Hi everybody, I am a new member of the ford family. Purchased a 1986 F150 with a 351M bolted up to a C6 but needs a transmission, will any big block trans. work? This is my first ford and not real familiar and any help would be appreciated. Will post pics and updates as i move along with my project. Thank you all in advance!!

 

'big block' is a chevy term, it gets confusing using it in a Ford sense because there are a lot of 'big' Ford engines with different bell patterns. Ford FE series engine guys call theirs 'big blocks', and Ford 385 series engine guys call theirs 'big blocks' too.

in your question, there are both FE and 385 series bell pattern C6 transmissions. the bell pattern is not the same, you'll need to specify which bell pattern you need or you may get the wrong one.

any 385 series trans will bolt to your engine, but three different length tailshaft housings are available; 7 inches for trucks, 14 inches for passenger cars, and 17.4 inches in Lincolns. and Lincoln mounts are different from the others. tailhousings can easily be swapped, but the internal output shaft needs to match the tailhousing and that needs to be done on the bench(rebuild).

are you looking to buy a used trans and put it in yourself? for not much more you can have yours rebuilt as a 'bench job' and not do it again next week, and have the correct speedometer gear tooth count on the output shaft so your speedo is still right. the gear is cut into the output shaft and is not changeable, except to change the internal output shaft. without checking, you could get a different tooth count on the shaft and your speedo will never be right. some output shaft, tire and rear gear combinations cannot be corrected by changing the driven gear on the speedo cable.

if you're gonna install the trans yourself, before you put in any bolts, just make sure that the torque converter is free to wiggle between the trans and flexplate with the engine and trans mated. the bolts are there to hold them together, not to bring them together. if the trans doesn't mate up to the engine easily, something is wrong, most likely the converter isn't installed into the trans fully

 

Well that will get me started, thank you. I guess i will need to measure tailstock first. This truck is originally a 300 6cyl and the 351 was swapped in. Should find out where the drivetrain come out of first of all.

 

C6 was available on a 6 pop, but it would be the smaller 335 series bell pattern ... is there a door data sticker in the door jamb? should be a trans code you could look up that will tell you what the truck came with anyway. i guess if the trans in there now isn't original you'd need to check the speedo anyway(if you haven't) in case the tooth count is wrong now, and if the trans is F'd it might be kinda hard to check...

 

I have had the VIN ran and the truck came with 300 6 cyl. automatic. The tranny in there now is screwed, won't even try to move the truck at all. Your info earlier has really helped me in finding a transmission to be sent in for rebuilding. Thanks again.

 

well either your 351 is actually a W or the transmission was also swapped at the same time the 300-351M was. Just pull the transmission out and look at the bellhousing to know for sure