Z1-class

In 1972 Rupert Hamer became Premier of Victoria, promising new trams, which had been highlighted as needed in the 1969 Melbourne Transportation Plan. Comeng, in anticipation of a tender, dispatched workers to Europe who, knowing of the fondness within the MMTB of the Swedish tram design, acquired the plans for the Gothenburg M29 tram from Hägglund & Söner. It was understood that ASEA would supply the electrical equipment, as they had been involved in the supply of equipment for the Gothenburg M28 which was almost identical to the Gothenburg M29 trams, and had recently acquired the rolling stock division of Hägglund & Söner.^{[5]: 196–197}

Tenders for 100 trams based on prototype PCC 1041's design were called for in 1972 with Comeng awarded a contract in 1973.^[16] The plans purchased by Comeng proved to be less useful than anticipated, due to them being metric, single ended (with doors only on one side), and to some extent 'over-designed'. Comeng essentially started anew, but retained elements of the structural design and ASEA as the electrical equipment supplier, who would supply equipment from the Gothenburg M28 design.^{[5]: 197–198 [17][18]}

There were a number of design changes made which differentiated the Z-class from PCC 1041, including the destination display arrangement.^[5]: 198 Internally they, like PCC 1041, had conductors consoles that passengers would have to queue for, and only two doors per side, these two features hampered loading and proved unpopular.^[5]: 196 Fitting the ASEA M28 equipment into the Z-class body, which was heavily based on the M29, posed a problem due to the extra doors, tapered ends, and second cab Comeng had added to make them able to operate in Melbourne, this necessitated lengthening the design to accommodate the equipment.^[5]: 199

Construction started at Comeng Dandenong in 1974, with Dandenong's workforce tripling to cope with the order.^{[5]: 199–200} The first Z1-class tram was delivered in December 1974, and the last in May 1978.^[5]: 203 Major construction was carried out at Dandenong, with bogie frames fabricated at Granville, and final fit out and commissioning occurring at the MMTB's Preston Workshops.^{[5]: 199–200, 202}

After being unveiled to the press on 30 April 1975, the first entered service on route 64 on 5 May 1975 and the second on route 72 two days later.^[19] As more were delivered, the first 15 were concentrated at North Fitzroy depot to operate route 96 from 30 June 1975.^[20][21]

Soon after commissioning it became apparent that the Z-class had ride problems due to stiff suspension, and track differences between Gothenburg and Melbourne. The issues were rectified by the time the 80th tram was constructed, and the fix, rubber secondary suspension, was retrofitted to all trams. The braking systems also had issues, and were seen as insufficient by the MMTB.^{[5]: 203 [22]: 31}

In anticipation of the Z3-class contract, Z1 No. 5 was fitted with chopper control in November 1977 for evaluation purposes and reclassified ZC-class No. 5.^[9][23] Although it was converted back later, the test successfully demonstrated chopper control trams could operate on the Melbourne tram system without causing interference, and all Z3-class trams were fitted with chopper controls.^[22]: 31

In March 2006, Z1-class' 81 was returned to service as the Karachi to Melbourne Tram for the 2006 Commonwealth Games. Renumbered W-11 in recognition of buses operated in Karachi, Pakistan famous for their entertainment value, it was decorated with lush designs and played Bhangra and Pakistani music. For the duration of the games it operated on the City Circle.^[24] It returned to service in the summer of 2006/07 operating Friday night City Circle services.^[25]

Most of Z1-class were withdrawn following the introduction of the C and D class trams in 2001/02. Most were sold at auction, with some being donated to tram museums. The last remaining Z1-class trams were withdrawn on 24 April 2016.^[9][2] Four have been preserved.^[26] Their internal refurbishment had less refurbished features than Z3-class, only seat pads and grab rails/anchors were replaced.^[27]

Z2-class

Z2 101 on Swanston Street in October 2012

Between June 1978 and February 1979, 15 more trams were built as Z2-class, as an extension of the Z1-class' order. These varied very little from the Z1-class, the main visual differences being the deeper bumper (6-channel like the Z3-class; Z1-class having 4-channel bumpers), and the slide-opening portion of the drivers side-window also being deeper (although at least one Z2 later had a Z1-type drivers side-window fitted).^[5]: 203 The final Z2-class tram was withdrawn in April 2016, also being replaced with the C and D trams. ^[9][27]

Z3-class

Refurbished Z3 183 in December 2009

A tender for 100 new trams was called by the MMTB in early 1977, Ansair, Comeng and Siemens tendered. Although Comeng originally planning on using ASEA control equipment, as in the Z1 and Z2-class, they opted to give the MMTB a variety of options, leading to 28 different possible configurations of control equipment, bogies, and suspension types. Comeng were ultimately selected, and between 1979 and 1983, 115 Z3-class trams were built.^{[22]: 31–36}

Although superficially similar to the preceding Z1 and Z2-class trams' externally, they had significant design differences – and were a significant improvement on the Z1 and Z2-class trams.^{[22]: 31–36 [28]} They are fitted with AEG control equipment and Duewag bogies, have an additional door each side (for a total of three rather than two for the Z1 and Z2), drop down (as opposed to top sliding) Beclawat windows and improved headlights. The unreliable flap type destination displays and route number indicators were replaced by rolling plastic film destination displays. They also had much smoother acceleration and braking performance, and improved suspension. Even though the rear door is only half-width (2-leaf, as opposed to the others being 4-leaf), this in combination with the centre doors being directly opposite contributed to better passenger-flow. The Z3-class build process went smoothly, with few problems, bar a slow delivery of equipment from AEG, and a few minor faults that required remedying after construction.^{[7]: 32 [22]: 31–36 [29]} One (Z3 149) was scrapped after being destroyed in a fire in 1999.^[30]

On 31 July 2000, Z3 214 was used to convey the Olympic flame along Dandenong Road from the intersection with Hawthorn Road to Chapel Street as part of the 2000 Summer Olympics torch relay.^[31] On 26 October 2011, Z3 158, specially liveried as a Royal Tram was used to convey Queen Elizabeth II and Prince Philip along St Kilda Road from Federation Square to Government House during their visit to Melbourne. The Royal Tram remained in regular service until February 2013.^{[32][33][34][35]}

In 2013, a program commenced to refurbish all remaining 114 Z3-class trams at Preston Workshops. They received new seats, painted interior walls, glass replacement with scratch proof film applied, and the Public Transport Victoria livery at Preston Workshops.^[36][37]

As of March 2022, 101 Z3-class trams remain in service.^[4]