I am making this so that hopefully it is an easily searchable thread for anyone who does not want to do all the searching and research I went through.
To use friction modifier or not to.
This can get confusing because I myself have not kept up with the changes in technology on this and there is a LOT of conflicting information between chiltons manual, ford specs, lube advertising, and what can be found on google.
Bottom line up front: for 2005+ cars 75w140. If it has friction modifier in it you don't need to add any. It actually is possible to use 75w90 but then you have to use friction modifier. Also 75w140 is reverse compatible with earlier mustangs that have trak loc.
I am referring specifically to Trak loc axels. If you have an eaton or a whatever contact whoever made your diff.
All the major brands of 75w140 have the correct additives in it already with only one exception that I could find which was Motorcraft. However always read the label because I will not be held responsible for you buying some off brand like Super Tech and assuming things.
By major brands I mean RP, Amsoil, Lucas, Moble 1, ect. But still read all labels first.
If you feel as though you have net been bent over enough today you can go to a ford dealership and buy Motorcraft which is more expensive than Royal Purple and then also have to buy the friction modifier on top of it.
This is the reason why in Ford publications it says to add a separate bottle of friction modifier. Chiltons bases what they publicate off of what Ford tells them the car needs so that is why chiltons also says specifically to add a separate bottle of friction modifier.
Why is 75w140 reverse compatible? The numbers refer to the measured oil weight as in its thickness alone. However 75w140 is synthetic and 75w90 is conventional. The chemical makeup of synthetic gear oil is completely different than that of conventional and though the oil weight measurement is different the 75w140 is plenty slick. The conditions in your rear axle are not like the conditions of your motor or auto trans where the thickness of the oil alone can make a huge difference.
Something to know about friction modifier: It makes your lube more SLICK, it does NOT add friction. One of the old problems with LSDs is that they make all these noises and shudder effects when going around a turn. This is because of the friction between the clutches when one wheel is going faster than the other around a corner. 75w90 conventional and lubes like it are not slick enough to allow the clutches to work the way they are supposed to. Friction modifier balances this out. One would imagine then if you add friction modifier to a lube that has the additive built in you would loose some of your trac loc function. However I have not found anyone using a synth with a modifier complaining about this.
This is also why some people experience chatter or hear a moaning sound coming from the rear when they use 75w90.
As far as fill amount both Ford and chiltons say 4.25 pints. This is to account for 4 oz friction modifier. Therefore the actual fill capacity for using 75w140 with a built in additive is 4.5 pints. Most gear and diff cover kits come with 4 pints (2 quart bottles). I only imagine this is because of the availability of containers and you are better off a half pint less then 1.5 pints over.
If you think the .5 pint is a big deal try this. Get a pitcher and put 2 quarts in it. Then get a measuring cup and add a half pint. Look at the difference, its not a bid deal is it?
However that being said I ordered 3 bottles and will be filling mine to spec. I got some Lucas 75w140 from Jegs $11.99 per bottle free shipping.
If you don't already have a favorite brand throw darts at a board. All the major brands are good. This is not F1 racing and you are not going to win any more races because the brand of gear oil you picked gave you a .002 sec advantage. Besides without F1 level equipment I doubt you would be able to scientifically prove one over the other.
This information was gathered between quotes from a Ford rep, and LOTS, and I mean LOTS of separating the wheat from the chaff in online searching and reading publications.
I hope this helps somebody and if somebody has information they would like to add or perhaps can prove me wrong on something go for it.
To use friction modifier or not to.
This can get confusing because I myself have not kept up with the changes in technology on this and there is a LOT of conflicting information between chiltons manual, ford specs, lube advertising, and what can be found on google.
Bottom line up front: for 2005+ cars 75w140. If it has friction modifier in it you don't need to add any. It actually is possible to use 75w90 but then you have to use friction modifier. Also 75w140 is reverse compatible with earlier mustangs that have trak loc.
I am referring specifically to Trak loc axels. If you have an eaton or a whatever contact whoever made your diff.
All the major brands of 75w140 have the correct additives in it already with only one exception that I could find which was Motorcraft. However always read the label because I will not be held responsible for you buying some off brand like Super Tech and assuming things.
By major brands I mean RP, Amsoil, Lucas, Moble 1, ect. But still read all labels first.
If you feel as though you have net been bent over enough today you can go to a ford dealership and buy Motorcraft which is more expensive than Royal Purple and then also have to buy the friction modifier on top of it.
This is the reason why in Ford publications it says to add a separate bottle of friction modifier. Chiltons bases what they publicate off of what Ford tells them the car needs so that is why chiltons also says specifically to add a separate bottle of friction modifier.
Why is 75w140 reverse compatible? The numbers refer to the measured oil weight as in its thickness alone. However 75w140 is synthetic and 75w90 is conventional. The chemical makeup of synthetic gear oil is completely different than that of conventional and though the oil weight measurement is different the 75w140 is plenty slick. The conditions in your rear axle are not like the conditions of your motor or auto trans where the thickness of the oil alone can make a huge difference.
Something to know about friction modifier: It makes your lube more SLICK, it does NOT add friction. One of the old problems with LSDs is that they make all these noises and shudder effects when going around a turn. This is because of the friction between the clutches when one wheel is going faster than the other around a corner. 75w90 conventional and lubes like it are not slick enough to allow the clutches to work the way they are supposed to. Friction modifier balances this out. One would imagine then if you add friction modifier to a lube that has the additive built in you would loose some of your trac loc function. However I have not found anyone using a synth with a modifier complaining about this.
This is also why some people experience chatter or hear a moaning sound coming from the rear when they use 75w90.
As far as fill amount both Ford and chiltons say 4.25 pints. This is to account for 4 oz friction modifier. Therefore the actual fill capacity for using 75w140 with a built in additive is 4.5 pints. Most gear and diff cover kits come with 4 pints (2 quart bottles). I only imagine this is because of the availability of containers and you are better off a half pint less then 1.5 pints over.
If you think the .5 pint is a big deal try this. Get a pitcher and put 2 quarts in it. Then get a measuring cup and add a half pint. Look at the difference, its not a bid deal is it?
However that being said I ordered 3 bottles and will be filling mine to spec. I got some Lucas 75w140 from Jegs $11.99 per bottle free shipping.
If you don't already have a favorite brand throw darts at a board. All the major brands are good. This is not F1 racing and you are not going to win any more races because the brand of gear oil you picked gave you a .002 sec advantage. Besides without F1 level equipment I doubt you would be able to scientifically prove one over the other.
This information was gathered between quotes from a Ford rep, and LOTS, and I mean LOTS of separating the wheat from the chaff in online searching and reading publications.
I hope this helps somebody and if somebody has information they would like to add or perhaps can prove me wrong on something go for it.
