I have a '90 F-150, 4.9L straight 6. I'm having a problem or 3 with this transmission. I just bought this thing and considering what i paid for it i expected to run into a few snags.
Now, this truck has a C-6 trans in it. and from what I understand, ford stopped using the C-6 in F-150s in 86 or 87. Not to mention that the shift indicator says that its supposed to have OD, so im assuming that there was an AOD in it at one time.
The problem im having is that the tranny basically operates as a manual transmission. I have to put it in 1st to get 1st gear, 2nd to get 2nd. However in D, it won't do a 1-2 shift, it stays in 1st, then you have to shift to 2nd, then once you hit 50km/h you put it back in D to get a 2-3 shift. I've pulled the dip stick and the fluid is a mess, and quite brown, however it's not burnt.
Now i know this is a C-6 cuz of the shape of the pan, and looking on the side of the transmission i see something that looks like a range sensor, where the linkage goes into the case. What i was thinking is that this problem is either an issue with the "range sensor" or a valve body problem - possibly an accumulator spring or something.
Do these transmissions have modulators like a4lds and c-3s?
I don't have a C-6 manual around, but im hoping one of you do, and can help me out.

thanks
Ben

 

The C6 does use a vacuum modulator, just like the C3, C4, C5, A4LD, etc. Without it the trans won't shift right.

 

ok, thanks. I have a feeling the modulator isn't the whole problem, but it's a place to start.