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Old 06-27-2010, 12:11 PM   #1
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2nd Gear Syncros

Hey guys,
Here's the situation: My 2nd gear grinds when I try to downshift into it. Normally only when decreasing from a higher speed (say 40). Now it grinds when the clutch in or transmission disengaged. Sounds as if the clutch IS NOT in but it is. This is the only time it happens. Do you guys think this is my syncros going out? Anyone else experience this before.... doubt I will be able to fix it myself so how expensive do you think it will be?

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Old 06-27-2010, 12:17 PM   #2
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There is no reason to downshift into second at 40 mph. I think the trans is spinning too fast for the syncros to line up.

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Old 06-27-2010, 12:21 PM   #3
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Before spending lots of money on it, try changing the tranny oil. Use what the mfgr specifies, not the phoney knock offs parts houses have that claim they meet the specs.
Best to get the MoPar stuff right from the dealer specifically for your trans. Yes, it does make a difference.

It's only slightly more than a quart - so it's not a huge investment.

The oil itself doesn't wear out, but the additives in it eventually evaporate. The knock-offs work for about a year, then you have to do it again.

Problems with sticky synchros usually start with 2nd gear.
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Old 06-27-2010, 01:31 PM   #4
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Quote:
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It's only slightly more than a quart - so it's not a huge investment.
The Manual tranny on the TJs holds just over 3 quarts.
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Old 06-27-2010, 02:22 PM   #5
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Thanks, I stand corrected - I thought this computer was supposed to correct my typos.

But still you shouldn't have to refinance your house to afford it.

Not a bad idea to flush it either.

Put the T-Case in neutral.
Drain the trans.
Add a quart of kerosene to it (same stuff as WD-40.)

Start it, let it idle - don't rev it. Shift up and down through the gears 3 or 4 times.
Do not run it for a long time, and of course DO NOT DRIVE IT!

Shut it off and drain it.
Look at all the shavings that came out! A little bit of tiny particles like metal dust is normal. But big pieces indicate problems.

Use a magnet to pull out the steel filings - the ones left are from the brass blocking rings.

Let it drip until it stops dripping.

Fill it with new.

Of course if something is broken inside it won't help, but in most cases a flush and fill does wonders.
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Old 06-27-2010, 02:36 PM   #6
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Before spending lots of money on it, try changing the tranny oil. Use what the mfgr specifies, not the phoney knock offs parts houses have that claim they meet the specs.
Best to get the MoPar stuff right from the dealer specifically for your trans. Yes, it does make a difference.

It's only slightly more than a quart - so it's not a huge investment.

The oil itself doesn't wear out, but the additives in it eventually evaporate. The knock-offs work for about a year, then you have to do it again.

Problems with sticky synchros usually start with 2nd gear.
He didn't specify what year jeep he has, if it's pre 2000 Mopar discontinued the AX 15 lube and superceded it with Mopar motor oil.

I know you think Redline is a "home brew" rrich, but that is what I use in me '99 tranny (Redline mtl or mt90.) It has proven itself as a very good lube for the AX15.
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Old 06-27-2010, 04:54 PM   #7
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Lots of things will work - with enough experimenting you could probably use peanut or olive oil along with some type of modifier. But when the designers design the transmission they specify the co-efficient of friction needed. The additives keep that friction stable.

Synchronizers are friction devices, so they need something that lets them have friction, but the bearings need slippery lubrication - it's a critical balance between them.

Adding food coloring, or killing a sheep at midnight on a moonless night really doesn't add anything - unless of course you are a believer.

I'd rather trust the designers to know what works the best, rather than a psychic.
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Old 06-27-2010, 05:19 PM   #8
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I'd rather trust the designers to know what works the best, rather than a psychic.

That's funny stuff right there !
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Old 06-27-2010, 06:01 PM   #9
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Quote:
Originally Posted by Atthehop View Post
There is no reason to downshift into second at 40 mph. I think the trans is spinning too fast for the syncros to line up.

I agree with this statement right here...I'm usually out of 2nd gear at 20mph running approx. 3000 RPMs (might be closer to 2000 but it's definitely higher than a good cruising speed).
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Old 06-27-2010, 06:02 PM   #10
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Lots of things will work - with enough experimenting you could probably use peanut or olive oil along with some type of modifier. But when the designers design the transmission they specify the co-efficient of friction needed. The additives keep that friction stable.

Synchronizers are friction devices, so they need something that lets them have friction, but the bearings need slippery lubrication - it's a critical balance between them.

Adding food coloring, or killing a sheep at midnight on a moonless night really doesn't add anything - unless of course you are a believer.

I'd rather trust the designers to know what works the best, rather than a psychic.
I'm not going to get into a verbal boxing match with you rrich. Did you read what I said ? Chrysler DISCONTINUED the AX15 lube. They have to sell you something, so I guess they thought MOTOR oil was the next best thing. Do you really think it's the exact same formula as the discontinued lube ? Check it out. Go to the dealer and tell them you need manual tranny lube for your '99 4.0. The guy will get on his computer, scratch his head and say "Huh..? err ..it says I should sell you motor oil". Been there done that. Maybe I can find some old stock AX15 lube , put it in my motor for improved performance.

Then again the heads at Chrysler may have had their crystal ball tell them something we don't know...
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Old 06-27-2010, 06:30 PM   #11
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I'll try it.
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Old 06-27-2010, 06:49 PM   #12
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I'll try it.
I assume you mean you'll go to the dealer and see what they try to sell you. I agree with you about using factory lubricants if available. One of the dealers I went to was your hometown dealer, Yucca Valley Chrysler/Jeep. The other was Orange Coast in Costa Mesa. Both parts guys seemed a bit puzzled with the motor oil recommendation, and both told me the AX15 fluid was discontinued.
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Old 06-27-2010, 07:14 PM   #13
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Just to throw it out there I also got many reccomendations from others on this forum and other forums to just use plain old motor oil....idk
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Old 06-28-2010, 12:29 AM   #14
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first off 40 might have been exaggeration. I never intended to let out the clutch near that speed. I simply meant that if I was preparing for say a right hand turn and was decelerating from 40 and knowing I will be in 2nd coming out of the turn I would put the transmission into 2nd and when i was down to 10 or 15 and ready to accelerate again i would engage the transmission. But all in all, thanks a lot guys. I will try the flush and fill. That is a sticky situation with the oil... but I guess today motor oil is pretty well engineered.
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Old 06-28-2010, 01:20 AM   #15
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I had the same issue with my AX-15 since I got a little over a year real bad when it was cold here, the oil I drained was gear oil but nice and clean, I swithched it to Mobil1 full syn in 10/30 flavor and it has never shifted nicer. Granted I have 140000 miles on mine so it's not perfect but leaps and bounds better than what it was.
Oh and rrich greetings from down the 247!!! if you see a green flattie equipped ride with Leds in town that's me!!
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Old 06-28-2010, 08:29 AM   #16
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Devil - are you a participant in HiDesert4x4?
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Old 06-28-2010, 09:12 AM   #17
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No sir I keep missing the meetings at Carrows right? Since I'm not working at the moment I might be able to go now, when's the next one?
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Old 06-28-2010, 09:15 AM   #18
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first off 40 might have been exaggeration. I never intended to let out the clutch near that speed. I simply meant that if I was preparing for say a right hand turn and was decelerating from 40 and knowing I will be in 2nd coming out of the turn I would put the transmission into 2nd and when i was down to 10 or 15 and ready to accelerate again i would engage the transmission. But all in all, thanks a lot guys. I will try the flush and fill. That is a sticky situation with the oil... but I guess today motor oil is pretty well engineered.
When I downshift into 2nd like you are doing it does not glide right in so I just hold slight pressure into 2nd until it engages and then let the clutch out if the speed is low enough, if not I shift it into 3rd. If you force it it will grind since the syncros are not aligned. You can always double clutch but it will most likely gring too.
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Old 06-28-2010, 09:35 AM   #19
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First Thursday of every month, 7:00 PM, Carrows
And usually at least one good off road run every weekend. So that means next Thursday eve.
We usually get 20-30 at each meeting - A very friendly group - unlike many other clubs.
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Old 06-28-2010, 09:46 AM   #20
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I have heard I worked with Ken Gunn at the hospital for a long time and he always had good things to say, would love to have a group to wheel with... So next Thurs it is!!

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