Improving synchro shifting problems by using different gear lube weights or additives?


machoheadgames

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For some reason folks seemed to think MT-1 means great for all stick trannies. Not the case. The designation API MT-1 denotes lubricants intended for nonsynchronized manual transmissions used in buses and heavy-duty trucks.
GL5 oils have a sulfur content that that destroys softer metals "yellow metals" as many call them. That would be the syncro rings and possibly bushings in some cases. GL4 and down does not have the damaging sulfur thus the recommendation. There are some manuals that now use carbon fiber syncros andIi dont believe the GL5 will do damage. I think I mentioned it that the likes of Summit racing or Jegs and other do in fact carry GL4 lubes as well as synthetic ATF.
I have never heard of anything called API MT-1 nor have I seen it recommended by anyone for anything related to Jeep.
 

Gary747

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Just to follow up... I use Mopar ATF in my transmission (AX-15) ONLY because it is the Jeep manufacturers brand... I've no specific technical reason other than brand loyalty. As for 30W engine oil in the Transfer Gearbox, I actually called the rebuilder (The Gear Shop, Middle River, MD) and asked why they void the warranty if I use the red ATF fluid. They said that the transfer gearbox is vented and that ATF "mists" pretty heavily when energetically lifted by gear action (lower shear stability), resulting in a gradual loss of fluid via the vent. All things being equal, many owners don't check the transfer oil level very often and end up running the transfer gearbox at too low of an oil level for extended periods. 30W engine oil "mists" much less and adheres to the rotating parts inside the gearbox much better, greatly reducing the possibility of running with low lube levels and improving internal lubrication. I used to be in the group that didn't regularly check the transfer gearbox oil levels very often, but when I did, I found the ATF level to be pretty darn low. However, I use ATF in the transmission (with spinning gear shafts) and I don't seem to be losing ATF fluid over time. Whatever, it works for me.

The cold oil "shifts good" and the warm oil "shifts hard" observation may be associated with the oil chemistry. Multi-weight fluids such as 75W90 or 5W30 change viscosity inversely with temperature. The lower the temperature the "thinner" oil, and as the oil heats up, it get "thicker". Starting an ice cold engine requires thinner oil in order to move around the engine, but the oil needs to "thicken up" as everything gets hot. So, while GL4 as suggested by Gilaguy23 is definitely the way to go for normal transmission lubrication, you might also consider a single weight version if you can find it. After my experiences, I'm more comfortable with lighter weight lube oils when dealing with "meshing" rotating components, but I stick with 75W90 in the axles.
 

Gilaguy23

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have never heard of anything called API MT-1 nor have I seen it recommended by anyone for anything related to Jeep.
(API, American petroleum institute) By no means insinuating you have or had recommended that one. I Just mentioned it as most auto parts stores Ive been in will tell people that MT-1 means it great for ALL manual trannies. They typically direct you to Mobil 1 synthetic GL5 or something with that spec. For that matter with the exception of our local Napa GL5 is all you can find in my neck of the woods.
And like Macho said every AX15 or AX5 equipped jeep Ive owned did not shift well with dino 75/85 or anything of that brew. When its in the teens here its near impossible to shift into any gear. The Redline did help my 98's AX15 but Im just running straight 30 or 40 HD in my AX5 now and change it every year or so. Shifts buttery smooth. In you case, Id say things are getting worn out. The thick oil is great when things are cold but once heated up and thinned out you start to get hard shifting dues to syncro wear. Just my $.02 on that one.
 
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machoheadgames

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(API, American petroleum institute) By no means insinuating you have or had recommended that one. I Just mentioned it as most auto parts stores Ive been in will tell people that MT-1 means it great for ALL manual trannies. They typically direct you to Mobil 1 synthetic GL5 or something with that spec. For that matter with the exception of our local Napa GL5 is all you can find in my neck of the woods.
Gotcha. I would definitely not listen to a parts store recommending that. And yeah, they pretty much always sent me straight to the GL5 section when I'd ask, and they never carried the GL4 stuff, which is why I always buy from the internet instead. Even 20 years after the TSB, they are still incorrectly recommending GL5.
 
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YJcharlie

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I have an AX15 and had similar synchronizer issues when hot. Two things... 1.) Chrysler-Jeep came out with a service bulletin that recommends replacing the transmission 75W90 gearbox oil with 30 weight engine oil. Interestingly, my rebuilt TRANSFER gearbox has a warranty based upon using 30 Weight Engine Oil in it instead of the factory red automatic transmission fluid. Using the lighter weight oil in the AX15 helps the synchronizer issues, and using 30 weight in the transfer gearbox reduces oil loss due to vaporization. I use 30 weight in my transfer gearbox, which leads me to 2.) My synchro problems disappeared when I drained the 75W90 oil from the AX15 and replaced it with Red Mopar Automatic Transmission Fluid (ATF). After the initial fluid swap, I ran for 100 miles or so to "wash" the internals with fresh red fluid, drained and refilled it again with ATF. I've operated the Jeep as my daily driver with this fluid for over two years now in the Mojave Desert area with NO problems... no fluid leaks and the smoothest shifting since I bought the Jeep in 1999. I've checked the transmission oil level at every engine oil change and have not had to add any ATF. After the first year, I drained the ATF just to "have a look" for contamination, overheating, etc, and the fluid looked, felt and smelled like new. Refilled the AX15 with fresh ATF and never looked back. Maybe others can comment, but I know I'm not the first to run an AX15 on ATF. My 1990 Jeep now has 401,000 miles on it.
Do you know specifically what atf you used? That sounds like something I'd like to try. I googled it and see:

Chrysler (68218057AA) Genuine Mopar Fluid ATF+4 Automatic Transmission Fluid​


but not sure that's what you used.