Is gasket needed when replacing the differential oil?

[dcdyd]

I plan to replace the front and rear differential oil for my 98 V8 AWD. I wonder anyone knows whether both need new gasket for the drain plugs?

 

[deweyville65]

I dont know about the front, I'm guessing it is the same as the rear, but there is no drain plug. You have to remove the rear differential cover to drain the fluid. There is originally a gasket, but you do not need to replace it. You can clean the cover and smear some RTV silicone on it. Did mine nearly two years ago. no leak yet.

 

[LONO100]

Use rtv black.

 

[SoNic67]

Front diff doesn't have a gasket. It's RTV from factory.

 

[1996BLKBauer]

I used Ultra Grey to seal mine up, had no leaks what so ever.

 

[drdoom]

Blue Permatex work good also, just follow the instructions on the package.

 

[Flash]

The best way to use silicone as a gasket is to squirt a bead onto one of the surfaces and when the silicone gets stiff but is still malleable press it gently into place and do up the bolts finger tight.

it works best to clean the surface you lay the bead on and lightly oil the other so that you don't glue the part on.

When the silicone has set torque the bolts up.

I've done that with engine pans and cam covers and haven't had a leak.

 

[dcdyd]

Thank you all for good suggestions.

 

[mikepier]

On my front diff, I purchased one of those cheap oil hand pumps at Auto Zone, and sucked out all the fluid from the front diff from the fill plug. Then I replaced with new fluid. It's better than dropping the whole front diff.

Also some tips. Do it in warm weather where the axle fluid flows more freely.

When doing the rear, jack up one rear wheel at a time to tilt the axle tube so all of the fluid comes out.

 

[bobflood]

In my 2WD there was no gasket on the real differential. I used RTV Black to reseal the diff before filling. IMPORTANT - make SURE that you can break the fill plug loose (it's a 3/8 or 1/2 in square drive) BEFORE you take the back of the diff case off. Really a bummer to drain all the old oil, then find out you can't get the fill plug out.

 

[mikepier]

In my 2WD there was no gasket on the real differential. I used RTV Black to reseal the diff before filling. IMPORTANT - make SURE that you can break the fill plug loose (it's a 3/8 or 1/2 in square drive) BEFORE you take the back of the diff case off. Really a bummer to drain all the old oil, then find out you can't get the fill plug out.

Just a thought. Let's say you can't get the fill plug to come out. Can you resort to removing the VSS on top of the diff and filling it there?

 

[dcdyd]

Just realized that I need to take the cover of the rear differential off in order to replace the oil, right? For my 98 5L V8, it calls out 80W90 (I will probably use 75W90 synthetic) for the front and 75W140 synthetic gear oil. Do I need any additive for both? The owners manual is hard to understand as below.
-------------------
Note 2, Vehicles equipped with 4.0L SOHC and 4.0L EI engines may have a
limited slip differential. If your vehicle is equipped with a limited slip
differential, add 118 ml (4 oz.) of additive friction modifier
C8AZ-19B546-A, Ford specification EST-M2C118–A, for complete refill of
8.8 inch and 9.75 inch rear axles.

Note 3, Vehicles equipped with 4.0L SOHC or 4.0L EFI engines and 3.73 or 4.10 rear axle ratios or 5.0L engines require synthetic rear axle lubricant. Rear axles containing synthetic lubricant are lubricated for life. These lubricants are not to be checked or changed unless a leak is suspected, service required or the axle assembly has been submerged in water. The axle lubricant should be changed any time the axle has been submerged
in water. For Traction-Lok rear axles, add 118 ml (4 oz.) of additive friction modifier C8AZ-19B546-A, Ford specification EST-M2C118–A, whenever the lubricant is changed.

 

[bobflood]

Just a thought. Let's say you can't get the fill plug to come out. Can you resort to removing the VSS on top of the diff and filling it there?

Don't know - my fill plug came out so I did not have to pursue any further. Should be easy enough to test - remove VSS, see if you can stick a wire or flexible tool down in the hole and touch oil.

 

[bobflood]

Just realized that I need to take the cover of the rear differential off in order to replace the oil, right? For my 98 5L V8, it calls out 80W90 (I will probably use 75W90 synthetic) for the front and 75W140 synthetic gear oil. Do I need any additive for both? The owners manual is hard to understand as below.
-------------------
Note 3, Vehicles equipped with 4.0L SOHC or 4.0L EFI engines and 3.73 or 4.10 rear axle ratios or 5.0L engines require synthetic rear axle lubricant. Rear axles containing synthetic lubricant are lubricated for life. These lubricants are not to be checked or changed unless a leak is suspected, service required or the axle assembly has been submerged in water. The axle lubricant should be changed any time the axle has been submerged
in water. For Traction-Lok rear axles, add 118 ml (4 oz.) of additive friction modifier C8AZ-19B546-A, Ford specification EST-M2C118–A, whenever the lubricant is changed.

After 238K miles, I decided that it was past any "lubricted for life" point and went ahead and changed it in Sept 2010. I used a synthetic that contained a friction modifier - 3 Qts Mobil Synthetic LS 75W140 - and has been fine so far. At about 272K miles now, so been in there for about 35K miles.