Locking centre differential
12-02-07, 09:03 PM
#1
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Locking centre differential
I am not a technical guy when it comes to this.
What is the point of locking the centre differential on the LX?
I was only the impression that the LX as a fixed ratio of front to rear torque.
What is the point of locking the centre differential on the LX?
I was only the impression that the LX as a fixed ratio of front to rear torque.
12-03-07, 07:09 AM
#2
You answer is correct when all 4 tires have traction. But as soon as one wheel, say up front, breaks loose, the front diff (open diff) will put all torque to the spinning wheel. Similarly, the center diff (being open if unlocked) will put all torque into the front driveshaft. In other words, if you lose traction in one wheel, even w/ all wheel drive, you are stuck. By locking the center diff, you guarantee that 50% of the power goes up front, 50% goes to the rear. Now consider the same scenario w/ CDL locked. The front diff (open) still applies all the torque to the spinning wheel, but the rear driveshaft now gets half the torque, and since both rear wheels have traction, you are out of the bind. Best scenario is to have center diff locked and front/rear diff locks. If you lock all 3 diffs, you guarantee that 25% torque goes to each wheel, so even if you lose traction on 3 wheels, the 4th wheel can save you.
Note that you should NOT drive w/ the CDL locked on high-traction surfaces. This binds up the drivetrain since the t-case is forcing the front/rear driveshafts to turn at the same rate, yet the front/rear axles are turning at different rates due to different turning radii. In other words, you can damage the drivetrain by doing this. Clues that the CDL is locked and drivetrain binding is you can't shift from 4wd high to low, vehicle leans to one side when turning slowly, etc. There have been some cases when the light in the dash has burned out and the CDL unknowingly locked.
So in summary, in slipperly situations:
1) open front, open center, open rear diffs: if one wheel slips, you lose all traction on the other 3 wheels.
2) open front, locked center, open rear: (98-07 LX, 00-07 LC) You can lose traction on either one front wheel or one rear wheel, but not simultaneously or you'll get stuck.
3) open front, locked center, locked rear ('98-99 landcruiser came this way as an option): You can lose traction on one wheel in the front and one wheel in the rear and be ok
4) locked front, locked center, locked rear: '93-97 LX450: you can lose traction on 3 wheels and be ok.
The new LC has a torque-biasing center diff, so it helps prevent situation (2) above yet allows you to turn the vehicle on high-traction surfaces w/o binding the drive train.
Note that you should NOT drive w/ the CDL locked on high-traction surfaces. This binds up the drivetrain since the t-case is forcing the front/rear driveshafts to turn at the same rate, yet the front/rear axles are turning at different rates due to different turning radii. In other words, you can damage the drivetrain by doing this. Clues that the CDL is locked and drivetrain binding is you can't shift from 4wd high to low, vehicle leans to one side when turning slowly, etc. There have been some cases when the light in the dash has burned out and the CDL unknowingly locked.
So in summary, in slipperly situations:
1) open front, open center, open rear diffs: if one wheel slips, you lose all traction on the other 3 wheels.
2) open front, locked center, open rear: (98-07 LX, 00-07 LC) You can lose traction on either one front wheel or one rear wheel, but not simultaneously or you'll get stuck.
3) open front, locked center, locked rear ('98-99 landcruiser came this way as an option): You can lose traction on one wheel in the front and one wheel in the rear and be ok
4) locked front, locked center, locked rear: '93-97 LX450: you can lose traction on 3 wheels and be ok.
The new LC has a torque-biasing center diff, so it helps prevent situation (2) above yet allows you to turn the vehicle on high-traction surfaces w/o binding the drive train.
12-05-07, 08:49 PM
#3
What i will write is for 2000-up LX only:
In reality, the MAIN reason most people LOCK the center diff in the LX is to turn OFF VSC (stability control that has a tendency to dethrottle). Otherwise, very few off-roaders (esp. beginners) will ever see the need of the true 50/50% split. An example is if BOTH your front (or rear) wheels or 3 wheels are in mud (no traction)...in which case, locking the center diff is a good thing because it allows 50% of power to be routed to the AXLE that still has the wheel(s) with traction. Without the center diff LOCK, 100% power will be routed to the axle that has both wheels slipping (thus, you are stuck). However, this is rarely encountered in off-roading.
When off-roading in rough terrain or mud, you need to LOCK the center diff because it turns OFF VSC. Because, if you are stuck in mud, VSC may interpret your attempts to get out as oversteer/understeer (especially if you are sliding back and forth). Therefore, it WILL cut power (dethrottle). With VSC off, ATRAC (4-wheel traction control) can function with full engine power to get you out...aka to power your way out. Thus, you can spin all four wheels! I have seen this on my brother's Lexus LX470 and Discovery. THAT IS WHY YOU LOCK THE CENTER DIFF, among other less important reasons!
Other reasons? (CDL = center diff lock)
1: ATRAC requires a certain minimal wheel rotation speed to work. If you are moving very slowly, it won't do much. Backing slowly down a steep hill is one scenario where ATRAC does not work well.
2: If you have an electrical failure that takes out the system, or take a stick in a wheel sensor harness, you are stuck. With a CDL you can regain much of the lost traction.
3: If you break a driveshaft U joint, you are stuck - your rig will go nowhere under its own power. With CDL you can lock the center diff, remove the offending shaft, and attempt to drive out of the woods.
4: If you want to add limited slip or locking diffs in the axles for improved low speed traction (see #1) then they won't be effective without a CDL.
5: ATRAC is hard on the brakes and the differential spider gears. A CDL helps by reducing the workload on the ATRAC (aka redistributing the workload better).
Hope this helps.
BTW, if you want to read more about ATRAC, then see: http://www.toyota-4runner.org/showth...&threadid=5036
In reality, the MAIN reason most people LOCK the center diff in the LX is to turn OFF VSC (stability control that has a tendency to dethrottle). Otherwise, very few off-roaders (esp. beginners) will ever see the need of the true 50/50% split. An example is if BOTH your front (or rear) wheels or 3 wheels are in mud (no traction)...in which case, locking the center diff is a good thing because it allows 50% of power to be routed to the AXLE that still has the wheel(s) with traction. Without the center diff LOCK, 100% power will be routed to the axle that has both wheels slipping (thus, you are stuck). However, this is rarely encountered in off-roading.
When off-roading in rough terrain or mud, you need to LOCK the center diff because it turns OFF VSC. Because, if you are stuck in mud, VSC may interpret your attempts to get out as oversteer/understeer (especially if you are sliding back and forth). Therefore, it WILL cut power (dethrottle). With VSC off, ATRAC (4-wheel traction control) can function with full engine power to get you out...aka to power your way out. Thus, you can spin all four wheels! I have seen this on my brother's Lexus LX470 and Discovery. THAT IS WHY YOU LOCK THE CENTER DIFF, among other less important reasons!
Other reasons? (CDL = center diff lock)
1: ATRAC requires a certain minimal wheel rotation speed to work. If you are moving very slowly, it won't do much. Backing slowly down a steep hill is one scenario where ATRAC does not work well.
2: If you have an electrical failure that takes out the system, or take a stick in a wheel sensor harness, you are stuck. With a CDL you can regain much of the lost traction.
3: If you break a driveshaft U joint, you are stuck - your rig will go nowhere under its own power. With CDL you can lock the center diff, remove the offending shaft, and attempt to drive out of the woods.
4: If you want to add limited slip or locking diffs in the axles for improved low speed traction (see #1) then they won't be effective without a CDL.
5: ATRAC is hard on the brakes and the differential spider gears. A CDL helps by reducing the workload on the ATRAC (aka redistributing the workload better).
Hope this helps.
BTW, if you want to read more about ATRAC, then see: http://www.toyota-4runner.org/showth...&threadid=5036
Last edited by tigmd99; 12-05-07 at 08:55 PM.
12-11-07, 04:29 AM
#4
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I have RX350 in which VSC cannot be disables but there are some techniques to do so by playing with Brakes and Parking Brakes. My question is if I disable VSC, will Attraction control still work. My understanding is that Attraction control is good in Off-Road especially on sand becuase it moves the torque to the other normal tyres leaving the slipping one. However, with VSC enabled Attraction is not doing well on sand because of the engine being slowed down by VSC which keeps my RX350 stuck in sand.
Can someone help?
Can someone help?
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