Transmission syncros grind when cold

EROCK

EROCK

TJ Enthusiast
Joined
Dec 1, 2018
Messages
183
Location
Arkansas
Hey guys, my 2000 TJ 6cyl 5 speed. Grinds going into 2nd and 3rd. Only when cold. After it warms up. It shifts beautifully. I changed the Transmission fluid 2 weeks ago. I used the Mobil 1 synthetic 10W30 engine oil after reading though some of the forums on here. It did seem to help very slightly but it still grinds when it's cold. Is it worth trying Redline MT-90 gear lube?

Also Ive called some local shops in my "small town" and none of them want to open the transmission to change the synchros they just want to replace it. I have the NV3550. From reading on here my transmission and the ax15 are interchangeable if i want to change it. What's the best transmission option I have or would it be better to just pursue fixing this one? Or do u think the Mt-90 can fix the cold shifting?
 
EROCK said:
Is it worth trying Redline MT-90 gear lube?
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Absolutely. This makes a world of difference, and it may very well fix your cold shifting issues. Try it and report back, I think you'll be surprised.

I will say however that transmissions only last so long. In my experience, transmissions tend to need rebuilds every 200k miles give or take.
 
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X2 to the recommendation to try Redline MTL. Synthetic 10W-30 is only a second-choice acceptable alternative when you can't get the proper GL-5 75W-80 (as MTL is) as the NV3550 and NSG370 transmissions are spec'd for.
 
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My TJR with 220K miles is just starting to make noise, clik gears when shifting. We changed the fluid today, a small pile of filings in the plug. We added Lucas oil additive hoping to extend it a bit but I'm likely looking at a Chrysler exchange this spring.

As everyone says, 200K miles seems to be the expected life.
 
Jerry Bransford said:
X2 to the recommendation to try Redline MTL. Synthetic 10W-30 is only a second-choice acceptable alternative when you can't get the proper GL-5 75W-80 (as MTL is) as the NV3550 and NSG370 transmissions are spec'd for.
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MTL or MT90? I live in the south. It ranges from low teens in the winter to 105 degrees summer.
 
+1 to the MTL, but resign yourself to the fact that your NV3550 will be notchy in cold weather. Mine goes fine into every gear but 2nd when cold—I have to pause briefly between shifts for the first few miles. It was much worse with the mopar fluid however.
 
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Well I got the new MTL in. I flushed the tranny with one quart of MTL poured from the shifter before closing the drain and filling it to the fill plug. I had to pull the shifter to clean it because of a worn and torn boot on top of the shift tower that let dust collect and congeal with the the oil. It wasn't as bad as a suspected. So i got it all cleaned and rebooted. Also got a new inner boot. "I did notice the MTL was less slick and was very grippy (metal to metal) when putting the drain and fill plugs back in. I'm hoping this helps the Syncros grip to the gears better." Anyways; got it all put back together. Like stated above it did not miraculously fix the syncro scratching when cold but it did go away pretty quickly once warmed up. Since it was doing that before, currently I notice no major difference. I will give it a couple of hundred miles and post my results.
 
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EROCK said:
Well I got the new MTL in. I flushed the tranny with one quart of MTL poured from the shifter before closing the drain and filling it to the fill plug. I had to pull the shifter to clean it because of a worn and torn boot on top of the shift tower that let dust collect and congeal with the the oil. It wasn't as bad as a suspected. So i got it all cleaned and rebooted. Also got a new inner boot. "I did notice the MTL was less slick and was very grippy (metal to metal) when putting the drain and fill plugs back in. I'm hoping this helps the Syncros grip to the gears better." Anyways; got it all put back together. Like stated above it did not miraculously fix the syncro scratching when cold but it did go away pretty quickly once warmed up. Since it was doing that before, currently I notice no major difference. I will give it a couple of hundred miles and post my results.
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Thanks for the update so far! I look forward to a more long term update as well.
 
So it finally got cold here in Newer Mexico and the trans started getting a little notchy between 1st and 2nd as they all do. I decided to dump the Royale Purple and put in some Redline MTL. After about 100 miles the MTL looks to be out performing the Royale Purple to a noticeable degree.
 
Well, I'm at 300 miles now. I have seen marginal improvement with the MTL. The syncros still grinds when it's cold but seems to run great once warmed up. I'd say a 10% improvement. Thanks. E.
 
It's getting to be time for a rebuild, that's what your syncros are telling you ;)
 
NV3550s with notchy sychros can go a longgggg time before a rebuild if you're careful. But if you get to that point, I'd swap in a brand-new AX15 as the NV3550s are reportedly hard to rebuild and have few parts available.

My 1–2 shift when cold is a bit rough, but as you said it goes away when warm. Just shift halfway and wait for the synchro to "engage"—you'll eliminate the grind.
 
bromel said:
NV3550s with notchy sychros can go a longgggg time before a rebuild if you're careful. But if you get to that point, I'd swap in a brand-new AX15 as the NV3550s are reportedly hard to rebuild and have few parts available.
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X2 to this, solid advice.

You can get a brand new AX-15 from Advanced Adapters for $1574:
https://www.advanceadapters.com/products/26-ax15--aisin-ax15-5-speed-transmission-new/

The NV3550 can be had, but it's usually around $2500 for a new one.
 
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