Hard slam when accelerating?

lmao. Actually there IS a piston return spring. Several to be exact. They are normally called "accumulator springs" and are used to supply cushioning pressure to the accumulators.

 

People seriously need to look at their slips. Mine was bone dry and most of my drive-line clunks went away. F150's have had this issue for years. It's a quick simple thing to try and if not, well you know it's not that.

http://www.ford-trucks.com/article/idx/9/395/article/2004_F250_Slip_Yoke_Service.html

 

ok if your truck hits really hard when you put it in reverse or drive and if it does the hit when you accelerate, check your U-joints. i had the same problem with my truck, and i thought it was the tranny, but found out later it was just the u-joint closes to the rear axle, changed it and it fixed the problem