From my Experience with the first of my stratos replicas, I knew the Alfa gearbox was capable of 400+ BHP & around 400lb/ft of torque, but at that level of power it was just about at its limit.
The Alfa gearbox is from the same family of gearboxes as the Lancia Delta Integrale & it is common for Integrale owners to modify the gearbox with a strengthening plate in between the two halves of the gearbox.
Due to the extra power of this engine it was decided to fit one of these plates to the new Alfa 164 gearbox that I had sourced.
Installing the plate involves having the thickness of the plate machined off of the centre casing, about 3mm. The casing was machined down apart from the areas indicated below, which are baffles and they don’t interfere with the fitting of the plate.
The plate was supplied with some rod to use for extra dowels, I fitted as many dowels as possible to the plate, those that didn’t have a bolt passing through or that only located in one of the casing halves I made from solid bar, as seen below.
The two holes at the bottom right of the photo didn’t line up with anything, so I drilled and tapped two holes in the casing to suit.
The new box I had was fitted with a taller Final Drive ratio (3.11:1) that I wanted, so I swapped it with one of the final drive ratios from a used gearbox. As the pinion is part of the output shaft, this involved changing all the gears over from one shaft to the other so that I could keep the new gears…
After changing the shaft & Crown wheel the new ratio was 3.41:1
While the box was apart I also installed a plate type LSD to help with the traction. This was supplied by AHM Motorsport & set of for fast road/track use.
Then it was a relatively easy job of assembling the box as per the manual, the diff been assembled first so that sealant could be applied where the plate now fitted instead of the O-ring sealed cover.
Not forgetting the spacer ring to keep the bearing preload correct. The preload was too much when checked, I assume due to the aftermarket diff having a slightly different length. The shim needed to correct this was not available, so material was removed from the end cover instead. Having done a few more gearbox rebuilds since I have discovered that they all seem to have the same shim from the factory, but the covers are all slightly different, so I can only assume that Alfa also machine the cover to set up the initial preload!
I also removed material from the outer side of diff bearing cover, the one that fits on the top in the above photo; this is needed as the driveshaft is 3mm further into the cover due to the plate. Material was removed as shown, from the seal and the cover.
When this cover is fitted, the O-ring seal is not used.
As mentioned elsewhere in the rebuild thread, a Tilton concentric release bearing was installed on a home made adaptor. This was now installed and connected to a bleed nipple on the top of the gearbox & a dry break coupling en route to the master cylinder.
Due to the fact that the turbo is placed above the Gearbox I was concerned with the extra heat that would put into the gearbox, so I decided to fit a temperature sensor. This is linked to a stack gauge which controls a pump which circulates the oil through a cooler. Below is the suction and filter. The suction is from the usual drain on the diff housing.
The pump is shown here
And it pumps the oil to the cooler on the off side of the car.
This takes the air from the upper of the two NACA ducts on the drivers side – the lower duct just blows at the alternator to keep it and the area infront of the engine cooler.
However, after the car had been mapped on the hub dyno, it only lasted 70miles on th eroad before there was a big bang and a loss of drive while in 4th gear. The Car made it home, but when I drained the oil, out came the gear teeth as seen below
And on stripping down the gearbox it became obvious that I had stripped 4th gear.
As the box was new I had expected it to last slightly longer than a few miles, I had thought a few thousand at least! All the mapping was done in 4th, so it’s possible that it was too much too soon on a new box, or that there was a defect in 4th or that the box just isn’t up to the jobL.
On closer inspection of the casings when the box was apart, the bores that the bearings fit into had worn slightly oval allowing the shafts to spread apart. At the input/diff and of the casing it is possible to machine the casing and install a figure of 8 steel strengthening plate. The other casing is not so simple to modify & I don’t believe it has been done before.
I had a couple of used gearboxes, so for now I decided to rebuild the box as is to get the car back on the road again. I didn’t want to remove the engine so the box had to be dismantled and re assembled in place….