Not saying that he should use that particular weight of the RP oil. The original question was if he needed to add the limited slip additive to the Royal Purple oil. I was simply making reference that the Royal Purple stuff is designed to be used in racing and severe use applications. The recommended grade from Ford for the 10.25 and 10.50 rears is 79w140, my old 95 had the recommended grade of 75w90. He should run the ford specified grade. Again, I was just making reference that the gear oil hold up under racing conditions without the need for additional LS additive.

Oh, and just in case you were wondering, the 97 and up F-150's (that run a much smaller axle than your 250) have a specified gear oil of 75w140, heck even the Mustang's rear has a Ford specified gear oil of 75w140. So don't think that just because your SD has some big ole massive rear that is has it's own special gear oil specifications......

 

I have only pulled 1 ford diff down that was run with 75w90 Castrol Full synthetic. I put the oil in at 75,000 miles and the diff was in good shape. At 120,000 miles the axle brg failed and I had to pull the c-clip. what I found was the face of the gears had worn through the surface hardening into the porsitiy of the steel underneath. The entire rear had to be trashed.


I drove the same type diff in other Ford products for about 400000 miles using 90W EP approved oil with never a failure. So perhaps concidence on the Castrol or perhaps not. Now I only use oil that specifically states meeting the Ford spec in the manual for refill. I changed my 7.3 Diesel Diff 2 months ago at 130,000 miles and it was in great shape. So I figured once again I would stay with the Ford lube. The price is insignificant given the frequency of change and I do know it works.

$.02 worth,, maybe $.03

 

Weather its syn or dino oil, the correct weight should be used. I'm going Royal Purple this weekend, with new diff cover.

 

That was the point before the **** hit the fan.

 

I like this forum but, I noticed the original posts sometimes wonder into an area where the original question is kicked to the side, so somebody can express an opinion that has nothing to do with the post. I am trying to say this in a good way. I have gotten a lot of good info on mods here, and hope to in the future.

 

Thats when you use these Emoticons -> Or

 

I think we need to see them more often.

 

 

Good job.

 

so, since i'm the OP, and after all of thie talk here, i think that for the 2 bottles that i bought for $10, it would cost about $4 to drive back. i think i am going to just put it in this weekend when i do the fluid changes. thanks guys. i hope nobody here gets that upset when a topic gets all blown out for nothing..

 

Yes...I know it is but...

What diff cover did you buy? And where? Just curious...because I am in the market for one before winter. I was thinking of doing a diff gear oil change (YES going to use RP gear oil)...and figured might as well install a new cover while at it.

Thanks,

biz

 

Yes...I know it is but...

What diff cover did you buy? And where? Just curious...(see previous post)


biz

 

Check out this Ford OEM cover that Diesel Manor carries. It comes on the '08's stock and promotes faster fluid cooling that the crappy peeling steel cover that comes on most of the older trucks. This one also comes with the hardware included (takes longer bolts because it's thicker).

http://www.dieselmanor.com/motorcraft/FD-3Z4033A.asp

 

biz4two, I bought the cover that npccpartsman's link shows from diesel manor. It came last night. Looks real good. Came to $62 with shipping. Nicer than the steel one I have. capacity isn't increased with this pan but, going with syn should cure that.

 

i am going to stay with the stock cover. since these trucks already came with synthetic fluid anyway, going with the RP oil should work well. and besides, i cant even see the rear under my truck. maybe if they made one for the front, that would be a different story.