Our beloved Magnums were equipped with (due to
government mandates for better fuel economy) not
so durable lock-up torque convertors.
One way to delay or totally eliminate them is to
go to your local Mopar dealer and ask for a
spring that is sprung to lock-up at a speed
higher than the 28-33 mph in '78 and 45 or so in
They sell springs that go from the
aforementioned 30 mph to infinity. The spring
goes in a passage on top of the valve body. Most
"shade tree" mechanics and/or local tranny shops
would just place a checkball in the passage to
block off fluid to the convertor.
Seems when this is done that little or no loss
of mileage is noticed. I've got a 79 w/a 318
that has had it disabled, this car delivers
around 19-20 mpg's. And the motor isn't lugging
so much. These cars are geared high, with the
highest gear being 3.23. So motor noise isn't
too much of a concern.
I recommend that the spring be used instead of a
checkball. I had this done to a 78 GT that I
owned. A couple months after the "checkball"
procedure the tranny started slipping between
2nd and high. Keep in mind the car had 120K + on
it. So maybe the end was near anyway.
Pre-78 904's, especially with the 360 engine,
had a 2.74 (?) low gear set, used to offset the
near 2 ton weight and high gears. I believe the
pre-lock ups were a more durable unit, although
I've owned numerous Magnums with the lock-up
tranny and have had minimal problems.
So if your considering a tranny switch go that
route. If you wish to keep your "number's
matching" tranny, go with the spring thing. I
believe that shift kits came with the proper
items to disable the convertor. This is
second-hand info., so check with your kit's
manufacturer to be sure.
the above thumbnail to see the cover to be
removed for access to this spring.