i am having problems with the oil in my axles on my 01 f150 4x4. i dont do a lot hard driving or alot of off-roading but every month i check my fluids as a precausion because i have seen what can happen when you dont. i guess my question is why does my oil turn grey in color and smell bad. for instance i changed the fluid in both axles back in may and last month i was chacking the fluids and i had the grey color and an awful smell. i changed the fluid that day and less than 30 days later its coming back again. i checked the rear and it has started to do the same thing. and lets face it the gear oil for these trucks is not cheap and changing the fluid every month is not realistic can some one please help me thanks
Dan

 

What you are smelling is the EP or extreme pressure additive in the differential lube. If you do not smell that smell, that is when you want to worry.

Read a bottle of gear oil and should indicate GL-3 or GL-5 extreme pressure additive in the lube. GL-5 is better than GL-3.

 

but what would cause the grey color it should be a brown or black right.
thanks for thew info on the smell though thats a little worry of of my mind
Dan

 

Due to the sliding action (design) of the spiral / bevel of the R & P, they naturally will induce alot of wear. The spiral of the pinion is always trying to "worm" it's way out of the ring gear. This is why it is very important to use a lube with a high "EP" rating, to resist these forces and keep the wear at a minimun.

Some gray or "paste" is not uncommon due to the above described conditions. In this case I reccomend making sure you have the correct "EP" additive lube in the axle assembly. Another worthy note: you may consider sealing a small magnet to the bottom of the center section housing (below and near to the ring gear). This will help pick-up any grey "pasty" debris and enable you to view the debris the next time you open the diff. for service or viewing. This will also aid in the early detection of potential emerging issues.

 

thanks man that was a big help. one more quetion though i use mobil 1 gear oil 74w-140 in the rear and 75w-90 in the front and i use the transx stuff you can get from the auto zone is this okay or should i use something else.
Thanks again for all the info
Dan

 

I just did the front and rear diffs 2 weeks ago. Both diffs had 75,000 miles on the oil and it looked new when I drained them.

The bad smell should be the additive that is used on the rear diff. The front doesn't get the additive. Make sure you are using the right oil. The diff plates should have an attached metal strip which states the correct oil on it.

Oil turning grey sounds like a wear problem from your axles or gears.