1979 ford F100 diff seal leaking do u have to replace the brg or can u just replace the seal

Given the age of the trucks there should be old paper manuals and parts lists about where you can compare axle ratios, drive shafts, suspension parts etc. Try ebay. Would it not be easier to get another F250 front end?

needs a saver sleeve on the yoke..or a new yoke

It would be very hard to give instructions on how to do this over the Internet. If your not good with auto electrical stuff then I suggest going to a auto electrician, any auto elec should have no problem with this. Or get the wiring diagram fir your old truck and the 79 and mix and match to make it work.

The slave should not leak. Either it is defective, or there is a mechanical problem with the clutch pressure plate or throwout bearing, and the slave it over extending.

It should however you may need to use the mounting bracket from the 79 there bolth 302 ;s it should work

if it is leaking from the front of the diff where the drive line goes into it you have to drop the rear of the drive shaft from the diff, if you look at the flange on the diff where the driveshaft bolted to you will see a nut, possibly about 25 to 30mm, you have to remove the nut and remove the flange off the spline of the input shaft of the diff, the nut is really tight and it is difficult to get enough pressure on the nut to "crack it" while the car is on the ground as there is not enough room to get a long bar on the socket to remove the nut. if you happen to get the nut loose and you remove the flange get a big screwdriver and pry the seal out of the diff, check the surface where the seal ran on the input shaft as it may have a groove worn into it, if it has the groove the new seal will still leak, they make a sleeve you can slide over the shaft to give the seal a good surface to run on, we call them a speedy sleeve here but not sure what they may call them there. replace everything in the reverse order that you removed it and don't forget to tension the big nut that holds the flange onto the input shaft

leaking where? axle shafts? pinion seal? diff cover?
should inspect diff internals and bearings-may require overhaul not just
seal replacment. also check vent tube-if plugged will cause all seals to leak.

they need reamed

To replace the seal you must pull out the carrier assembly and the pinion gear and install a new crush sleeve if you do it by the book, I have found that if the yoke is removed a new seal installed and the yoke tightened to about 50 foot lbs of torque it is ok, as far as the lube goes there is a plug on the cast case of the diff, it will either be a square drive plug or a large allen plug, fill the diff so you can just touch the fluid with your little finger, don't overfill or the axle seals will start leaking.

check your rear diff vent if pluged clean it out and clean up the pinion seal.sometimes if the leak is caused by pluged vent and has not been leaking long once vent is clean sometimes the leak will stop.there is not a specific torque amount because it is rotational torque(how hard to turn pinion).there is a crush sleve on the pinion and if torqued too tight or too loose brg preload will be wrong and brg damage could result.mark and remove drive shaft.remove rear wheels,brakes,axles.so when turning pinion you dont have any drag from brakes or axles.mark the position of the yoke on the pinion.remove yoke,replace seal,reinstall yoke be sure to replace pinion nut.tighten nut until it takes the exact same amount of force to turn pinion as before taking original pinion nut off.hope this helps.