the basic question is this: when parked on level ground, where should the end of the slip yoke be relative to the bushing? (in other words, how long should the driveshaft be) the reason i ask, is my used 84 finally bit me in a rather funny way. it had always sagged a bit in the rear, which looks awful to me, so i added a 1 inch lift kit and it looked better, and according to the trim piece was close to level. so, about a week later i feel a vibration whenever i back off the gas. i see that the driveshaft slip yoke has an amazing amount of play, so i go get a bushing and seal and plan on putting them in on saturday. but on friday, at about 65 mph, the vibration gets louder. then it starts jumping out of gear. so i check the trans fluid and it's gone, because the seal has been beaten to death. i fill it up and limp home. so i pull the drive shaft out, and look at the bushing. most of it is pristine, showing no signs of wear whatsoever. the rear 1/2 inch or so is polished for the first quarter or so, and then beat all to hell for the remaining 1/4 inch. so, my 1 inch lift kit had pulled the slip yoke out of the bushing, and it was being supported by the rubber seal, which died along with my transmission. lol. the knucklehead who owned this truck before me had swapped the trans and driveshaft, and had been happy with about 1/2 inch engagement. so, when i buy my rebuilt trans, how long should my driveshaft be, to establish the proper bushing/yoke relationship at rest. and i apologize for the huge paragraph. all my line breaks disappear on this forum for some reason.

 

Here's all the different factory driveshaft combinations for a 1984 f150. If you are going to get someone to build you a new longer driveshaft, I would see what they recommend when the do a custom one. As you can see below it depends on the tranny, and the type of rearend you have also. If you know your combo, there probably is a factory one made for it.

139" WB, M.T., Fr section, Ford (3 & 4 spd)
139" WB, A.T., Fr section, C6
139" WB, M.T., Fr section, New Process
139" WB, M.T., Fr section, Warner
155" WB, A.T., 4x2, Fr section, C6
155" WB, A.T., 4x4, Fr section
133" WB, A.T., 4x2, two-piece, Rr section
117" WB, M.T., 4x2, New Process
117" WB, A.T., 4x2, AOD
133" WB, M.T., 4x2, one-piece, Ford (3 & 4 spd), removable carrier
133" WB, M.T., 4x2, two-piece, Fr section, Warner
133" WB, A.T., 4x2, one-piece, C6, removable carrier
133" WB, M.T., 4x2, one-piece, Ford (3 & 4 spd), non-removable carrier
133" WB, A.T., 4x2, one-piece, C6, non-removable carrier
155" WB, A.T., 4x2, Rr section, removable carrier
155" WB, A.T., 4x4, Rr section, removable carrier
133" WB, A.T., 4x2, two-piece, Fr section
117" WB, A.T., 4x4, flange joint (thru 1/84)
117" WB, M.T., 4x4, flange joint (thru 1/84)
133" WB, A.T., 4x4, flange joint (thru 1/84)
133" WB, M.T., 4x4, flange joint (thru 1/84)
117" WB, M.T., 4x2, Ford (3 & 4 spd)
117" WB, M.T., 4x2, Warner
117" WB, A.T., 4x2, C6
133" WB, M.T., 4x2, two-piece, Rr section, non-removable
155" WB, A.T., 4x2, Rr section, non-removable carrier
155" WB, A.T., 4x4, Rr section, non-removable carrier
117" WB, A.T., 4x4, slip yoke joint (from 2/84), non-removable carrier
117" WB, M.T., 4x4, slip yoke joint (from 2/84), non-removable carrier
133" WB, A.T., 4x4, slip yoke joint (from 2/84), non-removable carrier
133" WB, M.T., 4x4, slip yoke joint (from 2/84), non-removable carrier
117" WB, A.T., 4x4, slip yoke joint (from 2/84), removable carrier
117" WB, M.T., 4x4, slip yoke joint (from 2/84), removable carrier
133" WB, A.T., 4x4, slip yoke joint (from 2/84), removable carrier
133" WB, M.T., 4x4, slip yoke joint (from 2/84), removable carrier
133" WB, A.T., 4x2, two-piece, assm (4R602 id)
139" WB, A.T., Fr section, AOD
155" WB, A.T., 4x2, Fr section, AOD
133" WB, M.T., 4x2, two-piece, Rr section, removable carrier
139" WB, A.T., Rr section, removable carrier
139" WB, M.T., Rr section, removable carrier
155" WB, M.T., Rr section, removable carrier
155" WB, M.T., Fr section, 4x2, Warner
155" WB, M.T., Fr section, 4x2, Ford (3 & 4 spd)
133" WB, M.T., 4x2, two-piece, Fr section, Ford (3 & 4 spd)
155" WB, M.T., Fr section, 4x4
133" WB, A.T., 4x2, one-piece, AOD
139" WB, A.T., Rr section, non-removable carrier
139" WB, M.T., Rr section, non-removable carrier
155" WB, M.T., Rr section, non-removable carrier
155" WB, M.T., Fr section, 4x2, New Process
133" WB, M.T., 4x2, one-piece, Warner, removable carrier
117" WB, A.T., 4x2, C5
133" WB, A.T., 4x2, one-piece, C5
133" WB, M.T., 4x2, one-piece, Warner, non-removable carrier
133" WB, M.T., 4x2, one-piece, New Process, removable carrier
133" WB, M.T., 4x2, one-piece, New Process, non-removable carrier

 

thanks. that's a lot of combos my problem might be more complex, though. it's possible that the transmission did not come out of an f150, because the wiring harness has a few extra feet that they just piled up beside the trans. and the speedo gear is off by 10 percent, which just means wrong match to rear end/tire dia, i would think. the limiting factor is this: when the axle is highest, the slip yoke must not hit the rear seal. i will look at the geometry and calculate this, add 1/2 inch for safety, and ask the drive shaft shop to add the length. thanks for the data

 

I was taught to squat the vehicle completely, push the yoke to base and back off about 1/8", then measure yoke to yoke.

If you go online to a drive line MFG they have the measurement procedure.

-Enjoy
fh : )_~