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Been having issues keeping her in first and found this on the jeepsunlimited.com (thanks to user marc1kim), thought it'd be useful to share. This info is only for the Aisin (AX5/15 5 speed manual) transmissions, not the BA-10 or AW4: *Pennzoil Syncromesh, and Royal Purple Synchromax are only recommended for the NV3550 and other NV trannys. (Not recommended for AX-5/AX-15). *Pennzoil has a GL4 lube, and Royal Purple recommends 10W40 motor oil for all 98 and newer jeep manual transmissions WITHOUT the NV trans. (Ax-5/Ax-15 fall in this category) *10W30 and (Jeeps recommended) GL-3 are roughly the same viscosity, and Gl-4 and 10W40 same viscosity as well. *All GL lubes have some kind of Sulfur content in them (needed for the High pressure Hypoid gears in rear ends, but not necessarily needed for most transmissions.) *Sulfur addadives react to brass internal parts. *GL-5 has twice the sulfur content of GL-4. *AX-5 and AX-15 are japanese manual transmissions, and the majority of manual Japanese transmission do not recommend the use of GL-5. because of the way it reacts to brass. *Red Line MTL is classified as a 70W80 gear lubricant satisfying the API Service requirements of GL-3 and GL-4. MTL also satisfies motor oil viscosities SAE 5W/10W/30, and the viscosity requirements for ATFs. *Redline MT-90 is a 75W90 GL-4 and also satisfies motor oil viscosities SAE 10W/15W/40. So it's safe to say: AX-5/AX-15 can use (synthetic?) 10W30, 10W40, GL-4, Or Redlines MT-90 or MTL and the New Venture transmissions Pennzoil Synchromesh, and Royal Purple Synchromax. Allthough I searched many website Here are some references with some good info: Good basic info and a mention of GL/ motor oil equivalents, and one mention of Japanese gear boxes. http://en.wikipedia.org/wiki/Gear_oil Viscosity chart: http://www.bobistheoilguy.com/visc.html Gear Lube Definitions: http://www.finalube.com/reference_ma...tegories.h tm Redline MTL / MT-90 info and what they can substitute: http://www.roadraceengineering.com/p...-mtl-info.html And from the Amsoil website: "The difference in GL-4 and GL-5 is that GL-4 gear lubes have half the extreme pressure additives of GL-5. Because the gear types in manual transmissions do not necessitate the use of GL-5 gear lube, GL-4 is the correct recommendation called for by most OEM’s when gear lube is required." GL-4 definition: "This designation denotes lubricants intended for axles with spiral bevel gears operating under moderate to severe conditions of speed and load or axles with hypoid gears operating under moderate speeds and loads." - so GL-4 will have additives for the Hypoid Gears. And here's where it all comes home (and probably explains why Chrysler made the change): GL-3 Definition: "Gear lubricants designated for API GL-3 service are not intended for axles with hypoid gears. Some transmission and axle manufacturers specify API Category "CC" or "CD" motor oils for this service." note: "CC" and "CD" oils have been upgraded to newer designations and are equivalent to 15w40

Love this forum by the way. I was able to put in a headlight & ignition key chime module today that I got at a pick-n-pull because of a posting from 'hornbrod'. Thanks for that....... Subject: 88mj, 4.0L,5sp Anyway, here's the reason for this post.. My gears won't engage when shifting forward or reverse. With engine running, the clutch pedal pushed to the floor and trying to shift to reverse you can feel and hear the gears as the stick moves closer to reverse. The other gears won't reproduce the same result. It feels like it goes into gear but won't go forward or reverse. I put it in gear before starting engine and the result is the same. What I've done recently......... Swapped the original '88 Peugeot 5spd for an AX15 from a '96 Cherokee along with its transfer case. The clutch master cylinder along with slave cylinder is new from Rock Auto for a '96 Cherokee...... The slave cylinder push rod didn't seem long enough to push the throw out arm but I went ahead and installed anyway. '96 tranny and '96 slave cylinder should work correct in tandem. Its possible I received the wrong part in the correct label box, but what are the odds........ Oh, the flywheel is '88 original that's been machined (I know I opened a can of worms with that statement.) Clutch and pressure plate are also new. Thanks in advance for any ideas or guidance.