1998 XJ 4x4 - Really 2x4?

Last year I had a single vehicle accident in my XJ. It was early in the morning and during a mildly severe rain storm. (tropical depression moving through).

It had been raining for hours so it wasn't a situation where the oil from the road had just been brought up from the rain.

I was driving down a toll road at about 60 mph, in full time 4x4.

I had been driving this XJ daily for the 9+ years we've owned it, and it was the safest thing I have ever driven in the rain, rock solid.

To my utter amazement things started to feel funny, like hydroplaning. I took my foot off the gas, instinct from prior years 2 wheel drive vehicles, and about 1 second later the XJ is at a 45 degree angle sliding. Less than a second later at 180 degrees, and foot now solidly applied to the brake petal, I was wondering where the 20 foot high concrete wall was, a 1/2 second later I knew where it was as the XJ slammed into it at about 270 degrees from my beginning of the out of control spin. At the 360 degree mark I slowly came to a stop, foot still mashing the brake petal.

In retrospect I thought it might have been better to apply more gas encouraging the wheels to gain traction. What I have found out recently makes me wonder if this would caused a better outcome.

Recently, from this site, I have been learning lots of things about my XJ that I didn't know.

The most disturbing thing I have found was that the Corp. 8.25 uses clutches to apply power to the two rear wheels, and that the clutches go out at about 35k miles. I had about 100k when the accident occurred. So that means only 1 rear wheel was "active" prior to the spin.

I also found out that only 1 front wheel has power applied to it in 4x4 full time transfer case setting. This means only 1 front wheel was "active" prior to the spin.

Since I was in Full Time 4x4 this means the transfer case was not locked front axle to back axle. Does this mean that only 1 wheel had traction?!?!?!

So what I would like to know from you guys, is what I have surmised here make sense? Could it be that in my JEEP 4x4 I was in effect a 1x4!?!?!?

I have lost confidence in my XJ during the rain. I want to get it back to at least the point it was in it's earlier years.

I am planning on putting a LockRight noslip in the Corp 8.25 first, then another in the Dana 30 later. I am currently trying to get my NP242 repaired so I can at least put it in full time.

As you may be able to tell I was at the end of life on the rear tires, which certainly contributed to the spin, however I really thought that the front tires would play a bigger role in the traction and stability of the XJ.



I have since replaced these OEM tires with 32x11.5x15's. They are wider so more traction.

Also my understanding is that PART TIME 4x4 should only be used in very slippery circumstances. Certainly the spin qualifies as a very slippery situation, however I don't think that driving in the rain qualifies as a PART TIME 4x4 application. What do you guys do with the NP231 since you do not have a FULL TIME 4x4 selection? PART TIME 4x4 and risk stretching your chain?

Teach me, I am a sponge. :dunce:

Clutches in the axle??? Do you have a locker?

Personally, I think your problem was driving 60mph in a "mildly severe" rainstorm - man, there's so many things I want to say here, my brain is about to overload...you seem surprised that you lost control of your vehicle. The hydroplaning was caused by excessive speed for your tires - you were literally floating on water - I personally wouldnt be driving in 4wd unless I needed the traction off-road or in the snow - not just because "conditions were less than optimal" and I sure as heck wouldnt be driving over 45mph in 4wd - any setting.

Just because you got wider tires doesnt automatically mean better traction. Wider tires are actually worse in snow and some other situations. And you got Mud Terrains I see, which arent very good for rain or snow.

Good luck...I'm glad I dont live in TX.

You hydroplaned. You are really over thinking the rest of it.

Full-time mode with an NP242 provides an extra safety margin in the rain but it can't overcome excessive speed and bald tires.

muckleroy said:

As you may be able to tell I was at the end of life on the rear tires...

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That's the key phrase here...

yea, you are overthinking this.

your tires were bald, that's why it happened.

Lol get your sponge ready , as threads like this tend to generate lots of replies.
First off, full-time/part-time ...your transfercase has no bearing on how torque is travelling through the front differential. Your front diff alone decides that, and unless you bought a locker or LSD for it, it is an open diff. What many don't understand is that an open diff in reality will send equal torque to each tire all the time, BUT
power follows the path of least resistance, meaning the diff recieves total torque input equal to the resistance of the tire with the LEAST traction, so if one tire has no resistance it require almost no torque to spin, so the tire with traction recieves so little torque that it does nothing. The same applies to your rear differential, and your oem clutch style LSD should last past 35k miles. It won't lock up both tires but should certainly make it self known during rain fall.


As far as part-time vs full-time, this has to with the difference in wheel travel of the the front vs rear tires. When you go around a corner the front tires travel more distance than the rear tires, which means that since the vehicle speed is constant the front tires must turn faster. But what happens when the front tires are connected to the rear tires via a 4x4 system?
Since the front driveshaft wants to spin faster than the rear when going around a corner some magic has to happen in the transfercase or a wheel has to slip somewhere.
Partime transfercases do nothing to combat this problem, full time cases use a differential, viscous coupling or other method to deal with "bind up". This is also why you don't
see 4x4 with different size tires on the front and the back and why you must run the same gears in your front and rear diffs. Generally speaking so long as your are driving straight
you can run part time in high traction environments at speed.

You are one the right track but you still don't quite get how the transfercase and differential work by themselves and as a system, by the end of thread hopefully it will be clear.

Putting lockers in both diffs makes "Full Time" useless, ask my wife.

JNickel101 said:

Clutches in the axle??? Do you have a locker?

Personally, I think your problem was driving 60mph in a "mildly severe" rainstorm - man, there's so many things I want to say here, my brain is about to overload...you seem surprised that you lost control of your vehicle. The hydroplaning was caused by excessive speed for your tires - you were literally floating on water - I personally wouldnt be driving in 4wd unless I needed the traction off-road or in the snow - not just because "conditions were less than optimal" and I sure as heck wouldnt be driving over 45mph in 4wd - any setting.

Just because you got wider tires doesnt automatically mean better traction. Wider tires are actually worse in snow and some other situations. And you got Mud Terrains I see, which arent very good for rain or snow.

Good luck...I'm glad I dont live in TX.

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I have Trac-Lok Differential Rear Axle. Which my understanding is a set of clutches that help lock up the rear wheels as necessary.

I didn't state it directly in my original post, but over the 9+ years of driving faster and in worse weather the XJ has never gone out of control. This is why I am concerned that there is something that I need to fix, or at least understand what has changed. It may be as you guys say, just worn tires. That would be great but i'd be willing to bet that over the 5 or so set of tires I have had on this XJ I've driven them this worn and in weather as bad as I did this time.

I am not dismissing the information given here, just responding so you will have a better idea why I am concerned and confused as to why this happened. Thank you all for all the information given so far.

goodburbon said:

Putting lockers in both diffs makes "Full Time" useless, ask my wife.

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Please tell me more. I like the idea of having better traction, but I don't want to break something in the process.

My understanding of FULL TIME vs. PART TIME is the front and rear axles are not locked together.

My thinking was that having FULL TIME with no slip front and rear would allow me to have BETTER traction in FULL TIME rather than worse.

PART TIME should be the best traction with true locked left right and front back 4 wheel drive.

Ronbo said:

That's the key phrase here...

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X100

muckleroy said:

Please tell me more. I like the idea of having better traction, but I don't want to break something in the process.

My understanding of FULL TIME vs. PART TIME is the front and rear axles are not locked together.

My thinking was that having FULL TIME with no slip front and rear would allow me to have BETTER traction in FULL TIME rather than worse.

PART TIME should be the best traction with true locked left right and front back 4 wheel drive.

Click to expand...

Full time, as you have discovered, allows differentiation front to rear, open differentials allow differentiation left to right. Lockers allow differentiation left to right when disengaged. As soon as throttle is applied the locker engages locking left and right tires together. In 2wd a rear locker will cause sudden understeer if you apply power in a corner, if you are powering through a corner and let off the gas you get sudden oversteer. It is a predictable pattern and can be fun Full time 4wd helps negate this effect a bit with the front wheels pulling in the direction they are turned.


Now add to the mix a front locker. In 2wd it is disengaged as no torque is being applied to the diff. Put it in 4wd full time and suddenly you have a completely different animal. Now when power is applied you have 4 wheels trying to spin at the same speed, and all pulling the vehicle straight ahead. The Understeer in corners when power is applied is Massive, as is the tendency for the wheels to pull themselves straight. Let off the gas and you get a huge swing to oversteer. It is dangerous.

You currently have a clutch type LSD in the rear, those are nowhere near lockers and the springs keep constant pressure on the clutch plates so there is no sudden shift of torque as with a locker. These are decent for street traction and only marginal offroad.

If you want a Daily driver that can still use 4wd full time in the rain either use selectable lockers or Limited slips all around or a locker in the rear and limited slip / selectable in the front.

In 4wd My jeep with a 231, selectable rear and Truetrac front handles wet roads waaaaaay better than my wifes 242 with detroit rear and lock=right front. I just tried it once with each, now when it rains we are both 2wd,

Hope this helps

like everyone else said,
bald tires + rain + high speed = bad
mashing teh brake under slipery conditions = bad
and full time 4x isnt going to magically save you from hydroplaining/spinning

goodburbon said:

Full time, as you have discovered, allows differentiation front to rear, open differentials allow differentiation left to right. Lockers allow differentiation left to right when disengaged. As soon as throttle is applied the locker engages locking left and right tires together. In 2wd a rear locker will cause sudden understeer if you apply power in a corner, if you are powering through a corner and let off the gas you get sudden oversteer. It is a predictable pattern and can be fun Full time 4wd helps negate this effect a bit with the front wheels pulling in the direction they are turned.


Now add to the mix a front locker. In 2wd it is disengaged as no torque is being applied to the diff. Put it in 4wd full time and suddenly you have a completely different animal. Now when power is applied you have 4 wheels trying to spin at the same speed, and all pulling the vehicle straight ahead. The Understeer in corners when power is applied is Massive, as is the tendency for the wheels to pull themselves straight. Let off the gas and you get a huge swing to oversteer. It is dangerous.

You currently have a clutch type LSD in the rear, those are nowhere near lockers and the springs keep constant pressure on the clutch plates so there is no sudden shift of torque as with a locker. These are decent for street traction and only marginal offroad.

If you want a Daily driver that can still use 4wd full time in the rain either use selectable lockers or Limited slips all around or a locker in the rear and limited slip / selectable in the front.

In 4wd My jeep with a 231, selectable rear and Truetrac front handles wet roads waaaaaay better than my wifes 242 with detroit rear and lock=right front. I just tried it once with each, now when it rains we are both 2wd,

Hope this helps

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This is great information! Thank you for taking the time to type it all in.

Put on your flame suit. . .

You "like the idea of better traction", were you driving on bald tires, and after losing control on the street. . . installed mud-terrrains and a lift. Slow your a-- down, or the next time you will roll it.

As you were traveling at cruising speed and NOT attempting to accelerate when it broke loose, I'd say you did not have a problem with "traction."

An NP242 in full-time with a good set of tires is as good as it gets for driving on rain-slick streets. Do some searching, modifications based on your thoughts will only degrade street performance

So with what I have "learned" so far I'm an idiot (lol), and a good set up for a daily driver with good off road performance would be Lock Right slip for the front diff and a Lock Right no slip for the rear.

Lock Right is my choice, maybe not yours.


I like this! This will save me a couple of hundred dollars on the Lock Right stuff.

muckleroy said:

So with what I have "learned" so far I'm an idiot (lol), and a good set up for a daily driver with good off road performance would be Lock Right slip for the front diff and a Lock Right no slip for the rear.

Lock Right is my choice, maybe not yours.


I like this! This will save me a couple of hundred dollars on the Lock Right stuff.

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That'll work off road but it will SUCK on road in full-time. . .

OMFG dude, did you put ricer neon on a f**king jeep :laugh::roflmao::laugh:



sorry to :flame: ya man, but wtf

EDIT: x2 on what 3XJ said, aggressive limited slips don't have the best on road manners, especially in the rain, if you don't plan on much off roading skip the front LSD and if its just going to be a pavement pounder/mall crawler don't waste your money on the rear LSD

FoMoCo said:

OMFG dude, did you put ricer neon on a f**king jeep :laugh::roflmao::laugh:

sorry to :flame: ya man, but wtf

EDIT: x2 on what 3XJ said, aggressive limited slips don't have the best on road manners, especially in the rain, if you don't plan on much off roading skip the front LSD and if its just going to be a pavement pounder/mall crawler don't waste your money on the rear LSD

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lol, not a problem.



No they are red rock crawling LED lights. I was torn between WHITE or RED LEDs, the pimp in me clicked RED. :sure:

No I definitely want to do off road. I loved it years ago with my first 4x4, 1983 Chevy pickup.



I have a family now, so it's taken 10 year before I could start building up my XJ.

I know I need to do something about that Trac-Loc. I don't want to be replacing the clutch pads every 35k miles.

goodburbon- A major concern with me is keeping the part time function. I knew I'd want just a limited slip in the front. Does it also need to be a limited slip in the rear or could you run a "real locker"?

Slow down, and go wheeling with what you have, then add mods as you see fit. You are asking very basic questions about parts that cost a significant amount of money. You can wheel some serious trails before you begin to need looking at your open front diff. And even then since it seems like this jeep does road duty why would even consider a lunchbox over a selectable locker in your front diff? The only thing you probably NEED at this point is some armour.