A few things on this.

1: The mechanism of why a synchro loses brass due to EP additives is well understood. Under temperature and pressure of a shift the oil film is sheared when the narrow surfaces of the synchros clutch face press against the cone on the gear. Under pressure the oil film sheers, localized temperature increase and the EP additives are activated. The activation of the EP additive corrodes the copper from the brass.

2: The claim author of the article makes that the mechanism for metal loss is based on film strength causing the metal to peal does not appear to be based on any technical article I could find on the SAE web site or searching Google scholarly docs. I found nothing to back his claim. I also checked several tribology publications, same thing the standard explanation is corrosion when the EP additive is activated from temperature and pressure.

3: The author of the article is a retired McDonalds manager. His main professional experience with oil appears to be whatís used in the fryolator. You would typically expect an expert opinion with what appears to be a new explanation of a wear mechanism to come from a white paper or article of an industry insider or someone doing basic research. I reviewed quite a few SAE articles.

4: When making a novel claim, some research or article should be reference. The same author has published hundreds of similar "expert" opinions on Quora. MAny are questions with regards to McDonalds food. Expert on lots of stuff He does give good general advice, but by no means is the end all authority on wear mechanisms ( not compared to the research articles I typically read).


5: The basic claim that Gl-5 is bad for brass synchronizers is true.

6: GL-5 does not harm brass parts that are not subject to film breakage and the resulting increase in temperature. This means that for any GEN1 we can continue to follow the factory recommendation of GL4 or higher in the transfer case.

7: I have run GL-5 in the 4cyl Gen 1 manual transmission. No kittens died, it shifted fine. At the same time, I know that the synchro rings would not last as long.

8: If you have a later model transfer case that has synchros donít use GL-5. The manual and TSB's are a good guide.

Example of a real paper, fun read

Another fun read


87 Turbo Intercooled Raider, roller cam, torsen rear diff, LSD front diff, lockup auto with modified converter, V6 brakes, low transfer case gears...