Vehicle weight capacity with Diff Lock

[Shamish]

Well I just finished reading the owners manual for my 2020 ORP. On page 522, the following "Vehicle Capacity Weights" are listed.

1165 lb without diff lock system
835 lb with diff lock system

Seems weird that the rear diff lock system comes with a 330 lb penalty. Any idea why this is?

 

[mteolus]

Well I just finished reading the owners manual for my 2020 ORP. On page 522, the following "Vehicle Capacity Weights" are listed.

1165 lb without diff lock system
835 lb with diff lock system

Seems weird that the rear diff lock system comes with a 330 lb penalty. Any idea why this is?

Maybe they didn't adequately translate this into English? Or maybe the diff locker weighs 330 lbs so the capacity is the same? But that would mean it would have to be the tires that are the limiting factor as the sprung weight would be the same with or without a locker. I doubt the locker weighs 330 lbs too. Weird.

 

[kjbenner]

Never noticed that before, that's pretty weird. I did find this old thread, which clarifies pretty much nothing: Low(er) TE Cargo Weight Limit

 

[Captain Planet]

I would assume the locking mechanism is less strong than having the diff unlocked.

 

[Narat_524]

The reduced weight rating is because max GVWR is the top-end set point, which the engineers set based on may factors like (safe) braking capacity vs traction, etc.

When you add extra equipment, like a locker, you're subtracting that additional weight from the max vehicle weight rating. But a locker doesn't come by itself, you usually get skid plates, possibly larger tires (including spare), and I don't know if the ABS actuator is different on models with crawl control or not.

So it's not the locker being weaker, it's simply the subtraction of the locker package from the vehicle weight rating.

 

[Jetboy]

A locking differential can send twice as much torque to one side of the axle as an open differential. The limit is almost certainly the result of the torque limit of the rear axle shafts. If you leave the rear diff open it would have the same weight capacity as the non-elocker model.

The diff lock assembly along with all of the wiring and ECU weigh about 10lb total difference from the open diff model. The rear axle is otherwise identical and uses the same ring and pinion parts. The E-locker diff has a larger carrier bearing on the locker side and the same one on the non-locker side. The e-locker diff also has a different carrier preload design that is adjustable with threaded caps where the open rear diff model uses shims to adjust. When not locked, the elocker and standard rear diffs are identical in strength and function.

But... go break a rear axle shaft. It's extremely difficult if not impossible to do with stock size tires. For that reason I wouldn't really consider it an issue at all. I have no hesitation about loading up with over sized tires and using the rear locker. It's a typical Toyota scenario where the components are substantially more durable than the ratings.

 

[jhguth]

this is 100% about the axle, which unless you are operating in an extreme edge case won't ever make a difference to you, but those extreme edge cases matter to engineers and attorneys

 

[nevada]

A locking differential can send twice as much torque to one side of the axle as an open differential. The limit is almost certainly the result of the torque limit of the rear axle shafts. If you leave the rear diff open it would have the same weight capacity as the non-elocker model.

The diff lock assembly along with all of the wiring and ECU weigh about 10lb total difference from the open diff model. The rear axle is otherwise identical and uses the same ring and pinion parts. The E-locker diff has a larger carrier bearing on the locker side and the same one on the non-locker side. The e-locker diff also has a different carrier preload design that is adjustable with threaded caps where the open rear diff model uses shims to adjust. When not locked, the elocker and standard rear diffs are identical in strength and function.

But... go break a rear axle shaft. It's extremely difficult if not impossible to do with stock size tires. For that reason I wouldn't really consider it an issue at all. I have no hesitation about loading up with over sized tires and using the rear locker. It's a typical Toyota scenario where the components are substantially more durable than the ratings.

is this something that changed for the 5th gens? all the non locker toyotas I have ever seen, had the adjusting collars. although the Elocker side collar IS different, it requires a different tool, and is roughly 2x as big in diameter.

 

[Jetboy]

is this something that changed for the 5th gens? all the non locker toyotas I have ever seen, had the adjusting collars. although the Elocker side collar IS different, it requires a different tool, and is roughly 2x as big in diameter.

Yeah. I think this is something unique to the 8.2 as far as I know.

Open diff version of the 8.2 = shim
E-locker = threaded caps.

Why??? I have no idea. Ring and pinion and pinion bearings are all interchangeable.

 

[nevada]

Yeah. I think this is something unique to the 8.2 as far as I know.

Open diff version of the 8.2 = shim
E-locker = threaded caps.

Why??? I have no idea. Ring and pinion and pinion bearings are all interchangeable.

interesting. it doesn't make any sense why they would change designs like that. strange. thanks for the info.

 

[Shamish]

this is 100% about the axle, which unless you are operating in an extreme edge case won't ever make a difference to you, but those extreme edge cases matter to engineers and attorneys

I happen to be a reasonably competent engineer who is often asked about my legal background (usually as some sort of a veiled insult :whipping2)...which is exactly why I am curious about this. I would love it if the weight of the locker was what was causing the reduction in carrying capacity - that thing would be a captain insaneo locker!

I need to ponder the comments about the stress on the axleshafts when the locker is engaged. I suppose this could be a factor but it seems weird...but as I said, I am a REASONABLY competent engineer, probably not worthy of working at Toyota.

It'd be funny if this was all the result of someone forgetting to carry the remainder or some other dumb math mistake.

I truly appreciate all the comments. It's fun to hear (read) what others are thinking, and it helps me learn.

 

[Jetboy]

I happen to be a reasonably competent engineer who is often asked about my legal background (usually as some sort of a veiled insult :whipping2)...which is exactly why I am curious about this. I would love it if the weight of the locker was what was causing the reduction in carrying capacity - that thing would be a captain insaneo locker!

I need to ponder the comments about the stress on the axleshafts when the locker is engaged. I suppose this could be a factor but it seems weird...but as I said, I am a REASONABLY competent engineer, probably not worthy of working at Toyota.

It'd be funny if this was all the result of someone forgetting to carry the remainder or some other dumb math mistake.

I truly appreciate all the comments. It's fun to hear (read) what others are thinking, and it helps me learn.

The axle shaft torque is a pretty easy concept to think through. Open diff can never under any circumstance apply more than 50% of the torque to one side. It's a physical property of the open differential mechanism. A locking differential can apply 100% of the torque to one side. In a scenario where the vehicle is on a 30* slope and loaded at max capacity, I'm guessing that's about what Toyota uses and then adds a safety factor of about 3:1 for the drive train.

We know the drive train, body, suspension, etc. are all the same otherwise. So the only meaningful difference is the increased traction of the rear locker and the resulting ability for significantly increased torque on the rear axle shafts. That's why I assume that would be the reason - basically because there is no other rational basis for a different rating.

Or it could just be a mistake. The 2020 4Runner brochure has a higher GVWR for the locker models than the non locker models. 6,100lb for all non-elocker models and 6,300lb for all elocker models. https://www.toyota.com/4runner/ebrochure/

The biggest oddity for me is that the 4Runner has a 5,000lb tow rating and the Tacoma with less power and smaller brakes has a 6,800lb tow rating. I'd chalk it up to the short wheel base or suspension, but the GX460 has a tow rating of 6,500lb with the same wheel base and suspension. Why the 4Runner is lower I can't really think of any basis other than maybe the trailer hitch isn't rated for it.

 

[syedlink27]

Does the lower payload of the TRD ORP have anything to do with KDSS?
I have KDSS and the rear locker and my sticker says 880 lbs.
Wondering if it’s the KDSS system that can’t handle the extra 300 lbs the SR5 can handle?

 

[honda250xtitan]

Does the lower payload of the TRD ORP have anything to do with KDSS?
I have KDSS and the rear locker and my sticker says 880 lbs.
Wondering if it’s the KDSS system that can’t handle the extra 300 lbs the SR5 can handle?

no. the system doesnt hold any weight.

 

[MAST4R]

Does the lower payload of the TRD ORP have anything to do with KDSS?
I have KDSS and the rear locker and my sticker says 880 lbs.
Wondering if it’s the KDSS system that can’t handle the extra 300 lbs the SR5 can handle?

The answer was provided above. The difference is between engaged e-locker and an open rear diff.

My takeaway: careful if ever using the locker on a fully loaded vehicle.

Might help explain the constant axle issues that very heavy OZ rigs have when trying to climb something challenging.