NOTE: This is NOT the only way to do this. It is merely 1 way.
Ok, so you've decided that you want that extra gear. The Borg Warner T-5 is a pretty common option these days. These boxes can be found in almost everything around the world. BMW's, Mercs, Mustangs & even the local Commodore & Falcons.
While the gearbox is basically the same for all applications, the input shaft length, bell housing,(both determine how far the box sits from the engine) gear sets & rear extension housings (determines where the gear shifter sits & speedo drive output) are different to suit the application.
So which gearbox should i buy?
Here is where it gets tricky. First you will need a bell housing to fit your engine. The most common option is the Commodore gear box. Besides being plentyfull, they also have the 'turbo' bolt up pattern. Using this box saves mixing/matching clutches & if you already have a V8 with the Turbo bolt pattern it will fit with simple tunnel mods. I will get to that bit.
A lot of people are using the local Ford T-5's with aftermarket bellhousings (approx $8-900) which will put the gearshift in the correct position. I believe Dellow & Mal Wood have these 'kits' in stock. Personally i don't understand why anyone would drop $900 on a bell housing instead of $100 on a rear extension but hey ..... it's your money.
So here's what i done on a shoe string budget.
I picked up this nasty old Commodore T-5. It was hanging off the back of a 304, both of which had been under water. I initially only wanted the fly wheel & b/h bolts but for $60 i wasn't complaining.
Quick trip to my gearbox guru for a complete rebuild & this is what returned.
We had to change the input shaft due to wear on the hard facing. Another stock Commodore input shaft was installed. I also sourced a rear extension housing from a XF Ford & had it fitted. It's a straight bolt on. This brought the gearshift about 40mm from the stock position & the speedo drive output is on the drivers side.
The main concern when fitting the T-5 is where the rear of the box ends up. It comes close to hitting on the floor x-member (under the front seat bolts) which is a structural member. Yes you can box this section in with steel plate but it is up to your engineer to pass the mod. By using the XF rear extension there is NO cutting of this x-member, which keeps even the most fussy engineer happy.
Here you can see where the rear extension sits. I had to fold down the lip slightly to get the threaded part through. Stupid short throw shifters!
Gearbox up & in.
I should also mention that before i could fit the box, i Had to bolt the bell housing & clutch assembly in first.
With the box in & bolted up it was time to move on to the the x-member.
A trip to the steel merchants & about $28 later i returned with some 40 x 40 x 4 angle & a meter of 50 x 25 RHS. Little bit of cutting, measuring, cutting, measuring, welding ....... did i say measuring? & a squirt with some black paint & ta da!
Using 40 x 4 angle i put the cross bar as high as i could. The 'drop' in the center worked out to 27mm. Because i am using the XF rear gearbox mount all that was required is a simple mount plate with 1 hole.
Now to fill the hole in the tunnel for the shifter.
Because i knew what seal i was using, i just made up a cover plate from 1.2mm zinc & welded it in. . It took maybe 3hrs from start to finish. I made certain that the console would still fit before welding anything.
Next was the speedo.
The Commodore used an electronic speedo sensor at the gearbox end. I simply unscrewed the electronic bit but kept the mechanical drive parts.
Around $80 later & a brand new speedo cable arrived from Autocables. Screwed on 1 end & pushed on the other, the speedo works. You may need to play with the speedo gear to get your speedo reading accurately.
The only other 'modification' i made was a gearshift shaft which is 1" forward. I don't think this is necessary & i will swap it out for a straight shaft next time the console is out.
So there it is. Interior back in. 5 forward gears to play with & it didn't break the bank.