Ive got a 91 F150 4X4 with a 302. When i first bought the truck a few months ago the tranny slipped a little in 1st gear. I added some lucas oil to it and crossed my finger. The next day on the way to work it started slipping horrible and the all of the sudden it didnt slip anymore. When i got to work i went to back into a parking spot and NO REVERSE AT ALL. I did a fiter &fluid change with no results. When i put it in reverse all id does is rev, but wont rev past about 2.5k. Now my nutral seems to be a first gear also. It drives fine in (D) without slipping, with the once every so often hard shift. Im stumped here.. I really cant afford a new tranny at this time. Ive asked around and a one guy told me a bad valvebody. One other guy told me a clogged torqu convertor. Does any have any ideas?

 

If neutral is misbehaving, there is a decent chance that the MLPS has gone bad.
(Manual Lever Position Switch)

This is a potentiometer arrangement on the side of the trans. When you move the lever, it produces a variable resistance, which in turn informs the PCM what gear you want. The MLPS is noted for getting corroded due to water splashed up from the road. Lots of strange results happen -- hard shiftsl, popping out of drive into neutral, check engine lights. Ford change the design in a later model year to reduce this problem.

The trans and PCM must cooperate to shift gears. If the PCM is confused about what gear the trans is in (due to MLPS problems) it may not engage the appropriate solenoids, or it may leave some engaged when it shouldn't. This can put the trans in two gears at once, or otherwise leave things so the truck can't move.

If this is what the problem is, it is a much cheaper fix than getting into the trans. It is a reasonably straightforward process to diagnose the MLPS with an ohmeter.

On the other hand, one or more of the internal components in the trans may be worn out, in which case you will have to get out the wallet.

 

What is a MLPS worth? My tranny is actin up as well, so this could be the problem? It will clunk sometimes when I take off from a stop, or when I let off the gas, and sometimes shifts hard. If anyone has any ideas, can you help please?

Trevor

 

That sounds like a bad u joint to me.

 

It's not, I checked both on rear driveshaft. It has me stumped......and ridin the bus as much as possible.

Trevor

 

The MLPS costs between $100 and $200. Horribly expensive for what it is. You do get the retrofit and more splashproof design if you change it out.

The PCM controls the line pressure inside the trans and thus the firmness of shifts. If it is unhappy about the trans sensors, it raises the line pressure to "protect" the trans. Do a search on "E4OD hard shift", or look at my other recent post.