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Unread 10-16-2012, 04:07 AM   #1
michaelreed
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Default Center diff and vsc off.

So it started raining super hard today so turned on 4wd to give it a workout since I hadn't used it much this summer. I also locked the center diff to work it out for a sec and the vsc off light came on. Is that normal? Maybe I just hadn't noticed it before. Haven't really had to use it much to be honest.
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Unread 10-16-2012, 05:17 AM   #2
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yep...
A-OK...
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Unread 10-16-2012, 08:20 AM   #3
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I think because everytime I've used 4wd I see the center diff lock light flashing so I assumed the center diff button was pushed. First 4wd vehicle so still getting used to it. When would you lock the center diff as apposed to just using it in awd(4hi)? Snow? Or is the center diff more if your stuck in the mudd?
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Unread 10-16-2012, 09:19 AM   #4
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Quote:
Originally Posted by michaelreed View Post
So it started raining super hard today so turned on 4wd to give it a workout since I hadn't used it much this summer. I also locked the center diff to work it out for a sec and the vsc off light came on. Is that normal? Maybe I just hadn't noticed it before. Haven't really had to use it much to be honest.
There's no need to lock the center diff to "work it out". You shouldn't lock it on pavement, either.

You should, however, switch to 4HI every now and then to keep everything up front lubed.
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Unread 10-16-2012, 10:09 AM   #5
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Gotcha. I read something that bulldog or expat wrote that said you should lock it every once and a while, not the case?
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Unread 10-16-2012, 10:45 AM   #6
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It can make it lock up easier the more it is used, but it doesn't lube anything like going into 4HI does. Just don't lock it on pavement, that's the important part.
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Unread 10-16-2012, 11:01 AM   #7
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Ok cool thanks man.
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Unread 11-14-2012, 03:02 AM   #8
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hmmmm..ur center diff light flashes when 4wd is engaged?.......thats not right. it shud be a solid green, when its engaged
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Unread 11-14-2012, 08:17 AM   #9
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hmmmm..ur center diff light flashes when 4wd is engaged?.......thats not right. it shud be a solid green, when its engaged
Not quite right, solid green is for 4HI selected and engaged. Solid amber with the little "X" in the center is when the center diff is engaged. Both will flash initially when selecting 4HI but after everything engages, only the green 4WD symbol should be on until you select center diff lock as a separate step. The VSC light comes on to let you know its been disengaged due to the inherent wheel slip required when the center diff is locked. Otherwise the system would basically be fighting itself. As others have mentioned, I usually engage 4HI a couple times a month and then every now and then, if I haven't wheeled in while and when I am stationary, I will engage the center locker, 4LO, and the rear locker just to exercise all the actuators.
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Unread 11-14-2012, 05:24 PM   #10
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Not sure what the concern is with locking the center diff on pavement.

My understanding of the function of the center diff is that it assures near even distribution of torque to front and rear drive shafts (in my V8 4WD). It has no implication on how the wheels are turned left to right. My understanding is that I can engage my center diff any time I want, pavement or no. It may be less efficient by taking out the self adjusting of the distribution of power but no harm done.
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Last edited by jdkilroy; 11-14-2012 at 05:33 PM. Reason: clarity
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Unread 11-14-2012, 06:24 PM   #11
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Originally Posted by jdkilroy View Post
Not sure what the concern is with locking the center diff on pavement.

My understanding of the function of the center diff is that it assures near even distribution of torque to front and rear drive shafts (in my V8 4WD). It has no implication on how the wheels are turned left to right. My understanding is that I can engage my center diff any time I want, pavement or no. It may be less efficient by taking out the self adjusting of the distribution of power but no harm done.
The function of the center diff is to allow the front and rear driveshafts to spin at different speeds, just like your front or rear diff in relation to either axle shaft. This creates an "AWD" effect. The functinon of the center diff lock is to split the torque to the front and rear 50/50. With the diff open and no traction on the rear tires, they'll sit there and spin, just like a locked vs. open rear diff (not counting ATRAC) *Edit* The center diff does have a limited slip function when open, this would apply some of torque to the axle with traction, but not equal. With the diff locked if you have poor traction on either front or rear, the opposing axle still gets equal torque applied.

The problem with pavement and center diff locked is binding of the transfer case gears or front or rear diff gears. Now I'm not exactly sure what the stock gear ratios are on my '05, but on my 94 Cherokee the front diff gearing was like 3.58 and the rear was 3.55 (no center diff, same as locked 4runner diff). If you drove on pavement in 4WD that difference in the gearing causes the diffs, driveshafts, and transfer gears to want to turn at different speeds, even though the tires are making the same revolutions. Eventually this would cause something to break. If you are on a loose surface (where diff lock is meant to be engaged) the tires can slip a little bit to make up for the difference, instead of loading up the driveline.

This is essentially why they put the center diff in in the first place, so you can drive on pavement in poor traction situations with it open (like snow or rain). Then on when you want to wheel on dirt you can lock it up to distribute the torque 50/50.

Sorry for the use of a cherokee as an example, i just dont know what the ratios are on my Runner.

Last edited by El-Coyote; 11-14-2012 at 06:35 PM.
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Unread 11-14-2012, 06:30 PM   #12
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Quote:
Originally Posted by jdkilroy View Post
Not sure what the concern is with locking the center diff on pavement.

My understanding of the function of the center diff is that it assures near even distribution of torque to front and rear drive shafts (in my V8 4WD). It has no implication on how the wheels are turned left to right. My understanding is that I can engage my center diff any time I want, pavement or no. It may be less efficient by taking out the self adjusting of the distribution of power but no harm done.
I can see why you would arrive at this conclusion but here is where you are wrong. Locking the center diff physically locks the front and rear drive shafts together so they are now turning as one. Where this is a problem on pavement is the front end and rear end do not travel the same distance through a turn. Just as the outside wheel and inside wheel travel different distances in a turn, so too do the front and rear ends. Since the driveshafts MUST turn at the same speed (they have been locked together) the only way to dissipate this differential rotation is through wheel slippage. This is not a problem off road as dirt or gravel offers much less grip and the wheel can easily slip to dissipate the torque. Pavement, however, is too grippy and instead of dissipating this torque, it is transferred right back into the drivetrain, causing massive loads and binding that can lead to failure. The normally unlocked full time transfer case of your V8 allows the front and rear driveshafts to turn at different speeds allowing full time, on road use. Locked up though, you can hopefully now see how you can overload and damage your transfer case when using it this way on road.
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Unread 11-14-2012, 06:43 PM   #13
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Two answers at once!!!! We're on top of it!
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Unread 11-14-2012, 06:49 PM   #14
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Epic amounts of knowledge are being thrown around here...almost deleted my post after I saw yours but hey, the more the merrier!
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Unread 11-14-2012, 06:54 PM   #15
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Yeah, and I wasn't sure if the ratios are actually different on the 4Runners, or if it just binds because of the turning, so now we got both bases covered
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Unread 11-15-2012, 05:06 AM   #16
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Thanks for info.

I guess I was getting a little confused with the function of the Torsen; there is some inconsistency when information sources discuss its operation; torque vs rotation.

So the center diff acts to split/distribute torque when not locked but when locked, it just becomes a mechanical connection between front and rear drive shafts forcing them to rotate at some fixed relationship to the transmission speed ..... right ?

Due to the physics of anything other than a point source traveling along a arc, the 4 corners all need to be able to rotate at different speeds.

So is it fair to say that if the front and rear differentials were geared the same then this would be less of an issue ? (I realize that that might not make sense from a real word application perspective)

Not trying to be a pain in the ass, just trying to better understand what I want to do with my rig in the area of lockers and gearing. Thanks for your patience.
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Unread 11-15-2012, 07:59 AM   #17
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Regardless of differential gearing, each axle "sees" a different distance when turning. Lets isolate the front end from the rear end for this discussion and remember, this only applies to a turning vehicle. Some number of driveshaft rotations is required to move the vehicle forward a certain distance around a turn, lets say 100 rotations. So 100 rotations are fed into the front axle and the tires rotate, the inner less than the outer, and the vehicle moves forward. To travel the same distance, however, the rear driveshaft only needs to turn 97 times because the rear tires travel a shorter distance and subsequently the axle rotates fewer times and so does the rear driveshaft. So, each axles differential allows the wheels on that axle to turn at different speeds but in the case of the vehicle as a whole, each axle turns at different speeds and so do their respective driveshafts. So, in the example above, a AWD type torsen center diff, unlocked, allows the front driveshaft to make its 100 turns as the front axle rotates and 97 turns for the rear driveshaft. This 3 rotation "differential" is dissipated through the differential gearing in the torsen. When it is locked, however, the front driveshaft still needs to rotate 100 times to travel a certain distance but now so too does the rear because they are locked together. The rear wheels must now slip this extra distance away and since the ground is relatively slippery, this is not a problem. On pavement and still locked, the front driveshaft is still trying to rotate 100 times but the rear wheels cannot slip and are instead transmitting all the torque of those 3 extra rotations back into the gear train. As the distances and differences between front and rear becomes greater, the torques and loads build until something mechanically breaks to dissipate the load. If you travel in a perfectly straight line, front and rear driveshafts turn at the same speed and you can lock up the diff on pavement. As soon as you turn though, front and rear wheels take different paths over the ground and things start to bind.
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Last edited by Synister; 11-15-2012 at 08:29 AM.
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Unread 11-15-2012, 08:52 AM   #18
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The green light is your 4HI mode on feature, the VSC orange light is your VSC OFF feauture (happens when Center diff is engaged or VSC is turned off in 08-09 models) The center diff light is the X going through the axle driveline.


I have some general questions about locking my center diff on a 2008 Toyota 4Runner. When is a good time to lock the diff in a difficult terrain, mud, rocks? TORSEN Yes, locking the differential would work best in situations where you would need to have all 4 tires moving such as deep mud or rock climbing.

Can you still make turns on loose terrain with the diff locked? TORSEN You can make turns when the differential is locked but you are driving the entire drive line as one axle and since the outer tires are turning on a larger radius you will wheel hop or slip the inside wheels.

Mainly how does this work? TORSEN We explain the Torsen as a torque multiplier in that it multiplies the available torque by the bias ratio. If you have a center differential with a bias ratio around 2.0:1 then the Torsen doubles the available torque in the system and send it to the axle with the slower moving tires which also happens to be the ones with better traction.

Does it just split the power from the front to rear axles or to all 4 wheels? TORSEN The torque is actually split from the front to rear axles. To split the torque to the wheels you would need a Torsen on each axle.

Is a rear locker better than the center locker? TORSEN That is a loaded question! We have always stated that a Torsen in each drivetrain segment would work best but to say one is better than the other depends on how you are using your vehicle. Center differential works best in AWD and 4WD situations whereas a rear locker works best in situations where you need to push the vehicle.


I hope this helps.
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Unread 11-21-2012, 03:39 AM   #19
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Not quite right, solid green is for 4HI selected and engaged. Solid amber with the little "X" in the center is when the center diff is engaged. Both will flash initially when selecting 4HI but after everything engages, only the green 4WD symbol should be on until you select center diff lock as a separate step. The VSC light comes on to let you know its been disengaged due to the inherent wheel slip required when the center diff is locked. Otherwise the system would basically be fighting itself. As others have mentioned, I usually engage 4HI a couple times a month and then every now and then, if I haven't wheeled in while and when I am stationary, I will engage the center locker, 4LO, and the rear locker just to exercise all the actuators.

just a little clarification pls,...apart from 4hi and 4lo,,,is there any other way i can engage 4wd?.. i hv a v6 sr5 05 runner.. i normally drive on H2..and D, beside the D there is 4, 3,2........when can one engage 4 or 3 or 2?.....i know they r for better engine braking.........but i could be wrong
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Unread 11-21-2012, 05:00 AM   #20
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Just stick it in "DRIVE" and... drive
But seriously... "D" is where you'll be for almost every
situation
Although you can select a lower gear in the transmission
the computer will figure that out before you do (...9 times outa 10)
I only pull down a gear out of D on long climbs when I'm fully loaded
And I stay in 1st gear when I'm wheeling

As far as the 4wd system
4hi and 4low will BOTH be AWD
until you LOCK the center diff ...then it functions as Part-Time or 50/50 4WD
which is what you would use in low traction situations (...mud ...deep snow ...rocks)
AWD is safe on pavement year round or on snowy or ice roads.

Make sense?
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