Originally Posted By: jake88
Originally Posted By: Shannow
Not familiar with the vehicle, but in a rear wheel drive, there is typically a lot of "rubbing" within the pinion/crownwheel, as not only is there a 90 degree change of direction, it is usually set up so that the driveshaft is below the axle centreline to allow a lower floor height...this means that rather than straight "lego set" mesh, there is rubbing between the gears, and it needs a higher level of EP additives...e.g. GL5 (or obsolete GL6)
I'm assuming your set up is transverse FWD, so there's no 90 degree direction shift, the gearbox and differential are in the same housing, and due to the isolation and mass of the combined engine/gearbox, they tend to be a little more aggresive in their final drive gear arrangement (more lego gear like, straight gear contact, not rubbing)...and need less EP, and can get away with a GL-4
Excellent explanation of the difference in EP requirements between the hypoid (offset pinion/ring) and spiral bevel gear arrangements.
This question comes up all the time, but if you look for a fluid that meets the MT-1, MIL-L-2105E, or J2360 qualifications then you will get the added benefit of the "copper-safe" EP additives which do not corrode brass and bronze synchros. These lubes are much easier to find and are of a much higher quality than GL-4 lubes.
Really there are not GL-4 lubes anymore because the test equipment is obsolete. There is an industry standard that the GL-5 additive at 1/2 treat rate will qualify as GL-4 - but there are better specs now for gear lubes which require the brass/bronze compatibility.
I'm REALLY pleased I asked this I'm learning a lot today and for a long time I wondered what the difference was, I certainly didn't work out that my gearbox didn't have the hypoid gears, and the great explanation why cars do have them.
I'm really pleased to be able to ask and have my questions answered in a manner that even a novice like me can understand, I did work on racing motorcycles over 20 years ago but gearbox's on motorcycles and cars are so different, I have never taken a car gearbox to pieces but I have the engines many years ago, in those days I knew what spec to look for on oil but I never changed gearbox oil or axle oil in the past, I'm enjoying being on here it's a great place to learn.