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

[Gary747]

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]

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.

 

[machoheadgames]

(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.

 

[YJcharlie]

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.

 

[Brian]

Bleeding the brakes never gives me any real trouble but bleeding clutch setups definitely never works when I give it my best shot. I still stand by the recommendation for Redline MT90 75w-90, but whatever way you go, good luck. I have always run Redline since experimenting with 10w30 motor oil and the incorrect GL5 gear oil years ago (following the owner's manual). Redline has always been buttery smooth for me, as well as thousands of other AX15 owners. Doesn't mean that other options are not also smooth, but Redline is for sure a good option coming from myself and many others.

I invested($$$) in the Redline MT90 for my AX15 in hopes of improving 3rd gear syncro issues. Did not make any improvement at all, actually it seems to be worse. Mine is probably too far gone. I have to learn to double clutch all over again! Now I am a little confused???? Is a recommendation to run ATF in a manual gear box?

 

[machoheadgames]

I invested($$$) in the Redline MT90 for my AX15 in hopes of improving 3rd gear syncro issues. Did not make any improvement at all, actually it seems to be worse. Mine is probably too far gone. I have to learn to double clutch all over again! Now I am a little confused???? Is a recommendation to run ATF in a manual gear box?

Sorry to hear that. No fluid is magic, so it can only do the best it can, dependent upon the physical condition of the transmission. My previous transmission was pretty notchy and 3rd was it's worst gear. The factory filled these with the wrong fluid (GL5 hypoid gear oil with sulfur) and that fluid remained in mine all the way from 1993 to 2013, so it probably did some damage. Similar to other transmissions that ran the same bad fluid for really long times. Redline improved the overall feel of my old transmission but it couldn't make it perfect, third still never felt great. I put a new transmission in years ago though and it has shifted smoothly. It has only run redline in its life.

I have never recommended ATF in the transmission, though some people do. I don't personally trust it in there, seems too thin to me. There are manual transmissions that call for ATF, Ford comes to mind on that, but for the most part most of them use a non sulfuric gear oil.

Basically, the Jeep manual transmissions were cursed by being filled with the wrong stuff which took it's toll, worse on some than others. The new transmissions do exist but are not cheap, although they are a problem free, smooth shifting solution.

 

[Brian]

Sorry to hear that. No fluid is magic, so it can only do the best it can, dependent upon the physical condition of the transmission. My previous transmission was pretty notchy and 3rd was it's worst gear. The factory filled these with the wrong fluid (GL5 hypoid gear oil with sulfur) and that fluid remained in mine all the way from 1993 to 2013, so it probably did some damage. Similar to other transmissions that ran the same bad fluid for really long times. Redline improved the overall feel of my old transmission but it couldn't make it perfect, third still never felt great. I put a new transmission in years ago though and it has shifted smoothly. It has only run redline in its life.

I have never recommended ATF in the transmission, though some people do. I don't personally trust it in there, seems too thin to me. There are manual transmissions that call for ATF, Ford comes to mind on that, but for the most part most of them use a non sulfuric gear oil.

Basically, the Jeep manual transmissions were cursed by being filled with the wrong stuff which took it's toll, worse on some than others. The new transmissions do exist but are not cheap, although they are a problem free, smooth shifting solution.

In your opinion...I should just leave the Redline in since that is the best I can get? I watched a trans rebuild video and I think it would be beyond my capabilities.

 

[machoheadgames]

In your opinion...I should just leave the Redline in since that is the best I can get? I watched a trans rebuild video and I think it would be beyond my capabilities.

When did you put it in and how long (miles) has it been? A lot of people are quick to judge fluids right after install, I like to wait a few weeks and see how I feel without thinking about it. For example, in my 6 speed truck, I installed Redline MT85 after driving the truck a few weeks. Initially I thought no improvement, but a few months later it is definitely better than it was before. Not saying it gets better with time, but it takes some time to truly evaluate it I think.

I'm not saying Redline is magic or necessarily the way to go either, just that its always worked well for me. If you truly think it made yours shift worse, maybe go back to something else. I'd at least give it some time if you haven't had it in there long. It can't hurt the transmission anyways, if damage is done, nothing will reverse that, and it isn't going to get worse from the Redline either because it meets the spec the transmission wants.

I too didn't want to mess with a rebuild. It was also my DD at the time so that was a big factor but I still have no desire to teardown another manual after the T150 CJ rebuild I did 8 years ago. I didn't enjoy that one.

 

[Brian]

When did you put it in and how long (miles) has it been? A lot of people are quick to judge fluids right after install, I like to wait a few weeks and see how I feel without thinking about it. For example, in my 6 speed truck, I installed Redline MT85 after driving the truck a few weeks. Initially I thought no improvement, but a few months later it is definitely better than it was before. Not saying it gets better with time, but it takes some time to truly evaluate it I think.

I'm not saying Redline is magic or necessarily the way to go either, just that its always worked well for me. If you truly think it made yours shift worse, maybe go back to something else. I'd at least give it some time if you haven't had it in there long. It can't hurt the transmission anyways, if damage is done, nothing will reverse that, and it isn't going to get worse from the Redline either because it meets the spec the transmission wants.

I too didn't want to mess with a rebuild. It was also my DD at the time so that was a big factor but I still have no desire to teardown another manual after the T150 CJ rebuild I did 8 years ago. I didn't enjoy that one.

I will give it some time....there are always other issues to deal with. I have a bad joint in the steering shaft. Do you know if I can buy the joints or do I have to get the whole shaft? It has only been 50 miles at the most.

 

[machoheadgames]

I will give it some time....there are always other issues to deal with. I have a bad joint in the steering shaft. Do you know if I can buy the joints or do I have to get the whole shaft?

Whole shaft, as far as I've seen. I bought the dorman shaft for mine, works fine. About $115 if I remember right.

 

[SirDoopYJ]

I will give it some time....there are always other issues to deal with. I have a bad joint in the steering shaft. Do you know if I can buy the joints or do I have to get the whole shaft? It has only been 50 miles at the most.

Don't do Crown. My first one didn't fit on the steering box. I think there might have been a barb in the teeth. The second one was still an odd fit but went on better than the first.

 

[Brian]

Don't do Crown. My first one didn't fit on the steering box. I think there might have been a barb in the teeth. The second one was still an odd fit but went on better than the first.

OK Thx

 

[Brian]

Whole shaft, as far as I've seen. I bought the dorman shaft for mine, works fine. About $115 if I remember right.

A little while ago you said you might be able to pick the speedo gear for me..Tire size is
265/70-17. They are on stock jeep rims. 5X5

 

[machoheadgames]

A little while ago you said you might be able to pick the speedo gear for me..Tire size is
265/70-17. They are on stock jeep rims. 5X5

Do you know how much the speed is off by? Those are basically a 32” tire so you probably need 26 or 27 tooth gear. Knowing how much you are off by at a certain speed should confirm.

 

[Brian]

Do you know how much the speed is off by? Those are basically a 32” tire so you probably need 26 or 27 tooth gear. Knowing how much you are off by at a certain speed should confirm.

Have to look into that. TRied to follow a friend today. Looks like only about 5 off. I can deal with that.

 

[Henry3309]

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.

Hey, I also have a Ax15 with my Syncros grinding in 2 and 3, is there a specific version you use for your ATF, say non synthetic vs synthetic.