Well i rad all the debates over gl4 and 5 and found a dealer near where i am that has 75W90 royal purple for 7.95/quart. its actually a speed shop, so is this the same as mobil 1 where its gl4 and gl5 combined and not good for the synchros? if it is then il get 5 quarts but if its not then il just hafta order some MT-90. thanks for any help

 

DO NOT USE ANYTHING MARKED GL-4/GL-5. Any gear oil that can meet GL-5 specs has an additive in in that is not good for the syncros in a GL-4 trans, like ours.............and Mobil 1 does not make a GL-4 gear oil.

 

Ok... thats what i meant, where i work we have that Mobil 1 spec'd for gl3-5, i knew i shouldnt use it but wasnt sure about royal purple. ok well thanks, guess its on to Amsoil or MT90

 

The copper corrosion testing per ASTM D130 shows a value of 1B after 3 hours at 100 ēC. The scale goes from 1 (a,b or c) through 4 (a, b, or c). 1A means there is no effect of the lubricant on copper. 1B is the second best possible result. I am not aware of any true synthetic GL-5 gear lubricants being less corrosive to copper than 1B but there is always a chance . The copper corrosion test is used to measure the corrosiveness of lubricants to yellow metals .

These lubes vary in both viscosity and friction modification . Sometimes after calling the maker to ask about yellow metal campatability the only way to know how your car will shift with it's type syncro rings and the friction additives in the given fluid is to try it .

Not all syncro's are built and act the same when driving .

 

Redline MT 90 or Pennzoil's 75W-90 synthetic would be fine, both are GL-4. I have no exerience with Amsoil products..........