Please help me understand 4x4 drivetrain options

I'm shopping for a used 4x4 Tacoma, model year 2005 or newer, V6/automatic. I am going a little wiggy trying to understand the various 4x4 drive train options and which ones I may need.

Questions:

1. What is the disadvantage of a base 4x4 Taco with no form of limited slip or locking rear differential? In other words, when might I have trouble with the plain vanilla 4x4 that I wouldn't otherwise?

2. The base 4x4's with tow option apparently come with an automatic limited slip rear differential. Am I correct that these operate as a limited slip differential even in 4x2 mode? If so, is it not true (as I was taught in winter driving class many eons ago in Michigan) that the limited slip differential can be difficult/dangerous to handle in borderline wet/slippery road conditions in which you cannot engage the full 4x4 mode?

3. The TRD option adds a locking rear differential. Am I correct in assuming this is acts like a normal differential until the driver decides to lock it? And that the advantage of this is that you don't have limited-slip kicking in when you don't want it to in 4x2 mode?

4. I've always been told that limited slip differentials lose effectiveness as the miles accumulate, so by the time you've racked up 100K or so they are essentially worn out and behave as regular differentials unless you rebuild them. Does this wisdom still apply? And if so, doesn't that mean a locking rear differential is likely to be more effective over the long haul, since it is only engaged when it is really needed?

5. Why don't the Tacos come with a locking transfer case??? This really puzzles me! I thought a locking transfer case was the ultimate 4x4 option!

FYI - I plan to use my Taco to tow a smaller travel trailer (3000#) and do some off-roading in areas of the Southwest that are described as requiring a "high clearance 4x4 vehicle". I know from my limited experience (when I had no idea what I was doing) that I will encounter sandy and muddy areas, deeply rutted roads, and some fairly rocky areas. I do not plan to tackle the Rubicon, however!

Looking forward to hearing your collective wisdom on this!

Andy

 

Well, I'll give this a shot.

1. Any truck without an LSD or locker can stop dead if one of the rear tires spins and nothing else helps (ie, front wheels on a 4wd). That means if you have a 2wd with an LSD or locker and one tire hits some ice, snow, sand, mud, is in the air, etc you could be stuck bad enough to need to be pulled out be another vehicle even if the 3 other wheels are on solid ground. At least if you have an LSD or locker the other rear tire can get power to get you out. Without an LSD, locker or traction control system there's nothing to send power to the wheel with traction.

2. Maybe. The LSD is just that "limited" slip. It still slips to allow for turning, and if the RPM difference between each tire is large enough IIRC. It doesn't FORCE both tires to spin the same speed all the time to cause fish tailing like a locker could. On the other hand, some of what I've read suggests the LSD is useless if one wheel is off the ground or you REALLY need both tires to push. Some people have applied the brakes slightly to stop the tire without traction and help the LSD engage, but that's something you'd have to play with. Personally, I prefer hitting the locker button and knowing both tires are locked together all the time when I hit the trails.

3. Yes. It is open until you lock it. In the 2wd Prerunners, it can be engaged anytime below 5MPH IIRC. In the 4wd trucks it can only be engaged while in 4LO unless you do the locker mod (listed in the cheap/free mod section in the Tech Chat).

4. Not sure. I think the Tacoma LSD is clutch based so I suppose it could wear out, but don't quote me on that.

5. Probably for turning. The Tacoma is marketed towards the average consumer who doesn't know a locker from their ass. God forbid someone lock the transfer case, whip around the corner into their driveway, roll the truck, and sue Toyota. Look at the limitations placed on the locker. It can safely be used beyond those artificial limits, but Toyota probably limited it to a "safe" zone to protect people from themselves and avoid lawsuits. Not to mention this truck has a longer wheelbase than a jeep or buggy that's fully locked. That might lead to more drive line stress and more broken parts if people used it. Toyota doesn't want to do any more warranty repairs that is has to! That's my guess anyway!

 

Close, we still have to be at a stop to engage it.

 

#5: The Tacoma type 4WD is a part time 4WD, without any type of center diff, usually a viscous coupling, so it is "locked" anytime it is in 4WD. A full time 4WD/AWD uses center diff with the ability to slip when cornering on hard/dry high friction surfaces, but these types generate lots of heat and wear when in more adverse offroad conditions, so most have a method to "lock" both front and rear axles together just like part time 4WD. So, to have a full time 4WD/AWD with a locked option is more advantageous than one without, and therefore would be better. A part time system is a much simpler, more rugged type system that requires more driver input as when to engage, and some mechanical knowledge to know enough how the system operates to prevent drivetrain damage. Again, the Tacoma does not need a "locked" option, because it is locked all the time when in 4WD, and has no method of being partially unlocked like most full time 4WD/AWD systems.

note: The current N American market Tacoma uses electric/electronic actuation of the 4WD system versus the manual shifter, but that has no control of the transfer case once it is in engaged a given mode.

 

That sounds better than my attempt! I must have been thinking about locking the front axles through the differential (like locking the rear).

 

PT and LRH explained everything well I'll just add to 2 & 4.

2. I beleive this 'auto LSD' button option was rare, only non-TRD's and was only on 05-06's. My neighbor has on his 04' Tundra. Can only be used in 2wd up to 55 mph and basically the brakes apply to the spinning wheel to make an open diff act like a Mech LSD. But he never uses cause he has 4wd. Pointless for the most part in a 4wd truck.

As for handling, yes the back end can come around quicker on LSD than an open diff in 2wd on snow. More of an issue for inexperienced/noob drivers though. I've had LSD on my 2wd trucks and on my TRD sport 4x4 now. I drive in 2wd all the time on snow, and prefer having both wheels working when I need it, no buttons. Pulling off my gravel or snowy road in front of a dump or milk truck, I dont want one wheel spinning away. Also getting up my icy uphill driveway, I dont want to have to put in 4wd for 50ft.

4. That has some truth, clutches can wear. But most trucks are lucky to get their diffs changed every 60K. My father's 90K LSD on 97 F150
still leaves two marks. Our manual says LSD change every 30K. I did my first at 20K. I think mine will work fine even after 100K. 3 years on tacoma forums haven't heard of one wearing out yet.

Good luck with your choice. I'm sure you'll be happy either way, SR5, Off-Road, or Sport.

 

What is "IIRC"?

Thanks.

 

Thanks everyone. Realizing that the transfer case on the Taco is always locked clarified a lot of things. Also, thinking about the scenario of pulling out of a soft-slippery road onto dry pavement make me appreciate the value of a LSD. That's really not the time to engage the 4WD with locked transfer case, especially since there's probably a turn involved. And in that situation one had better be quick to unlock the rear differential on a TRD truck!

Andy42

 

With a TRD Offroad truck the locker only works in 4LO. There's a mod to get around that so if you do the mod, be sure you know when to use it! (and when not to use it) It's one of the better mods I think as long as you're careful about using it. Best part is it only costs around $6-$8 for the relay at radioshack and some of your time.

 

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I'm glad it was understandable, I know how many things operate, but I am at times not good at explaining them in a style where others can understand.

 

You mean that you are not??? (I am going to cry now)

 

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Wow! That's weird, I cannot see how it refers to this forum???













LOL

 

Just putting in my 2 cents, I like limited slip on a sporty car, but i'd much rather have the locker for a truck. I had limited slip on my Beamer and loved it but you are right, it was dangerous in snow or in rain. the back end could easily spin you around. as far as wearing out, i dont know anything about that. i do know that my car had over 200K miles on it, and i put on about 100K and the limited slip still worked great.

 

Many people who appreciate the LSD in 2 wd with a 4 wd truck, live in snow country. You pull out of a snow covered street into traffic on a bare road while turning, you will want to use the LSD feature and not 4 wd. 4 wd is used more for sustained traction needs rather then occational on slippery roads and off road. For temporary use like climbing a drive or the one I referred to, nothing beats the button for quick and easy engagement as well as quick and easy disengagement.