Using an NSG370 6-speed out of a JK

[Darkwing327]

I have questions on the 6-speed hoping that someone with good knowledge can confirm.

My TJ is a 2005 with a 4.0 6-speed that shifts beautifully 98% of the time. Only time it gives me grief is trying to get into reverse while actual off roading in 4LO. Seems like after being jostled around, it gets cranky and takes some finesse to get to stay in. At the moment it is a minor annoyance, but things hardly ever self repair, so I am looking for future ideas for when I have to fix. I have put in Redline MTL and checked all motor/trans mounts, as well as shifter clearances etc. It is the shift fork issue that was common to these years.

Here's what I know:

1. The shift fork is the same for all years of NSG370s as far as I can surmise.
2. The cases/bellhousings are different for all motors.
3. I am in Canada, there is only ONE used trans in the country on the Auto wrecker network and it has 50k more on it that mine so a no go
4. I cannot find anyone who rebuilds these as a core swap unit in Canada
5. The 2006 reverse update kit from OEM is $1500 currently...contains updated reverse gear and shift assembly.
6. No problem mechanically doing the rebuild myself.

So, with all that, here are my questions.

1. Are the guts all the same across the years? Can I buy a trans from a newer JK which will have all the updated parts inside and swap out? (this is my first option if feasible as there are lots of options and low mileage units around for less than the 2006 upgrade kit)
2. If I can use the guts from a newer trans, does anyone have insight on if there are any years/models to avoid?
3. Last option, has anybody used the shift forks available from STX Gear? Seems to be the only readily available aftermarket unit available here.

Thanks much for your help. Darren

 

[Steel City 06]

I reached out to Zumbrota a while back to see about changing gear ratios in the TJ to ones used in the Mercedes SUVs or the overdrive in the late JK. Their thought is that the internals would not be compatible.

Here is the quick summary:
https://wranglertjforum.com/threads/nsg370-gear-ratios-in-4-0-2-4-3-8-3-6-liter-engines.23477/
Since that post I have learned that the “wide ratio” option came in certain overseas Mercedes SUVs, and not in the 4 cylinder TJs.

You may be able to get some parts from the early JKs to work, but IIRC the input shaft is a different length.

Have you checked if RockAuto will ship a Zumbrota reman to Canada? You might also check with individual remanufacturers.

 

[Darkwing327]

Awesome info! I checked and found out two things. One, yes they will ship a reman unit to Canada, but 2k for the core, which to be honest I would like to keep for as I say, my trans is near perfect...just pooched the shift fork by missing 6th and hitting reverse once. Hadn't done it since I bought the Jeep until last year. I know the exact moment I did it which pisses me off LOL.

However I never thought to use Rock Auto to check part compatibility. Randomly I selected a 2015 JK and looked up different parts - input shaft, rebuild kit, synchros, gears...ALL the same numbers used for the 2005!!!

I am going to dig further down this route via part numbers and double check a few things with my buddy at the dealership as well so see if everything seems to jive on his end too.

Thanks again for the suggestion

 

[retlawblackhawk]

Following . I also have an 05 6 speed and it gives me issues when cold in reverse and 2nd, once it warms up for about 5 min it’s golden. However planning for the future so am interested in the JK option as well.

 

[Bowhunter]

I looked into this pretty deep when I had an 05 with the six speed. From what I saw you have a few options (rebuild by a trans shop, remanufactured by someone like high gear ($1900), or getting a bell house adapter from advanced adapter and putting in a AX15 transabiut $2k).

I was leaning toward installing one of those remanufactured units but then the previous owner wanted the Jeep back so I sold it back to him

from what I read, you are unable to use NSG370 from a JK because it doesn’t bolt up to the 4.0 and the bell house is integrated into the NSG370 transmission.

good luck! I spent many hours reading and many hours of sitting on the phone talking to transmission people trying to find a solution but there isn’t much on the topic

 

[Darkwing327]

from what I read, you are unable to use NSG370 from a JK because it doesn’t bolt up to the 4.0 and the bell house is integrated into the NSG370 transmission.

Yes, that is correct, the bellhousing is part of the case and is engine specific. What I am pondering is if the guts are the same across years. Therefore if you were to buy a low mileage used assembly from a late model unit, could you pull the innards out (that include all the newest updates) and use those in the 2005 case. So far all my parts cross referencing shows that 2005 to 2015 all use the same current part numbers. Will keep digging.

 

[Darkwing327]

Ok, so here's an update that shows promise, but also a big MAYBE as a caveat.

I have checked part numbers for shift fork assembly, 1st to 6th gears and reverse, rebuild kits and a few other bits for 2005 4.0, 2010 3.8, 2015 3.6. The listings show all the guts using the same numbers. Oddly, when I go to 2017 or 2018, I find 1st, 2nd and reverse being listed as the same, but no listings for higher gears which is odd. That is for the 3.6, have no idea on the 2.0.

What shows promise is that if I want a used 4.0 unit, there is only one used one in Canada at $3k, with more mileage than what I have. But if the others will work, there is a 2017 for $600, a 2010 with 20,000km that comes with transfer case for $1000. So lots cheaper and more readily available to be sure IF you have the ability to do the part swaps.

Here's the caveat in case somebody tries this and it doesn't work out. I am not actually going to rip into my tranny at this time...perhaps not for years...as it is working well enough to just be a minor annoyance one time a week. This is only paper research and not actually hands on data. I was hoping someone who rebuilds these might have chimed in.

Where I am at is that I am confident enough to buy the lowest mileage/best price unit I can find and sit on it...might be that 2010 if I can verify mileage, then I would have spare TC bits too. I just wanted to add this final data to the post for reference in the hopes that if someone looks at this, takes a chance on a later model unit parts swap and it all does or doesn't work out, they could add to the discussion for future reference for others.

Cheers
Darren

 

[TX tj]

Thanks for taking the time to share your research, Darren. Any updates since then?

 

[Darkwing327]

Hey TX...that is crazy timing you asking about this. Yes, my brand new AX15 plus install goodies will be in my hands tomorrow morning!

My 6 speed is just the same as it was previously. Just the occasional difficulty getting it into reverse in 4LO...but I have got it down to a science now, where a 4th gear shift first with the clutch in allows it to go into reverse nicely. Again, this is only a very occasional problem. Tranny makes no noise and works fine otherwise. It has been in 4LO for over a month since the snow arrived and of the hundreds of forward and backs I have done since then, can only think of it doing it twice...and they were literally two second 4th to reverse shifts to fix.

So why did I buy an AX-15? I don't know...looked like a fun project...just like the stupid ARBs and on board air that I put in. And the cooled and heated seats...and the rock rails...and LOL Been retired a long time, so I just buy things to keep myself entertained...especially now that we have been held close to home for the last couple of years. Just wiring up a 30 panel solar system for the house...but I digress!

On to the switch to AX-15. My buddy has a late 90s jeep with 37s, more suspension goodies underneath than my Jeep is worth, 8.8, C2 front axle, ARB, etc, etc. He has beaten his jeep like a rental for 15 years...blew the original rear diff to smithereens, ate all the teeth off the 30, sheared his front control arms off...twice. And, wait for it...rail slid it down a 100' fallen tree (not on purpose) and folded up the rear driveshaft. It has 240,000ish kms on it with the original 5 speed and t/c and they both sound and shift great. So I did some research on the Advance Adapters setup and decided to give the 5 speed a go.

Big issues that helped in this decision is that the specialty tools for the NSG are silly expensive and hard to come by. Getting the dealership to rebuild is horridly costly...over $5K here with ZERO guarantees as they only replace the parts they THINK are worn. And there has not been any upgrades to the shift fork. They still use the plastic inserts. So even if I got a rebuilt from Zumbrota, I would still have a used/with some rebuilt parts unit that may have had one of the myriad other issues these things have. The AX-15 is brand spanking new and the latest version of synchros, etc as I literally had to wait for Advance to get it off the boat and ship it out on boxing day...Merry Christmas to me! Even with the bellhousing, shifter, shipping to Canada, and taxes/duties it will land here at $3300 Canadian. So a brand new tranny and two grand left over just seemed like the thing to do.

Plus I'll have the only 4.0 NSG-370 in Canada to sell to someone who has one with worse problems that also doesn't want to cough up $5K and hope it works.

They tell me it is a straight bolt up application with their bellhousing and shifter. Only time will tell but have seen videos that shows it is just that easy. Not sure when I'll get it in. Have some wiring to do in the garage to clean up my solar mess, plus the plow is on the Jeep and can't be without. Got 6" of snow last night and my driveway is 600 feet long...not going to shovel that!

Hope that helps.

Cheers
Darren

 

[pc1p]

When my NSG ultimately shits the bed, it will get an AX replacement (if I haven't Hemi or LS swapped by then)...

 

[freedom_in_4low]

When my NSG ultimately shits the bed, it will get an AX replacement (if I haven't Hemi or LS swapped by then)...

I considered that...but losing that 4.46 first gear is a kick in the nuts. If I did the AX15 I'd probably want to do a 241 as well, and by that point I'd have quite a bit more money in it than just buying a rebuilt NSG370.

 

[Darkwing327]

I considered that...but losing that 4.46 first gear is a kick in the nuts. If I did the AX15 I'd probably want to do a 241 as well, and by that point I'd have quite a bit more money in it than just buying a rebuilt NSG370.

Yep, that is something each person would have to consider for their setups. For my type of use I think that the little taller first gear will be a big help on the forestry roads we frequent. With the 6 speed I am too slow in first and screaming going at the usual inclines on the roads...and in second I am lugging or trying to hold too high a speed for the terrain. So I am usually in 2LO 3rd gear with the assistance of the Tera2Low kit. I don't even use 1st for snowplowing. Usually start in 3rd 4LO and burn down the driveway in 4th which flings the snow off the blade nicely

Only time 1st gets used is when there is a incline at the lights to get going. But even then I am jackrabbiting to 3000 rpm in what feels like 8 feet of travel before I have to abruptly shift to second, so I am hopeful the 5 speed may help here as well. Again, each setup and combo of tires, transfer case and gear ratio will perform very differently. I am 31s on 3.73s with a 231.

PS....please keep in mind I am in Canada. US based jeepers enjoy cheaper shipping and no duties or hassles in buying or sending cores back across the border.

 

[freedom_in_4low]

Yep, that is something each person would have to consider for their setups. For my type of use I think that the little taller first gear will be a big help on the forestry roads we frequent. With the 6 speed I am too slow in first and screaming going at the usual inclines on the roads...and in second I am lugging or trying to hold too high a speed for the terrain. So I am usually in 2LO 3rd gear with the assistance of the Tera2Low kit. I don't even use 1st for snowplowing. Usually start in 3rd 4LO and burn down the driveway in 4th which flings the snow off the blade nicely

Only time 1st gets used is when there is a incline at the lights to get going. But even then I am jackrabbiting to 3000 rpm in what feels like 8 feet of travel before I have to abruptly shift to second, so I am hopeful the 5 speed may help here as well. Again, each setup and combo of tires, transfer case and gear ratio will perform very differently. I am 31s on 3.73s with a 231.

35s with 4.88 and a 231 here. The low first gear annoyed me when I was on 32s but it's perfect on 35s.

 

[pc1p]

I do like the extra gear for sure and especially the low 1st gear. That said, there are some quirks of the NSG that I don't care for. First is shift quality, if you can call it that. It reminds me of my dad's 79 Bronco, which I learned to drive on. Clunky and slow and more typical of an old 435 truck trans.

While the lower first gear wins, I wish OD were closer to the AX. Being on 35"s and 5.13's (I regeared for my TJ, which was an AX), I would probably go 4.56 or 4.88 if I were to regear for the NSG.

Even still, while there is an extra gear in there, I have found a handful of occasions where they don't prove to be helpful. For example - driving 50mph. It's at ~3100 RPM in 4th with my current setup. Too high (RPM) for casual driving up long country roads, but 5th drops too low. Drives me nuts as I find myself constantly up and down shifting at the slightest incline change.

Next is 1st gear in general - I feel like Paul Walker, speed shifting for 2nd after 30 ft of driving...

These are of course First World Jeep problems The real reason is overall lack of aftermarket support and availability for parts. Rebuilds are pricey and many shops won't even work on one (due to some specialized tools from my understanding).

 

[freedom_in_4low]

I do like the extra gear for sure and especially the low 1st gear. That said, there are some quirks of the NSG that I don't care for. First is shift quality, if you can call it that. It reminds me of my dad's 79 Bronco, which I learned to drive on. Clunky and slow and more typical of an old 435 truck trans.

While the lower first gear wins, I wish OD were closer to the AX. Being on 35"s and 5.13's (I regeared for my TJ, which was an AX), I would probably go 4.56 or 4.88 if I were to regear for the NSG.

Even still, while there is an extra gear in there, I have found a handful of occasions where they don't prove to be helpful. For example - driving 50mph. It's at ~3100 RPM in 4th with my current setup. Too high (RPM) for casual driving up long country roads, but 5th drops too low. Drives me nuts as I find myself constantly up and down shifting at the slightest incline change.

Next is 1st gear in general - I feel like Paul Walker, speed shifting for 2nd after 30 ft of driving...

These are of course First World Jeep problems The real reason is overall lack of aftermarket support and availability for parts. Rebuilds are pricey and many shops won't even work on one (due to some specialized tools from my understanding).

Looking at the numbers, AX15 5th gear with 5.13 is almost identical to an NSG370 6th with 4.88. I think you'll be happier with the AX15, and I think I would be too if I had 5.13 axles.

 

[Ericshere03]

I do like the extra gear for sure and especially the low 1st gear. That said, there are some quirks of the NSG that I don't care for. First is shift quality, if you can call it that. It reminds me of my dad's 79 Bronco, which I learned to drive on. Clunky and slow and more typical of an old 435 truck trans.

While the lower first gear wins, I wish OD were closer to the AX. Being on 35"s and 5.13's (I regeared for my TJ, which was an AX), I would probably go 4.56 or 4.88 if I were to regear for the NSG.

Even still, while there is an extra gear in there, I have found a handful of occasions where they don't prove to be helpful. For example - driving 50mph. It's at ~3100 RPM in 4th with my current setup. Too high (RPM) for casual driving up long country roads, but 5th drops too low. Drives me nuts as I find myself constantly up and down shifting at the slightest incline change.

Next is 1st gear in general - I feel like Paul Walker, speed shifting for 2nd after 30 ft of driving...

These are of course First World Jeep problems The real reason is overall lack of aftermarket support and availability for parts. Rebuilds are pricey and many shops won't even work on one (due to some specialized tools from my understanding).

Then use an NSG out of a 3.6 JK, they have the same ratios, except OD is lower; .72 instead of .84, something like that. Just need to swap the "bellhousing" ... I put quotes because the bellhousing and the front half of the tranny is the same casting.

 

[Akitadog]

From my understanding the innards of the NSG370's are interchangeable through the years.
Have not run into anyone stating otherwise.

 

[Ericshere03]

From my understanding the innards of the NSG370's are interchangeable through the years.
Have not run into anyone stating otherwise.

I would just swap the front case half. The input shaft is the same Mopar part number for TJ and JK …

 

[freedom_in_4low]

seems like a lot of work just to still end up with the transmission that Jeep engineers didn't even want to use and had forced down their throats by Daimler leadership.

 

[JMT]

seems like a lot of work just to still end up with the transmission that Jeep engineers didn't even want to use and had forced down their throats by Daimler leadership.

What is the way to go here? Is the AX-15 or NV3550 swap the easiest route with reliable results? The Advance Adapters Bellhousing adapter works for both of those swaps. It's over $500 right now. The NV3550 has a better 1st gear ratio at 4.01 vs 3.80.