AEC Reliance Export Models


The AEC Reliance bus chassis has had extensive treatment in the literature, with reasonable mention of the export versions. What I have endeavoured to do in this posting, which will be in two parts, is to extract from available sources the chronology of the export models, which I haven’t seen done elsewhere in a standalone fashion. Some references to the domestic models have been necessary for context and clarity. I have used “Commercial Motor” (CM) magazine articles and items as chronological markers. The CM archive is available at: http://archive.commercialmotor.com/.

The AEC Reliance was announced in CM 1953 October 30. In its original form, it was a 16’4” wheelbase chassis with 5’13/8” front overhang, suitable for carrying 30 ft bodies with a gvw of 9½ tons. It was offered with a choice of the then-new AH410 and AH470 engines, and with a choice of 5-speed synchromesh or 4-speed air-operated epicyclic gearboxes. Vacuum brakes were standard for the domestic version with synchromesh transmission. Air brakes were standard with the epicyclic transmission , and optional with synchromesh. Its model number was MU.

From the start, an export version was offered, dimensionally similar, but with a thicker section frame. This no doubt had a higher gvw. I have not seen a number for it, but 11 tons, as for the later 2MU export model seems likely. It had air brakes as standard equipment. The same model number MU was used, but with an E suffix for the right-hand drive versions. The left-hand drive versions were export-only, and so did not require this suffix.

During 1956 the export version of the Reliance MU was replaced by a dedicated export model, the HMU. The chassis was flitched between the axles, rather than using a heavier section as had been the case with the MU-E. The HMU was available in two wheelbases, namely 16’0” and 17’6”, suitable for respective nominal body lengths of 30 ft and 32 to 33 ft. Both had a front overhang of 5’9¾”. The longer variant was new in the Reliance range, and used the same 17’6” wheelbase as had earlier been chosen for the core model in the Regal IV series, which was also intended for 32 to 33 ft bodies. It looks as if the shorter HMU variant was obtained simply by subtracting 18 inches from the wheelbase. That gave it a longer front overhang than the MU model, making it more suitable for urban applications where reasonably wide front doors were desirable. Gvw was 11½ tons. Details were provided in a sales brochure dated 1956 July:



Only the AH470 engine was available, whereas the domestic model still offered the choice of the AH410 and AH470, as recorded in a 1956 May brochure. The gearbox options remained the same as previously, namely 5-speed synchromesh and 4-speed Monocontrol.

Mentioned in CM 1958 September 26 in a report on that year’s Earl’s Court show was a chassis change for the Reliance, namely the adoption of mechanical rather than belt drive for the auxiliaries. With this the MU and HMU models became the 2MU and 2HMU respectively. A road test of the 2HMU in 17’6” wheelbase form was published in CM 1959 May 30. Curiously, a 1959 September sales brochure featured the new auxiliary drive, but still referred to the series as HMU, not 2MU. I suspect that this was an editing error.



Also recorded in that same CM item was the availability of an air suspension option for the Reliance. Chassis so equipped were known as the 3MU and 3HMU, although not many were built.

There was an extra-short version of the Reliance produced for export, with a 13’7” wheelbase, in both the MU and 2MU eras. But whether this was derived from the domestic (2)MU or the export (2)MU is unknown.

In mid-1961, two longer Reliance chassis, suitable for 36 ft bodies, were introduced, as announced in CM 1961 August 11. These were a response to the change in the UK C&U regulations that allowed a 36 ft maximum length for buses in place of the previous 30 ft.

Both models had an 18’7” wheelbase with a 6’6½” front overhang. One was the Reliance 470, model number 4MU, with the same running units (and options) as in the 2MU. Initially the gvw was 11 tons. Evidently AEC thought that there was enough change as compared with the 2MU to warrant a new model number, and 4MU was the next available in the MU series. The 4MU chassis was similar to the 2HMU chassis in that it included a between-the-axles flitch.

From about the time that the 4MU was introduced, the Reliance 470 name was also used for the 2MU (and presumably the 2HMU models), which continued unchanged. It appears to have been applied retroactively to earlier-built (2)MU and (2)HMU models, although whether that was done officially by AEC or informally by common usage is unknown.

The other new model in 1961 was the Reliance 590, model number 2U, which had a very similar chassis to the 4MU. This had the AH590 engine, which was effectively a smaller bore version of the AH690, the engine used in the Regal VI export chassis that had been announced in CM 1960 August 26. It was successor to the Regal IV, and was very similar to the Reliance in its layout. Its model number was U, which explains why the closely following Reliance 590 was the 2U. That was the beginning of an interleaved U series, with the Regal VI having the odd prefix numbers and the large-engined Reliance the even numbers.

The 36 ft version of the Regal VI had a 19’6” wheelbase, inherited from the long version of the Regal IV, to suit overseas requirements. To meet the UK requirements for 36 ft buses, particularly the turning circle, a somewhat shorter wheelbase was needed, and as noted above, AEC chose 18’7”, already in its inventory as the wheelbase of its longer version of its Regent V front vertical-engined chassis.

The Reliance 2U gearbox options were 4-speed synchromesh, 6-speed overdrive synchromesh and 4-speed Monocontrol. Gvw was 12½ tons. Details of the domestic Reliance 470 and 590 models were provided in a 1962 July sales brochure. By this time the gvw of the 4MU had moved up to 12 tons.



The 4MU was essentially a domestic chassis, and although some were exported, these appear to have been to the domestic specification, there being no evidence that there was an E-suffix export version. On the other hand, the 2U was also intended for export. To that end, a 17’6” wheelbase variant was also offered. This had the same 6’6½” front overhang as the 18’7” wheelbase variant, so in that respect it differed from the 17’6” wheelbase variant of the 2HMU. Both wheelbase options were shown in this 1962 August export sales brochure, #724, and gvw was the same as for the domestic model, namely 12½ tons:



The only Reliance 470 variant listed in that brochure was the 2MU export version, with 16’4” wheelbase, 5’13/8” front overhang, and 11 tons gvw. From that one may infer that AEC may have abandoned the 2HMU, and returned to an updated version of the original MU export version. Only the 2U was described as having a flitched chassis., which indicates that the 2MU was not flitched.

However, an undated French language brochure for the Reliance presented a somewhat different picture. This had number 724B, so it was probably somewhat later than #724:



No model numbers were given, but the Reliance 590 was shown in both 17’6” and 18’7” wheelbase variants, albeit with a gvw of 14 tonnes (13.8 tons). The Reliance 470 was shown in both 16’4” and 17’6” wheelbase forms, both with a 12.5 tonne (12.3 ton) gvw. The short version was dimensionally identical to the 2MU export. The longer version was dimensionally identical to the 17’6” wheelbase variant of the 2U. That gave it a 6’6½” front overhang instead of the previous 5’9¾”. Presumably that was done for standardization.

On paper at least it would appear that at the time or soon after the 2U was introduced, AEC modified the 17’6” wheelbase version of the 2HMU to align with the same wheelbase version of the 2U. Then rather than leave the 16’0” wheelbase 2HMU as an “orphan” model in front end terms, it opted instead for an export version of the 2MU. Also, it appears that AEC offered different mixes of Reliance variants in different overseas markets.

An updated version of the AEC air suspension system was announced in CM 1962 July 13. This used four rather than two air bellows per axle. The 3U model number was applied to the air suspension version of the Regal VI, with 4U applied to the Reliance 590. The air suspension versions of the 2MU and 2HMU continued to be known as the 3MU and 3HMU respectively, with 5MU used for the air suspension version of the 4MU. The last-mentioned was probably quite rare, although 2 are known to have come to New Zealand.

During the currency of the Reliance 470, an additional gearbox option was added, namely 6-speed overdrive constant mesh. This had happened by the time home market specification #711 was issued in 1964 January. It is reasonable to assume that the same option was offered on export models.





To be continued.


Cheers,

AEC Reliance Export Models, continued.


The next step was the introduction of the Reliance 505 and Reliance 691 models, respectively replacing the Reliance 470 and Reliance 590. The major change was that the relatively new and improved dry-liner developments of the older AEC engines displaced the previous wet-liner types.

The dry-liner engines themselves had been described in CM 1964 September 11. The AH505 engine was used in the then-new Swift rear-engined chassis, announced in CM 1964 September 04. Also mentioned therein as a future model was the similar Merlin, to be powered by the AH691 engine. So both the AH505 and AH691 engines were nominally available in 1964 3rd quarter.

The Regal VI export-only model had been updated with the AH691 engine replacing the AH690 during 1965. It was announced in CM 1965 August 27. Initially at least, it was known as the Regal 691 rather than the Regal VI. The Regal 691 name was used in a 1965 August sales brochure. The model number was 5U, which was the next available in the “U” sequence. Air suspension was optional, but there was no indication in the brochure that a different model number applied in that case. If it did, then 7U would have been logical, but I haver not seen any evidence that it was actually used. A 1966 August sales brochure simply referred to it as the Regal, without suffix, and still with the 5U model number.

I cannot find an exact date for the introduction of the Reliance 505 and 691. The CM 1965 October 01 article “British Passenger Chassis” recorded “All AEC passenger chassis are now fitted with a dry-liner engine the A691 or A505,…” Thus it is reasonable to assume that the Reliance 505 and 691 were announced at about the same time as the Regal 691.

The Reliance 505 had the 6MU model designation, the next available in the MU series. The 6MU replaced the 2MU, 2HMU and 4MU models. The export version was available in three wheelbase variants, namely 16’4”, 17’6” and 18’6”, for respective nominal body lengths of 30, 33 and 36 ft. Details of these were provided in a 1966 June sales brochure:



The 16’4” wheelbase variant had the 5’13/8” front overhang, this being the original Reliance dimension. Its gvw was 24 700 lb (roundly 11 tons) gvw.

The 17’6” and 18’7” wheelbase variants had the 6’6½” front overhang that had arrived with the 4MU in 1961. Both had a gvw of 27 000 lb (roundly 12 tons). These had flitched chassis, whereas the short variant did not. Gearbox options remained as for the Reliance 470, namely 5-speed synchromesh, 4-speed Monocontrol and 6-speed constant mesh.

Whether the 16’0” wheelbase variant of the 2HMU had remained available, perhaps as a special order model, until 1965 is unclear, but that dimension was not carried over to the 6MU.

Whereas the 4MU had been, nominally at least, a domestic-only model, the replacement 18’7” wheelbase variant 6MU was an export model from the start. Perhaps AEC had more confidence in the ability of its AH505 engine (and its associated cooling system) to handle a long export bus than had been the case with the AH470.

The domestic version of the 6MU was available only in two wheelbase variants, 16’4” and 18’7”, with gvws of 9½ and 12 tons respectively, as shown in this 1966 June sales brochure:



I imagine that the 6MU would have been available with air suspension had any customer wanted it, but it was not mentioned in either of the 1966 sales brochures. Logically the 7MU designation would have applied, but that is pure speculation on my part.

The Reliance 691 had the 6U model designation, the next available in the U series. The export version was available in two wheelbases, namely 17’6” and 18’7”, for nominal body lengths of 33 and 36 ft. Both had a 6’6½” front overhang. Thus they continued the dimension sets that had been introduced with the 2U in 1961. Both had a gvw of 28 000 lb (12½ tons). Details were provided in a 1966 August sales brochure. An interesting point that the 17’6: wheelbase was standard, with the 18’7” wheelbase being a special order variant.



The domestic version of the 6U was available only in the 18’7” wheelbase, also with the 12½ tons gvw:



Air suspension was an option for both the export and domestic 6U models, with no indication in those brochures that a separate model number was used for chassis so fitted. However, in a Bus & Coach journal 1967 November road test of a Reliance 691 with coil spring suspension, it was said: “The chassis designation prefix 8U is used as for the air-sprung version”. The coil spring suspension was basically a “poor man’s” version of the air suspension, with coils replacing the airbags but retaining the same location linkages. To what extent the coil spring suspension was specified for export chassis is unknown, although I understand that it was used for the rear axle of some export Swifts. Whether the 8U designation was actually used for air-sprung Reliance 691 is unknown. All of this model that came to New Zealand were recorded as being of the 6U type, and I am fairly certain that some of those had air suspension.

An even longer wheelbase variant of the Reliance 691 6U was announced in CM 1966 September 16. It was said to have a 20’6” wheelbase, a front overhang of 6’10”, and a gvw of 14 tons, suitable for 12-metre bodies. At the time it was export-only, as 12-metre buses were not yet legal in the UK. The availability of the 12-metre chassis for the domestic market was announced in CM 1967 November 24. This was described as having a 20’0” wheelbase and a 7’2” front overhang. Exactly what happened here is unknown, but perhaps the dimensions were revised somewhat to meet the British C&U regulations for 12-metre buses once they became known. The 1967 CM article indicated that with the two alternative transmissions (Monocontrol and synchromesh) there were then four versions of the 12-metre Reliance, two export and two domestic. The export version with 20’6” wheelbase does appear to have been discontinued by 1969. A CM 1969 June 20 listing of all British Leyland commercial vehicle chassis showed the 12-metre variant as being RHD-only, with a gvw of 29 120 lb (13 tons). One supposes that this was the domestic version gvw from the start.

The 17’6” wheelbase variants of both the 6MU and 6U appear to have been withdrawn circa 1970. Both were still included in the CM 1969 June 20 listing of all British Leyland commercial vehicle chassis. A 1970 July sales specification sheet for the export Reliance 691 shows only the 18’7” wheelbase variant, by then with a gvw of 13 tons. (It had still been 12 tons in the CM 1969 listing). The 4-speed synchromesh gearbox option had been deleted by then, leaving the 6-speed synchromesh and 4 or 5-speed Monocontrol options. The lack of the 20’0” wheelbase variant suggests that this was seen only a domestic model at the time.




It is reasonable to assume that the 17’6” wheelbase 6MU was withdrawn at the same time as the 17’6” 6U. By the end of the 1960s, the export demand for 17’6” wheelbase chassis was probably much diminished. The city operators who previously specified this had largely moved on to longer chassis. Also by then, the Reliance was not favoured for citybus operations, the Leyland Leopard being much preferred. Leopards with 17’6” wheelbase were built into the 1970s.

In the same timeframe the short wheelbase variant of the domestic 6MU was altered dimensionally. The 1969 June listing showed the original dimensions. A 1970 July sales specification sheet showed the wheelbase reduced slightly to 16’2” and the front overhang increased to 6’6½”, the same as for the long variant.



Apparently these changes were made to meet British Bus Grant regulations, the chassis then being viewed as suitable for 10 metre (roundly 33 ft) bodies. It seems likely that the short export 6MU would have been similarly altered at the same time, although less likely that export operators would have seen it as a suitable replacement for the 17’6” wheelbase variant.

Circa 1972 the Reliance 505 was withdrawn from the product line, and the Reliance 760 replaced the Reliance 691. The Reliance 760 used the AH760 engine, a larger bore version of the AH691. The vertical AV760 had been introduced in 1964 September, along with the AV691. Apparently it had performed better than the AV691, and effectively displaced the latter in heavy truck applications. Thus the adoption of the AH760 for the Reliance was a logical consequence. The 6U model number was retained for the Reliance 760.

An undated specification sheet shows that the Reliance 760, in both 18’7” wheelbase, 13 toms gvw and 20’0” wheelbases, 14 ton gvw variants was offered for both the domestic and export markets. It had the options of 6-speed synchromesh or 4 or 5-speed Monocontrol transmissions. It would appear then that the 20’0” wheelbase variant, which had originated as a domestic market model, was also offered for export following the change to the AH760 engine.





Cheers,