So back last April I started having intermittent hard shifts. I ran the code myself and 634 came up (MLPS voltage higher or lower than expected). The shop I took it to ignored that and ended up replacing the solenoid pack, which solved the problem until this past June. It shifted hard up until November, then it was fine until now when the temperature outside is warming up, it is always fine in cold weather. I ran the the codes today and the same 634 came up. Can this be the cause for hard shifting? why would the temperature outside matter? This is a 1992 F150 302 with 185K miles 4x2 supercab. It runs great otherwise, so I would love to get this figured out. Thanks!

 

Yes it could most certainly cause hard shifting. Sound like the shop just wanted to cost you money if they ignored the MLPS code. The MLPS is relatively cheap, and pretty easy to change. You don't even need to open the transmission up.