I am wanting to change my rearend oil to Royal Purple to see if it helps the l/s. Where can I buy it, what viscoisity do I need, and how much does the reareand hold? Thanks for the help!

 

Royal PUrple is a superior lubricant as is Amsoil. Now, what are you trying to fix? if there is something wrong with your rear end, no oil is going to fix the problem. You need to find the problem, then fix it or it will eventually show it's self

 

I believe with my mag hitech it was just over 3qts, and the cover should have been just over a Qt. So 2 quarts should do the job if I am remembering it all, but the manuals should have capacities in it.

My 02 took a heavy weight in the rear, I think I used the 90 or 75 w 140. The front used a lighter oil, i believe it was something in the 75w-90 area.

 

Its 3.5qts for the sterling with stock cover. RP is good stuff, as is mobil 1. My autozone/advance has RP and mobil 1 in stock. 75-140 is what you need. Its both just shy of $20 a quart.

As for Johnny Bravo's post, your obviously not familiar with the ford LS diff, (or any clutch type for that matter) Once the fluid and friction modifier breaks down it can make the cluches chatter not to mention the ls not work properly. I have fixed MANY clutch type LS's over the years with a simple drain, clean and new fluid with correct amount of friction modifier.

 

That's good info~ What is the friction modifier and how much should one use? I will change my rear end fluids as soon as possible. I just purchased my turck and I am type A when it comes to such things.

Thanks for the info!

 

The RP oil has the required friction modifiers, I had my LS rebuilt when my gears were installed and I used RP. It never chattered and worked pretty good for 10k miles. Now it's weak again, the stock LS isn't the greatest.

 

Like Reax said, the RP has the modifier already in it. THe mobil 1 you can get it with or without it, I use the stuff that already has it in it.

The stock unit pretty much sucks, its just one step better then an open diff IMO.


Johnny, congrats on the new truck, not to hijack this thread but what did you buy?

 

We purchaesd a 28ft sea ray boat that we keep on our property. Moorage is way too expensive!

 

Here is some more info. I have a '03 with 3.73 l/s. The truck has 200k on it, and will gets stuck very easy. Actually got stuck in the yard today, thats why I'm looking into this. Only one wheel would spin. Thought I would try changing the fluid to start with and see what happens. I've had the truck since it had 147k on it, so I'm not sure if or when the fluid has been changed. I checked at the local Autozone, probably will go with the Mobil 1 for l/s.

 

Ford Motorsports offers a synthetic gear oil with additive already installed. Stuff works great, in fact when those LS came factory the clutches were too tight, Ford authorized its use instead of going in and resetting all the clearances. You should be getting way more than 10K miles service from those fluids, I believe the recommended is 60K with 30K severe duty. If yours is breaking down that fast, I suspect you may have a overheat problem, or you tow a lot of weight.

 

If the mileage was directed towards me, I had gears installed, ran the 500 mile break in and replaced the fluid. The clutches started wearing down and the LS not working as well as it had in 10k miles. Before, I could get the back to slide out and then in with power, now it's just out when I play going around 90 degree turns.

 

Oh, everything was tightened up. That sounds pretty much like what the factory units were doing, the clutches worked fine, but after a few months they would start grabbing and chattering due to fluid breakdown, mostly felt in reverse, hard turns. That is what we cured with the Motorsport stuff, then go out and turn figure eights until you couldn't see straight anymore.

 

Yes, no noise, just poor clutch life with 35" tires. It still works somewhat, but not like that first few months. Really made me want to put a clutchless locker or LS in.