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Using a Citroen GS gearbox instead of the standard 2CV gearbox

The idea is to fit a GS/LNA/ Axel G type gearbox onto a Moto guzzi or BMW engine and fit into a pembleton/2CV based car.It is much easier with a 2CV box as it already fits -you have just to get the engine to fit.

I always felt that pushing 80 to 100 bhp through a 2cv gearbox intended for 35bhp was rather cruel.Also the ratios of a 2cv box are based on a 3 speed plus overdrive 4th.There is far too big a gap between second and third gear, drop into second and the car tends to nose dive at too high a speed with high wining noises. The final drive miles per 1.000 rpm in a 2cv box is 17kph also not good for a bigger engine as reasonable speed means very high engine revs-even with a 2CV motor, I have fitted long time ago a dyane diff to lengthen the ratios and in a 320kg hopper that makes a big difference to rpm at high speeds and to performance [although it was put in when I built it in 2003 so I don't know how a standard box behaves..I would imagine you reach peak revs pretty quickly.

Now with a G type 4 speed box the gears are far better spaced, a much stronger box altogether and several ratios are possible -

If I wanted to use 135x 15 tyres then axel high diff box works fine but if as I plan, I want to fit 4.00x 19" wheels then an LNA ratio is preferable [although theoretically 19" wheels and an Axel box as its very high geared could run at a crazy 200kph without bursting the engine...but practically un-driveable.

Now to fit one, the problem is the G type box is longer than a 2CV box. The constraints are the length between steering and king pin/drive shafts is fixed because of the suspension arms.Drive shaft connectors are also slightly or very different -depends on model.The LNA one does fit.

Plus point is that all G boxes have the same 4 bolt fixing to the engine. So, I cut 26mm off the rear casing holding the speedo drive-ah yes I cut that off also,merely using the scroll nut to retain the lower bearing-but machined thinner and nut shaped. I will use a bicycle speedo-as has Silverfish - sensing from the inner driveshaft. I also cut 17mm from the front of the Visa / LNA bell housing [the visa bell housing is shorter than a GS ] as in my case I could get the guzzi engine slightly tighter to the gearbox, still lining up with the starter and ring that it sits visually better in the bodywork and with 19" wheel look better.

It now fits but still a way to go for it to be running.

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7mm_cut from_bell puts_ring gear closer back plate minus 26mm cut off old speedo scroll nut
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original-end casing 45mm deep shorter end of box

David Stephenson

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