I have a 2003 F250 7.3L 4x4, the transmission has been upgraded with the sonnax valve and tricummulator springs. I loved the hard shifts but now the tranny is starting to shift very soft and feels like a slip of sorts. When the tranny is cool it has soft shifts, if the temperature reaches 125 or anything higher the tranny will really slip bad.

I have wired a lock up switch for the torque converter and on occasions I will have to hit that switch in order to get it to shift into the next gear. This usually happens around 35 mph and the engine is revving in the 2200 - 2500 rpm range. (clearly slipping i think)

I am wanting to change the torque converter with a better one but will this cure part of my problem?

My guess is that I have a line pressure problem where the transmission is not getting enough pressure in order shift gears. I have recently serviced the transmission and the fluid was not burnt at all.

Any ideas?

 

I think your clutches are toast. Have it checked out before you put money into a converter, because Factory Tech builds a slick trans with a good converter. When mine goes, I'll get one of his.

 

Thanks, I'll have a shop take it for a drive to see what they think. Appreciate the help.

 

No problem. I am not very handy with transmissions, but slipping cold and slipping worse when hot is not good. And I bet it's hard to fully diagnois it online.