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Old 10-20-2011, 04:13 PM   #1
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Transmission helppp

Hi, I have a 1990 YJ manual with 6 cylinders. The transmission has been acting odd for a while but has been acting more weird since the weather has gotten colder. Sometimes, when downshifting into second, it WILL NOT shift into second. If i slow down enough to get it into first it will then shift into second. But this only happens occasionally. Also Ive tried letting the clutch out and pushing it down again a few times and then downshifting. No luck. Before the cold weather there was a little bit of a grind when shifting into third. It would only happen if you dont shift into third slowly and smoothly. In the cold weather, before the car is warm it grinds when shifting into second and grinds when shifting into third. Once it is warm though it returns to the occasional non downshift into second and the grind in third if not shifting smoothly. What could this be? ive changed the transmission fluid and that helped a little bit but it still happens. Thanks!!

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Old 10-20-2011, 05:16 PM   #2
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Bad syncros most likley.

Try double clutching and see what happens.

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Old 10-20-2011, 05:29 PM   #3
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Originally Posted by 95YamJam View Post
Bad syncros most likley.

Try double clutching and see what happens.
That's it.
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Old 10-21-2011, 06:37 PM   #4
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How hard is it to change out the syncros? and if it is a pain how much would it be to take it to somebody to have changed?? Thanks a ton btw!
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Old 10-21-2011, 11:26 PM   #5
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How long has it been since you changed the oil in the tranny?
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Old 10-22-2011, 04:14 AM   #6
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Originally Posted by YJoelKellogg View Post
How hard is it to change out the syncros? and if it is a pain how much would it be to take it to somebody to have changed?? Thanks a ton btw!
If your tranny is stock, it is an AX15. They are common. Mine is a four banger and it has an AX5. I had a third gear synchro that was problematic. As long as I let the revs come down (pausing between gears) it didn't grind. This is going to be my son's jeep and I was pondering teaching him this technique. He doesn't get his license until December. So I went out on Craig's List and looked for a replacement. Found an AX5 from a 2000 TJ close to where I live. For $150.00 I got the transmission, NP231 transfer case, exhaust manifold with O2 sensor, a relatively new clutch and pressure plate and a few other assorted parts that he threw in. I swapped the bell housing over from the original transmission and bolted up the newer one. I now have five solid gears. In the spring, I'm going to crack the case and take a look at the gears. I may put a rebuild kit into it if it looks worth rebuilding.

The main issue with the original transmission is that the rubber parts had begun to deteriorate to the point of letting impurities into the transmission. The shift riser cap was split and allowing road sand in. There was a lot of sand that I cleaned out of the top of the shift riser. God only knows how much got into the transmission. The seals were worn to the point that road sand was in behind both. When I changed the oil after putting a clutch in, it looked dirty. On the newer transmission the oil was still in it. When I drained it in preparation for installation, it was clear and the shifter felt solid compared to the original transmission. The original felt real loose and difficult to tell if it was in the right gate for the gear that I wanted. The newer transmission the gates are well defined and the snap rings on the synchros provide a very positive and distinct click while shifting. I'm guessing the the one from the TJ had been rebuilt within the last 20 or 30 thousand miles. I got a super deal and 5 solid gears. It was a $150.00 gamble. Not so much of a gamble when I got there in person and felt what it was like shifting it. Soon as I did that, I pretty much knew that it would work well based on the "tightness" I felt in the shift pattern and the positive clicking of the snap rings on the synchros.

The two transmissions, even though one came out of a jeep 8 years newer, were identical.
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Old 10-22-2011, 10:39 AM   #7
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I had this problem before changing my transmission fluid and i changed it about 1,300 miles ago tops. So it would probably be easier to get a good used transmission and do a transmission swap?
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Old 10-22-2011, 10:56 AM   #8
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Fill it up with Royal Purple Synchromesh, that stuff does wonders. You will need 4 quarts (wont take but only 25% of the last quart). Give that a try before you start talking rebuilding your transmission or buying a used one.
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Old 10-22-2011, 10:59 AM   #9
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Originally Posted by YJoelKellogg View Post
I had this problem before changing my transmission fluid and i changed it about 1,300 miles ago tops. So it would probably be easier to get a good used transmission and do a transmission swap?
When I bought the YJ last December, I never really got a chance to drive it because the clutch was slipping badly. When I finally got to do the clutch replacement over the summer, I finally got a chance to drive it in late August. It was then that I knew that third gear synchro was really pretty bad. I caught a small grind going into third either up or down shifting. I knew it was only a matter of time before something bad happened. So I started searching around on Craigs's List and to my surprise I immediately found an AX5 from a TJ which was 8 years newer than mine. It bolted right up...no issues. Works like a brand new transmission. There was evidence of a rebuild on this transmission as there was form-a-gasket instead of regular gaskets on the surfaces sealing the two halves to the center plate. I'm guessing by the way it cleaned up real nice with a quick power washing that it was rebuilt within the last 20 or 30 thousand miles. $150.00 for that, the transfer case, an almost new clutch, and a few other assorted parts made the deal really sweet. You never know until you start looking around what you will find.
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Old 10-22-2011, 11:00 AM   #10
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Quote:
Originally Posted by YJoelKellogg
I had this problem before changing my transmission fluid and i changed it about 1,300 miles ago tops. So it would probably be easier to get a good used transmission and do a transmission swap?
I had grinding and difficulty downshifting and still had the same problem after fluid changes until I used RP synchromesh. Shifts like butter now...... that's why I reccomended it above!
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Old 10-22-2011, 11:23 AM   #11
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I will have to try to rp first. Hopefully I will have the same results as you.
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Old 10-22-2011, 09:22 PM   #12
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I will have to try to rp first. Hopefully I will have the same results as you.
Yeah that would be good. Hope for the best
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Old 10-23-2011, 01:35 AM   #13
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Yeah that would be good. Hope for the best
It worked pretty well. there is a little grinding in third still if i shift quickly, but its not nearly as hard to shift into all the other gears. And it got down pretty chilly tonight and boom no grinding either!! great fix!
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Old 10-23-2011, 01:37 AM   #14
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Good! Royal purple is some good stuff.
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Old 10-23-2011, 01:45 AM   #15
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Eventually you will have to rebuild or replace but royal purple just bought you a ton of time. So that you may be able to do the rebuild/replace when you are ready and want to not need to. I have had my RP in my tranny for a while now and it still shifts good......... I haven't driven it as much as I wanted too though damn d35 spider gears!
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Old 10-23-2011, 04:43 AM   #16
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Or, if you can't afford the down time you might keep an eye on Craig's List for a good deal on a replacement like I did. Now I can rebuild the original taking my time to do it rather than having to hurry and possibly make a mistake.
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Old 10-23-2011, 08:59 PM   #17
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thats what im going to do. Ill probably just keep an eye out for a good replacement. Now instead of a transmission being the next step my next step is hard top and hard doors for winter

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