Rear diff leaking..

[mitchdog7]

So i have a 2000 7.3l f350 lbcc swb and i just noticed that it looks like the rear diff is leaking around the cover. the trucks got almost 200,000 miles on it and i doubt my dad has ever had the fluid changed... the tag on the cover says only use 75w140 synth oil. i'd assume it means synthetic, but how do i know if its limited slip or not? the other tag says s 409 h on the first line then (3)L73 10 5 ob28 on the second. the (3) is slightly covered by the bolt, so i'm not 100% sure. does that mean i've got a limited slip 3.73 10.5" ford sterling axle? if so, can i buy a new gasket for this? or do i need to just use a gasket maker stuff? Also, would advanced auto have synthetic oil with friction modifier in it? so i wont have to worry about getting it right. And am i supposed to fill the axle up the the bolt in the front of the axle towards the bottom?
thanks for yalls help.

[cj45lc]

Originally Posted by mitchdog7

So i have a 2000 7.3l f350 lbcc swb and i just noticed that it looks like the rear diff is leaking around the cover. the trucks got almost 200,000 miles on it and i doubt my dad has ever had the fluid changed... the tag on the cover says only use 75w140 synth oil. i'd assume it means synthetic, but how do i know if its limited slip or not? the other tag says s 409 h on the first line then (3)L73 10 5 ob28 on the second. the (3) is slightly covered by the bolt, so i'm not 100% sure. does that mean i've got a limited slip 3.73 10.5" ford sterling axle? if so, can i buy a new gasket for this? or do i need to just use a gasket maker stuff? Also, would advanced auto have synthetic oil with friction modifier in it? so i wont have to worry about getting it right. And am i supposed to fill the axle up the the bolt in the front of the axle towards the bottom?
thanks for yalls help.

Yes you have the axle you stated, some people say the syn 75w140 with the friction modifier already added has too much in it. If it has too much you end up with a one wheel wonder, I put 4oz of the modifier in mine & seems to work fine. Just use RTV instead of gasket, & the fill is on the driver side front of the diff 3/8 ratchet to take out the plug. It takes a little over 3 qts so get a gallon.

[shane30577]

You can fill it by taking the rear end sensor out. If you take the sensor out of the top its easier to fill. Take the plug out of the side to so when you fill from the top you wont put to much. It will run out of the side plug instead of it overfilling. The motorcraft gasket sealent will work fine for a gasket.

[mitchdog7]

thanks for the fast responses. well, since advanced didnt have the differential gaskets i guess i'll get the gasket maker and change out the front diff as well. will i need 75w140 in the front as well? just without the friction modifier right? would wal-mart have gallons of 75w140 synthetic oil? because advanced only had quarts of it if i remember right.. not to get the oil debate started, but what are a COUPLE different brands that are decent? advanced only had mobil 1 synth in the 75w140 blend, but they only have 3 quarts of it in individual bottles.

[Zaairman]

You don't need gallons of oil. You need 3.5 quarts for the rear and just under 2 for the front. And there is no gasket for the rear end, just use the black RTV. I used Royal Purple 75w140 in the front and rear.

[Mikey's250]

I put royal purple 75w140 in mine which already has the friction modifier in it and have not had any problems out of it. And I used the red rtv and no leaks.

[mitchdog7]

well, i figured it'd be cheaper to buy a gallon and then 2 quarts, rather than 6 quarts..

[dannanw]

I used the mobil one that you spoke of. X2 on the "RTV" type no gasket. I also used 85W but mines a dually and I alot of pulling, a ford tech friend said thats the best for the dually.

[PolarBear]

The front takes 75W90 also to put that out there. I also run the Royal Purple in my diffs. Limited slip still works fine and have not have a limited grip problem and have not needed to add the additive either.

[03_Turbo7.3]

When he says use the sensor hole, ontop of the diff is an ABS sensor, just unscrew the 10mm bolt and wiggle that sensor back and forth, jsut put a funnel in the hole and pour in your liquid, leave the check plug out and once the oil comes out of it your good to go.

Like they said there is no gaskets they are just RTV, Ford actually makes tubes of silicone that are ment to go in the guns, its grey and says diesel or something on it, it works amazing but just about any RTV that is oil safe is good to go.

When you take the rear cover off if your ever unsure if its an open diff or not just by looking at the gears inside on either side of the carrier where your axles are there will be clutch packs if they are there then you have limited slip, if not then one wheel peel.

Amsoil and royal purple make amazing diff oils id strongly suggest either of them