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Discussion Starter #1
The manual transmission (NV3550) on my 2002 Wrangler isn’t quite as smooth as I’d like it to be. It’s nothing serious yet but from time to time it doesn’t go into 1st gear, occasionally gets some grinding and shifting into 3rd can be a bit rough.

I recently changed the fluid with Royal Purple Syncromax hoping that would help the problem but the issue is still present (might even made it worse).

I’d like to try a transmission flush as the next step. I’ve read people flushing the NV3550 transmission with either Kerosene or Seafoam (hydra?) Trans Tune and was wondering if anyone knows if there is an advantage/disadvantages with one vs the other?

After I'm going to drain and refill with manufacture recommended manual transmission fluid Mopar #4874464 in hope that it provides the best results.
 

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Discussion Starter #3
I wouldn't....
Thanks for the feedback. You wouldn't do a flush of either? Do you have any personal experience you can speak from or other suggestions to help the issue? I'm hoping you could elaborate.

I could continue to drive as is but my fear is the issue will only get worse. I'd rather take proactive measures maintaining rather than be reactive once it gets really bad.
 

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I know kerosene was popular with the ax-15 crowd. Haven't heard of it being used in the NV3550, but the internals are very similar. If you do decide to flush it, keep the back axle lifted, wheels off, and just idle through the gears.

If it's not too bad yet, you may want to just try different fluids. I had a notchy/grindy 1/2 synchro, and some catching going into 3rd on the factory fill. Pennzoil Synchromesh made it much worse, and then Redline MTL completely fixed it. These transmissions seem to get a bit picky with age.
 

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Discussion Starter #5
If you do decide to flush it, keep the back axle lifted, wheels off, and just idle through the gears.
I was planning to just lock the parking brake and put the transfer case in neutral to run it through the gears. Would this work as well or is it better to lift the wheels off the ground?

If it's not too bad yet, you may want to just try different fluids. I had a notchy/grindy 1/2 synchro, and some catching going into 3rd on the factory fill. Pennzoil Synchromesh made it much worse, and then Redline MTL completely fixed it. These transmissions seem to get a bit picky with age.
Thanks for the recommendation. I've heard the NV3550 is finicky which is why I decided to go with the original manufactures recommendation of Mopar manual transmission fluid. I fear that if I just refill it won't fix the probably and I'll need to buy yet another round of fluid. I previously added Royal Purple and now purchased the Mopar... the fluid costs are starting to add up.
 

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I wouldn't flush... I would change the oil as needed but I wouldn't operate the transmission with anything but a proper lube in it
 

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Discussion Starter #7
I should probably clarify how I plan to flush the transmission. Based on what I've read I think these steps seem like the best approach….

1. Park the Jeep and place the transfer case in neutral
2. Drain the transmission fluid
3. Inspect magnet for any large debris
4. Refill with a bottle of Seafoam Hydra Trans Tune or Kerosene
5. Lightly run through the gears (slight release of clutch) with transfer case in neutral and Jeep parking brake on
6. Drain Seafoam or Kerosene
7. Add about a quart of transmission fluid
8. Lightly run through the gears again to release any gunk
9. Drain transmission
10. Completely refill with Mopar Manual Transmission fluid

Final step is to hope nothing explodes and the gears shift smoothly again:)
 

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Yep... as I said, I wouldn't..... it isn't going to help and it isn't'd good for the trans....

If you'd ever disassembled a manual transmission..... there just isn't anything in them that is that sensitive that needs 'washed' out.... new lube will immediately dilute and rinse away any remains of the old lube.... at most, change it, and change it again 100 miles later.
 

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Discussion Starter #9
Thanks, I definitely don’t have any experience disassembling a manual transmission so this is all new to me. I suppose I’ll just do another fluid change and hope that fixes it.
 

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MetalMonkey: Transfer case in neutral is a fine alternative to picking up the rear end.

Gottagofast: At least with the ax-15, the immediate predecessor to the NV-3550, I have seen a kerosene or diesel flush wash out grit that didn't make it out with a gear oil flush. Especially if water has ever gotten into the case, it makes a gummy foam that hangs out on the rails/synchros and holds onto metal shavings/dirt. You can run the drained oil through a coffee filter, then pour kerosene/diesel into it and run it through the gears, then filter the (now black) diesel/kerosene and see a bunch more grit in the filter.
 

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I did the kerosene flush on my nv3550 didn't hurt it. Flushed about 3 times before all the gunk came out. The one thing I do recommend is leaving it open for a day to let the kerosene evaporate out. Now the question did help didn't me had bigger issues that was causing my shifting problem.
 
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