Please read the instructions fully to make sure

you have everything on hand before starting.

1. Disconnect the battery

2. Locate the gearbox end case (Fig. 1)

3. Drain both the gearbox and differential by

removing both drain plugs (Fig. 2 and 3).

4. Remove all 8 bolts securing the end case. The

bolts are of varying length. On the Scorpion, the

longer bolts will have to come out while still in

the end case because of interference with the

chassis. Mark the bolts order to relocate in the

same positions for installation (Fig 4 and 5).

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Fitting Instructions

Fifth Gear Upgrade

5. Once the end case is removed, you will clearly

see the two 5th gears (Fig. 6) and the shift fork.

The gears are held by two special ring nuts with

4 indentations. The nuts are also crimped to the

shafts at 2 points around their circumference.

In order to remove and install the nuts, you

need a special four-legged tool that can be

fabricated by grinding a 1 1/16 inch socket (fig.

7). It is recommended that your order a pair of

special nuts before attempting to fabricate the

tool. This will help to ensure that you grind the

socket properly and that it fits the nut well

before you attempt to dismantle the gears

6. Before attempting to remove the nuts, you

must straighten both crimped sections on each

nut with a center punch. DO NOT ATTEMPT TO

REMOVE THE NUTS BEFORE PROPERLY

STRAIGHTENING THE CRIMPED SECTIONS.

OTHERWISE YOU RISK RUINING THE SHAFT

THREADS.

7. If you have difficulty loosening the special

nuts with the fabricated socket, you can do this

by carefully using a straight punch and hammer

by positioning the punch radially, as seen on Fig.

8. A couple of sharp hammer blows on the

punch should loosen the nut which can then be

removed with the special tool.

8. Remove the bolt securing the shift fork to its

shaft (Fig. 9). Make sure the synchro ring on the

primary shaft (on the right side of Fig. 9) is in

the disengaged position, that is pulled back from

the gear box. This is necessary so that the

springs, balls and pins do not jump out of the

synchro. Hold the gear and synchro assembly

firmly together and carefully slide the assembly

off the shaft. Should the balls and springs jump

out of the synchro, you will have to use patience

to put them back in before reassembly.

9. Remove the ring nut from the end of the

mainshaft and remove the gear (left side of Fig.

9).

10. Note on Fig. 10 that 3 of the hex bolts (8M

1.25) securing the retaining plate behind the

gears have been replaced with 3 Allen-head

bolts in order to allow the larger gear to clear

the bolts. Allen-head metric bolts (Fig. 12) are

available at Ace Hardware. Make sure you install

the new Allen-head bolts at this stage.

11. In order to clear larger gear, it is also

necessary to grind the shift fork as seen on Fig.

10. DO NOT overdo it. To make sure the fork

clears the gear teeth, install the fork all the way

in on its shaft and turn the gear by hand to

check that it is not touching the fork.

12. Remove the fork.

13. Start reassembly by fitting the new larger

5th gear larger to the primary shaft (upper one

on Fig. 10).

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

14. Place the new smaller 5th gear on the

synchro mechanism and hold as an assembly.

Slip the fork over its synchro groove. This is not

easy to do, so be patient.

15. Fit the assembly on the mainshaft and mesh

the gear to the larger primary gear while

slipping the fork on its shaft.

16. Refit the fork bolt and tighten.

17. Refit the ring nuts and torque to 100 lb-ft

with the special tool.

17. Before crimping the nuts, turn the gears

over to make sure they turn smoothly and

engage 5th gear with shift lever in the car. All

gears should engage normally.

18. Crimp the two ring nuts.

19. Install the end cover.

20. Fill the gearbox and differential with oil. I

use RedLine MT 90.

Figure 11

Figure 12