Shift kits were originally designed for the drag race crowd,
where shorter shifts produce lower ETs. They generally work by
decreasing the duration of upshifts. GM automatics are normally
very smooth shifting. Installing a shift kit will make the
shifts firmer and more noticeable to the driver. As with all
automatics, this is load sensitive. Increasing the load will
increase the time required for the next gear clutch to engage
completely. If you are using the truck to tow a heavy load (what
the TH400 is made for) the shorter shift will produce less heat
in the tranny due to less clutch slippage. At the same time, the
shift will become more abrupt, creating quite a jolt in the
drivetrain when not loaded heavily. In a heavy 4x4, this is THE
way to find out if your U-joints are in good shape (as long as
you're not too far from town). IMHO, the valving in GM autos is
just fine in stock configuration. It is a good compromise
between comfort, driveline durability, and tranny longevity. If
your towed load is producing too much heat in the tranny, buy an
additional fluid cooler : ) My $.02
Mike Snow
1953 3100
Group,
> what will installing a shift kit do for a TH400
> tranny? I'm going to get one
> rebuilt and rebuilder said he could throw in a shift
> kit, but I'm ignorant.
> comments?
> Bob Adler
> oletrucks is devoted to Chevy and GM trucks built
> between 1941 and 1959
>
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