Pretty sure its separate

 

Haha its cool man. This is very useful info. I'm going to drain my rear next week and add the modifier. See what happens. Its so freakin annoying.

 

I use royal purple..it has the added modifier.. but i also add a bottle of modifier also

 

OK, Royal Purple vs. Mobile One??? Opinions???

 

There both good stuff... Either way you go...

 

Hopefully you can get away with just changing the fluid out. I'm curious to know what you find out TJ. I wasn't so lucky with mine.

 

Ok so my 04 FX4 has a rearend noise BUT only at temps anywhere from 50-30 degrees outside? Maybe I'm crazy but summer time no noise or viborations but as soon as fall and winter come around so does the noise. I can also feel it in the floor boards. It starts at low speeds and sometimes the noise goes in and out with bumps. It does not matter if I am driving staight, turning, or on the brakes. It drives me nuts! Anyone have this going on?

 

A few posts ago someone mentioned that these rear ends are good but they had their's replaced at 60K? These rear ends suck, I know I have one. At around 35K, the pinion seal and both output seals had some leakage. The pinion seal was replaced under warranty, the output seals were not (dealship claims this is normal). I've owned two previous generattion F150s that did not do this. At 49K my pinion bearing self destructed and my rear ends was rebuilt. At about 69K one of the output shaft seals started gushing oil. The mechanic that replaced it told me that the seals on this rearend tend to eat the output shaft over time, and there was some evidence of that on my shaft however, had yet to reach the point where the shaft had to be replaced. If your first problem was at 149K consider yourself lucky. All limited slips require friction modifier or they will clatter especially while turning. If your problem started after an oil change, a 3 or 4 ounce bottle of modifier will resolve and should have been part of your oil change. Also, our manual as well as the tag on the rear end call for 75w90, however the Ford dealer states that my VIN calls for 75W140 which is what I went with the last time and havent had any problems

 

that was me that posted that they had theirs replaced at 60k. it is a good rearend. just needs to be appropriate maintenance. when i got my truck the fluid had never been changed and it was completely shot. these rear ends have a clutch type setup and just like your automatic transmission, if the fluid is bad the rearend goes bad. My dad got rid of his 04 with 289000miles on it and the only thing he had to do was change the oil and put tires on it. and it towed a 4500lb trailer 3-5 days a week. He kept up on all the maintenance.....wait i take that back....he did have to replace the tailgate latch! he broke it off in sub-zero temps one morning. even had the original ford windshield in it when he traded it....

 

So I just spent $1200 to have an Eaton Trutrac put in the truck and the fn thing clunks more than the old one. Does anyone know anything about Eatons? The mechanic says its normal and that they do that occasionally. Sounds like bs to me. Any input would be appreciated.