NO down shift ax15 - JeepForum.com
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post #1 of 13 Old 11-22-2021, 02:54 PM Thread Starter
tommbstone
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NO down shift ax15

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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post #2 of 13 Old 11-22-2021, 03:50 PM
calisk8er1080
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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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post #3 of 13 Old 11-22-2021, 03:55 PM
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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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post #4 of 13 Old 11-22-2021, 05:58 PM
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check the fluid level.
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post #5 of 13 Old 11-22-2021, 06:53 PM Thread Starter
tommbstone
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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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post #6 of 13 Old 11-23-2021, 12:23 PM
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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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post #7 of 13 Old 11-23-2021, 03:56 PM
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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.

If you cannot fix it with a hammer then it has to be an electrical problem.
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post #8 of 13 Old 11-23-2021, 07:49 PM
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Quote:
Originally Posted by timatoe View Post
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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post #9 of 13 Old 11-23-2021, 10:18 PM Thread Starter
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Quote:
Originally Posted by calisk8er1080 View Post
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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post #10 of 13 Old 11-24-2021, 07:33 AM
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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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If you cannot fix it with a hammer then it has to be an electrical problem.
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post #11 of 13 Old 11-25-2021, 05:52 PM
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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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post #12 of 13 Old Yesterday, 06:48 PM Thread Starter
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Quote:
Originally Posted by timatoe View Post
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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post #13 of 13 Old Yesterday, 09:30 PM
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Probably made its way under water at some point.

Quote:
Originally Posted by George Orwell
We sleep safe in our beds because rough men stand ready in the night to visit violence on those who would do us harm.
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