Anyone using this?

Trying to figure out which which one to get. 75w90 or 75w140 Also I'm trying to find out if I need to add any extra friction modifier to it.

 

With your mod's, go with the 75w-140.

 

That's the way I was leaning but didn't know what luck others were having.

Has anyone had to add extra FM to the royal purple?

 

I did not add any and found the amount in the RP was sufficient to not chatter at 70K miles.

Unfortunately, at 130K miles I don't think I have much left on the clutch packs to make any difference!

 

I hope that was due to wear and not the fluid..

 

I was surprised it would still lock up at 70K, honestly.

I got a little stuck in a logging road last October and had to put it in 4WD to crawl out when I noticed my left rear was only spinning when it unwieghted....assuming I need a refit of clutchpaks.

I think the Royal Purple is great lube, so no, I can't blame them.

I went with the heavier stuff in the rear for towing and the thinner in the front diff.

 

Sixslug, when you changed over to the RP how clean we're you able to get the diff? If pave drained the rear end but there is still a wee bit of the old fluid in there.

 

I sprayed some diesel in there with a bottle sprayer and let it drain off the carrier and mopped out the bottom of the housing.

Not too much metal paste in the housing or on the drain plug magnet...

 

Well this rear end may need more FM. It's grabby under extremely low speed tight turns and when doing the same in reverse.

 

I bought a bottle of FM just in case, but in my test using the figure 8 turns on dry pavement, I didn't get any bite or chatter so I never added any...

Depending on your tire's tread design, width, age, air pressure and rolling resistance, a low speed run may be the tire fighting the pavement rather than the diff trying to lock up...Not sure how to tell, maybe someone else does....

Mine will still leave two scratch marks on dirt when I slip the clutch, just tested it yesterday after getting in on this thread!!

 

My '99 was that way out of the factory. Very good LSD in the Dana 70.

 

I am pretty sure my fluid changes at 53K were the first the truck had seen. Fortunately, I do not think the axles ever got dipped at a boat launch or anywhere else...

Both front and rear were quite clean inside as far as visible debris goes.

 

Well mines makin all sorts of noises.

 

I've been running Lucas 80-90 with good luck until I blew the pinion seal and filled the rear diff with swamp water last year. Then drove 70miles home like that. Cleaned it out real good the next day, changed seal, filled with Lucas again, and got a ton of low speed/sharp turn rumbling. Swapped fluid out to RP 75-140 a hundred miles later or so and it's been good since then, about 15k miles, posi still works. I can still leave 2 perfectly even black stripes on dry pavement, 240k on original rear now. I've also never needed to add FM to either lucas or RP gear oils, they say right on the bottle not required.

 

Thanks for the feed back guys. I took a video of it to show y'all the pipping. It was doing this when I received the truck back from having the rear end rebuilt about 900 miles ago.

I first noticed the pop when I was backing up and turning locked to the left in my girlfriends drive way. I wrote it off to the new parts breaking in. But now since I ch aged the fluid and drive the truck in tight circles myself I'm finding these of there symptoms besides the popping. The reared feels grabby under extremely slow tight turns in forward or reverse.