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Discussion Starter #1
Hey Everyone,
To start off I'm driving a JKUR 2012 Manual. I'm probably gonna have to get it looked at but, I know you guys will get me on the right track of whats going on.

Issue:
If i'm rolling slowly in reverse and shift to 1st(clutch down) I could ease it in and pull off no issues. Thats a lie with clutch fully down it clanks but not as bad was whats next.
If i'm rolling forward slowly,1-2 miles an hour and try to switch into reverse(clutch fully down) it just grinds gears, while the clutch is still all the way down.. only way I could get into revers is in a full stop.

I've owned numerous manuals so this isn't a me issue.

Second side issue, not as important is what ever blocks you from shifting into reverse while shifting through gears especially on a 4-6 jump, doesn't always stop it from happening.. I'm aware of it so its not an issue, but I'm not comfortable letting my wife drive it cause she will.

Thanks for everyones advise in advance and have a HAPPY THANKSGIVING!!
 

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Discussion Starter #2
I should add that I purchased this jeep a year ago used and this has been the issue since i purchased it.
 

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No body has had similar issues? Just trying to get an idea if this is a big problem or an adjustment problem.
 

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From my knowledge of how transmissions work reverse is not synchronized so if you are rolling it will grind. I don't think I have ever tried to put it in reverse while rolling. I think your transmission is fine. The clunking you hear when you put it in gear is the drive line slap. It's common.
 

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Reverse doesn't have a synchro, pretty much all manuals will grind into reverse if you are moving. Put the shifter into second gear before going into reverse, this will stop the reverse gear from moving and you can go into reverse cleanly.
 

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every manual I have ever owned/driving (mazda/VW/honda/toyota). You have to be at a full stop before shifting into reverse or you will grind.
 

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Actually, I'm pretty sure reverse is synchronized in this transmission. I remember reading this when I bought it and I could shift into it without grinding when rolling.

In fact, I have the opposite problem. When they tried to fix my transmission noise the last go around, they must have assembled something wrong. I can only shift into reverse if i'm rolling (works great in parking lots)... I'm pretty sure my repair sheet mentions the reverse sychro.
 

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Actually, I'm pretty sure reverse is synchronized in this transmission. I remember reading this when I bought it and I could shift into it without grinding when rolling. In fact, I have the opposite problem. When they tried to fix my transmission noise the last go around, they must have assembled something wrong. I can only shift into reverse if i'm rolling (works great in parking lots)... I'm pretty sure my repair sheet mentions the reverse sychro.

If so, try to out it in reverse going 20mph. Let me know how that goes ;)
 

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Some manual transmissions have a reverse synchronizer, some just have dog teeth engagement, others have a sliding idler gear. I think the JK trans does have a R synchro, but in any case you are supposed to stop before shifting into reverse. If you are moving forward, you are asking the friction from the synchro collar against the gear to not only match speed of parts rotating in the same direction like shifting through forward gears, but also change the direction of the gear, countershaft, input shaft and clutch disc which do not immediately stop spinning after you push the clutch down and move into neutral.
 

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OP, also keep in mind that this is more of a truck transmission than a car transmission. It is big and beefy, and kind of clunky. It will not behave the same as a Subaru or Volkswagen. For example, if you try to "drag race" it through the gears, you will find that it doesn't shift as smoothly as a car will. It takes some getting used to.
 

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Discussion Starter #14
Thanks for the posts everyone. I wanted to clarify because I think I explained myself wrong. When I say rolling I mean still coming to a stop say in a three point turn. So as I'm breaking and a second or two from stopping(clutch all the way down) I shift into reverse (clutch still down) so that when I stop, I am set to go in reverse. I'm getting the grinding while shifting at that roll with the clutch all the way down. In my experience this hasn't been a problem in other cars/trucks as long as clutch is all the way down, again super slow speed. Would it having R syncrose or not make that difference?
 

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Thanks for the posts everyone. I wanted to clarify because I think I explained myself wrong. When I say rolling I mean still coming to a stop say in a three point turn. So as I'm breaking and a second or two from stopping(clutch all the way down) I shift into reverse (clutch still down) so that when I stop, I am set to go in reverse. I'm getting the grinding while shifting at that roll with the clutch all the way down. In my experience this hasn't been a problem in other cars/trucks as long as clutch is all the way down, again super slow speed. Would it having R syncrose or not make that difference?
Reverse is NOT synchronized in this or almost any manual transmission. You should NOT shift into reverse unless you are at a complete stop. Some transmissions tolerate this better than others, but it is NOT good for any of them. You are killing it slowly by doing this.

1st gear, OTOH, is synchronized and you can shift there while moving slowly... BUT...... remember the job of the synchronizer is to match the input and output shaft speeds so the gears can cleanly mesh together. The greater the difference, the more the syncro has to work and the faster it will wear out. When shifting into first while moving, generally that speed difference is the greatest it ever is.... Personally, I do not shift into first unless I'm at a complete stop. There is no real need or advantage to doing this, so why do it?

You can ignore this advice or not.... You should know that I've never had to replace syncrhos or rebuild a manual tranny due to wear in my entire life and some I've driven for well over 200,000 miles. I've owned over a dozen manual vehicles. All but one, in fact.
 

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I see a reverse synchro on the parts list MOPAR Reverse Synchronizer, NSG370 6-Speed Manual Transmission - 5134498AA

I've rebuilt several different manual transmissions with reverse synchronizers as well. But that doesn't mean it's designed to allow shifting into R while the vehicle is moving forward.
I stand corrected..... Part 58... thanks for setting me straight!

Daimler NSG370 6-Speed Transmission Parts

That said, I would still not shift into R with the vehicle moving...
 

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Discussion Starter #19
Appreciate the info! Gives me a better understanding of what's going on. I rarely do it, but that's when I noticed it. Will check fluid as well.
Thanks again!
 
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