Limited Slip Differential for 4x4 Tacoma? Why Isn't This A Thing?

[fredygump]

On my SR5, 4x4, I think a true limited slip differential (LSD) would be a big upgrade. But I don't see anyone talking about it. Everybody wants lockers, but for me, a LSD is far more practical. Especially for driving in wet roads, winter roads that are 99% clear, or turning down a gravel road for short distance and it isn't worth switching to 4wd.

I believe the 2wd SR and SR5 do have limited slip, so that kind of proves that when you are in 2wd, the traction control system isn't enough.

Even if you think 4wd with open diffs is better than 2wd with LSD, we drive in 2wd most of the time.

So yeah, lets talk about upgrading to an LSD. Can I take an LSD from a 2wd SR/ SR5 and install it in my 4x4?

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[The Dude]

On this gen., the LSD is a brake-actuated mechanism, where, if the speed sensors detect slipping, they apply the brakes like ABS on the offending wheel. This prevents the wheel spin a mechanical LSD would also stop. The brake version is likely what you have.

 

[redlimitediforcemax]

If you have a full-time 4wd Taco it's got the center torsen style LSD. Works wonders in rain and snow. I literally cannot detect any slipping wheels at any speed in rain. Feels like a tank, sure-footed, safe.

 

[Mercedes]

Some traction features available to the 4G I am familiar with. Several I am not. Attached are some references.

The Owners Manual will also give some guidance on how and when to use.

The second video below focuses on the Auto-LSD feature.

https://www.tacoma4g.com/forum/threads/2wd-4h-4l-when-why-created-some-cheat-sheets.17946/

https://www.tacomaworld.com/threads/3rd-gen-traction-control-modes-explained.530695/

 

[fredygump]

If you have a full-time 4wd Taco it's got the center torsen style LSD. Works wonders in rain and snow. I literally cannot detect any slipping wheels at any speed in rain. Feels like a tank, sure-footed, safe.

Unfortunately I do not have a "full time 4wd" option. I just have 2wd, 4 hi, and 4 low.

I agree that 4 hi makes a huge difference on gravel. The truck feels helpless on gravel in 2wd.

I saw the TFL video from 2024 about the tranction control system. But those tests are meaningless to me, because a real LSD engages instantly and before a wheel starts to spin. An LSD isn't going to be as strong as a locker for rock crawling, but it is much better for on road driving. It would be plain silly to engage a locker for on road driving!

I mostly figured that eliminating limited slip diffs is a cost saving measure.


Maybe I figured it out? (just now...) I'm realizing that a LSD would affect the "stability control" part of the ABS system in some situations. If the ABS system thinks it needs to brake just one wheel, say the left rear, the LSD may lock and force the left and right wheels to turn the same speed. So with an LSD, the ABS system has less control.

My GTI has an electronically controlled, clutch based LSD, and that allows true limited slip functionality, while allowing the traction control/ stability control to over-ride the LSD.

I'd be interested if someone has any specific knowledge on this subject. LSD is not close to being replaced by a traction control system. But the LSDs have all but gone away. If they have gone away because of stability control in modern cars, what a sad world we live in! A lot of old cars sucked, but atleast they did what you told them to do!

 

[Texas Bob]

Unfortunately I do not have a "full time 4wd" option. I just have 2wd, 4 hi, and 4 low.

I agree that 4 hi makes a huge difference on gravel. The truck feels helpless on gravel in 2wd.

I saw the TFL video from 2024 about the tranction control system. But those tests are meaningless to me, because a real LSD engages instantly and before a wheel starts to spin. An LSD isn't going to be as strong as a locker for rock crawling, but it is much better for on road driving. It would be plain silly to engage a locker for on road driving!

I mostly figured that eliminating limited slip diffs is a cost saving measure.


Maybe I figured it out? (just now...) I'm realizing that a LSD would affect the "stability control" part of the ABS system in some situations. If the ABS system thinks it needs to brake just one wheel, say the left rear, the LSD may lock and force the left and right wheels to turn the same speed. So with an LSD, the ABS system has less control.

My GTI has an electronically controlled, clutch based LSD, and that allows true limited slip functionality, while allowing the traction control/ stability control to over-ride the LSD.

I'd be interested if someone has any specific knowledge on this subject. LSD is not close to being replaced by a traction control system. But the LSDs have all but gone away. If they have gone away because of stability control in modern cars, what a sad world we live in! A lot of old cars sucked, but atleast they did what you told them to do!

I feel exactly the way you do, fredygump. The 'traction control' or "Auto-LSD" does not seem to be effective at all in my truck. If it intervenes, it is so slow or weak that I don't even notice since I've already had to back off the accelerator and/or partially disengage the clutch.

I've had the truck for about 18 months now, so I've learned to try to accelerate VERY gently under the following conditions: 1. Making a right turn from a stop. 2. Anytime the road is damp or wet. 3. Starting up a hill. 4. Starting on gravel-covered or dirty pavement. I live in rural Texas so #4 is nearly ALL the TIME.

I frequent one nearby road which has a major intersection halfway up a steep hill, therefore every cycle has dozens of cars and trucks queued up dripping air conditioner condensate on top of the normal leaking coolant and oil that are present. Between the slow and non-linear off-idle response (God help me if the turbo spools up before I'm really rolling...) and the invisible traction of my poor overworked right rear tire, there have been times when the back of the truck jukes left, catches traction and jukes again before it really gets going. I feel sorry for the people behind me.
Maybe I'm being a little dramatic, and I admit I was spoiled by the perfect traction of my previous Subaru, but a good old-fashioned mechanical or Torsen-style LSD would be a huge upgrade for me. I wish the AWD system of the Limiteds had been available with a manual transmission because that would be the perfect setup for me. And before anyone says it, they are correct: I'm not a hard-core off-roader. I only bought the 4WD to get the manual.

 

[ThatBronze4G]

i was told Alldogs Offroad has an 8.5 Toyota LSD coming for test fit on their new gen tacoma and 4R. not sure on their timeline for it to be available though.

 

[fredygump]

Okay, so my suspicion seems correct. Electronic stability control appears to be a requirement for "light vehicles". The link is to the requirements for an electronic stability system, but in this section it does not explain when this system is required. So I am just assuming that somewhere in these rules it specifies that all light vehicles are required to have electronic stabiity systems.

https://www.ecfr.gov/current/title-49/subtitle-B/chapter-V/part-571/subpart-B

Search for section 571.126 (Electronic stability control systems for light vehicles)

The important part:

"S5. Requirements. Subject to the phase-in set forth in S8, each vehicle must be equipped with an ESC system that meets the requirements specified in S5 under the test conditions specified in S6 and the test procedures specified in S7 of this standard.

S5.1 Required Equipment. Vehicles to which this standard applies must be equipped with an electronic stability control system that:
S5.1.1 Is capable of applying brake torques individually to all four wheels and has a control algorithm that utilizes this capability.
S5.1.2 Is operational during all phases of driving including acceleration, coasting, and deceleration (including braking), except when the driver has disabled ESC, the vehicle speed is below 20 km/h (12.4 mph), the vehicle is being driven in reverse, or during system initialization
S5.1.3 Remains capable of activation even if the antilock brake system or traction control system is also activated".


Interestingly, it allows the exception "except when the driver has disabled ESC". Maybe there is another whole section explaining how and when the driver is allowed to disable ESC? But at first glance it looks like the driver can "turn off" part or all of the system's functions, which is what would happen if a LSD was installed.

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