I may have screwed up... was checking the rear end fluid in my F150 (2007) and noticed it was a little low so I added about 6 ozs of 75-90 gear oil. (I had it on the shelf) I know, I know... later after reading the owners manual it said it uses 75-145w. Did I screw up, should I drop the cover and replace with new?

 

I will be fine...but it may need to be serviced anyhow ...how many miles on it ??

 

Only have 50K

 

its getting close to needing serviced anyhow...so I would do it...

 

yeah your fine! Just get it serviced. Your seal is probably bad since you said it was low. Get a new seal or use gasket maker.

 

As said previously, check your pinion seal, and the axle seals. I don't believe these rears use gaskets, just permatex. That fluid went somewhere, hopefully not on your rear brakes.


Also, Ford calls for synthetic I believe.

 

X2. Calls for 75w-140 synthetic, also if its a limited slip differential you need a bottle of friction modifier to go with it otherwise you will have rear end chatter. There should be a metal tag attached to the rear cover bolts that specifies fluid weight to use but you did mention you have an owners manual. No cover gasket, permatex rtv silicone. Check for leaks, axle seal leaks are common on these trucks.

 

This may be a stupid question, but I'm gonna ask it any how.

Does the front "rear end", need the friction modifier as well ??

 

Front wont need it if it is factory, but technically someone could have added a limited slip diff to it but I doubt it.

 

Your right on the 75w-140 synthetic... saw that when I finally looked up what type of fluid to use in the manual, thanks for the response. I've looked everywhere and don't see any leaks or signs of a leak.

Years ago bought a new 1998 Chevy. Decided to take a trip to Florida with less than 2,000 miles on the truck and the rear end went out traveling down I75. The dealer said the factory had never filled it correctly is why it failed.

This is why I always have that unsettled feeling about checking the fluid level in the rear end.