I have a rearend leak that I am gonna fix and I am wanting to know can I just top off my current oil level after I fix the leak or should I change all the current oil our for new? The oil looks good and has good color. It's not dirtly looking or anything. What oil should I use? I have a 2005 F-150 5.4, 4x4.

 

Has it ever been changed? Miles and driving conditions? Since I presume you have to drain to make repair, I would take the opportunity to replace the fluid. My 2cents.

 

If you have never changed your rear oil its best to open it up inspect everything and change it out. With a leak you may have gotten some water in the differential so you would want to drain it out good and clean the cover off. Then reinstall and re-fill.

The oil is 75w-145 and it takes a little over 3 quarts. Also if you have the limited slip rear end you will need 7oz's of the friction modifier.


I just did both of mine last weekend and found out I had a bad seal on the front differential at the top and it had water in the case. I got it all cleaned out and resealed and everything is running nice.

 

Coskid,
The front diff looks difficult to access bolts to remove cover. Any secrets?

 

Man that was a pain in the ****. I used 2 sockets, 2 open end wrench, and my air socket to get them all off. The one at the very top you have to remove the plastic piece under the oil filter in order to get to it easily. Once that is out of the way 2 of the top 3 bolts are actually pretty easy.

I had a standard size socket for most bolts that the air socket wouldn't reach and a smaller socket for the bolt on top to the right side when looking straight at the cover. The smaller socket has some sort of canister in the way and can not fit anything bigger.

 

Thanks, Coskid, you confirmed money well spent when I had the dealer do it.

 

LOL..As long as they actually took it all the way off. Mine I found was never sealed right on the top. The way I found this out was once I removed the cover I saw the original seal bead still sitting there on the cover as though no one had pushed it tight against the case. The bolts where all in tight on the top but the bead had been placed too low. I am not use if this was done by previous owner or if it came from the factory like that. But its fixed now and no damage had taken place from what I saw so I am pretty happy.

 

I called my local ford dealer to price their motorcraft synthetic rearend oil and it is $22 a quart. Is this the normal price for motorcraft? If it isn't where can you find it cheaper and if it is are there some cheaper alternatives that still offer a good product?

 

I've always read that if you use the synthetic oil you don't need the friction modifier. Royal Purple is another good choice

 

Don't know about Motorcraft specific, but I recall $18-26/qt at Autozone.

 

No you will always need the friction modifier if you have the limited slip. They actually come with synthetic from the factory.

 

I used Mobil 1 synthetic. Gear oil is expensive though the 18-26 per quart is about right. Your front differential is a different oil though so if you decide to change it make sure you get 75w-90 for the front. A pump is also recommend especially if you plan to change out front oil. The rear is easier with the pump but not needed.

 

The front seal on the rearend of my truck that is leaking has a nut that I have to take off. I have been told that it has to be torqued to a certain number. Is this true? If so, what do you torque it to?

 

If you are referring to the fill plug that is just a 1/2 racket to take it off I am not aware of a torque spec for it. Mine had some lockite or something on it to help it seal up better that might be an option for you to help keep it from leaking again.

 

I'm thinking about changing my rear diff fluid this spring. Where did you get your fluid and friction modifier at?