Five Speed Gearbox Conversion
The decision to change the original gearbox for a 5-speed alternative is an individual one, regarded as one of the best up-grades by some and shunned as unnecessary and damaging to the originality by others. Fortunately those in favour seem to outweigh those against now, which includes the official clubs. For me it was all about practicality and suiting the kind of use I had in mind for the car, in particular touring on the continent. The benefits of the fifth gear are enormous – greatly reduced engine revs, decreased fuel consumption, reduced wear on the engine components and relaxed, quieter cruising.
The cost of the conversion using a Ford Sierra Type 9 gearbox with the Hi-gear conversion kit is high, but I think a worthwhile investment, if the car is to be used. The conversion kit is of superb quality and fitting requires the minimum of surgery to the structure, even to the point that the gear lever is in exactly the same position as the original, meaning that visually, nothing has changed.
The reconditioned Ford Sierra Type 9 gearbox mated to the new Hi-gear bell housing. The gerabox was purchased from First Motion Transmissions, fully re-conditioned in 2010 for around £350. Prices have now risen to nearer £750 (2016), as the conversion becomes more popular and the gearboxes become scarcer.
Fitting the new Hi-gear bell housing to the 5 -speed gearbox. The original clutch fork had worn badly at the fulcrum bolt point and a replacement was sourced. New thrust bearing.
First job for the 5-speed gearbox conversion is the removal of the first motion shaft spigot bush and replacement with the one supplied in the Hi-gear kit, to take the Type 9 spigot.
Trial fitting of gearbox with new quick shift gear selector fitted. Best to check at this stage that all the gears can be selected.
Revised mounting as supplied in Hi-Gear kit.
Speedo cable location position is different for the Type 9 gearbox, which requires surgery to the tunnel. Error in positioning the hole, put stress on the cable flange, popping the locating circlip with the result of a broken drive pinion.
Access to pinion is via a metal plug on the opposite side of the extension.
Destroying the core plug is the only way in – new core plug and drive pinion from First Motion Transmissions who supplied the reconditioned gearbox in 2009. total damage £35.
Once installed with the transmission tunnel back in place, nothing is different than with the original four-speed box, other than the routing of the speedometer cable, which exits the tunnel at floorboard height, curving through to the bulkhead. The new cable will be hidden by carpet.
Once the rear axle was removed from the chassis as a complete unit, overhauling it was relatively straightforward.
The stripped down back axle casing after much cleaning and wire brush action (I forgot to send it for blasting with all the other parts). The diff was removed and cleaned and deemed to be in excellent condition, so I have left it well alone. Removing the large hub nuts needs care as the threads are ‘handed’ according to the side – normal right-hand thread for the right side, leaft-hand thread for the left side. Also, undoing the nuts requires a substantial socket or box spanner capable of dealing with 180lb.ft. of torque and age related siezing. The lazy way in the past, was often to resort to a club hammer and cold-chisel, but this should be avoided at all cost. The risk of damaging the threads is high and extremely difficult to rectify, in addition to being impossible to achieve the required torque on the nuts, when re-assembling.
This was the cleaning up position for the axle, but also the same for hundreds of parts and countless hours. Dozens of different wire brushes were consumed, but the most effectice and least damaging were the brass type, although harder to source.
Unfortunately time had taken it’s toll on the banjo casing and daylight could be seen. I decided to build it up with weld and grind it back, which worked well.
Final repairs on banjo did the job.
Rear brake back plates were in poor condition, but as these are now scarce, they were renovated.
Parts finished and prepped for paint.
New bearings and seals were fitted.
Finished rear axle, other than painting the diff casing.
MGA 1500 Rear axle
The backplates were stripped and carefully cleaned up, particularly areas that have contact with the brake shoes. New wheel cylinders, cam adjusters and springs were fitted, with copper slip grease lightly applied to all contact faces. Location of the return springs in the correct holes is important.
The original drums were cleaned up and the inner surfaces lightly cleaned back with emery cloth. New drums were fitted to the front axle as these take the main braking force.
Bill Jeffries – firstname.lastname@example.org