Hello everyone. I need some help trying to resolve my transmission problem. I recently purchased a 1999 TJ with a 4.0 engine and a 5 speed manual transmission. My problem is when I first start up and get going the transmission shift as it should with no issues. Once the engine and trans get warmer (up to normal operating temp) I can not shift into any gear other than reverse and only reverse with a grinding noise. I just replaced the master and slave cylinder and still have the same problem. The only way I can get it into gear is To shut off the engine. Once the engine is off I can shift in and out of any gear with no problem. Does anybody have any idea what’s causing this issue.
AX-15 manual transmission won't shift once warmed up
- Thread starter Tinker
- Start date
The clutch might be toast.
Try putting it into 1st gear, depressing the clutch, and revving the engine on flat ground. Does the vehicle move? If so the clutch is probably toast. If not it's still suspect, but it could be something else.
There also could be a bad bearing somewhere.
You're lucky in that a brand new (not rebuilt) AX-15 transmission can be found for about $1500. So even if it is a bad transmission, it's not horribly expensive to replace.
Have you tried changing the oil in the transmission? A lot of people here recommend Redline MTL
Try putting it into 1st gear, depressing the clutch, and revving the engine on flat ground. Does the vehicle move? If so the clutch is probably toast. If not it's still suspect, but it could be something else.
There also could be a bad bearing somewhere.
You're lucky in that a brand new (not rebuilt) AX-15 transmission can be found for about $1500. So even if it is a bad transmission, it's not horribly expensive to replace.
Have you tried changing the oil in the transmission? A lot of people here recommend Redline MTL
Thanks. In first gear clutch depressed it doesn’t move. I will check the oil. Does it take 75W90?
These transmissions take Manual Transmission Fluid instead of gear oil.
Vavoline Synchromesh is available at most auto parts stores, and should work.
If you notice a lot of metal shavings when you drain it, the writing may be on the wall for that transmission. Some shavings are normal
As for which fluid, I found this quote from @Jerry Bransford :
“Redline MT-90 for the older AX-15 and AX-5 transmissions but Redline MTL for your newer NV3550 as well as the later NSG370. MTL is a GL4 gear lube just like MT-90 is, it just has a slightly lower viscosity that meets the requirement of NV3550 and NSG370.”
Link:
https://www.amazon.com/dp/B002INX20C/?tag=wranglerorg-20
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Red Line works very well, I tried regular gear oil with very poor results. Switched to Red Line and the grinding stopped. I still need to replace my slush box NV3550 at some point, but Red Line really made a difference. What you are describing is strange to me. As your rig is new and if it was me, I'd take a risk and start with a fluid change. Hopefully oil drains out when you pull the plug.
https://www.amazon.com/gp/product/B002INJ69I/?tag=wranglerorg-20
https://www.amazon.com/gp/product/B002INJ69I/?tag=wranglerorg-20
lostintime
Member
I would say it is probably your pressure plate and clutch that needs replacing. You pressure plate could have been heated badly and warped. Just my 2 cents
It takes a special GL-4 version of a 75W-90, don't fill it with the most commonly sold GL-5 version found on store shelves. Redline MT-90 is a superb GL-4 75W-90 which you can get on Amazon.com.
There are SOME GL-5 75W-90 gear lubes you can find locally that are ok to use. Those that are safe to use will say something like 'Safe for yellow metals' on the back label.
The most commonly found GL-5 gear lubes are not safe for yellow metals which means they're harsh on the transmission's synchronizers that are made from softer yellow metals like brass.
Valvoline Synchromesh manual transmission fluid is GL-4 rated and at 75w90 is the proper viscosity for your transmission. It is reasonably priced and readily available at nearly every auto parts store.
I recently read a series of threads on a sports car forum discussing manual transmission fluids. As expected on any internet forum, there were those preaching that only the high priced racing and specialty brands would do which included a Ford product made in Germany with an MSRP of $26/liter often referred to as unicorn tears. However, some well respected racers reported that Valvoline worked just as well for them and in some cases the 1-2 shifts were noticeably better with Valvoline than with Redline MT90, Redline MTL, or the vaunted Ford XT-M5-QS. Of course there were also Amsoil guys weighing in who are convinced that anything with an Amsoil label works better than everything else on the market.
Best of luck with your repair. Hopefully a fluid change will help, but the symptoms point toward something more.
I recently read a series of threads on a sports car forum discussing manual transmission fluids. As expected on any internet forum, there were those preaching that only the high priced racing and specialty brands would do which included a Ford product made in Germany with an MSRP of $26/liter often referred to as unicorn tears. However, some well respected racers reported that Valvoline worked just as well for them and in some cases the 1-2 shifts were noticeably better with Valvoline than with Redline MT90, Redline MTL, or the vaunted Ford XT-M5-QS. Of course there were also Amsoil guys weighing in who are convinced that anything with an Amsoil label works better than everything else on the market.
Best of luck with your repair. Hopefully a fluid change will help, but the symptoms point toward something more.
The GL-5 ratings ar what most newer gearboxes use. It has an additive to help with foaming. The problem, as previously stated, is that it will eat on certain metals used for synchro's. The GL-4 oils do not have this additive. This according to Pennzoil. When in doubt go with GL-4. But in this case there is no doubt. Use a GL-4 rated oil.
Redline MT-90 is a 75w90 GL-4 gear oil. Many Miata guys think it works better in the Mazda 5-speed than MTL. No reason not to use it.
(BTW, MTL is 75w80 GL-4)
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According to the Red Line website, the MT-90 is not recommended for the NSG-370, only the MTL.
From what I can see 75W80 is the correct fluid, not 75W90.
Mainly want to make sure I’m not going to damage the synchros or gears more than they already are
The difference in viscosity shouldn't hurt anything but you should use what Chrysler recommends for your NSG-370 if you want certainty.
Just recently starting having the exact same problem, just not to Tinker's extent, fine when cold, the hotter it gets the harder it is to shift, reverse grinds, if I shift before I come to a stop I'm OK. come to a stop in neutral and can't get it in gear. Just last weekend, changed the oil to Red Line MTL 75w80. https://www.advanceadapters.com/categories/fluids--lubricants/64/
still have the same issue, going to try bleeding my slave cylinder next. If that doesn't work, sounds like I need to go after the clutch.
Pulled this from another forum, transmission expert. (can't remember where, do remember it being dated)
Mopar offered a specific AX5/AX15 gear lubricant with its own part number. Mopar Manual Transmission Lubricant P/N 04897622AA
The Aisin transmission synchro’s are very touchy, and the issue with the Aisin transmissions is too much lubricity in the lube, the synchro rings will not brake against the gear hubs—and there will be clash on shifts. Too little lubricity is also an issue, the unit will run hot, damage bearings and fail.
I learned years ago to match the OEM ratings for that reason...Sounds like Redline is close. If you do use that lube, make sure there is no clash and that synchro’s shift okay when cold—or hot. Again, my preference would be the OEM Mopar AX5/AX15 or exact equivalent lube if available. Mopar's 75W-90 synthetic gear and axle lube sounds more than adequate, but only if the synchro’s like it. My concern would be the braking action of the synchro rings when cold or hot.
Cannot find the Mopar P/N above anywhere online except for 1 quart at a time,,, expensive!
still have the same issue, going to try bleeding my slave cylinder next. If that doesn't work, sounds like I need to go after the clutch.
Pulled this from another forum, transmission expert. (can't remember where, do remember it being dated)
Mopar offered a specific AX5/AX15 gear lubricant with its own part number. Mopar Manual Transmission Lubricant P/N 04897622AA
The Aisin transmission synchro’s are very touchy, and the issue with the Aisin transmissions is too much lubricity in the lube, the synchro rings will not brake against the gear hubs—and there will be clash on shifts. Too little lubricity is also an issue, the unit will run hot, damage bearings and fail.
I learned years ago to match the OEM ratings for that reason...Sounds like Redline is close. If you do use that lube, make sure there is no clash and that synchro’s shift okay when cold—or hot. Again, my preference would be the OEM Mopar AX5/AX15 or exact equivalent lube if available. Mopar's 75W-90 synthetic gear and axle lube sounds more than adequate, but only if the synchro’s like it. My concern would be the braking action of the synchro rings when cold or hot.
Cannot find the Mopar P/N above anywhere online except for 1 quart at a time,,, expensive!
Something is not making any sense in my mind. When hot, won't go in gear, shut the engine off and it works just fine. Ever try to put your car in gear without pushing the clutch in, impossible, wont even grind. That is exactly how it acts. Is like the clutch is not disengaging. What doesn't make any sense is why only when hot?
The transmission is also being spun by the axle. When in fear and moving the trans spins the tires, so that is a mechanical connection. The clutch breaks the connection to the engine, but when in a driving gear ( 1st, 2nd, etc) the trans is still connected to the rest of the drivetrain. Only when in neutral is that connection broken to the driving gears, though still connected to the output shaft in the trans. Only way to break that is to have transfer in neutral.
I know this is an old thread but did you ever figure out what the cause of your problem was? By the sound of it, I'm experiencing the same symptoms.
babyjeep
New Member
In my many travails of rebuilding my AX15 prior to just getting a new one from Novak...one of the new shift forks had a small burr on it and was contacting the case. 1st wouldn't engage because the bearings were shot.
It's not hard to pull apart... guessing you're going to need to do that because everything is speculation until you open it up.
-Mac
It's not hard to pull apart... guessing you're going to need to do that because everything is speculation until you open it up.
-Mac