I need help identifying how long my tail shaft should be
 

So I have an 86 f150 with a c6 in it and it's starting to fail. I want to replace it with an aod but I have no idea how long my tail shaft needs to be. It's a single cab short wheelbase with a 300 in it.

You do not have much choice, most AOD's have the same tailshaft. You will have to install the trans and then measure for your driveshaft, and make it longer or shorter. Most large cities have a shop that can do the work. You my need a new yoke to slip into the trans also, I am not sure the c6 yoke will fit the AOD.

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The parts store I work at has 2 different lengths for the band. A 10 inch and an 11 inch. But after doing some research I think I'm going to put another c6 in my truck. I cant figure out which one I have though. The number on the side doesnt match up to what we have listed at work rf-d7up-7006-aa is what's on my c6.

Don't hold me two this, but I believe due to the bell housing being cast as part of the tranny, they have both a big block and small block c6.

This is the ID number marked on the trans case, it is not the trans ID number. TRANS ID tag bolted to the servo cover. It's probably missing by now.

it is missing so thats all i have to go off of. i need to know what trans i need to order. there are 2 listed.
one that states

Automatic Transmission Assembly Rear Wheel Drive; Transmission Code: C6; 3 Speed; 7 Tooth Speedometer Gear; Tag ID: PGD-AW27, PGD-FF

and another that states
Automatic Transmission Assembly Rear Wheel Drive; Transmission Code: C6; 3 Speed; 8 Tooth Speedometer Gear; Tag ID: PGD-BD9, PGD-FE


from what i can tell the only difference is the spedo cable

See if you can shine a flashlight up in the hole and see how many teeth it has. I am going to assume the 8 tooth gear are for the lower numbered ratio trucks and the 7 tooth for the higher rearend ratios.

If you pull the cable and then pull the housing out of the tailshaft, you are left with a fairly large hole. But you may not be able to get your head up in there to see it.

i work in a parts store, that being said can i just swap the gear? is there any real difference in the trans?

The speedometer drive gear is an integral part of the tail shaft . So, it can't be changed

What do you mean the transmission is failing? Checked the fluid level and condition ? Slipping in 2nd? intermediate band might need adjusting.

I can change the cable gear or the whole cable. The transmission wont make it up hills and second gear is non existant. The trans had water in it when I got the truck. So back to the topic are the transmissions the same?

No they are not the same. The output shaft is different with a different speedo gear. If you want to mess around with the speedo gear and have your speedometer not read correctly, then it will not matter.

Functionally they will be identical. As for the drive gear. It can be compensated for with the driven gear (the one on the cable) as it is replaceable. So I would not get too wound up about the number of teeth on the drive gear.

If you give us the stock rear axle ratio stock tire size and number of teeth on the driven gear we can tell you the number of teeth on the current drive gear.

C6 output shaft with F150/350 2WD & Econoline is 23 3/16" long with 25-34-38 teeth, 31 splines, but...

There are FOUR different output shafts, because there are FOUR different drive gears rolled onto the shafts (made as part of it) with 6, or 7, or 8, or 9 teeth.

https://cimg0.ibsrv.net/gimg/www.for...65a2065128.jpg
I'm not so worried about the speedo
gear as my speedometer is 8 mph fast. I plan on going to a gps speedo before to long. I'm just worried about getting a transmission that is to long or to short for my shrte wheel base truck.i dont want to have to do any thing with the drive shaft.