Disclaimer: This page only provides information based on the personal opinion of the author. The author can't be held responsible for damage in any way that could result from modifications mentioned here.
This page will deal with fitting a G series gearbox to your A-type Citroën. The gearbox can be found in Ami Super, GS, GSA, Axel and LNA. The LNA box is different in that it has different driveshaft input shafts and no thread for fitting calipers, but this can be changed. However, I'll not refer to the LNA gearbox on the rest of this page.When you have a much stronger engine fitted to your a-type you will find the gearbox is not suited for the extra power. As a rough guideline, the standard gearbox can cope with up to 40bhp. Another gearbox is need for more power. Easiest is to stick with Citroën and look for another gearbox with inboard disc brakes. The G-series gearbox is the first alternative. Problems with this:
GS 1220 pre 1978 / Ami Super.
All other boxes have too tall ratios for fitting into A-series when using standard 652cc engines. For tuned engines they may well be very suitable though. 5 speeds can be fitted but need a LOT of modifications and ratios are way too long for 652cc power.
By far the easiest is to use the G-series brakes as well. Pipe fittings are identical, much improved hand brake mechanism, bigger discs and straight fit on the gearbox. If needed, Axel vented discs and calipers can be used, converted to LHM brakefluid using G-series rubbers.
DriveshaftsTo fit the a-type driveshafts on the G-gearbox adaptor plates are needed. Here are 2 pictures of these plates made by duckservice.
The original mounting on the G-series and Ami Super gearbox interferes with the steering rods. This whole mount is cut off the gearbox completely, do this in steps to make sure you don't cut a hole into the gearbox housing.
Looking at the back of the gearbox you'll see 2 bolts which seem to be in the same location as the a-series gearbox. Unfortunatly they are not but we're going to use them anyway. Take out these 2 bolts and replace them by longer ones. The easiest way to modify the original rear support is to weld 2 ring onto it with the coreect spacing for the bolts on the gearbox. Make sure the holes in the rings are high enough so the steering rods don't touch the back of the egarbox under any circumstance! If you make sure the box is as far back as possible, the front engine supports will only be 1cm further forward then orignal and with a bit of persuasion the original bolt holes in the chassis can be used. Below are some examples. The mount that has the slide in holes as on the original mount was not a good idea. Under heavy braking the gearbox kept coming out of the mount! The closed rings for the bolts to go through works much better.
Bellhousing and Input shaft
These come from either the visa 652cc gearbox or the LNA 652cc gearbox. Bellhousing and input shaft belong together so don't mix up different types and models. The bellhousing needs 2 slots cut out to clear the brake discs. Only cut away a minimum of metal required. If you cut away too much, the bellhousing will be weakened and will break. Also tidy up the edges of the holes you cut with a file which can be done easily as the metal is very soft. This will prevent cracks in the bellhousing and will keep the modifications invisible to the untrained eye.
Because the gearbox is slightly longer, the pipes on the exhaust cross box will have to be cut off and modified and/or lengthened. There are no mounting holes on the G box for the cross box so either make up a bracket or leave the box unsupported. Make sure the box and pipes stay as far away from brake discs as possible. Make sure the pipes clear the handbrake cables!
After fitting the engine and gearbox, the original gearlever rod on the gearbox won't fit anymore. Put the gearlever in it's neutral position in the car and on the box and make up a rod to connect the two.
The engine moves forward about 10mm, this can cause slight space issues:
Ami 8 Berline
The 1220 GS gearbox was found to have too tall ratios. 4th was nearly unreachable. Better would be a earlier GS 1220 gearbox (or Ami super box which has the same ratios).
The Ami Super box was found to be slightly too tall. The aditional aerodynamic drag of the 2cv compared to the Ami is the main cause of this. A GS 1015cc gearbox would be better but these are hard to find. However, the car is VERY driveable. 1st, 2nd and 3rd have very wide operating ranges, 4th is a real overdrive, only used on motorways.