231 / 242 / 249 Transfer Case Question
01-16-2015, 12:36 PM
#1
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231 / 242 / 249 Transfer Case Question
I am about ready to swap transfer cases - from a 249 to a 242.
As I understand it the viscous coupler in the 249 is prone to go bad. I also understand that when using the 249 transfer case you should NOT have over a 1/4 (.25) inch variance in tires.
Here's the question: I thought I read somewhere that the 231 and the 242 transfer cases were not true 4 wheel drive. I think I read it that if a wheel is spinning in 2 wheel drive it will also spin in 4 wheel drive also. I thought I also read that in the 249 case that this is the opposite- power will be sent to all four wheels even if one is slipping.
So if this is true wouldn't the 249 case be better because then you would have true 4 wheel drive?
As I understand it the viscous coupler in the 249 is prone to go bad. I also understand that when using the 249 transfer case you should NOT have over a 1/4 (.25) inch variance in tires.
Here's the question: I thought I read somewhere that the 231 and the 242 transfer cases were not true 4 wheel drive. I think I read it that if a wheel is spinning in 2 wheel drive it will also spin in 4 wheel drive also. I thought I also read that in the 249 case that this is the opposite- power will be sent to all four wheels even if one is slipping.
So if this is true wouldn't the 249 case be better because then you would have true 4 wheel drive?
01-16-2015, 02:28 PM
#2
Old fart with a wrench
Okay, this is what I know about 4 wheel drives, period. First of all, 4wd vehicles have a differential in both axles, front and rear, to accommodate differences in wheel speed when cornering. Because of this, if one wheel of an axle spins, the other will not drive, UNLESS that axle has a limited slip devise or "locker" in it. With me so far?
Now we get to the power transfer to those axles. As you already know, 4WD vehicles have a transfer case that divides the power output to both axles. HOW this power is divided is the subject of your question.
The 249's viscous coupling is basically a torque converter in respect that it sends power to both axles at all times and absorbs differences in axle speeds by "slipping". This slipping generates heat which is the major reason it eventually fails. The "good" part about it is if one wheel spins, the other axle is still driving. The "bad" part is there is no direct lock-up between both axles. It explain it further, imagine sitting with both wheels on one side on ice. Both those wheels will spin and you'll go nowhere. The same thing happens with the 231 and the 242, but we'll get to that later.
The 231 has a 2WD function and a "part time" 4WD function. In part time. both axles are driving together at the same speed with no slippage between them. That's why it should only be used on slippery or loose surfaces.
The 242 has the 2WD function and 2 different 4WD selections. In part time, again both axles are driving together at the same speed with no slippage. In full time, there is a devise that acts like an open differential inside the case so you can drive it on dry pavement to no ill effect. I've been told that it's not a true differential in that it divides the power 60/40 to the axles so really shouldn't be used for long periods on dry pavement. I've been going to do some research into exactly how it works, but I haven't yet.
Now we get to the axles themselves. With standard differentials, if one wheel looses traction, it will spin, period. A limited slip differential has clutches in it, so if one wheel looses traction, the other will still drive. A "locker" does the same function but is stronger than an LSD. If you're looking for the ultimate traction set-up, use a locker in the rear diff and a selectable locker in the front diff. A selectable locker is usually engaged by hydraulics or air pressure and is controlled by the driver or sometimes by automatic systems.
This whole post is my understanding of how jeeps work. I'm sure there are other opinions and, guys, feel free to correct me.
OH! One thing I forgot to mention. With my 242 in full time, if I've got one wheel on ice, only that wheel will spin and I go nowhere. Then I shift to part time and drive off.
Now we get to the power transfer to those axles. As you already know, 4WD vehicles have a transfer case that divides the power output to both axles. HOW this power is divided is the subject of your question.
The 249's viscous coupling is basically a torque converter in respect that it sends power to both axles at all times and absorbs differences in axle speeds by "slipping". This slipping generates heat which is the major reason it eventually fails. The "good" part about it is if one wheel spins, the other axle is still driving. The "bad" part is there is no direct lock-up between both axles. It explain it further, imagine sitting with both wheels on one side on ice. Both those wheels will spin and you'll go nowhere. The same thing happens with the 231 and the 242, but we'll get to that later.
The 231 has a 2WD function and a "part time" 4WD function. In part time. both axles are driving together at the same speed with no slippage between them. That's why it should only be used on slippery or loose surfaces.
The 242 has the 2WD function and 2 different 4WD selections. In part time, again both axles are driving together at the same speed with no slippage. In full time, there is a devise that acts like an open differential inside the case so you can drive it on dry pavement to no ill effect. I've been told that it's not a true differential in that it divides the power 60/40 to the axles so really shouldn't be used for long periods on dry pavement. I've been going to do some research into exactly how it works, but I haven't yet.
Now we get to the axles themselves. With standard differentials, if one wheel looses traction, it will spin, period. A limited slip differential has clutches in it, so if one wheel looses traction, the other will still drive. A "locker" does the same function but is stronger than an LSD. If you're looking for the ultimate traction set-up, use a locker in the rear diff and a selectable locker in the front diff. A selectable locker is usually engaged by hydraulics or air pressure and is controlled by the driver or sometimes by automatic systems.
This whole post is my understanding of how jeeps work. I'm sure there are other opinions and, guys, feel free to correct me.
OH! One thing I forgot to mention. With my 242 in full time, if I've got one wheel on ice, only that wheel will spin and I go nowhere. Then I shift to part time and drive off.
Last edited by dave1123; 01-16-2015 at 02:33 PM.
01-18-2015, 08:50 PM
#3
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Join Date: Jan 2015
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Year: 2001
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Okay, this is what I know about 4 wheel drives, period. First of all, 4wd vehicles have a differential in both axles, front and rear, to accommodate differences in wheel speed when cornering. Because of this, if one wheel of an axle spins, the other will not drive, UNLESS that axle has a limited slip devise or "locker" in it. With me so far?
Now we get to the power transfer to those axles. As you already know, 4WD vehicles have a transfer case that divides the power output to both axles. HOW this power is divided is the subject of your question.
The 249's viscous coupling is basically a torque converter in respect that it sends power to both axles at all times and absorbs differences in axle speeds by "slipping". This slipping generates heat which is the major reason it eventually fails. The "good" part about it is if one wheel spins, the other axle is still driving. The "bad" part is there is no direct lock-up between both axles. It explain it further, imagine sitting with both wheels on one side on ice. Both those wheels will spin and you'll go nowhere. The same thing happens with the 231 and the 242, but we'll get to that later.
The 231 has a 2WD function and a "part time" 4WD function. In part time. both axles are driving together at the same speed with no slippage between them. That's why it should only be used on slippery or loose surfaces.
The 242 has the 2WD function and 2 different 4WD selections. In part time, again both axles are driving together at the same speed with no slippage. In full time, there is a devise that acts like an open differential inside the case so you can drive it on dry pavement to no ill effect. I've been told that it's not a true differential in that it divides the power 60/40 to the axles so really shouldn't be used for long periods on dry pavement. I've been going to do some research into exactly how it works, but I haven't yet.
Now we get to the axles themselves. With standard differentials, if one wheel looses traction, it will spin, period. A limited slip differential has clutches in it, so if one wheel looses traction, the other will still drive. A "locker" does the same function but is stronger than an LSD. If you're looking for the ultimate traction set-up, use a locker in the rear diff and a selectable locker in the front diff. A selectable locker is usually engaged by hydraulics or air pressure and is controlled by the driver or sometimes by automatic systems.
This whole post is my understanding of how jeeps work. I'm sure there are other opinions and, guys, feel free to correct me.
OH! One thing I forgot to mention. With my 242 in full time, if I've got one wheel on ice, only that wheel will spin and I go nowhere. Then I shift to part time and drive off.
Now we get to the power transfer to those axles. As you already know, 4WD vehicles have a transfer case that divides the power output to both axles. HOW this power is divided is the subject of your question.
The 249's viscous coupling is basically a torque converter in respect that it sends power to both axles at all times and absorbs differences in axle speeds by "slipping". This slipping generates heat which is the major reason it eventually fails. The "good" part about it is if one wheel spins, the other axle is still driving. The "bad" part is there is no direct lock-up between both axles. It explain it further, imagine sitting with both wheels on one side on ice. Both those wheels will spin and you'll go nowhere. The same thing happens with the 231 and the 242, but we'll get to that later.
The 231 has a 2WD function and a "part time" 4WD function. In part time. both axles are driving together at the same speed with no slippage between them. That's why it should only be used on slippery or loose surfaces.
The 242 has the 2WD function and 2 different 4WD selections. In part time, again both axles are driving together at the same speed with no slippage. In full time, there is a devise that acts like an open differential inside the case so you can drive it on dry pavement to no ill effect. I've been told that it's not a true differential in that it divides the power 60/40 to the axles so really shouldn't be used for long periods on dry pavement. I've been going to do some research into exactly how it works, but I haven't yet.
Now we get to the axles themselves. With standard differentials, if one wheel looses traction, it will spin, period. A limited slip differential has clutches in it, so if one wheel looses traction, the other will still drive. A "locker" does the same function but is stronger than an LSD. If you're looking for the ultimate traction set-up, use a locker in the rear diff and a selectable locker in the front diff. A selectable locker is usually engaged by hydraulics or air pressure and is controlled by the driver or sometimes by automatic systems.
This whole post is my understanding of how jeeps work. I'm sure there are other opinions and, guys, feel free to correct me.
OH! One thing I forgot to mention. With my 242 in full time, if I've got one wheel on ice, only that wheel will spin and I go nowhere. Then I shift to part time and drive off.
01-18-2015, 08:54 PM
#4
Junior Member
Join Date: Jan 2015
Location: Georgia
Posts: 65
Likes: 0
Received 1 Like
on
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Year: 2001
Model: Grand Cherokee
Engine: 4.0 litre
Okay, this is what I know about 4 wheel drives, period. First of all, 4wd vehicles have a differential in both axles, front and rear, to accommodate differences in wheel speed when cornering. Because of this, if one wheel of an axle spins, the other will not drive, UNLESS that axle has a limited slip devise or "locker" in it. With me so far?
Now we get to the power transfer to those axles. As you already know, 4WD vehicles have a transfer case that divides the power output to both axles. HOW this power is divided is the subject of your question.
The 249's viscous coupling is basically a torque converter in respect that it sends power to both axles at all times and absorbs differences in axle speeds by "slipping". This slipping generates heat which is the major reason it eventually fails. The "good" part about it is if one wheel spins, the other axle is still driving. The "bad" part is there is no direct lock-up between both axles. It explain it further, imagine sitting with both wheels on one side on ice. Both those wheels will spin and you'll go nowhere. The same thing happens with the 231 and the 242, but we'll get to that later.
The 231 has a 2WD function and a "part time" 4WD function. In part time. both axles are driving together at the same speed with no slippage between them. That's why it should only be used on slippery or loose surfaces.
The 242 has the 2WD function and 2 different 4WD selections. In part time, again both axles are driving together at the same speed with no slippage. In full time, there is a devise that acts like an open differential inside the case so you can drive it on dry pavement to no ill effect. I've been told that it's not a true differential in that it divides the power 60/40 to the axles so really shouldn't be used for long periods on dry pavement. I've been going to do some research into exactly how it works, but I haven't yet.
Now we get to the axles themselves. With standard differentials, if one wheel looses traction, it will spin, period. A limited slip differential has clutches in it, so if one wheel looses traction, the other will still drive. A "locker" does the same function but is stronger than an LSD. If you're looking for the ultimate traction set-up, use a locker in the rear diff and a selectable locker in the front diff. A selectable locker is usually engaged by hydraulics or air pressure and is controlled by the driver or sometimes by automatic systems.
This whole post is my understanding of how jeeps work. I'm sure there are other opinions and, guys, feel free to correct me.
OH! One thing I forgot to mention. With my 242 in full time, if I've got one wheel on ice, only that wheel will spin and I go nowhere. Then I shift to part time and drive off.
Now we get to the power transfer to those axles. As you already know, 4WD vehicles have a transfer case that divides the power output to both axles. HOW this power is divided is the subject of your question.
The 249's viscous coupling is basically a torque converter in respect that it sends power to both axles at all times and absorbs differences in axle speeds by "slipping". This slipping generates heat which is the major reason it eventually fails. The "good" part about it is if one wheel spins, the other axle is still driving. The "bad" part is there is no direct lock-up between both axles. It explain it further, imagine sitting with both wheels on one side on ice. Both those wheels will spin and you'll go nowhere. The same thing happens with the 231 and the 242, but we'll get to that later.
The 231 has a 2WD function and a "part time" 4WD function. In part time. both axles are driving together at the same speed with no slippage between them. That's why it should only be used on slippery or loose surfaces.
The 242 has the 2WD function and 2 different 4WD selections. In part time, again both axles are driving together at the same speed with no slippage. In full time, there is a devise that acts like an open differential inside the case so you can drive it on dry pavement to no ill effect. I've been told that it's not a true differential in that it divides the power 60/40 to the axles so really shouldn't be used for long periods on dry pavement. I've been going to do some research into exactly how it works, but I haven't yet.
Now we get to the axles themselves. With standard differentials, if one wheel looses traction, it will spin, period. A limited slip differential has clutches in it, so if one wheel looses traction, the other will still drive. A "locker" does the same function but is stronger than an LSD. If you're looking for the ultimate traction set-up, use a locker in the rear diff and a selectable locker in the front diff. A selectable locker is usually engaged by hydraulics or air pressure and is controlled by the driver or sometimes by automatic systems.
This whole post is my understanding of how jeeps work. I'm sure there are other opinions and, guys, feel free to correct me.
OH! One thing I forgot to mention. With my 242 in full time, if I've got one wheel on ice, only that wheel will spin and I go nowhere. Then I shift to part time and drive off.
01-19-2015, 08:38 AM
#6
dave pretty much said what needed to be said but to put it in on sentence....
249 and 242 allow differential action between the front and rear axles when in full time mode, leaving the possibility that with open diffs one wheel could be left spinning on loose ground.
249 and 242 allow differential action between the front and rear axles when in full time mode, leaving the possibility that with open diffs one wheel could be left spinning on loose ground.
01-19-2015, 06:54 PM
#7
Old fart with a wrench
Thanks for the back-up. I needed that! Some of this tech crap gets so complicated, it needs to be spelled out.
Last edited by dave1123; 01-19-2015 at 06:56 PM.
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