Spring cleaning-Fluid replacement HELP.

[RED MONSTER 4X4]

It is about that time! Going to run the gambit and do a complete Fluid service on my 91 V2500 4x4. So Trans fluid,Transfer case and both Axles(10f/14r).

I have Googoled this topic for days and have nothing but confusing information. I figure I can break it down here and see if some friendly folk can help with this!

Transmission = 4l80e So What should I be running? DEX III?
Transfer =Np241 Same as trans? DEX III
Axles =(10f/14r) What gear oil 75-90? What about Royal Purple?

Few other questions, Do I have a limited slip diff that I would need additive?
I would assume not since it is a 4x4?... This Monster does not get driven much, it is just a Vacation/Utility Vehicle. I just want it ready for the need. I got it without knowing the trans fluid condition or if the axles have had a service, so I am just going to do it all.

This is all new to me, I appreciate the help ahead of time.

 

[black dawg]

dex 3 in the trans and t case, and I like synthetics in the diffs (it gets cold here) for cold flow properties.

I pulled the fill plug out of a diff this morning that had been driven 10 miles (low of -10 last night) and the 90w would not run out of the hole.

 

[RED MONSTER 4X4]

Well, Here in So-cal it rarely gets below 30* in fact it gets well over 100* over the summer, so i would like some sort of protection there. I don't plan on doing anything but towing a trailer occasionally and hauling junk in the back like camping gear with the occasional Off-Road adventure. I am not against synthetic(royal purple?) cost is not really an issue if it is a fill and (almost) forget solution.
just looking to you, the experts and what you would recommend.
This is my first Big truck let alone 4x4, and i am looking for the best advice, and so-far CK5 is the place! and I thank you all so far!

 

[black dawg]

in your temps I would use 75/140 syn in the rear and 80/90 syn in the front. And I usually use valvoline synthetic gear lube

 

[ratlover]

Could have a factory locker. They don't take an additive. If someone happened to add a clutch type limited slip(kinda unlikely) and you run it without the additive it will act up while turning but you can put the additive in after the fact.

Always had good luck with mobil 1 products but lots of quality oils out there. Syn holds up to heat better too in addition to cold. I'd run syn in transfer case too.

With a trans you can't really change all the fluid without some work and a trans takes ALOT of fluid. I'd lean twards leave it alone.

 

[Mastiff]

When I got my CUCV it had been abused so I drained all the trans fluid that would come out easily and replaced it. I think that gets in the vicinity of half the fluid? I figure as long as it looks clean and red it's probably not that bad.

For my K5, I was thinking about replacing the trans fluid with Royal Purple (mostly for the fun of it). Is there a way to really replace the fluid at home, safely? I don't want to accidentally run it dry while trying to purge. Since RP is expensive, I don't want to waste a bunch of it either. Don't mean to hijack here, hopefully this is on topic.

 

[ratlover]

Done it on an Allison. Pop cooler lines, puke with one into a bucket and have it suck with the other. Have a little extra than capacity and it will kinda flush itself.

Or you can use the dilute method. Like you said if you dump pan and refill you get part of the old fluid out. If you dump pan a few times after running and refill you will get a good chunk changed over.

 

[black dawg]

have to add fluid through dipstick tube, the lines wont pull any fluid