Np 231 Transfer Case Problem

[hillbilly51]

Hey.

I'm having a problem with my 88 comanche chief.....4.0 straight 6 with ba5/10  5 speed and NP231 transfer case. 

 

I recently changed transmissions (yea, I replaced the Peugeot again) and I installed the Transfer case that I got with the transmission ($200 for both).

 

The problem is that when I'm driving on dry pavement and the truck is in 4 wheel high there will be a slight jump along with a bump and noise (bang) ...like the transfer case is jumping in and out of gear.

 

If it was a straight shift chevy, I would thing that I have a broken gear (tooth missing) in the transmission, but it will only do it in 4 wheel, so I'm sure it's coming from the transfer case.

 

If  I'm driving on snow or ice, the problem doesn't show itself.

I Have no problem if I'm in 2 wheel.

 

I'm afraid that there is a problem inside the case, although the front axle could be jumping in and out of lock-up.

 

Any help or opinions

thanks

steve

[Oyaji]

Ummm - what are you doing in 4-hi on dry pavement???

 

Use of 4x4 is plainly marked "part time", and is supposed to be used only in low-traction conditions. If there is no slip for the tires, geartrain binding builds up until something breaks...

[gogmorgo]

Building on what Oyaji said, unless you have a full-time 4x4 option, which I don't think any MJ's got from the factory (and if they did it's extremely rare), then you definitely should not be using 4x4 on dry pavement. There is no center differential in the transfer case, so both axles are locked together. This is fine when driving on a lower-traction surface, or in straight lines on dry pavement (although I'd still avoid using 4x4 on dry pavement at all).

 

When you go around a corner, your front and rear axles don't follow the same radius. Since they're following different radii, they try to turn at different speeds. When you're in 2wd, even on dry pavement, they can do that because the axles aren't locked together. When you're in 4x4, they can't turn at different speeds. On lower-traction surfaces, this is fine, as the wheels can slip, making up for it. On dry pavement, or even wet pavement and sometimes even hard-packed dirt, there's too much traction for the tires to slip, so stress builds up in the driveline, meaning the individual parts start trying to twist. When the stress is too high for the "weakest" part of your driveline, it gets released. Sometimes it's just that one wheel will suddenly hop and spin, leaving a nice patch of rubber. In your case, the transfer case pops out of gear. In some cases, you could pop a u-joint, break a half-axle, or pretzel a driveshaft. None of which is desirable.

 

TL,dr: DON'T use 4x4 on pavement. There's no need for it, and you seriously run the risk of breaking something.

[Blue88Comanche]

If you want to use 4wd all the time you will need a full-time transfer case like my NP242. But this TC did not come on any MJs stock as mentioned above.  The Cherokees that got them where also autos.  I have a NP242 mated to an AX-15 and haven't had any issues aside from not having the new linkage for the AX-15 (I had a BA10/5 NP231 combo stock).

 

The NP242 will give you 2wd, 4wd high part-time, 4wd full-time, neutral, and 4wd low part-time

[Eagle]

Just another voice to add to the chorus: YOU ARE DESTROYING YOUR TRANSFER CASE.

 

It isn't intended to be in 4WD on dry pavement.

[91Pioneer]

Just curious, how often do you drive on dry pavement in 4WD? And why?

[Jeep Driver]

Your chain is stretched.

 

Same thing happened with my XJ. I rebuilt mine.

 

 

 

 

To answer the question of others.......

 

 

 

When my little 2.5 does not what to pull  3000lbs worth of trailer and tractor up a steep incline (driveway or other), she goes into low. As long as I do not make a tight turn.........never a problem.

[yxmj]

Your chain is stretched.

 

Same thing happened with my XJ. I rebuilt mine.

 

X2

 

"The problem is that when I'm driving on dry pavement and the truck is in 4 wheel high there will be a slight jump along with a bump and noise (bang) ...like the transfer case is jumping in and out of gear."

 

That is the sound/feeling of your chain jumping a cog

[Blue88Comanche]

the stretched chain can be caused because the TC is not being used on the proper surface, no dry pavement. as both Oyaji and gogmorgo have stated the Transfer case is Locked in part-time, meaning the front drive shaft will not spin faster than the rear drive shaft and vice versa.  The front and rear gears are usually not the same exact ratio, they are usually close enough not to matter much on loose terrain. Tire pressure being different can cause the final ratio to be slightly off as well  Over time the stress builds up until it breaks something or in your case the chain jumps the gear.

 

as for the issue not showing on snow or ice, that because its low traction, less friction, less grip.  The stress build up can be more easily relived through a tire loosing traction on the loose terrain.

 

the NP242 has a open diff for full time use and can be locked for part time use.  the open diff works just like in the axles, allowing one shaft to spin faster or slower than the other when needed.

[Oyaji]

When my little 2.5 does not what to pull  3000lbs worth of trailer and tractor up a steep incline (driveway or other), she goes into low. As long as I do not make a tight turn.........never a problem.

 

Y'know, having an axle with a manually-selectable center axle disconnect would provide a nice, safe, trouble-free 2-LO option, now, wouldn't it.

 

As long as it wasn't used a great deal or for extended running, there wouldn't be much danger to the diff and spider gears, would there? (Thinking that having one axle disconnected would cause the diff to spin at double speed, potentially causing wear issues...) What do you guys think?

[hillbilly51]

Just curious, how often do you drive on dry pavement in 4WD? And why?

 

Not often.

I had to go to the store and there was snow on the mountain.

I have a problem with the shift solenoid on the transfer case, so I had to open the hood and hook the vacuum up to the front axle so that the axle would lock.

 

About half way down the mountain, I ran out of the snow, so I coutinued the trip the last 3 miles still in 4WD.

Going back up...while still on dry pavement is when the transaxle did its thing.

 

I was sure that the noise came from the transfer case, but I wanted confirmation.

 

I need to fix the vacuum solenoid to avoid this in the future.

 

I ran the other transfer case a few times for short distance without problems.

I guess the chain in this one is a little loose.

I have two spares because these transfer cases for the "'Puke geot"  transmissions won't fit anything else....the input spline count is different.

 

Thanks for the responses

steve

[Blue88Comanche]

The vac lines for the 4wd sustem only control the front axle disconnect and the 4wd light.

 

So if the CAD is locked them you can still shift the transfer case to 2wd with the shifter because it uses a physical linkage.

[gogmorgo]

Y'know, having an axle with a manually-selectable center axle disconnect would provide a nice, safe, trouble-free 2-LO option, now, wouldn't it.

 

As long as it wasn't used a great deal or for extended running, there wouldn't be much danger to the diff and spider gears, would there? (Thinking that having one axle disconnected would cause the diff to spin at double speed, potentially causing wear issues...) What do you guys think?

 

:offtopic: But it's a reasonably common mod. I saw it being used on the Dodge Cummins before I got into Jeeps. It really helps with tight low-speed maneuvers with a heavy trailer. As far as overspinning the diff goes, honestly, how fast do you plan on going in low range? Can't really be any worse than getting stuck with open diffs and only spinning one wheel.

[yxmj]

 

Just curious, how often do you drive on dry pavement in 4WD? And why?

 

Not often.

I had to go to the store and there was snow on the mountain.

I have a problem with the shift solenoid on the transfer case, so I had to open the hood and hook the vacuum up to the front axle so that the axle would lock.

 

About half way down the mountain, I ran out of the snow, so I coutinued the trip the last 3 miles still in 4WD.

Going back up...while still on dry pavement is when the transaxle did its thing.

 

I was sure that the noise came from the transfer case, but I wanted confirmation.

 

I need to fix the vacuum solenoid to avoid this in the future.

 

I ran the other transfer case a few times for short distance without problems.

I guess the chain in this one is a little loose.

I have two spares because these transfer cases for the "'Puke geot"  transmissions won't fit anything else....the input spline count is different.

 

Thanks for the responses

steve

The other cases could possibly be NP207's.....but that chain would fit the 231.......but for the hassle it might be worth while to get a new one....i picked up one for $70 with shipping off ebay (shipped to Canada).

 

The manual disconnect is another option that has been out for a while..

 

.http://www.summitracing.com/int/search/department/transmission-drivetrain/section/differential-rear-end-components/part-type/front-axle-engagement-systems-manual/stock-4wd-actuation-style/central-axle-disconnect-cad

 

I actually made my own for my Yj using a cable I picked up at an farm supply place ( comparable to your "Tractor supply" down there) I had already done the bolt it solid methode so I just replaced that bolt with the threaded cable end and ran the other to the cab by the shifter....It is a nice option to be able to quickly disengage the front (like in a sharp U-turn) then re-engage with just the pull of a knob. I have had it for a while and like it. (Google it and you will see blogs from YJ and XJ guys who have made there own and show step how to instructions

 

PS as you can see from my location I drive on snow/ice 50% of the time