It all started when Renault developed their front wheel drive vehicles
such as the Renault 16.
Most of the makers of front wheel drive cars went the route of
using transverse engines with the gearbox either under or in line
with the engine between the front wheels or thereabouts. This has
the consequence that the gearboxes from the vast majority of modern
cars are useless if you are looking for a low cost source of something
that you can use as a transaxle for a mid engined car. If you can't
find a suitable donor from the mass produced car makers, then you are
left with the Porsche family of gearboxes, and the dedicated race transaxles
such as Hewland, Xtrac etc, and the latter are usually straight cut dog
boxes, not ideal for the road as well as being pricey, new or secondhand!
Of the mass makers who went the route of front wheel drive cars
with fore and aft engine's, the obvious ones are Renault and
Audi.
To get the Audi issue out of the way, I have not worked on them,
but people who do have told me that they are by no means
bullet proof, and the ratios are not ideal, if you know any better,
let me know!
Which leaves us with the Renault family which to my knowledge started
as far as we are concerned with the 4 speed 367. Like a lot of early
5 speed gearboxes, the 369 was the 367 with 5th tacked on the back
in a bulged rear cover instead of the nearly flat end cover of the
367.
My first Renault gearbox was a 369 which I took out of a 30 TX in a Parisian
scrapyard, it cost me 30 francs believe it or not!
369's were used in the 30 TS and TX, the Alpine V6, Renault 20 and
the Renault 5 turbo.
Then the UN1 appeared, and it was used in the 21 turbo and the
25.
The differences between the UN1 and 369 were small and for most
purposes either will do if you can find them! The screws holding the
end cover on , in the 369 were a fine pitch (1 mm I think ) 8 mm
thread (so they strip easily! but are easily repaired with
helicoils) whereas the Un1 they were conventional
M8 (1.25 mm pitch).
The other more important difference is that the tooth profile
used on reverse was different. However I have found that apart from
these two differences, parts can be used interchangeably with care (
as long as clearances etc are OK), and in fact the gearbox in the
Lola (www.bell-performance.co.uk/lolat70.htm)
is a hybrid of the original 369 and a UN1 from a 21 turbo.
One other thing to be aware of is that the Alpine GTA version was
set up for the opposite direction of rotation of the diff. This
however is not fatal as with care the diff can be swapped around, as
long as you are able to adjust backlash and bearing pre load
properly. There is also the issue of the main side thrust of the
crownwheel being taken by the pre load adjustment nut instead
of the solid side of the casing, but this appears to be rather
massive. All the Renault bell housings I have seen for the gearbox
have two recesses cast into the rear face allowing the diff to be installed
either way round.
The UN1 was also used in significant volume in a number of mid
engined sports cars, for the same reason that they are widely used
in for example GT40 replicas, they are reasonably light, tough and
were once easy to get! They were used in the French Venturi sports
car, the Lotus Esprit (later versions) and the De Lorean, as well as
all sorts of small production and kit cars/replicas.
The UN1 has not been used in a Renault
mass produced vehicle for many years now, but a descendant the UN5
has had a longer life.
As far as I can see from the
UN5's I have dismantled, the UN5 is the UN1 adapted for use in
vans etc by modifying them so they can use large crownwheels
to give high final drive ratios (i.e. more geared down).
So the main difference is that the
axis of rotation of the diff is moved further away form the actual
gears, to leave space for the larger crown wheels. this also means
that the bell housing is different because it has a larger bulge in
it for the large crownwheel. This also means that the clutch extension
shaft is longer, and more slender as it has to reach further, and
pass closer to the face of the crownwheel ( as the pinion is smaller
in diameter), which also means that there is no longer space for the
steel tube used in the UN1, so the clutch shaft has it own oil
seal in the bell housing. As far as I could tell, the first motion
shaft ( the upper shaft in the actual gearbox) is to a similar design
to the UN1 although the ratios are usually quite different (and useless
for our purposes).
So although it is a close
relative, the UN5 is not much use to us as the ratios are wrong and
UN1 parts cannot be used in it except in certain limited areas. they
also have a speedo drive on the rear cover ( which is usually broken
by the scrapyard) and the crownwheel can be on either side depending
on application.
The last application of
the Un1 proper was the last version of the Lotus Esprit, production
of which seem to have been terminated by Renaults intention to stop
making the UN1 at all!
Finis for the UN1, but fortunately
many thousands were made and they can still be found although with increasing
difficulty.
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