How to troubleshoot my central different locker? - Defender Source
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  #1  
Old July 4th, 2005, 12:51 PM
MonLand
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Loic Fabro
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How to troubleshoot my central different locker?

Hi,

While replacing my front suspension setup, I found out (well.... I think) that my central diff does not lock properly. The light on the dash was on but the truck still backed with one wheel removed (and got off the jack.... :-( Yeah, I know, should have put something around the wheels....).

I gave it a quick look, but I can't see anything obvious from the outside that would show me if the central diff is locked or not. Do I have no other choice than to jack one wheel and try to move forward (well.... Using a floor jack with wheels this time!!!)? [I still don't like that idea anyway....]

Thanks,
Loic.
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  #2  
Old July 4th, 2005, 01:55 PM
dameek
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Dennis Meek
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When you place the lever in the position to lock the center differential is it not locking the differentials on the axles. Your transfer box normally assigns a percentage of output to either the front output shaft or to the rear output shaft. I have always assumed that under normal driving the transfer box assigns around 60% of the output force to the rear and 40% to the front. Then when one locks the center differential, each output is given half the force or 50% each.
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  #3  
Old July 4th, 2005, 02:38 PM
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Did you have the handbrake on? With it on and the diff locked the wheels won't move.
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  #4  
Old July 4th, 2005, 04:45 PM
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John B.
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Quote:
Originally Posted by dameek
When you place the lever in the position to lock the center differential is it not locking the differentials on the axles. Your transfer box normally assigns a percentage of output to either the front output shaft or to the rear output shaft. I have always assumed that under normal driving the transfer box assigns around 60% of the output force to the rear and 40% to the front. Then when one locks the center differential, each output is given half the force or 50% each.
No there is no such magic. Unlocked it is a normal differential. 50% of the toque is supplied to each driveshaft regardless of what is going on. When locked torque will vary up to 100% to either driveshaft depending on the wheel's speeds.

The light should actually sense the locking (not the movement of the lever). Put on the handbrake, gear box in neutral. Lift one front wheel. Unlocked you can spin the wheel, locked you can not.

It should not move if tthe handbrake is on and you lift one front wheel, regardless as the hand brake holds the rear axle by itself.
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  #5  
Old July 4th, 2005, 05:57 PM
redrover

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John ,I think you have it backwards. Take a standard front or rear differential. If you power it ,the wheels will both turn given equal resistence at each tire. Now decrease the resistence at one tire and all the power will go to it. Standard diffs send power to the tire with the least resistence.This allows the outside tires on a turn to rotate more and elliminate chirping. So on a CENTER TRANSFERCASE DIFFERENTIAL The unlocked center diff allows a full time four wheel drive case to compensate for different wheel speeds. Unlocked center in a tight turn allows the front drive shaft to rotate quicker than the rear drive shaft. Go to Moab and start up a 40 deg slope with the center unlocked. The center diff will send most of its power to the front slightly unweighted wheels. Why ,Standard diffs send power to the end with the least resistence. There are plenty of landys who have experienced a front end braking free and slide backwards due to forgetting to lock center . NOW locking the center diff or any other diff, transmits equal power to each side of diff. A locked center diff makes the front and rear drive shaft rotate at the same rate. With the center locked and the parking brake on will prevent the drive shafts from turning. But is this enough for all jacking situations? NOPE ,if you are parked on a steep incline with the center locked and parking brake on and highlift one side of the vehicle off the ground, you will see how the front and rear diffs will transmitt to the suspended tire. The result will movement down slope on the two grounded tires. Or jack fr and rr cady corner tires, the result being the same. This is why there are jacking proceedures, compliments of the function of open diffs. When jacking remember there is alot of gear slack in the drive train. Always try to be level , and block all wheels on the ground, use jack stands if you can/ which is always when at home. JP
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  #6  
Old July 4th, 2005, 06:09 PM
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John B.
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An open differential sends EQUAL TORQUE to each output shaft. If one wheel is spinning, the other wheel gets the same torque as the spinning wheel. Note I say TORQUE and NOT POWER. There is a big difference. You talk power and are mostly correct, but power is not important in this discussion. The distribution of torque from the gearbox out is what matters.

On an incline, the front wheels have less traction due to having less weight. When they lose traction, the rear wheels are still getting the same torque as the front wheels, however, it may not enough to propel the vehicle. With the center differential locked, the torque increases to the rear wheels as needed up to 100% if required.
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Old July 4th, 2005, 06:32 PM
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Hans Haase
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Due to the drivetrain design, I'd say check the parking brake drum first. The transfer case lock only means that the front and rear driveshafts will always turn the same... but it doesn't physically stop anything from moving.

But, due to the design of the truck, always use wheel chocks when jacking up a wheel. This is because the axle differentials are open diffs, and because the parking brake locks only the rear driveshaft. Unlike most cars, when you put the parking brake on it engages the rear wheel, which prevents the wheels from turning. When you lock the parking brake on a Defender, it locks the rear driveshaft from turning. BUT... it doesn't stop the wheels from turning.

If you only use the parking brake, and lift the front end up in the air, you might still have one of the back wheels start rolling.... or both roll in different directions. The truck won't go straight back, but it can kinda pivot in place if the other axle is up in the air.

-Hans
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  #8  
Old July 5th, 2005, 10:57 PM
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Loic Fabro
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Ok, to make sure I did not send everyone in the wrong direction:
- the hand brake was on (as mentioned before, to prevent the rear shaft from turning).
- three wheels were on the ground well.... One on the ground, two opposite (front left and right right were on small ramps).

Later on (once everything was in "normal" position without the ramps), I verified that I could not turn the wheel in the air..... Now I am suspecting that I was just stupid and jacked the front too high which allowed one of rear wheels to loose traction..... Should have choked the wheels!

Well.... somehow, better that than having a problem in the central diff! :-)

-Loic.
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Quote:
I have an ex MoD and an ex wife. The two no longer conflict with each other.
Quote:
it is not hoarding it is selective collecting
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1995 D90 NAS
1996 Discovery NAS
2006 LR3 NAS (hers, but comfy! :) )
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