a few basic questions.
I have a 02 F-250 4X4 7.3L at what Mileage should you change the rear axle lube?

Also what are some of your opinions of Royal Purple gear lube for this application? Am I correct in understanding that you do not need to add any friction modifiers with Royal Purple?

Royal Purple Gear Oil

A buddy of mine swears by this stuff and I read lots of good reviews about it but it seems pretty expensive. is it really worth it???

Also what is the fluid capacity for the rear axle?

 

Your owners & scheduled maintenance guides will list the lube service grade, viscosity range, capacity, traction-lock axle friction modifier type & amount to use & lube change intervial, depending on the kind of driving you do & the conditions under which you do it.

In 99 for instance, it said in rear axles using synthetic lubricant & light duity tucks equipped with Ford-designed axles, it's lubed for life, Unless the differential is opened for service, repair, or immersed in water, in whch case the lube is to be replaced then. So I don't see the need to replace your differential lube.

It also says that in severe service use, like police, taxi, ect, 100K mile should be the service intervial.

I think most folks that care about their vehicles, consider changing the differential lube at the 100K mile mark.

If you don't have an owners guide, you can down load one from https://www.fleet.ford.com/maintenan...ls/default.asp
Some thoughts for pondering.

 

My schedule is 120k - 150k miles or 10 years, whichever happens first.

I think the recommended oil is 75w140, and that's not going to be cheap, no matter whose oil you get.

 

Ive got a '99 with 145k I had ford change the rear end when i bought it (bought it used 60k) and I just changed it again recently, because it was leaking (of course)
I'm pretty sure i went to guzzles maint site and followed his directions when i did it, I used Ford (MC) and it wasnt cheap by any means. Some where and of course im not sure where, but i heard or read or maybe just made it up.... but i was discouraged from using royal purple. probably would be a good idea just to do some research on it.

 

My 99 owners manual has 5-5.3 pints of Motorcraft SAE 80W-90 Premium Rear Axle Lubricant specified & if we have a Traction-Lok differential, then we are to add 4oz of friction modifier C8AZ-19B546-A, Ford specification EST-M2C118-A.

"Fill" is defined as to be within 1/4-9/16 inch below the bottom of the filler hole.

 

I was able to DL the owners man and find the correct fluid and capacities. THANKS!!

as for the Royal purple I did some extensive research and I kinda get the impression that although their oil is very good their gear lube leaves a little to be desired. Seems that it has a tendency to shear instead of hold together.
After looking at numerous data sheets I think I will probably go with Motorcraft or might even try Amsoil. I hear some good things about them.

 

Amsoil, Redline, if you can get it; Schaeffer's.

 

Back in the day, you would change the rear lube every two years when
you do your coolant.

Now, its synthetics. No matter what the books say, they should be changed about 50k-75k. If you are mudding or doing a lot of off roading, towing, you should change every 20k-25k. This is because of moisture collection, metal particles from harsh use and higher temperatures that can degrade the lube faster and destroy the pumpkin.
The manufacturer recommends 100k mile changes for 2wd vehicles that are driven in perfect conditions...that doesnt include you or I.
For the average person nowadays, about 5 years along with your coolant.

As far as which one to use?
ONLY THESE BRANDS USE TRUE 100% SYNTHETIC OILS:
(All other brands falsely claim to be fully synthetic on the label)
Mobil 1
Royal Purple
Redline
Amsoil

We use Mobil 1 fully synthetic oils for everything in every one of our
vehicles and equipment. Along with Mobil 1 or Royal Purple filters.

Rent-A-Man! lawn & tree
Killeen, TX

 

It seems that when ever you read about the cars and trucks that make it over a half million + miles it seems like the owner used the best fluids and filters and completely disregarded the recomended intervals and did tranny and difs every 2 years when they change antifreeze.

I've heard the same about the royal purple stuff, Its still great stuff, if you only use your truck as a daily and tow on occasion I think you would be fine with it, and would probably enjoy the reduction in friction.

 

RP seems to have a problem with shear stability in general. It must me the VII additive chemistry that they use. In motorcycle transmissions, RP gives poor shifting within 1000 miles. Shell Rotella T synthetic, for instance, never experiences this problem over a normal change interval. We have also never had a problem with Castrol. Granted, we are talking motor oil vs gear oil here.

For the money, Id go with Castrol Hypoy dino if you want 80W-90 for an open diff, or Redline for 75W-140 with or without limited slip. Redline cured limited slip rear axle "chatter" in the BMW that was real bad with Mobil 1. Redline has the additive already in it. Mobil claims to, but maybe not enough.

Jim

 

I've got an LS rear end and I used the Amsoil gear oil (75-140). It has FM in it and no additional was needed. I followed most of Guzzie's tips except I used the directions on the black RTV instead of Guzzie's recommendation to let the sealant sit for awhile and then attach diff. cover. The sealant directions were a little different.

 

Thanks for all the replies, after doing my research and also based on many recommendations on this site, I believe I am going to go with Amsoil 75-140. I'll probably also purchase their friction modifier just in case I need to add more than is already in it. (better to have and not need than to need and not have)

After doing some research, I get the impression that Royal Purple gear lube has a tendency to shear under heavy loads. possibly because of their additives??

Thanks for the input!!

 

As was said, I would go with Redline, Amsoil Severe Gear or Schaeffer's, probably the best three gear lubes you can get and all cheaper than Motorcraft 75W-140 obtained through the dealer.

 

Changed the front and rear diff oil in my 04' SD last year with around 37k on it. The oil in the rear had more particles from the LS diff friction material than I thought. If you tow often or fairly heavy its a good idea to change it more often than if you don't. I'm currently running Amsoil severe gear both front and rear. Don't forget to change the atf in the transfer case too, I used amsoil ATF for that but pretty much any other atf that meets Mercon specs is fine. Never used RP, figured it was no better than anything else. Running the amsoil because I have an account with a local store that sells it. To seal the covers up (especially on the rear 10.5) I recommend getting the Permatex "Right Stuff" silicone, had leaks with another type of permatex where the "Right Stuff" sealed everything up.

 

For RTV, you can't beat Motorcraft TA-31 (it comes in the short caulk gun tube). It's designed for high temps, seals great and sets up extremely quick. If you use TA-31 on the diff. cover you can refill after an hour with no worries of leaks.