Felt The Tranny Slip

[Chambers]

Hi all, I was driving around and pushed the pedal to the floor and felt the tranny slip for a second then grab, It's a auto 4WD tranny and I was in 2WD at the time, there is plenty of fluid and the tranny has never slipped this bad before. So my question would be; what could be doing this? Also, most of the time when it shifts hard into second. Thanks.

 

[89REDRANGER]

What year and engine are the truck? Also, what trans if you have any idea?

 

[Chambers]

Ohh, sorry, its a 84 2.8l, I'm pretty sure its a C5.