autodoctor911 wrote:sorry to post another off topic reply, but the work on the mini gearbox interests me to the point of asking: What kind of physical changes to the valve body where necessary to achieve the extra ratio, and the desired quick gear changes?
Was a completely new control valve assembly fabricated, or where you able to use the existing casting?
I ask, because I want to know what kind of investment would be involved in doing a similar conversion to a popular rear wheel drive automatic gearbox, and which one would be best to use. I was considering something along the lines of a 4l80e GM or a 4r100 Ford, or maybe the NAG Chrysler/Mercedes.
The conversions I undertook on the Automotive Products APA transmission were over 30 years ago.
A new manual selector valve was machined to re-direct oil but the main conversion was to the main auto shift valve which in standard mode operates using a centrifugal governor balanced against a throttle position rod and detent spring.
This was remade using a seperate valve block with the extra ports for the new gear oil apply position and a new valve made with extra lands and facility for it to be moved either manualy or electricaly with a radial multi segment positioning motor instead of the mechanical centrifugal governor.
The AP box is/was very different from the modern 'clutch' boxes you mention.
It had brake bands as well as clutches (the original clutch plates and bands were phospher bronze and steel) with seperate servos which were easy to fit different feed piping to, there was also much more room to play with. The geartrain was/is a bevel epicyclic not the conventional spur and was much stronger more compact amd a better planetary concept all together. More costly to make though. The geartrain ran in engine oil with the engine.
There are competition conversions for modern auto gearboxes but modern units now have up to 8 gears anyway and the gains in rpm gaps would be minor. The torque converters are now more intigrated with the powertrain operation with lock up operation and the like. The modified Mini had no fluid link (the torque converter was not used) but used a conventional clutch. This can be achieved on any gearbox and many clutchflite units exist but the work involved in modern units would be great.
I could build another original Mini unit but I would prefer to use the geartrain in a lighter case.
Epicyclic geartrains are IMO much better than layshaft in many ways. It is the control systems that remain mechanical/hydraulic/electrical, which adds complication and reduces reliability. It also makes it hell trying to diagnose problems.