Transfer Case Replacement Options

[Jon0249]

Just bought an M998 A0. The 6.2 has been replaced with the 6.5, but the 3-speed tranny and NP218 T-case remained. Although I do respect the original config of only 4WD, I really would like to swap the TC for one with a 2WD option in addition to 4H, 4L and 4HL.

Long term plan is to drop in a Cummins 5.9 12v, Dodge 47RH tranny and a TBD T-Case. But short term, in terms of a doable project (that will invariably displace one of my honey-do's) and affordability, a T-Case swap will get me the 2H option, the resulting fuel economy boost and hopefully a slight noise reduction.

So, question for this august body of like-minded brethren: What transfer case will replace the NP218 on a straight bolt-on basis to give me a 2WD option? Are there any pitfalls with this swap that you would advise me on?

Thanks for the input - much appreciated.

Jon

 

[Bunkerbuilder]

What year is the M998?

And what are your plans for the vehicle ?
A np218 is a chain drive transfer case and IMO it would be a upgrade to swap it out for a gear drive transfer case like a np205.


If you are looking for a bulletproof (read tough as nails) transfer case and are ok with the low range being a 2 to 1 ratio there is one in the classifieds that is perfect for this application. A round pattern late 1991 NP205.

What transmission did you plan to use now or behind the future Cummins engine ?

 

[Jon0249]

It is a 1990, S/N 101192. Plans involve nothing really heavy, no off road competitions, if that's what you're asking. Hunting, farm use, etc.

If I recall, the 218 has a low range of greater than 2, correct? 2:1 is actually fine, considering the geared hub config and the 2.56 diff gearing, so I'll check it out. I'm looking for a direct bolt on replacement that has similar linkage detents to minimize cockpit mods. If the 205 does that, I'm in. I have the Dodge 47RH tranny in mind, but will not be swapping it until I have the Cummins 5.9 12v ready to install. I'll stick with the 3L80 and the 1:1 final. For now.

Where is the 205 listed?

Thx,
Jon

 

[Bunkerbuilder]

Pm sent.

 

[Augi]

You won't gain anything in 2wd. There are no lockout hubs, so you will still be spinning the full front drive train by way of the wheels. I get 10mpg empty on the highway and 10mpg loaded with a fully loaded M101A3 around town. It doesn't seem to care what the load is.

Also, the truck weighs 7000lbs (I weighed mine at the dump).

IIRC the 218 has a ratio of 2.42:1 and the 242 has a ratio of 2.72:1 or something like that.

If you put in a 242 you can change one of the shift forks for a civilian one and it will allow the extra position 2wd hi.

They do have "replacement" 242's that were set up to go behind the TH400 in the A0 trucks. This was so they wouldn't have to continue to buy the 218's as spares when the new t-case was introduced.


Augi

 

[Jon0249]

Thanks, Augi. I realize the absence of lockout hubs, but the resistance back from the wheels through a non-engaged front axle consumes less energy than it takes to propel those same wheels. However, I also realize at this point I'm basing this on the math, and fully expect to have a different viewpoint soon enough...

The 242 appears to be one of the stronger chain driven units in the proper config, and the 205 is the bulletproof gear driven version - both provide the 2WD option I want. And either will mount to a rebuilt K-frame 700-R4, giving me a little better highway performance. Going from a final drive ratio on the ground of 4.91 to an overdriven, 2WD ratio of 3.39 is appealing. Even though I do have plans for a Cummins 12v, it would be nice to get as much use out of that 6.5 as I can.

Thanks for the input - everyone on this board is genuine and knowledgeable. At this point, with great course corrections from a couple of you, I now have a decision to make!

 

[Augi]

There is no highway performance with the Detroit. The natural roll of the land the highway runs across is enough to slow the truck down and any mild grade and it'll be going 45 or 50. When I'm on the highway I'm usually in the slow lane with the semi's.

With the 3-speed TH400 that's in there now you are limited to 55mph. You can drive it faster but you will be rebuilding the engine sooner rather than later. They overheat immediately.

With the 4-speed you can go 65 or 70, but you won't see any economy gains doing that.

My truck had the 6.2/TH400/218 and I've had a 6.5/4L80/242 in for a few years now (This is the A2 configuration). I also drove around and for a while with no front drive shaft.

The truck is heavy enough that playing games like going 2wd just get lost in the noise.

You'll spend the same time and energy trying to adapt a 700r4 or a new t-case that you will almost be doing your Cummins swap twice. I'd drive it as is til you have the Dodge parts and do the work once. And learn to like the noise, because the Cummins will only be louder.

You can see what it takes to swap a transmission here:
http://hmmwv.dchosken.com/a2-power-pack-installation/

Augi

 

[Jon0249]

All valid points. Too bad someone doesn't make a lockout mechanism for those hubs. If it weren't too much trouble, I'd disconnect the front half shafts along with the OD and 242 T-Case. But you're right, I'd be doing a LOT of work that pretty much defeats the purpose of having a HMMWV anyway.

In the end, the honey-do list and budget will drive the decisions ands purchases I make for this machine. Frankly, I'm one of those guys that has a cadence a bit faster than most, for no good reason other than I like a little speed. Trips to and from the farm would be easier going 70, but for what I'm getting, I will dial back the cadence and enjoy the ride. With earplugs And a coat.

Thanks for the feedback.

 

[Jon0249]

I read the article on swapping the tranny - very thorough and a great read. Once I do put in the OD, I will not be using an ECM, opting for simplicity, thus the 700-R4 or a Dodge 47RH. His final thoughts sort of tell the story I have in my head - that once it kicks in OD, it was all worth it. Then I will be on the to the next improvement...

 

[dilvoy]

There are halfshafts with a sliding lock out setup on them for front wheel drive cars that are flat towed behind motor homes, but even if they could make one or two for your humvee, you can't use them for driving, because the brakes are inboard of the halfshafts so you won't have any braking on the ones that you disconnected. The torsen diffs work differently than other diffs and I was playing with one that I had out of a vehicle many years ago and though pinion rotation caused the output shafts to rotate, rotating the output shafts did not make the pinion rotate. If you put a part time t case or a unlocking type of front driveshaft, you will still have some parts in the diff rotating. Probably the little weird shaped spiral gears and they will be running on their back sides, but with much less load than when being driven normally.

 

[Jon0249]

Dilvoy,

Great observation on disconnecting the shafts and the impact on braking. Still getting my head around that concept!

I really like the idea of the rotating shafts not causing the diff to rotate. If this hoilds true, then the pursuit of a 2WD option on the t-case will actually provide some energy savings. I'll know soon enough.

Thanks for the insight to my newbie questions. There will be more...

 

[Jon0249]

Augi,

Your prior post reads: "If you put in a 242 you can change one of the shift forks for a civilian one and it will allow the extra position 2wd hi."

As it turns out, I have the 242 after all. Can you provide some direction on the shift fork mod required to access the 2H position? Will it necessitate the shifter console from an H1?

Thx,
Jon

 

[Augi]

Jon,

You'll have to google around to find out how to do the mod.

242's were in Jeeps in the 90's or something, so that's where the parts are coming from.

H1's didn't have 2Hi, they are mechanically the same as the HMMWV.

Augi

 

[86humv]

If you get it figured out...I have the military overdrive shifters available.

 

[TedG]

I believe it is a 241 tcase. You will need to modify the signal generator for the speedo (there is a kit for it) and you may have to move the tcase towards the drivers side just a tad to allow clearance to the fuel tank (should fit but may rub in off road conditions). I had a 770r4 with 241 and it was a fun slantback to drive. It would go fast and spin in circles.

 

[patracy]

I believe it is a 241 tcase. You will need to modify the signal generator for the speedo (there is a kit for it) and you may have to move the tcase towards the drivers side just a tad to allow clearance to the fuel tank (should fit but may rub in off road conditions). I had a 770r4 with 241 and it was a fun slantback to drive. It would go fast and spin in circles.

I was looking at swapping to a OD setup for my M1038. I know a 4L80e would "bolt in" more. But it raises electronics issues and then the TPS and Tach issues. I know the 700r4 is considered weak by a lot of people, but I've had good service out of them (after upgrades). Was just kinda interested in them since it can happen with a lot more simpler wiring and just a TV cable/bracket.

 

[Jon0249]

patracy, I've thought the same. Despite a few opinions here that don't actually encourage the 700r4, I'm gonna do the same thing TedG did. I'm not a hardcore offroader, just love to have a little fun and drive mine to my farm. As stupid as it sounds, I despise going 50 mph. I don't need super speed, but I'd rather get to the farm a little sooner, and I really just want the alternative of rwd. Just not asking for opinions, now that I have the parts acquired and staged. I have the 700r4 ready to upgrade and will pick up the 241C this weekend. The only thing I have to find is the right 27-spline input shaft for the t-case, but they're available. I'll keep you posted on this thread.

 

[bigred350]

Hi there just wondering how your 700r4 swap went any update. also looks like there is an advanced adapters kit that will allow you to bolt the np218 right to the back of the 700r4 part #50-6901 has anyone used this kit? because im thinking about doing this with a raptor 700r4 thank you

 

[Jon0249]

After endless waffling between the 700r4 and 4L80e, I ended up finding good deals on both, so I bought them. The decision on which tranny to use hinged on the degree of difficulty in the setup required for the 4L80e, since it was clearly the toughest one. US Shift/Baumann Electronics produces what was the most attractive TCM to me, the Quick 4, requiring only the addition of a Throttle Position Sensor. The TISS and TOSS from the 4L80e are the only other sensors required for the Quick 4 TCM to operate.

So I fully rebuilt the 4L80e, and my mechanic is now wrapping up the swap. I also found an NP241C T-case that bolted right up to the 4L80e using the adapter used by the TH400/NP242, so no issues there. The front and rear shafts needed modification, as the 4L80 is ~2.75" longer than the TH400. The NP242 I was running (not an NP21 has a mechanical speedo drive, while the 241 uses elec speedo. The tail housings are completely interchangeable, but the tone ring required for the mech speedo does not exist in the later model 241C. Fortunately, the Quick 4 TCM includes the signal adapter that can convert the pulse from the 241C to a usable signal for an electronic speedo. I found a 85 mph VDO unit that fits the existing hole, so that problem is solved, and no more mech speedo gears to replace. The TPS swap was crystal clear, thanks to a few Steel Soldiers, and that's done as well.

It's not done yet, but all obstacles are removed and it should be done in a couple of days. So far, the Quick 4 TCM has been the rock star, so I'll post results when I get it home.

 

[Tank007]

I have a simpleshift on my 4l80e mounted to the 5.9 and it is a pain in the butt... I look forward to your input on the quick 4. I know it is pricey but predator motorsports sells a 2wd selectable tcase for the Hmmwv.