I'm currently working on my 6th 500/518 based transmission I've built... Seems like I run into something new every time.

Anyways, the main accumulator piston only had the large spring installed, and was missing the inner spring. Every other one I've built had the inner spring, however after some research, it appears that this spring wasn't always installed from the factory. Some say it wasn't installed in trucks equipped with the tow package?

 

It's true, it wasn't installed in some trucks. I have no clue as to their reasoning there though....... not sure what the advantage of not having it would be...... Wish MonteC were still around.

 

That's what I heard also. All I can say is when I took my valve body apart it didn't have the smaller inner spring and came with the tow package. The only reasoning I can come up with is it changes the hydraulic pressure required to move the accumulator.