Of course, as many of you
already know who have approached or broken the 400 HP barrier, you can't
just build a big motor and stop there. A high horsepower motor
requires attention to the entire drivetrain to make sure that other
components won't turn into grenades when the skinny pedal hits the
floor.
We had already build much of the drivetrain heavy duty enough to
handle the stress that our new motor would subject it to, but there were
a few components that we knew would have to be replaced. Of those
components, the transmission was the biggest concern. Our old
TH350 was getting very tired. It had last been rebuilt nearly 10
years ago, and had many hard road miles on it even before we elected it
for off-road duties. We had also noticed that it's performance had
been declining over the last two years. Combining this with the
fact that TH350's just weren't built to handle lots of torque meant that
there was only one place to go... a TH400.
Since a TH400 was a stock tranny in late 70's Chevys, the theory is
that the swap should be relatively easy, and other than the fact that
the transfer case needs to be reworked, it is. The problem with
the transfer case lies in the difference in output shafts
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between a TH350 and a TH400. The
TH400 has a 31 spline output shaft compared to the 27 spline shaft on
the TH350. This means that the input shaft of the transfer case
needed to be swapped up to the 31 spline shaft, which required having
the housing of the t-case machined for the larger bearing used on the
new input shaft. Fortunately, I was able to find a transmission
& t-case shop nearby that did the machining, supplied the new input
shaft and bearings for less than the cost of a junk yard transfer case
with a stock 31 spline input shaft. Not to mention that 31 spline
t-cases can be difficult to find.
Here you can (kind of) see the new tranny, and a new urethane mount
too.
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