I just purchased this 2003 F150. The pinion seal was leaking, so I replaced the seal and took off the cover and drained all the gear lube out. I put in the proper 75w140 synthetic gear oil. Do I need some sort of friction modifier in there as well or is the synthetic gear lube all that is required. Thanks

 

if the synthetic gear lube is ford rated, no modifier is necessary

Mark

 

Be sure to clear the axle vent tube of dirt and debris. Most of the time pinion and axle seals fail is due to that tube being plugged.

 

Most of the aftermarket synthetics have the FM in them BUT if you have an open diff you don't need it anyway.

 

The synthetic gear lube I used was 75w140 Quaker State. I will have to go out and check the trash can and see if it is rated FM on the empty bottle. I believe it is a open diff anyways. The vent was clear but the nut on the pinion had started to loosen ever so slightly causing a bit of play. Plus it had 271,000 miles on it anyhow. As I side note, I did a tuneup today and it still had the original motorcraft plugs in from the factory. The metal under the electrode had melted back to behind where the electrode is and the spark was angling back. Plus the gap had widened to about double what it should have been. Think it was long overdue. Thanks to all for the help.

 

wow...that tuneup should really improve your mileage!

Mark

 

I just checked the Quaker State bottle and it did not mention anything about having a friction modifier in it. It was rated GL-5. Don't know what that means but does anyone know if the Quaker State has the modifier in it?

 

From Wikipedia

API classification subdivides all transmission oils into 6 classes:

API GL-1, oils for light conditions. They consist of base oils without additives. Sometimes they contain small amounts of antioxidizing additives, corrosion inhibitors, depresants and antifoam additives. API GL-1 oils are designed for spiral-bevel, worm gears and manual transmissions without synchronizers in trucks and farming machines.
API GL-2, oils for moderate conditions. They contain antiwear additives and are designed for worm gears. Recommended for proper lubrication of tractor and farming machine transmissions.
API GL-3, oils for moderate conditions. Contain up to 2.7% antiwear additives. Designed for lubricating bevel and other gears of truck transmissions. Not recommended for hypoid gears.
API GL-4, oils for various conditions - light to heavy. They contain up to 4.0% effective antiscuffing additives. Designed for bevel and hypoid gears which have small displacement of axes, the gearboxes of trucks, and axle units. Recommended for non-synchronized gearboxes of US trucks, tractors and buses and for main and other gears of all vehicles. These oils are basic for synchronized gearboxes, especially in Europe.
API GL-5, oils for severe conditions. They contain up to 6.5% effective antiscuffing additives. The general application of oils in this class are for hypoid gears having significant displacement of axes. They are recommended as universal oils to all other units of mechanical transmission (except gearboxes). Oils in this class, which have special approval of vehicle manufacturers, can be used in synchronized manual gearboxes only. API GL-5 oils can be used in limited slip differentials if they correspond to the requirements of specification MIL-L-2105D or ZF TE-ML-05. In this case the designation of class will be another, for example API GL-5+ or API GL-5 LS.
API GL-6, oils for very heavy conditions (high speeds of sliding and significant shock loadings). They contain up to 10% high performance antiscuffing additives. They are designed for hypoid gears with significant displacement of axes. Class API GL-6 is not applied any more as it is considered that class API GL-5 well enough meets the most severe requirements.

check your owners manual for recommended fluid type...

Mark

 

Unless someone already replaced them with motorcraft... but either way it should run alot better with new plugs in.