Rear diff seal

[Josh99]

How hard is it to change the seal where the driveshaft goes into the differential? Any write ups? also what do you guys recommend for rear diff fluid for limited slip? Thanks

[bwillis2003]

question #1: i dont know
question #2: i run amsoil 75w-140 synthetic..seems to do its job..good stuff!

[Josh99]

My plan is to take the driveshaft off, hang it out of the way, mark the shaft, nut, diff and socket and count the rotations it takes to get the nut off, pop the flange off, pop the old seal out, new one in and put it all back together and turn the nut the same amount of times as it took to get off. I'm gonna check my axle breather too and make sure its not clogged. From what I've pulled up on google, the best fluid is 90w gear oil with the additive in it.

[bwillis2003]

i put 75w-140 with the additive..90w is basically the non synthetic version of 75w-140..dont really need the synthetic i guess if you dont tow a bunch

[forddieseldoctor]

As long as you have the Ford axle and not the Dana axle. You need the 75-140 gear lube and if it's a limited slip rear axle then it needs the friction modifier additive.

Dana axles have the fill plug in the rear cover, Ford axles are in the side of the housing.

[DJM]

Mine has a leak there too just havnt got around to fixin it I bought the Royal purple 75 140 for mine when I get around to the seal.

[melmount]

it has synthetic in it now, use synthetic again. There are fidderent weights depending on whether or not you tow a lot. Thinner will get better mileage.(dont really know if you'll see it. If not sure onlimited slip, spin a rear wheeland see if the other goes in the same direction. If so its a limited slip. If oppisite it's not. You are supposed to replace the crush sleeve and measure the differential spinning ability in inch pounds. YOur way will work but dont overtighten it. There will be no sleevce cruching when you tighten it. So it will be a lot easier then if you replaced it.

[ryandamo]

there is a specific amount of preload that needs to be on bearings, after factoring in gear wear and different crush sleeve, it may be off if you just mark a line. the correct procedure is online somewhere, ill try to find it and get back to you, thats one of those things that you want to do right if you do it.

[cj45lc]

Check out the pinion yoke where the seal seals, if it's worn you may need to replace the yoke. That was the story with mine, it was leaking when I went to buy the truck used from dealer. I told them I wanted the seal R&R before I picked the truck up so they just put new seal & a few months later I had to R&R seal & yoke. There is a inch lbs measure on the drag on the diff as mentioned above.

[03_Turbo7.3]

Originally Posted by Josh99

How hard is it to change the seal where the driveshaft goes into the differential? Any write ups? also what do you guys recommend for rear diff fluid for limited slip? Thanks

Easy easy easy...

You have the right idea, mark mark mark everything...just put a punch mark on the nut and on the pinion gear itself., remove the nut and pop off the old seal, check the flange, if it has a ridge on it, youll need to replace it along with the seal, its a common issue.

You DO NOT need to replace the crush sleeve, if you do good luck tightening it back up..its a tuffy been there done that multiple times..

when tightening the nut back up if you go past your mark a hair that is ok, as if your re-using a crush sleeve your supposed to apply a little more tension then less.. it wont hurt it.

use 75-140 and a ford diff additive, your diff should have 2 tags on is itll tell you the fluid etc..