I need to drain both my differential and my 4 speed transmission. It is filled with non synthetic. I am reading all about redline and or royal purple however they are both synthetic. My understanding is you cant put synthetic oil in if it did not contain synthetic before. IS this true- what do you use if not the synthetic and or how do you convert to use the synthetic.

Any help is greatly appreciated

Red Line quitened mine down considerably.  There is particular types you use with the Zs, something about the brass synchronizers.  amazon.com has the best prices that I could find. 

 

for the transmission  http://atlanticz.ca/zclub/techtips/mtl/index.html 

 

for the differential  http://atlanticz.ca/zclub/techtips/differentialoilchange/index.html

Before removing the drain plugs, remove the fill plugs first.  Fill plugs are famous for being very tight.

 

Bonzi Lon

Redline for sure.  I like MT90 for the trans though.

 

The diff fill and drain plugs can be extremely hard to remove.  Use heat if needed.

That synthetic vs non synthetic is all bs. I don't see how people can make such claims with no scientific data to back up their hypothesis. Anyways, off my soap box. I believe motul gear oil 75w90 is great for our cars. It's a 100% ester base stock. So it's fully synthetic. Not a mineral base with synthetic additives. It's gl4 and gl5 certified. The next best thing I've heard is pennzoil synchromesh, the same stuff GM uses in their sports cars.

I'm using motul right now, their lubricants are proven to be top notch. I've used redline shock proof in my dad's sti but that's not gl4 rated.

I have used Red Line with good results. MT90 for the transmission and 75W85 GL5 for the differential.

I have also used Brad Penn 80W90 GL4 for the transmission with good results.