The SunTour MounTech was the first derailleur ever designed specifically for use on a mountain bike. Truly a milestone product. It was essentially the knuckles and parallelogram of the SunTour aRX with the addition of SunTour’s ‘Tech’ cage design. The result was a three pivot derailleur, with an unsprung pivot at the hanger and SunTour’s signature slant parallelogram. It gave a very small and consistent chain gap and a lightening quick and pin point accurate gear change.

When this derailleur appeared it was considered to be the epitome of sophistication - a wonder to behold. When Frank Berto first tested it he declared it the best changing gear he had ever tested.

But this second generation ‘Tech’ design had a fatal flaw. SunTour had decided to improve on the Design of the Le Tech by cunningly fitting the spring that tensions the third pivot inside the guide pulley. This meant that the guide pulley ran on a large diameter centre - and this rapidly attracted dirt. When the dirt got in, the pulley bearing became as rough as a badger’s arse and often jammed. To compound the problem the pulley was exceedingly difficult to remove for cleaning or for replacing. SunTour were inundated with expensive warranty claims, and, worse, lost the reputation for bomb-proof reliability that they had carefully and patiently built up over the decades.

In fact the MounTech had a couple of other flaws. The first was that it was seriously heavy and the second was that, like all three pivot designs, it rapidly went out of alignment and had a tendency to throw itself recklessly into the spokes of the back wheel. Like the Huret Duopar, it was God’s gift to wheel builders everywhere.

This is an example of the GTL version with an extra long pulley cage.

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• Derailleur brands: SunTour
• Categories: SunTour - the mountain bike gears, SunTour - Frank Berto and the curse of Duopar
• Country: Japan
• Date of introduction: 1982
• Date of this example: 1984 (two letter date code is AB)
• Model no.: 5500
• Weight: 298g
• Maximum cog: 34 teeth (Source: Sutherlands fourth edition)
• Total capacity: 38 teeth (Source: Sutherlands fourth edition)
• Pulley centre to centre: 85mm
• Index compatibility: friction
• Chain width: 3/32”
• Logic: top normal
• B pivot: unsprung
• P pivot: two, both sprung
• Materials: largely aluminium with steel pulley cage plates, link element plate and inner parallelogram plate