I have a 2000 f150 4x4 orp,4.6 w/4r70w trans.I took it in for an oil change and of course they checked the rear diff fluid and it was kinda dark so they recommended replacing it.I agree it was pretty black,but my question is,I thought the rear diff was lubed for life and didnt need to be changed.or should it be changed along with trans fluid change.Or did I get burned? The fluid was pretty dark though.Any replies would be appreciated. Thank you.

 

As you stated, the factory synthetic lasts a long time, supposedly. It should not be "pretty black" in a 2000 truck. Although the oil properties maintain their integrity, the lube does get friction material (LS), metal (worst during break in), and gear marking compound at setup. Many have complained of seal leaks, bearing death, and whines due to several problems. For the small cost of changing the lube, I'd change mine at regular intervals. Mine is a 2000 and when I dropped the cover, it had metal shavings and slight discoloration.

 

I cna't imagine an dealer suggesting that, or even checking it. Was it a quick lube joint, that makes their money selling/changing lubricants?

I haven't seen the synthetic fluid in a rear diff but I wonder if that color is not an issue? In the old days, that nasty stuff was dark, oh and nasty, right out of the bottle.

 

yes it was a quick lube place.I have 30000 miles on the truck.Like I said,it did look kinda dirty.As long as nothing gets *******'d up, I guess I will be happy.Thanx for the replies cause I couldnt find any change intervals in the owners manual for diff fluid and was under the impression it was lubed 4 life.

 

Mine says 150,000 miles; good luck with that.

 

ok,one more question,since the factory fluid is synthetic and didnt need to be changed,now that I changed it and dont know if it's synthetic or regular,how often do I need to change it now.What are the change intervals on regular differential fluid versus synthetic.frickin Jiffy lube!!

 

You could try to find out what they used. If you can't, play it safe and change it every 30,000 miles. You can always put synthetic back in at a later date.

 

drown21

I'd go by and find out what they use. If they truly didn't know it was synthetic, it would be a learning experience for them. Might no do you any good but to know what they used, but it might help them learn more about what they are supposed to be the experts in.

 

ok,I went back to the shop to get the trans fluid changed for the 30k interval.I asked them about the diff fluid and they use the 75-140 or whatever,I believe that is correct.I asked them if they used friction modifier also because I read off these boards you have to use that too for the limited slip.They told me they never heard of it and asked me if I meant the stuff they add to trans fluid to make it mercon v compatible.Needless to say they didnt put any friction modifier in the differential,just gear oil.Do I need the friction modifier?

p.s,could someone explain the difference between ls and non-ls.

 

I think you have found a shop that you should avoid like the plague.

There is no difference between the Ford ls and non-ls, except that Ford charges more for the ls. People are too busy in arbitration over incorrect radiator sizes and door cracks to notice. Seriously, there are numerous discussions on the "purported" advantages of a limited slip and its design in the transmissions and other drivetrain forums. Actually, I've been very happy with my limited slip's performance, but then again I'm a weekend warrior *ussy whose most intense offroading consists of hauling my girlfriend and her babbling sister around on the beach.

I also did go pick up some gravel once in some real loose sand. That counts too...

 

I have '97 SC and around 96,000 miles on it so just went through the rear fluid change... battling with a dealer as usual
my 2 cents on the issue...
If you have in your manual
"Motorcraft Synthetic Rear Axle Lubricant F1TZ-19580-B" and "Additive Friction Modifier
C8AZ-19B956-A" then you need SAE 75W140 and the frictrion modifier, nothing else. Service interval stated in my manual is 100,000 miles.
Don't substitute if with anything else...

 

dont sweat it they did not really cause any problems just change the fluid again in 30000miles and everything will be allright some gearlubes come with friction modifier and none needs to be added with the lube change changing the lube on a regular and early basis is just cheap insurance for some of us and puts our mind at ease that the lube is clean and doing its job

 

If they missed the "friction modifier" don't sweat it. It won't damage anything. You may feel that your LS is slipping more than usual if traction is required by both rear tires. That's what the friction modifier is for, otherwise the clutch plates can't grab each other... too slippery.

No damage though.

If the people in that lube shop don't know what a friction modifier is then don't go there again. These are the type of places than put regular ATF instead of Mercon V in your tranny and you end up with a big repair job.