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Discussion Starter · #1 ·
My brother in law just bought a yj 90
Anyway the only thing wrong is it shifts up fine but does not down shift.
Its this a problem with the shifter lever getting old and sloppy? Or is it in the transmission?
 

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Probably the syncros going bad. Pretty common. Has he tried double clutching while downshifting? If he does, and it shifts smooth, it's syncros. If it still doesn't, there's something else going on.
 

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Hard to say for sure but could be worn synchros. Although that should affect upshifts as well. My AX-15 lost all the synchro rings as shiny brass flakes when I changed the fluid in it. Since I grew up driving a few manual transmissions without synchronizers I just tailor the way I shift up and down to a combo of road speed, rpm, and whether to make the shift snappy quick or slowly.

For example downshifting from 3rd to 2nd is at the speed I turn corners in the neighborhood and is slow with a slight pause in the neutral gate. Some upshifts are similar while others have to be snappy to go smoothly (and quietly).
 

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Discussion Starter · #5 ·
I will tell him to check the fluid first or at least change it.

But its only down shifting poorly or not at all. Its like it wont go in unless its moving slow. Up shift from 1-2-3-4 etc is perfect. It goes into revers perfect too. His shifter lever is pretty sloppy but that's probably not it.

Also does the ax5 and ax15 shifter inter changeable?
 

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The hose from the clutch master to the slave gets dry and cracks allowing the hose to expand when trying to engage the clutch. When mine did this, I'd sometimes get a slight grind up shifting, but it was near impossible to down shift.

Synchros are also a likely culprit.
 

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Some folks have had troubles with the trans input shaft being rusty and the clutch disc binding on it which can cause it to still turn because it still makes contact with the flywheel. This happens more on a vehicle that has sat at times without driving it much.

How does it shift when sitting still with the engine running? Put it in neutral and let the clutch out. Push the clutch in and immediately try to shift it in gear including reverse. This is a spin down test and it proves or disproves if the input shaft of the trans is still turning due to a clutch issue. If it isn't this then it is most likely bad synchros.
 

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The hose from the clutch master to the slave gets dry and cracks allowing the hose to expand when trying to engage the clutch. When mine did this, I'd sometimes get a slight grind up shifting, but it was near impossible to down shift.

Synchros are also a likely culprit.
Yep, bad hydraulics would be my second guess.
OP, does it want to move a little bit at a standstill, foot off the brakes? That would be a good indication that the throwout bearing isn't getting all the pressure it needs.
 

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Discussion Starter · #9 ·
Yep, bad hydraulics would be my second guess.
OP, does it want to move a little bit at a standstill, foot off the brakes? That would be a good indication that the throwout bearing isn't getting all the pressure it needs.
It drives fine. I dove it for him today. Just doesn't like to down shift from 4 to 3rd unless moving around 30 or less.

Clutch feels good, throw out bearing seems good.
I told him change his fluid and if its still same its probably time to send to a rebuild shop.
 

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Now that you have it isolated to just a 4-3 downshift it certainly sounds like a failed synchro. Changing the fluid has a slight chance of improving it and prolonging the inevitable teardown.

As far as the fluid is concerned. All the Chrysler information says to use GL-5 even though I have read on different forums that there is a TSB stating to use GL-4 or if you go into any Chrysler dealer they will give you GL-4. This is not true that Chryslers info is updated and if it was it got lost when they became FCA or something along the line. A Chrysler dealer still shows GL-5 as the lube of choice. Some GL-5 gear oil is not yellow metal safe and others claim to be. What oil you choose to use from here on out is very widely debated and IMO there is a lot of mis information and it is difficult to sort it out. Valvoline makes a product that is supposed to be Yellow metal safe. Many others have used red line IIRC.
 
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Vavoline and Penzoil both make a synchromesh fluid that works, Redline MT-90 is a great choice as well.

Tons of guys run motor oil and I've heard there's supposedly a TSB on that as well, though I've never seen it (but I'm also not in the business).
 

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Discussion Starter · #12 ·
Vavoline and Penzoil both make a synchromesh fluid that works, Redline MT-90 is a great choice as well.

Tons of guys run motor oil and I've heard there's supposedly a TSB on that as well, though I've never seen it (but I'm also not in the business).
We changed the gear oil in it. It was some nasty half water have milk ****.
New gear oil
New ATF in T-case

seems to be much better. Probably just kicking the can down the road on a rebuild. that's on him.

thx for the help
 

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Yikes, might want to run the fresh fluid for a few days of driving and then do it again if it was that bad. And anything else with fluid that could have been under water like diffs

Sent from my SM-G991U using Tapatalk
 

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Yeah run it for a few days at highway speeds for 20 minutes then drain again. Shifting will be a lot better and maybe not damaged anything. Anytime its hard shifting something is wrong. Manual trans are tough but when they should signs of issues, start looking sooner not later as its sometimes a simple fix
 

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Not to be the buzz kill here but milkshake and water can be the death quickly. Sure, change out the fluid again and try it but keep expectations low. Milkshake destroys stuff quickly. What I am saying is change the fluid again, go for a road test and things seem ok but yet it does not make you eligible for a cross country tour. Milk shake and water are the worst destructors ever to lubricants. Bad JUJU.
 
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I had really bad worn out synchros, and had the same issue, even after I changed the fluid.

Some tips, look on here for a fluid, IIRC, the manual has a non safe fir Synchros fluid printed.

I drove for a loooooong time with bad synchros, lol. Like 3 years. It would sometimes totally lock me out from being g able to downshift. It was rare, but around 40 MPH. I would shift all the way to 5th, and then it would allow me to go back to 3rd? And be able to go to any gear after that.

I say 3rd with a question mark because it's been a while. But if it locks him out from going down, go all the way up to 5th, and then monkey around with it. Saved me a few times on a busy street.
 

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Discussion Starter · #19 ·
I had really bad worn out synchros, and had the same issue, even after I changed the fluid.

Some tips, look on here for a fluid, IIRC, the manual has a non safe fir Synchros fluid printed.

I drove for a loooooong time with bad synchros, lol. Like 3 years. It would sometimes totally lock me out from being g able to downshift. It was rare, but around 40 MPH. I would shift all the way to 5th, and then it would allow me to go back to 3rd? And be able to go to any gear after that.

I say 3rd with a question mark because it's been a while. But if it locks him out from going down, go all the way up to 5th, and then monkey around with it. Saved me a few times on a busy street.
Thank you I'll let him know
 

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rive it for 10 days and when I get back from Arkansas work trip we can dump it and put in better gear oil.
I have used 10W-30 for 10 years+ in AX15s
That was the chryco solution to early synchro failure with GL5

I tried pennzoil synchromesh and didn’t like it. Shifted poorly for me. I was going to change it but it started to growl. I changed it anyway back to 10-30. Lots of flake in the fluid. I don’t think pennzoil caused it but it blew 600 miles later. The fact it was fine for 25,000 miles and was still clear every time I changed or checked it, and then it made noise and blew a few thousand miles or less on pennzoil sorta soured me.

I’d just run 10W-30 walmartha dinosaur oil in it like was recommended by Chrysler and change it regularly like a good boy. Don’t run the high mileage stuff in it. Save that for your motor only.
 
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