question about 4x4 and locking differential

hi guys
I dont have a 4x4 vechicle, i have been saving and shopping around for a tacoma trd-off rd

i have a question about the 4x4 on how conjunction with rear locking differential

when the 4x4 engaged, i know it can't ride on dry pavement because of the same speed on 4 wheels
but what if the rear-locking engaged? it means the 2 rear wheels pushing the same time
Then how does 4x4 and rear differential engagment together? how does the front wheels will work?

Please help me claify this!!

 

I believe the only time you can engage the locking rear differential is when the truck is in 4-Lo (at least that is the stock configuration ).

It doesn't really effect the front axle at all. It just gives you the ability to get the most possible wheel spin out of the rear wheels to the ground (or whatever you are crawling over).

 

With the rear differential locked there is no slip in the rear differential. Differential locks disable the differential's ability to sense resistance.
By locking the rear differential the truck is forced to send equal amounts of torque to the left and to the right wheel.
This means that any wheel with traction will receive torque to move the car.
(Somewhere off the Web)

 

Ensure you do not run he rear dif lock without being in four low, you should never need it in any other circumstance. I don't think it will let you engage it but don't even bother trying, you shouldn't need to. It should only be used in circumstances where 4-lo isn't quite enough, there aren't too many places where 4-lo is't enough. It has no effect on your from dif. You should also try to only using while going in a straight direction as to not cause undue stress.

 

To confuse you more get a Prerunner TRD with the locking rear diff!!! you can run it locked anytime (complete stop to engage first) real kick in the pants fun....I had a 2000 prerunner and ran the crap out of it then traded it

 

The Toy manual indicates the rear should not be locked on hard surface roads and that you should not travel more than 5mph with it locked. Apparently they intended it for use only in exigent circumstances, ie to get out of a mud hole or a snow bank, then return to normal. They probably engineered it with that in mind. Someone on another thread said that once it is locked you can drive as fast as you want, but I would go with what the manual says. I can't think of any good reason to be trucking along at 20mph or faster and need the diff locked anyway.

There is an easy mod on the tech forum for altering the switch so that it can be locked in 4high or 2high, which might have some usefulness, but you would always have to remember to disengage it after using it, since the mod makes it so it doesn't automatically disengage when you shift out of 4L.

 

If your rear Diff is locked then both rear wheels will spin at the same speed no matter what the case. If you are offroading without the diff locked and you get your rear tire stuck between a stump that wheel will not turn and the other wheel that is free will. With it locked, even though that wheel is stuck between the stump, it will turn at the same speed as the free tire. Makes it easier to get out of that stump if its turning.

 

I have the 2wd with the locking rear diff. and I have only used it once. I got a little to far off the road and put the passenger side tires in a shallow ditch. When I got ready to pull out the tire in the ditch started to spin and sling rocks all over the guy parked behind me. I just engaged the rear diff., both tires got traction and my truck came right out. I probably could have got out without using it but the guy behind me would not be very happy.

 

Btw not that I would ever have done this ever, you can keep a PreRunner locked, steer and go about 65mph off road. Sand + locked prerunner =

 

you guys answer pretty much half of my questions...

what happens to the front differential when I'm in 4x4 and rear locked up?
wont it be a open differential then?

 

Ok here's the deal.

You front, and rear are open diffs all the time. Unless and only unless the rear diff is locked. Then the rear is a locked diff, with essentially each rear wheel receiving 25% of the power that the engine is making. The other 50% of the power is going to the front diff through the transfer case, most likely in a 70/30 split as in an open diff there is a dominant or drive side that generally receives more of the power.

 

the front is working the same when the rear locked or in reg 4wd

 

so when the 4x4 not engaged... the front wheels is just free moving wheels? or still open differential?

 

Just free moving wheels.

 

It is ony free moving wheels if you are running a 4x2, otherwise, if your transfer case is locked in four hi or low, you have 50% of the power running to your front wheels as an open differnetial. Having an open differnetial is quite different than running free moving wheels, your front tires will still be powered by the engine in the same fashion as before locking your rear differential. Hope this helps,

 

One more detail that might clear things up. Free-wheeling, as you call it, may not be what you think it is. When you are in 2wd mode (rear only), your front diff, which is an open diff all the time, is still turning (assuming you do not have manual locking hubs), it just doesn't receive any torque from the transmission because it is disengaged at the transfer case. So, your front wheels, axles, differential, and front drive shaft all still turn while you are moving. because they are locked all the time to the front wheels.

Now, if you have manual locking hubs, which is a different thing than a locking differential, you have to get out of the truck and lock the hubs by manually rotating the lock on the hub in order to lock the hubs up to have them turn with the axles when you are in 4wd mode. If you shift into 4wd, but forget to lock the hubs, your driveshaft, differential, and axles will receive torque from the transmission, but none will be transferred to the front wheels, because they are not locked. The biggest benefit to manual locking hubs is that when you are driving happily along a road at 70 mph in 2wd mode, and the hubs are unlocked, your front wheels spin as you travel, but the axles, differential, and driveshaft do not, because they are disengaged at the transfer case and also at the front wheel hubs. So, you save wear and tear on the front end and gain some precious gas mileage from not having to turn all that steel.

The benefit of auto-locking hubs is that you have shift-on-the-fly capability from 2wd to 4wd and you don't have to get out in the rain and mud when you get stuck to lock the hubs.

So, manual hubs = better gas mileage; auto hubs = convenience; locking diff is good when you need it; front and rear locking diffs = rock crawler (you can buy lockers for the Toy diffs).

Clear as mud?

 

Thenrie, you seem to be the guru of the power train! I just purchased an 07 TRD Sport and on the window sticker it lists under optional equipment for the sport package: Limited Slip Differential
I don't see any switch on the dash to lock it. Is this different than what you guys were talking about in the thread?

 

The sport model trucks do not have a locker, instead they have the limited slip, which is different. Where as locker will send 50% power to each wheel when engaged, the limited slip is capable of detecting the wheel which is slipping and trandfering most or all of the power to the other wheel. There is no switch because the limited slip rear is a limited slip all the time so the driver does not need to do anything.

 

I wouldn't put myself in the category of "guru" of anything. My son and I rebuilt a 54 Willys CJ3B a few years ago and we learned all sorts of neat things in the process. Maverick's post pretty well covers it. A limited slip is the next best thing to a locker, but you can use it on the road at any speed, because it allows the differential to "slip" a little to allow for the different turning radius of the inside and outside tires on the road. Using a locker on the road wears tires and breaks stuff, because there is no slip in the diff, so the tires have to slip on the road. If the tires don't slip, then stuff starts breaking in the drive train.

Here's how to tell whether you have an open diff or a limited slip: jack up the vehicle so that both wheels are off the ground on the axle you are testing. Put the shifter in neutral. Grab one wheel and spin it. If the other wheel spins in the opposite direction or doesn't spin, it is an open diff. If the other wheel spins in the same direction, it is either a limited slip or locked.

By the way, should you use the vehicle exclusively off road, some people make their own full-time lockers by welding up the diff, such that it becomes a locked axle. Cheap, effective, non-reversible without new gears. You can buy a "spool" for most axles in the aftermarket pretty cheaply, which does the same thing by simply replacing diff gears with the spool. It is reversible by simply replacing the original diff gears.

Now, the followup question is this: Are both of your axles limited slip, or just the rear? Anybody know? My guess is just the rear.

 

well...
I have been reading more about the 4x4 issue on howstuffworks...

they said... it is not good to run in 4x4 in dry payments...
I dont usee why not when in 4x4 the front and rear differentials are open.

I notice it needs a centrer differential to run good in dry payments.

expand... please...

I wish i hard a part-time job to work on cars...there are so many interesting things to make a vehicle.