Lockup Torque Convertors
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 79.
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.
Click the above thumbnail to see the cover to be removed for access to this spring.