A five-speed gearbox has been a long time on the list of wanted items. It should be equipped with the larger, constant velocity type inner joints, for rigidity. It is also possible to install a limited-slip differential, a racepart meant to be used on Lada Samara (FWD) gearboxes. They are robust and cheap, and that makes the particular item desirable. This LSD will not fit into the Fiat gearboxes with tripoid-type inner joint, though.

The gearbox was washed thoroughly, and dismantled (see here). Despite of its appearance, the gearbox was in good condition. Only the differential side bearings needed replacing.

The Samara LSD is not suitable for the Fiat gearbox as-is. The most difficult thing is that the mounting face of the crownwheel is differently located, seen from the side of the LSD unit. If the differential is placed in the middle of side roller bearings, the mounting flange should be located inside the crownwheel. A recess for the mounting face will need to be machined, but removal of so much material would leave the crownwheel too weak. Also, there would be no room for fasteners of the LSD unit. In addition, the material of the crownwheel is very hard to machine.

Fortunately, the original differential was wider than the new LSD unit, so this allowed the position to be altered laterally, in some extent. Some additional space was achieved by removing 4mm of material from the end of the differential. After that, a smaller recess was needed (crownwheel), the depth was roughly the same as the thickness of the diff flange. The diameter of the recess was left relatively small, so the crownwheel had to be heated before fitting it into the LSD unit.

Of course, the bolt patterns of the standard differential and the new one were not the same. Because of that, an additional clamp was fabricated to ensure that the diff unit keeps in place. This is fastened into the crownwheel with the original bolts. This, together with the interference fit mentioned before, ensures that the diff flance will not rotate inside the crownwheel.

Some recesses had to be ground into the diff flange, too, to clear the fastening bolts. This will also keep the diff flange in place (see the picture 6).

Removal of material from the diff end is seen in the pictures below. As told before, this was necessary in order to prevent the removal of too much material from the crownwheel. The diff unit with the crownwheel was laterally in right position when 4 mm was removed from the diff end.

Fiat diff has bigger roller bearings than the Samara one (inside diameter). Thus, a sleeve was needed to fit them into the diff. The right end of the diff did not need anything else, because the diff (and the crownwheel) was located laterally in place by removing material from this end.

The original diff is about 12mm wider than the Samara unit, when measuring the distance between the roller bearing mating faces. When taking the removed 4 mm into account, this results 16 mm. Because the right side roller bearing is now located correctly, this must be compensated by adding 16 mm of material between the left side roller bearing and the LSD unit.

Also a sleeve, similar as the one on the right side, was needed because of the different bearing size. One part wes fabricated to perform both of those things.

After fitting new bearings, the diff unit was ready to be installed into the gearbox. Of course, there will be some struggle with the driveshats because the differential is now located in different position. The bigger problem is the left side (driver side) shaft that needs to be longer, because the diff was moved to right. On the left side, there is only a short piece of shaft with a flange for inner driveshaft joint. The shaft is press-fit into the diff and it has a retaining ring that holds the shaft in place. The shaft needs to be about 8 mm longer now.

The problem will be solved by fabricating a short extension to the shaft that contains only a new groove for the retaining ring. The ring is only holding the shaft in place sideways, so the extension part will not be stessed much.

It is worth mentioning that fastening the diff flande to the other side of the crownwheel is not successful, because the fastening bolts and the flange will interfere with the 1st speed gears (see the pic 16).

Despite of the driveshaft problem, the gearbox could be assembled.

When the gearbox was ready, it could be fitted into the car. The driveshaft modifications were also started to carry out.

A short extension of the left driveshaft was fabricated from M8 bolt, two washers and nut. The similar grooves were machined into the larger washer, like the driveshaft has. This washer holds the circlip in place. The lenght of the bolt is selected so that the right driveshaft end prevents the left driveshaft from sliding too deep inside the differential.