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


Bryan

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I have synchro problems in the 95 YJ that I just purchased. It grinds mostly when shifting into 3rd and 4th. Has anyone had experience improving synchro shifting problems by using different gear lube weights or additives? I believe there is hope, because when first starting out and the transmission/transfer case are cold, I have very little grinding issues. So, the colder thicker lube makes a difference. Thanks in advance for the help Bryan
 

jeepjoe43

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Fluid isn't going to do it.
Sounds like the clutch isn't disengaging completely and you're just on the bleeding edge of that.
The clutch system probably just needs to be properly bled.
 
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Bryan

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Fluid isn't going to do it.
Sounds like the clutch isn't disengaging completely and you're just on the bleeding edge of that.
The clutch system probably just needs to be properly bled.
Oh, OK appreciate the information. I just put a new clutch in it when I installed the remanufactured engine,. I didn't replace the clutch slave cylinder, but it sounds like I should have bled the old clutch anyway. I'll give that a shot.
 

jeepjoe43

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It's always a pain to bleed the clutch and it's common to do it several times. One little bubble getting back into the slave can mess things up.
You are right, it is a pain and takes multiple attempts.
Not a fan of hydraulic clutches, but it's got what it's got.
I recently read somewhere that the way to bleed the clutch system is to force fluid into the bleeder (requires a hand pump).
Then the trapped air is pushed into the reservoir.
I have a very nice pump kit I bought for doing brakes, but had't tried this method, yet.
While mine is disengaging, it still doesn't feel right.
 
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machoheadgames

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I wouldn't bother bleeding a clutch linkage on a 94 or 95, it never goes properly in my experience. I just buy new assemblies. That said, usually you'll have issues in all the gears if that is the problem. If it's in 3rd or 4th only then you probably have issues specific to the transmission.

The best fluid I have found is Redline MT90, but it's only fluid, it isn't a miracle worker and won't fix a transmission suffering from broken or worn out parts.
 

Gary747

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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.
 

Gilaguy23

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Your not the first Ive read about using ATF in a AX15. Like any oil thread one can get numerous arguments as to using this or that for longevity and best shifting. The 30wt in the T case recommended by the rebuilder is a first to me though. I run Castrol HD 30wt in my AX5 and have used 90wt GL4. With the 90 its near impossible to shift into 1st when its in the winter here in AZ. Once its warmed up it shifts OK in every gear. You could try a 30wt and see how it does. If its still grinding away its likely the syncros going south. Todays gear, trans oils,diff oils, atf's, and the dozen types of coolants have become pretty much a mystery deciphering what you need. your basic MT-1 designated GL5 "gear oil" is NOT what you want to run in the trans and unfortunately that's what most chain auto parts stores sell. Places like Summit and Jegs do sell GL-4 type syncro OK lubes for these type trannies.
 
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Bryan

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I wouldn't bother bleeding a clutch linkage on a 94 or 95, it never goes properly in my experience. I just buy new assemblies. That said, usually you'll have issues in all the gears if that is the problem. If it's in 3rd or 4th only then you probably have issues specific to the transmission.

The best fluid I have found is Redline MT90, but it's only fluid, it isn't a miracle worker and won't fix a transmission suffering from broken or worn out parts.
Thanks for the info. I was actually thinking along those same line. If beading the brakes is that big of an headache that most report, then save the headache an just put a new one in. Thanks for confirming that.
 
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Bryan

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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.
Wow, thanks for sharing your experiences with this issue. I think I'll try the simplest fix first and run ATF (before other recommendations) to see if that makes the difference. Do you recommend that I use Mopar ATF, or do you think it doesn't matter the ATF brand?
 
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Bryan

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Your not the first Ive read about using ATF in a AX15. Like any oil thread one can get numerous arguments as to using this or that for longevity and best shifting. The 30wt in the T case recommended by the rebuilder is a first to me though. I run Castrol HD 30wt in my AX5 and have used 90wt GL4. With the 90 its near impossible to shift into 1st when its in the winter here in AZ. Once its warmed up it shifts OK in every gear. You could try a 30wt and see how it does. If its still grinding away its likely the syncros going south. Todays gear, trans oils,diff oils, atf's, and the dozen types of coolants have become pretty much a mystery deciphering what you need. your basic MT-1 designated GL5 "gear oil" is NOT what you want to run in the trans and unfortunately that's what most chain auto parts stores sell. Places like Summit and Jegs do sell GL-4 type syncro OK lubes for these type trannies.
Thanks for sharing your issues and recommendations/fixes. The 30wt may be the answer.
 

machoheadgames

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Thanks for the info. I was actually thinking along those same line. If beading the brakes is that big of an headache that most report, then save the headache an just put a new one in. Thanks for confirming that.
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.
 
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Bryan

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Your not the first Ive read about using ATF in a AX15. Like any oil thread one can get numerous arguments as to using this or that for longevity and best shifting. The 30wt in the T case recommended by the rebuilder is a first to me though. I run Castrol HD 30wt in my AX5 and have used 90wt GL4. With the 90 its near impossible to shift into 1st when its in the winter here in AZ. Once its warmed up it shifts OK in every gear. You could try a 30wt and see how it does. If its still grinding away its likely the syncros going south. Todays gear, trans oils,diff oils, atf's, and the dozen types of coolants have become pretty much a mystery deciphering what you need. your basic MT-1 designated GL5 "gear oil" is NOT what you want to run in the trans and unfortunately that's what most chain auto parts stores sell. Places like Summit and Jegs do sell GL-4 type syncro OK lubes for these type trannies.
Sorry to bug you again on this subject. I'm still somewhat confused regarding these different recommendations. It was stated a couple of threads above that "Using the lighter weight oil in the AX15 helps the synchronizer issues". why is that? With my transmission problem, when its cold in the mornings it shifts fine. therefore, I would think the heaver wt. fluids i.e. 90wt GL4 would work best in my situation. Your thoughts?
 

machoheadgames

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Sorry to bug you again on this subject. I'm still somewhat confused regarding these different recommendations. It was stated a couple of threads above that "Using the lighter weight oil in the AX15 helps the synchronizer issues". why is that? With my transmission problem, when its cold in the mornings it shifts fine. therefore, I would think the heaver wt. fluids i.e. 90wt GL4 would work best in my situation. Your thoughts?
You would be perfectly fine with 75W90 GL4. That is the official spec from Aisin Warner, the transmission manufacturer, and it has always worked perfectly for me. Chrysler wrote the owner's manual incorrectly and told people to use 75W90 GL5. After Chrysler realized their mistake, they put out a technical service bulletin to dealers to fill the transmissions with 10W30 motor oil because 75W90 GL4 is rather rare and not something dealers normally keep in stock (and probably not a fluid that Mopar even makes, which is what they use for virtually all fluid changes). 10W30 engine oil and 75W90 gear oil are almost the same viscosity, because they are measured on different scales. The difference really comes down to the additive package, and the fluids like MT90 are made for transmissions, and 10W30 are made for engines.....one might not contain the ideal additive package for the other. Engine oil likely doesn't have as good of an additive package for a transmission as GL4 transmission fluid itself would. No way to truly confirm that, but I'm going to rely on the transmission manufacturer's recommendation, not Chrysler or internet folk. Chrysler messed it all up to begin with anyways, so why would I trust their advice anyways? I at least wouldn't choose to listen to them when the transmission builder advises differently.

GL5 definitely did not shift well in my transmission. Not sure what weight it was because it was in there before I bought the Jeep, but it was definitely some form of GL5 due to the smell. GL4 is what is officially called for by the transmission manufacturer, I still don't understand why people try to dwindle from it. I have had a decent amount of below freezing days over the years and it always shifted perfectly. I have also never seen somebody else install MT90 and have bad results from it, it's always been an improvement.

Virtually all shifting issues I've seen people have stem from running GL5, synchro damage from long term use of GL5, and stiff old shifter boots. New rubber boots are nice and soft, and work well. Leather boots are a good option too.
 
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Bryan

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Wow, thanks again for taking the time to explain. Someone on this thread recommended Red Line MT-90 GL-4, so I think I'll go that route.
What would you recommend for my Transfer Case? Thanks
 

machoheadgames

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Wow, thanks again for taking the time to explain. Someone on this thread recommended Red Line MT-90 GL-4, so I think I'll go that route.
What would you recommend for my Transfer Case? Thanks
Lol, I think that was me who recommended MT90 to begin with.

But anyways, for the transfer case I just run the specified ATF. Never have heard of running 30wt in there, but sounds like it's working fine for Gary, I can't speak to that. No clue why the place he got it from requires 30W for warranty purposes though. I'm personally tearing down my transfer case and rebuilding and doing a new SYE, and will be filling it back up with the called out ATF when done.
 

machoheadgames

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Thanks again! What is the specified ATF? or what to you recommend?
Well, the official one in the manual is ATF +3, but that's outdated and the one to use in modern day would be +4. However, they only list the + portion because the automatic transmissions require it. Transfer case is not critical, so they list them the same to make it easier on dealers, etc to fill them all up with the same stuff. Any ATF you see will be fine, I plan on grabbing random stuff at the parts store or walmart when I need to fill mine.
 

Gilaguy23

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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.