Mating the rebuilt gearbox to the overdrive
One person, one engine crane, and several turnbuckles

Page list

The Jaguar service manual reads: Place the overdrive unit upside down in a vice. Sounds simple?

Except that the overdrive is not upside down; instead it has to be output shaft downwards, and there are no flat parallel sections on the round, conical overdrive casting to properly grip in a vice. Then later the manual reads: ... turn the gearbox on end and enter the mainshaft into the overdrive unit. The manual makes it sound easy, doesn't it? Except that it is not easy. The gearbox is heavy. And no weight can be placed on the internals of the overdrive until the spline of the gearbox output and the two splined sections in the overdrive are 100% lined up. Without a lifting aid, it's a three person job to do it - two to take the weight of the gearbox, and a third to manipulate the gearbox input shaft to line up the gearbox output spline with the overdrive splines.

But since anyone reading this far probably has access to an engine crane, there is an easy solution.

The rigging requires some preparation. The end result is that one person alone can mate the gearbox to the overdrive.

The topmost turnbuckle is the key item in the process, as it is used to gradually lower the gearbox into the overdrive when mating the splines. The engine crane's hydraulic release valve is far too coarse for the final lowering steps.

Materials required
(See photos)

- Three-sided timber box, preferably on four castors, and with a suitable hole for conical section of the overdrive casing in the top side.
- Three 8mm (5/16") turnbuckles
- Light steel chain 6mm or 1/4"
- 10-12 small shackles 8mm or 10mm, 5/16" or 3/8"
- spreader bar
- various bolts, nuts and washers
- two 7/16" BSF bolts or two 6mm or 1/4" eyebolts for second lowest pair of bell housing tapped holes
- two 7/16" BSF bolts for uppermost pair of bell housing tapped holes
- metal strips 25mm (1") wide

The concept is that the gearbox will be suspended by three (not four) links, two with a turnbuckle, so that the gearbox shaft axis can be perfectly lined up with the axis of the overdrive.


1. Place the overdrive unit conical casing in the hole in the timber box. Use eight +/- timber chocks to ensure that the overdrive unit axis is vertical. (I glued the chocks in place, and let the glue dry overnight.) Place the twelve springs in their correct position on the twelve spigots.

2. Remove the top gear selector unit from the gearbox to refit the gearbox to the overdrive. Put the gearbox into first gear before removing the selector unit, and do not try to change the selected gear with the top off, as you may move the operating sleeve too far and the detent balls will fly out. Be warned!

The reason for using first gear is that first gear provides the finest rotational adjustment when lining up the gearbox output spline with the overdrive splines.

3. Place the oil pump operating cam on the gearbox shaft with the cam to the overdrive end, and the plain section to the gearbox side. Secure the cam in place forward-most with a thin cable tie or other material than can be cut and removed later after the gearbox is resting on the overdrive springs.

4. Attach the rigging to the forward face of the gearbox, as in the photo. Ensure that the turnbuckle to be closest to the engine crane hook is fully closed.




5. Lower the engine crane boom to connect the rigging to the hook. Lift the crane boom, protecting the output shaft from damage as the gearbox is upended.

6. Adjust the two lower turnbuckles in the rigging to set the gearbox axis vertical.

7: On the upended overdrive, line up the two splines inside the overdrive, using a screwdriver to line up the top half spline with the bottom half.

8. Apply non-hardening sealant all aound on the overdrive side of gasket, and place the gasket on the overdrive case.

9. Apply the same sealant to the gearbox side of the gasket, but leave two 2cm wide gaps 180 degrees apart, on what becomes the left and right side of the overdrive when in the car. These gaps are to permit the use of two screwdrivers to allow the overdrive cam follower to be pushed back to allow the cam to be lifted to its final position on the gearbox shaft.

10. Place/roll the overdrive under the gearbox.

Before the next step, you may wish to take some measurements so you can ensure that the gearbox is not lowered too far into the overdrive before you align the gearbox output shaft spline with the overdrive splines.

Turn the gearbox input shaft only when you are certain that there is no contact between the gearbox and the overdrive. Likewise, do not turn the overdrive output after the gearbox spline has entered any part of the overdrive spline.

11. Using the crane hydraulic valve, lower the boom gradually until the gearbox output shaft is inside the overdrive shaft, but still well away from contact between the gearbox spline and the overdrive upper spline.

12. Then lower the gearbox using the single turnbuckle closest to the hook. At some stage, you will detect that the gearbox spline has reached the top of the overdrive upper spline. Now it is time to raise the gearbox slightly, turn the input shaft slightly, lower the gearbox, and repeat this stage until the gearbox output shaft spline has entered the upper overdrive spline. Once this stage has been reached, do not try to turn to overdrive output shaft as this would mis-align the lower half of the overdrive spline.

Now it is time to refer to the instructions in the Jaguar service manual ....

13. Continue to lower the gearbox into the overdrive using the upper shackle. Watch the uppermost turnbuckle - ensure that you do not lengthen it so far that one of the eyes is released! Ensure the upper end of each of the twelve springs is correctly located on its spigot. Cut and extract whatever material was used to hold the oil pump cam in place. Lift the cam to engage with the cam follower. With a small knife, apply sealant to the two 2cm long gaps in the sealant ring on the top side of the gasket.

.... and continue as instructed in the Jaguar service manual.


The gearbox and overdrive mating process when completed.