90' 4runner 22re 5spd

Rear axle and the transmission both have synthetic gear oil. Now I want to do the transfer case and front differential. Is it alright if I use the regular stuff (non synthetic)? The synthetic for the transmission and rear axle cost me over $100! lol Dino stuff is over 3 times cheaper. Might as well change it more often.

 

Sure can. Seal inside tcase/trans should keep from mixing the two, but it's not the end of the world should they accidentally mix (like draining one and refill with the other will mix the two)
I use dino gear oil because it's cheaper. I was recommended once to not switch any of my fluids to synthetic because sometimes you get problems - like the synth is "thinner" and gets past seals whereas the dino oil doesn't. Recently there was a thread regarding engine oil samples coming back as more contaminated with synthetic vs dino oil in a 22re.

For some reason I'm now thinking about how wretched gear oil smells....

 

Thanks! Yup very smelly. Of course I spilled a whole bunch on myself too haha

 

I like to use conventional oil in my axles of older trucks because you can afford to change it regularly and continually clean out the wear metal in the oil. I think the transfer case calls for a 75/W90 which will be hard to find in conventional but a lot of folks use 80/W90 with good results. I do know that, with engine oil in particular, the synthetic oils so a better job of cleaning the engine from the inside. The contamination readings people are talking about are from the syn oil breaking loose deposits that took years to lay down. I worked in an oil sample lab for several years and had to explain it hundreds of times. Samples will be clean after about 3 oil changes. Apart from breaking up those deposits and sending them through the system it also will break up deposits around your seals and show you all of your leaks you didn't know you had. Folks say synthetic oil caused a leak but that's not true. The fact is that the seal was already worn but the oil was not leaking out due to the deposits around the seal until the syn oil broke them up.

That being said. I convert to synthetic on components with less than 75K mi. on them and stay with conventional after that point. On new stuff, I'm synthetic all the way. Either way is fine on your drivetrain though. If you want to go to the synthetic. Go to a dealership for semi trucks and buy it in a 5 gal bucket. Most big truck rear ends call for it and they are pretty competitive on the price. I pay about $85 for 5 gal.

 

You;re right on the 75 w90. so I'll go for the 80. Will definitely look into getting the 5 gal too!