MAVIC 800 (4th style) derailleur

You may not know much about Geography, you may not know Trigonometry, you may not know much about Algebra and you may not know what a slide rule is for - but you will know that you love the MAVIC 800 as one of the finest and most distinctive aesthetic designs in the derailleur cosmos. In a universe dominated by the almost romantic, slightly curvy, possibly over-decorated, style of the classic Campagnolo Nuovo Record, the MAVIC 800 was a rigorously geometrical piece of ruthlessly pure machinery. Mark one up for Trigonometry and Algebra. Forget all that going-to-the-moon nonsense, this design tells you exactly what a slide rule is for.

Of course, most of the 1979 MAVIC 800's alluring futurism was a matter of styling. Underneath the 1977 Centre Pompidou's radical, uncomfortable, industrial exo-skeleton lies nothing more revolutionary than a gift shop and café with the obligatory art gallery attached. What could be more reassuringly comfortable than that? And, similarly, underneath the MAVIC 800's challenging, space-age looks, lies much of the functional geometry of the, afore-mentioned, soothingly familiar, arguably already out-of-date, Campagnolo Nuovo Record.

But importantly, as with the Centre Pompidou, the details are exquisite:

It is completely demountable, with the parallelogram pins held in place by elegant circlips.
The very wide rear parallelogram plate provides exceptional rigidity. Even a MAVIC 800 with pulley wheels worn down to the nubs will have no play in its parallelogram.
The adjustment screws take a 2.5mm allen key.
The main allen bolts (and on the 851 also the outer parallelogram plate) are hard anodised aluminium.
The pulley wheels have ball bearings, initially adjustable cup and cone systems, later sealed units.
And then there is the weight - the lightest examples weigh in at 167g, a serious chunk lighter than any Campagnolo Super Record of the time.

The Mavic 800 exists in a number of different variants:

It started life with large aluminium dust seal plates on the bearings of its pulley wheels. It also had a b-pivot adjuster mounted on a 3mm thick plate.
The second generation had different pulley wheels with small cup and cones for its bearings, without the large aluminium plates. It still had a b-pivot adjuster mounted on a 3mm thick plate.
The third generation had the same pulley wheels with small cup and cones for its bearings. It seems to have been available with 2 different fittings at the b-pivot - both now based around 2mm thick plates. You could either have the signature adjustment screw mounted on an egg shaped plate (but only 2mm thick), or you could have a folded 2mm plate that engaged with a Campagnolo dropout - as used on the later MAVIC 801s and MAVIC 851s.

All of these versions were manufactured with a mysterious slot through one pivot in the outer parallelogram plate. This slot is usually at the b-knuckle end (near the 'M' of the MAVIC logo). However sometimes it is at the p-knuckle end (near the 'C' of the MAVIC logo). Who can say what this is all about?

The fourth generation of MAVIC 800 had no mysterious slot in the outer parallelogram plate at the pivot at either knuckle (something that is also true of all the later MAVIC 801s and MAVIC 851s). These models have the 2mm thick plate at the b-knuckle. I believe that this generation was available with the option of either the adjustment screw type plate or the Campoagnolo dropout type plate.

Thats a lot of variants for a derailleur that was only manufactured for 4 or 5 years. But these are 'artisan' products, and any batch may be 'improved' in any way and at any time.

I think that this is an example of the third generation of MAVIC 800 dating from about 1981, because it has a 2mm thick plate at the b-pivot folded to fit a Campagnolo dropout. Some of its key features may be:

The logo is engraved on the outer parallelogram plate and is recessed in an oval cut out.
There is a mysterious slot in the outer parallelogram plate at the pivot by the b-knuckle.
There is a 2mm thick stainless steel plate at the b-pivot that engages with a Campagnolo end.
The pulley cage is silver and is not adjustable.
The pulley wheels have adjustable ball bearing races with small black cups and cones.
The pulley cage rotation stop engages with the head of a bolt screwed into the p-knuckle.

For British cyclists of a certain age the MAVIC 800 with the 2mm thick plate for a Campagnolo dropout is a cult object. British time-triallist-weight-weenies loved MAVIC derailleurs for their light weight (and for not being Campagnolo). They particularly worshipped the configuration of this example - as it weighed in a whole 6 grams lighter than any of the others (whether MAVIC 800s, 801s or 851s). A whole 6 grams! May the Lord bless them and keep them and shine his light upon them.