Automatic Transmission/Transfer Case Compatibility Notice
Sept 23, 2015 17:30:05 GMT -5
seanm26 likes this
Post by ES_97Sport on Sept 23, 2015 17:30:05 GMT -5
I know a lot of the people on here don't surf the dedicated tech forums so I thought I'd put this out there. This is kind of the unintentionally best kept secret in the Mitsu SUV off-road world. 
If you wheel the Montero or Montero Sport even a little, you've probably noticed that the t-case gearing sucks serious pond water. 1.9:1 is kinda ok if you're running the stock tires, but the minute you start up-sizing the tires to 32/33/35 - especially if retaining the tall A/T axles gears - your crawl ratio goes straight to hell in a hand basket. 
The 'velocity method' of negotiating obstacles is VERY hard on a vehicle and not particularly safe. In my experience, a googly number of roll-overs and a lot of breakage are the result of having to 'power through' rather than crawl.
For some there are transfer case gear options. Mark's 4WD does still sell t-case gears for some of the Mitsu t-cases. Their options are 2.88 and 3, depending on the t-case. This is sufficient for most people's level of wheeling. Believe me, even 2.88:1 makes a HUGE, ENORMOUS difference! Mark's a great guy and he produces top notch stuff - but its not cheap.
In the '90s and early 2000s, Chrysler/Jeep used the Aisin Warner AW4 A/T in the Jeep XJ, ZJ - otherwise known as the Cherokee and Grand Cherokee. Toyota also used the same AW4 in the 4-Runner - the Toyota A340 series transmission.
Everything you ever wanted to know about the AW4 - NAXJA
A little known fact is that Mitsubishi ALSO used the Aisin Warner AW4 in the '90s Montero and Montero Sport. For the Montero Sport, the relevant years are '97 and '98 and is known as the AW3. Unfortunately, in '99 Mitsu changed to a completely different transmission - which is neither all that great for off-road apparently nor even remotely close to the AW4 so no 'easy' modifications. The model/serial tag attached to the transmission from a 1997 Montero Sport is shown below.
The important thing to note here is that the AW4 is 'modular'. The bell housings as well as the rear adapter housings are removable. This allowed manufacturers to easily adapt the Aisin Warner transmission to their engines and transfer cases. Shown below is complete Mitsubishi 'AW4' with the removable bell housing on the right and the adapter housing for the Mitsu t-case on the left.
What is the point of this, you ask? During the '90s and early 2000s Chrysler/Jeep used various New Process (NP) transfer cases. (see link below) Predominately, they ALL have BETTER gear ratios than our Mitsubishi t-case. Most importantly, they used these transfer cases and bolted them to the AW4 automatic transmission!
New Venture Gear - Wiki
The three NP transfer cases that are relevant in this context are the NP231 (Cherokee), NP242 (Grand Cherokee) and the NP241OR RockTrac (Wranger). These have ratios of 2.72:1, 2.72:1 and 4:1, respectively. These three are either a direct bolt on to the Jeep AW4 - NP231 & NP242 - or in the case of the 241OR, bolt on but may require minor modification(s). Note: The NP242 is selectable 2WD/4WD/AWD.
Like the Toyota, the Mitsu AW4 uses a different rear adapter housing and output shaft to allow the manufacturers to bolt their transfer cases to the transmission. These two pieces are, as noted above, interchangeable. Shown below is the Jeep Cherokee XJ adapter housing and the Jeep Cherokee XJ 23-spline output shaft used to allow Chrysler/Jeep to bolt the NP transfer cases to the AW4 A/T.
Yes, you probably guessed by now that if you replace the adapter housing and output shaft with the appropriate pieces you can bolt a Jeep NP transfer case to your 'Mitsubishi' automatic transmission.
So, you get lower t-case gearing. If anything, what else do you get? Cheap parts availability for one thing. NP transfer cases are very common. Most transmission rebuild shops will sell NP parts for less than it costs in gas to get there. Also, since they're very common, there's quite the aftermarket out there. Tera makes their Low 231 which is a 4:1 gear kit for the NP231 (and NP242 with modifications). Many companies make Slip Yoke Eliminators (SYE) - this converts the slip joke on the drive shafts (always problematic on Mitsus) to a fixed yoke. An absolutely mandatory off-road modification! Several companies also make 'crawl boxes' or 'doublers'. This is a second set of gears that sit in front of the transfer case between the transfer case and transmission. Typically, these add a second gear range option multiplying the transfer case ratio by the 'crawl box' or 'doubler' ratio. So, if the ratio in the crawl box is 2.72:1 and the range in the transfer case is 4:1, you effectively end up with a 3-speed 'transfer case'. Lo=2.72, Lo-Lo=4 and Lo-Lo-Lo=2.72*4 or 10.88:1. Several companies also make 'upgrade' kits for the NP transfer cases designed to increase the strength of the shafts, bearings, chain, etc. This is not an extensive list of reasons or options or even transfer cases.
Now, before everyone gets all excited like, this is still not an afternoon bolt in modification. On a scale of difficulty and require skills from 1 to 5, this would be a solid 4. It would require a fair amount of planning and organization, a small amount of fabrication, wiring and a lot of plain old grunt work.
Besides the easy part of swapping out the adapter housing and output shaft the minimum few other things that would be required ...
1) New transfer case shifter assembly
2) Adapt the Jeep output sensor to the Mitsu TCU harness
3) New front and rear drive shafts
4) Adapt the NP 4WD switch to the Mitsu 2WD/4WD harness
5) Run new t-case vent hose
6) Mitsu dash cluster speedo conversion
Strongly recommended additional things ...
1) SYE kit for the rear drive shaft
2) Transgo 340-HD2 shift improver kits (locks transmission in 1st when in 1st)
Again, nothing here is rocket surgery. In fact, nothing here is even new. Which is great if you're not really in the mood to reinvent the wheel and just want a functional upgrade.
The down side to all this is that the only Montero Sports that came with the AW4 are the '97s and '98s. This is great because if you have a '97/8, you already have the transmission, Transmission Control Unit (TCU), etc. There's almost nothing to this swap in that case.
If you have a '99 or newer, this gets a lot more complicated and involved. Its not impossible (it has already and is being done again), but its not for amateur back yard weekend mechanics with 1/2 a set of basic hand tools and it WILL change your vehicle in ways you may not really like and may not be able to live with if you use your vehicle for a DD. This is a serious investment in time, money and labor. On the same scale of 1 to 5, this is more like a 7. On the other hand, if you're serious about wheeling your Sport, then this becomes a required modification.
I won't get into all the gory details here. If you want to see more of what's involved and so on, check out the link below.
1999 Limited 3.5L Crawler Build
Edward
If you wheel the Montero or Montero Sport even a little, you've probably noticed that the t-case gearing sucks serious pond water.
1.9:1 is kinda ok if you're running the stock tires, but the minute you start up-sizing the tires to 32/33/35 - especially if retaining the tall A/T axles gears - your crawl ratio goes straight to hell in a hand basket. 
The 'velocity method' of negotiating obstacles is VERY hard on a vehicle and not particularly safe. In my experience, a googly number of roll-overs and a lot of breakage are the result of having to 'power through' rather than crawl.
For some there are transfer case gear options. Mark's 4WD does still sell t-case gears for some of the Mitsu t-cases. Their options are 2.88 and 3, depending on the t-case. This is sufficient for most people's level of wheeling. Believe me, even 2.88:1 makes a HUGE, ENORMOUS difference! Mark's a great guy and he produces top notch stuff - but its not cheap.
In the '90s and early 2000s, Chrysler/Jeep used the Aisin Warner AW4 A/T in the Jeep XJ, ZJ - otherwise known as the Cherokee and Grand Cherokee. Toyota also used the same AW4 in the 4-Runner - the Toyota A340 series transmission.
Everything you ever wanted to know about the AW4 - NAXJA
A little known fact is that Mitsubishi ALSO used the Aisin Warner AW4 in the '90s Montero and Montero Sport. For the Montero Sport, the relevant years are '97 and '98 and is known as the AW3. Unfortunately, in '99 Mitsu changed to a completely different transmission - which is neither all that great for off-road apparently nor even remotely close to the AW4 so no 'easy' modifications. The model/serial tag attached to the transmission from a 1997 Montero Sport is shown below.
The important thing to note here is that the AW4 is 'modular'. The bell housings as well as the rear adapter housings are removable. This allowed manufacturers to easily adapt the Aisin Warner transmission to their engines and transfer cases. Shown below is complete Mitsubishi 'AW4' with the removable bell housing on the right and the adapter housing for the Mitsu t-case on the left.
What is the point of this, you ask?
During the '90s and early 2000s Chrysler/Jeep used various New Process (NP) transfer cases. (see link below) Predominately, they ALL have BETTER gear ratios than our Mitsubishi t-case. Most importantly, they used these transfer cases and bolted them to the AW4 automatic transmission!New Venture Gear - Wiki
The three NP transfer cases that are relevant in this context are the NP231 (Cherokee), NP242 (Grand Cherokee) and the NP241OR RockTrac (Wranger). These have ratios of 2.72:1, 2.72:1 and 4:1, respectively. These three are either a direct bolt on to the Jeep AW4 - NP231 & NP242 - or in the case of the 241OR, bolt on but may require minor modification(s). Note: The NP242 is selectable 2WD/4WD/AWD.
Like the Toyota, the Mitsu AW4 uses a different rear adapter housing and output shaft to allow the manufacturers to bolt their transfer cases to the transmission. These two pieces are, as noted above, interchangeable. Shown below is the Jeep Cherokee XJ adapter housing and the Jeep Cherokee XJ 23-spline output shaft used to allow Chrysler/Jeep to bolt the NP transfer cases to the AW4 A/T.
Yes, you probably guessed by now that if you replace the adapter housing and output shaft with the appropriate pieces you can bolt a Jeep NP transfer case to your 'Mitsubishi' automatic transmission.
So, you get lower t-case gearing. If anything, what else do you get? Cheap parts availability for one thing. NP transfer cases are very common. Most transmission rebuild shops will sell NP parts for less than it costs in gas to get there. Also, since they're very common, there's quite the aftermarket out there. Tera makes their Low 231 which is a 4:1 gear kit for the NP231 (and NP242 with modifications). Many companies make Slip Yoke Eliminators (SYE) - this converts the slip joke on the drive shafts (always problematic on Mitsus) to a fixed yoke. An absolutely mandatory off-road modification! Several companies also make 'crawl boxes' or 'doublers'. This is a second set of gears that sit in front of the transfer case between the transfer case and transmission. Typically, these add a second gear range option multiplying the transfer case ratio by the 'crawl box' or 'doubler' ratio. So, if the ratio in the crawl box is 2.72:1 and the range in the transfer case is 4:1, you effectively end up with a 3-speed 'transfer case'. Lo=2.72, Lo-Lo=4 and Lo-Lo-Lo=2.72*4 or 10.88:1. Several companies also make 'upgrade' kits for the NP transfer cases designed to increase the strength of the shafts, bearings, chain, etc. This is not an extensive list of reasons or options or even transfer cases.
Now, before everyone gets all excited like, this is still not an afternoon bolt in modification. On a scale of difficulty and require skills from 1 to 5, this would be a solid 4. It would require a fair amount of planning and organization, a small amount of fabrication, wiring and a lot of plain old grunt work.
Besides the easy part of swapping out the adapter housing and output shaft the minimum few other things that would be required ...
1) New transfer case shifter assembly
2) Adapt the Jeep output sensor to the Mitsu TCU harness
3) New front and rear drive shafts
4) Adapt the NP 4WD switch to the Mitsu 2WD/4WD harness
5) Run new t-case vent hose
6) Mitsu dash cluster speedo conversion
Strongly recommended additional things ...
1) SYE kit for the rear drive shaft
2) Transgo 340-HD2 shift improver kits (locks transmission in 1st when in 1st)
Again, nothing here is rocket surgery. In fact, nothing here is even new. Which is great if you're not really in the mood to reinvent the wheel and just want a functional upgrade.
The down side to all this is that the only Montero Sports that came with the AW4 are the '97s and '98s. This is great because if you have a '97/8, you already have the transmission, Transmission Control Unit (TCU), etc. There's almost nothing to this swap in that case.
If you have a '99 or newer, this gets a lot more complicated and involved. Its not impossible (it has already and is being done again), but its not for amateur back yard weekend mechanics with 1/2 a set of basic hand tools and it WILL change your vehicle in ways you may not really like and may not be able to live with if you use your vehicle for a DD. This is a serious investment in time, money and labor. On the same scale of 1 to 5, this is more like a 7.
On the other hand, if you're serious about wheeling your Sport, then this becomes a required modification.I won't get into all the gory details here. If you want to see more of what's involved and so on, check out the link below.
1999 Limited 3.5L Crawler Build
Edward
