Manual trans lubes

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Gilaguy23

YJ Enthusiast
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Apr 12, 2021
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Q town New Mexico
Before I hear the usual why wouldn't you "use what the Owners manual says" let me throw out who here is running anything close to a "stock" jeep, so poo poo on that argument. That being said for conversation purposes, cause its been slow these days around here, ha,ha, I'll ask who's running what in their AX5's or other manual gear boxes and T cases. Time to service both for me and Im pondering a few changes just because I can I suppose. The T case its been ATF since its birth. Im considering a 10/30 oil instead. The Trans has seen 90wt gear oil which was terrible in winter, so Ive been running a 30 or 40wt HD engine oil for the last year with fine results. But Im not thrilled running motor in it really. Im not impressed with Red lines products based off my own experiences so I'll avoid them. Ive been considering Mobil 1 Delvac SAE 50 Transmission oil which is GL1 thru 4 rated or??. Working with drives,gear boxes in industrial settings for 30 years Im really curious how one of the many synthetic ISO 100/AGMA rated lubes would do in a AX5 or 15 or other manual trans. Ive read lots of guys using that particular Mobil product in the Rams G56 manual trans with great results. As I said just a topic for discussion so fire away gents ;)
 
The owner's manual is wrong, so no worried about being suggested to do that. The owner's manual incorrectly tells folks to run 75W90 GL5. That was from Chrysler, NOT Aisin Warner. Aisin Warner has always recommended 75W90 GL4, of course the difference between the two being the GL5 rating which contains sulphur for hypoid ring and pinion gears found in differentials. Chrysler realized their screw-up years later and recommended 10W30 motor oil. I'm guessing that is because 75W90 GL4 is not super common, especially not in the dealerships. They probably wanted to use something that they have a hose for. 10W30 is close in viscosity, although it is not the same and doesn't have the same additives. For that reason I prefer to run what the MANUFACTURER recommends and has recommended since day one, which is 75W90 GL4. They did manufacture the transmission after all, so I trust them. Chrysler only installed them into Jeeps, so their recommendation is really pretty worthless to me, especially after they screwed it all up from the beginning.

What 75W90 GL4 oil do I like? Redline MT90 - I buy the gallon jug from Amazon. It is a bit pricey, but it shifts really well. Not like you need to change it very often either.

Why don't you like Redline? It's been known to be one of the most favored fluids for AX5 & 15...I like it enough that if I trade my automatic truck in for the manual version, one of the first things I would do is dump the factory fill for a jug of MT85 from RL.

As for the transfer case, I have always run ATF and don't plan on changing. I'm sure 10W30 is also fine. I don't really know why one over the other was chosen by the manufacturers. I personally do not see any downsides to ATF, hence why I feel no need to switch. As in, I don't think that motor oil will provide any benefits that ATF isn't already providing. And it would be the same if it were the other way around, if they told me to use motor oil, I would, and wouldn't switch to ATF because I wouldn't perceive any benefits there either. For that one I just don't see a reason to change.
 
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I'm sticking with GL90 for the box (I love the smell of hypoid in the morning, it smells like, Victory!):ROFLMAO:
ATF has always been fine in the 241s & 231s I have run, though I am aware of the motor oil debate and not heard anything bad.
I would think a synthetic might not be a bad idea since a t-case doesn't really need the special additives of ATF.
I like synthetic oil in my engine...If you can put the same in all three saves on shopping!

I used to run my SM420 with 4.5 quarts of GL90 and a quart of Morey's oil stabilizer to quiet it down a bit.
As much as loved that box, it was noisy.
 
machoheadgames said:
The owner's manual is wrong, so no worried about being suggested to do that. The owner's manual incorrectly tells folks to run 75W90 GL5. That was from Chrysler, NOT Aisin Warner. Aisin Warner has always recommended 75W90 GL4, of course the difference between the two being the GL5 rating which contains sulphur for hypoid ring and pinion gears found in differentials. Chrysler realized their screw-up years later and recommended 10W30 motor oil. I'm guessing that is because 75W90 GL4 is not super common, especially not in the dealerships. They probably wanted to use something that they have a hose for. 10W30 is close in viscosity, although it is not the same and doesn't have the same additives. For that reason I prefer to run what the MANUFACTURER recommends and has recommended since day one, which is 75W90 GL4. They did manufacture the transmission after all, so I trust them. Chrysler only installed them into Jeeps, so their recommendation is really pretty worthless to me, especially after they screwed it all up from the beginning.

What 75W90 GL4 oil do I like? Redline MT90 - I buy the gallon jug from Amazon. It is a bit pricey, but it shifts really well. Not like you need to change it very often either.

Why don't you like Redline? It's been known to be one of the most favored fluids for AX5 & 15...I like it enough that if I trade my automatic truck in for the manual version, one of the first things I would do is dump the factory fill for a jug of MT85 from RL.

As for the transfer case, I have always run ATF and don't plan on changing. I'm sure 10W30 is also fine. I don't really know why one over the other was chosen by the manufacturers. I personally do not see any downsides to ATF, hence why I feel no need to switch. As in, I don't think that motor oil will provide any benefits that ATF isn't already providing. And it would be the same if it were the other way around, if they told me to use motor oil, I would, and wouldn't switch to ATF because I wouldn't perceive any benefits there either. For that one I just don't see a reason to change.
Click to expand...
I know you're going to correct me on the "GL90", I was just abbreviating 90 weight Gear Lube, not the rating.
 
Ah..I knew I could count on you two for some feedback ;) FYI for those interested Summit and Jegs carries a couple brands GL4 trans lubes. IIRC one is Brad Penn and the other is " Driven Racing" which I used in a Toyota 4x4's with good results. Regarding the Red Line stuff I think it was when I pooped open 4 new sealed quart bottles and in the bottom was this gritty black sludge. Probably a 1/2 teaspoon in each bottle. It kinds turned me off although many said its the moly additive settle out, really Im thinking. I also Used to own several Harleys. They RL was recommended "shock proof" for the trans in some models. If you've ever seen what that looks like picture 350 wt Pepto Bismol. Just didnt get a warm fuzzy feeling seeing that. Ive heard guys on other jeep forums comment the MT90 worked for a few months then it was knotchy and hard to shift in all gears. I used the MT 90 inmy 98 TJ and really wasnt impressed for the $20 a quart they get so back to good old Dino GL4 in it. Guess I kinda look at RL like K&N filters. makes more HP, works great bla,bla and every racer uses them. The racers also rebuild their engines every season or more frequently. had one destroy my new XR600 engine after a few races. Never again for them. Its all personal preference and what makes one happy I suppose.
 
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Has been pretty quiet around here...
Lubes do bring up a subject I'm curious about, have others had experience with Polymer oils, like Slick 50.

40 years ago my dad was a distributor for a product called "NRG" by the Ariel corporation, prior to to Slick 50.
Don't know what happened to them, but I saw their product do some miraculous things with "wiped out" small engines.

Fast forward 15 years, I Slick 50'd the 2.0 in my '43.
A year later I poked a hole in the oil pan and wheeled it 8-10 miles back to the shop without a drop of oil in the motor.
Granted, I never went over idle and kept it in Granny, staying off the clutch while keeping an eagle eye on the temp.
Never overheated.
Got it back to the shop without any engine damage.

I don't know if it was the engine treatment or my diligence that saved it, but I'm curious if anyone else has had a similar experience.
 
Thats pretty incredible to not have had internal damages to say the least. I certainly recall when Slick 50 came out and Im not even sure if its still sold these days.I do recall reading a paper explaining why that particular lab or whatever they were claimed it to be unhealthy in engines. I recall a pint of ??? for auto trannies that was said to be the cats meow for trans longevity. Guy I bought my first Gen Ram Diesel swore by it. Anymore I think one can find as many bad stories as good regarding a particular product anymore. Im pretty anal about some things and try to use good quality lubes. Over the years Ive seen some pretty outlandish claims from one off lube distributors calming this and that and and their products were mediocre at best.Ive alsways used Chevron Industrial lubes in our equipment and had no issues. Years ago we were told to use ONLY Kolbenschmidt grease in our German built centrifuge. It was something like $30 a tube and warranty was voided if you didnt use it. Im familiar with the laws that say a MFG can say use ours or else but Im not sure if anybody made a equal by specs. One can spean endless days reading on lube technology these days.
 
I don't recall seeing Slick 50 on the shelves recently, but with this GD covid I don't recall seeing many shelves either.
Ya, you can find as many bad reviews as good, but when they're mixed, the bad tend to be from idiots who misapplied whatever product, or they were expecting miracles and didn't get their participation trophy.:cry:
 
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