I did this for 2 months and let me tell you it sucked! but it didn't harm anything just take it easy on the pedal.

 

I had the AMC 242 in my 85 Xj. It was 48/52 torque split in FT. 48% Front - 52% Rear.

 

^ Correct, the 242 used in our XJs also have 48/52 torque split.

 

I keep hearing that ratio, but I cannot figure out how a mechanical differential could be made to do that ???

 

Its not really a differential but a viscous coupling.

 

Could just be an artifact of the design, that they turned into a sales bullet. Extra resistance through the chain and output bearings, or something.

The 242 is mechanical

 

What's going on here
The exploded diagram I have seen shows a planetary and sun gear. This allows both the torque split and independent turning of output shafts.

 

In the NP242J, yes it was mechanical. I had an AMC 242 which used a vicous coupling.
Not all 231's and 242's were the same. There were various designs/changes through the years. The early model 242 was closer in design to the 249 found in the GC. Later on ChryCo switched to the mechanical design FT gearing

 

Seems like the torque would just go to the axle with the least traction ???


It doesn't really matter because it seems to work fine even on muddy roads. Don't need to use 4-lock (part time) unless there is a significant diagonal offset between the front/rear axles.


I just question the advertised torque split with a mechanical differential.

 

It goes to the axle with the least resistance, which is usually the wheel that is turning the fastest. When the car is driving straight, all wheels are turning at the same number of revolutions per minute, so the differentials in the axles are presenting similar resistance and distributing the torque to the wheels evenly. Then when you take a turn, the outside front wheel gets the longest arc and has to make more revolutions per minute so it has less resistance and gets more power. But it doesn't ALL go there--once the wheel is able to apply load, the amount of resistance equalizes so you still end up with all wheels getting some (variable) amount of power.

The only time it is 100% to a single wheel is when there is no resistance on that wheel (jacked up in the air or spinning in mud), so it never loads up and the other wheels do not ever get anything.

The chain and sprocket on the front output adds to resistance. The small bearing cup on the front output adds to resistance. Versus the rear output is right there and has less resistance. So the rear axle gets power until it equalizes with the front, and there is your 52/48 split

 

 

that's pretty good description/explanation.

 

Makes sense, I guess ... if you take the rear drive shaft out, then 100% of the torque is going to go to the rear output yoke where there is zero resistance (it's futile anyway, they tell me ) and you're not going anywhere unless you put it in "part time" 4wd (hi-lock).


Still I have to wonder about the jeep engineers calculating the difference in mechanical friction front to rear in order to advertise the 52/48 torque. Seems like to most people 50/50 would be good enough.

 

yes. definitely run it in part time high, not full time.

 

Correct,same thing if front shaft is removed, the center diff is sensitive.

I believe torque is mechanically split. Sun gear is connected to main-shaft, planetary gears turn housing and front output.