I used to race with an overdrive and I'm planning to go back to it. The
big difference between A and J types is that the A type uses an
accumulator which is held at high pressure by the pump. The J type
pumps only during engagement. I believe the A type is better because it
engages faster due to the use of the accumulator. The J type will take
some time to pump up. The pump in the A type will consume a few tenths
horsepower, but you also get oil forced to most of the bushings in the
transmission and overdrive. The best A-types are the ones with the
large accumulator used in non-IRS cars. A lot of TR4 overdrives have
ended up in big Healeys, since only the works Healeys had the large
accumulator. Most people modify it for higher accumulator pressure for
even faster engagement. You get a nice little kick in the butt when
shifting into overdrive.
|