agency of the problems sighting significant wear after 250miles.

It was then noted that it was only locos allocated to the Linköping area that were suffering abnormal wear and breakages. These locos had been used in trains at 40 km/h maximum speed.

The locos used in Norrköping spent the majority of their early lives switching and in use with with transporter wagons limited their speed to 30km/h.  As a result orders were issued that speeds should not exceed 35km/h and under no circumstances be greater than 40 km/h.

Work Problems

Upon entry into service drivers and staff expressed complaints about the locomotives suspension. It was considered inadequate and drivers ususally experienced headaches and muscle pain in the back and neck. The design was improved by the introduction of  cab resting on rubber pads and removing any mechanical fixing to the superstructure.

In the summer of 1957 tests with softer suspension springs on Z4p 404 were trialed unsuccessfully. New samples of other spring dimensions were tested during the winter of 1957-1958 on Z4p 402.  Neither experiment yielded success. The tests also coincided with trials of retractable buffers to reduce vibration transmission into the cab.

By the summer of 1958 attempts were made with flexible mats reduce problems but the problems persisted. In the spring of 1959 was amended suspension on Z4p 407 in the workshop in Finspång were installed. Leaf suspension was replaced with axle boxes springs made of rubber. By the late summer of that year pchanges were also made to Z4p 406. During the test time was changed construction then found that the rubber deterorated and performance was poor. The later addition  of suspension with shock absorbers to the rear axle. Whilst this provided an improvement at walking pace, performance was limited at speed and returned to leaf springs.

Drawings and Documents

Z4p Drawing and article *Note the drawing linked here may have some dimensional and scale inaccuracies.

Bonnet A (Side and End Elevation)

Bonnet B (Side and End Elevation)

Cab Front and Rear Elevations

Under Frame General Arrangement

Bonnet Front Grill


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