i have a 77 extra cab 150 and the tranz is doin some funky stuff:
when i got the truck the guy said that the bands need to be adjusted but i drove off and it was kinda sliding between gears when it shifted, now it only has 3rd gear and it is starting to go away
my question is,...could it be vacuum,or could i adjust the bands?
what do i look for to find the problem, i am trying to save myself from having to take to the local tranny hack.

 

i'm having the same problem some what with a brand new unit...i'm guessing its the vacuum.. i have an adjustable modulator and i'm planning on fiddling with it this afternoon, i'll let you know the results

 

have you guys checked the pin that goes into the modulator...i had a problem similiar to that ..i could only put my truck in 2nd and drive around in 2nd until i got to 60mph and then shift it manually into 3rd ...i changed the modulator and still nothing but i talked to a local trans shop and he told me that the pin had to be there and straight and mine was bent so i changed pins and shifted great eversince..also on the modulator you can turn it to the right clockwise and it is soppused to give you later and harder shifts and got the other way and sooner and softer shifts...let us know how it goes..take it easy

 

the modulator control's the shift between the gears, it will not stop the trans as bajascott's problem from going into first, more than likely you need band adjustment's. i take it you checked the fluid level? when was it serviced last? could need a filter kit and new fluid also

 

well thank you all for your comments. i will get out there and check some things out. i have a 5.0/aod i want to put in soon and dont want to spend a lot of money on this thing. so i will let y'all know what happens to day thanx again

 

well i went out and checked some stuff the modulator diddnt even have a pin in it,so i put one in it and it diddnt do a thing, i checcked the vaccum line and it is in tact
i called a couple tranny shops and they said that it was pretty much junk. so i have to find one that is good. no one in no.az has one for the 351m and a rebuild is areond 800-1200 bucks!!!!!! so if anyone on this forum lives near prescott az let me know if you got one to sell and i'll buy it if this price is right!!!
thanks again for all your help! scott