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Discussion Starter · #1 ·

Jason also tackles the clutch pack situation and longevity concerns (from the comments):

Won't constant clutch slip create a ton of wear?!
Before you consider the system to be unreliable and inefficient, take a moment to think about what's happening inside an engine. You have a metal piston, sliding against a metal cylinder wall, thousands of times per minute, at ~60-90 miles per hour. And none of the comments seem worried about this? Rightfully, because cylinder walls use oil spray to minimize the friction and reduce the wear. In this clutchpack, we're talking about different materials, designed for the application, bathed in oil, with a massive surface area thanks to many clutch discs (spreads out the friction, minimizing wear). 0.7% slip is extremely low, and the friction created causes a torque to be sent to the rear wheels, thus most of the energy still goes towards powering the vehicle, with a tiny amount lost as heat.

Still not convinced? Prior to this YouTube thing, I worked in the forklift industry. Some forklifts use the transmission to brake, rather than wheel brakes. These are wet, multi-plate clutch packs, exactly like you see here, and they do nearly all the braking for a 4-5 ton forklift. That's real heat, because brakes (in this case a clutch) are designed to turn kinetic energy (the forklift's movement) into heat. These clutches can last the life of the truck, thousands and thousands of hours. It's very cool, and pretty incredible! Not to mention, pretty much every multi-speed automatic transmission is using clutches. Heck, a single-disc, dry clutch inside a manual transmission, can also last the life of the car! 100,000 miles no problem, if you're not abusing it.

My only point here is, before you assume it will fail, why not wait and see how it turns out? Toyota has a reputation for cranking out reliability. Why assume they haven't done the testing and validation this time? If there's info on GR Yaris burning up these clutch packs (it's been out for a bit now) - definitely let me know, and I'm happy to share information on it! I'll remain skeptical that the clutch pack is the big reliability concern for this vehicle.
 

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Yeah but the system does overheat and Japanese tuners have found some weird quirks with the system, like when making a certain amount of power the system defaults to fwd.
Jason mentioned that in the video, stating that on straights when additional traction isn't needed, the system will default to fwd to allow the clutch pack to cool. Do you know if the Japanese tuners were seeing the same thing under similar conditions?
 

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Jason mentioned that in the video, stating that on straights when additional traction isn't needed, the system will default to fwd to allow the clutch pack to cool. Do you know if the Japanese tuners were seeing the same thing under similar conditions?
I’m talking about it completely defaults to fwd mode when it overheats, and it goes back to normal after it cools off.

Nope they just say after making a certain amount of power it defaults to FWD and by disconnecting the battery you can set it back

 

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Discussion Starter · #5 ·
I’m talking about it completely defaults to fwd mode when it overheats, and it goes back to normal after it cools off.

Nope they just say after making a certain amount of power it defaults to FWD and by disconnecting the battery you can set it back

Interesting, from the video they quote raising the engine power to 40 kg-m (392 N-m) is where they begin seeing traction loss, while 45 kg-m (441 N-m) results in the FWD only mode. I assume this explains why the torque figure is unchanged between the GR Yaris and GR Corolla. However, the Morizo must have different programmed limits and/or a modified clutch pack since they're already running at 400 N-m.

I also assume that if you're keeping it stock (370 N-m), you probably won't run into these limits (with the clutch pack overheating)?
 

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Interesting, from the video they quote raising the engine power to 40 kg-m (392 N-m) is where they begin seeing traction loss, while 45 kg-m (441 N-m) results in the FWD only mode. I assume this explains why the torque figure is unchanged between the GR Yaris and GR Corolla. However, the Morizo must have different programmed limits and/or a modified clutch pack since they're already running at 400 N-m.

I also assume that if you're keeping it stock, you probably won't run into these limits (with the clutch pack overheating)?
There’s actually some videos and people on the GRY forums who have overheated the system stock. They say it only lasts a couple minutes but it happens.

I love engineering explained but there’s already a bunch of information covered on the AWD system. It’s a great system but it does have its flaws. When Guff talked to Sakamoto-San about the issue he said they tried to remedy the issue with ducting under the vehicle.
 

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There’s actually some videos and people on the GRY forums who have overheated the system stock. They say it only lasts a couple minutes but it happens.

I love engineering explained but there’s already a bunch of information covered on the AWD system. It’s a great system but it does have its flaws. When Guff talked to Sakamoto-San about the issue he said they tried to remedy the issue with ducting under the vehicle.
How hard/long were they driving before it went limp? At the press event I was impressed with how well they were keeping cool. The youtubers aren't professional drivers by any means, but it looked like they were driving them decently hard. The cars were running all day and never showed any signs of overheating (from what I could see).
 

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How hard/long were they driving before it went limp? At the press event I was impressed with how well they were keeping cool. The youtubers aren't professional drivers by any means, but it looked like they were driving them decently hard. The cars were running all day and never showed any signs of overheating (from what I could see).
Some said they were driving normal without any specific time and other videos were on the track, some after a lap or 2, some after a couple corners. Lol.

It’s not a crazy huge issue across the board but it has happened
 

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I suspect that longevity will be OK but that certainly doesn't rule out uncoupling to preserve itself. Those seem to be slightly different points if you ask me.
By all means I think the system will stand the test of time, that’s what we’re here for right? The more we mess with it and stick with it, the more solutions we can have.
 

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From GR-FOUR AWD System Discussion

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I’ve tracked the car on multiple circuits, with standard ps4s on and never had a single temperature warning. But I know people, that running a stock car with other rims and tires (235/40) have had rear diff temperature issues, on the same trackday as me and with the Cusco rear diff cover that provides an extra 0.5L of oil at the back.
 

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Discussion Starter · #13 ·

Looks like the coupling is completely separated from the rear diff and doesn’t share fluid between the two. Additionally, the temp sensor is measuring air temp around the unit, and not the fluid.
 

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FYI, JTEKT supplies Type B Torsen LSD and ITCC for Toyota GR Yaris, it actually likes haldex (even technically simpler than old hydraulic Haldex) without the torque vectoring provided by two separate clutch on the rear axle.
it's not like an entirely brand new thing, a lot of car use ITCC like new cx60 and Outlander etc., but GR4 is kinda modified like using 12 pairs + 3 pairs (appears to be) of wet multi-plate clutch plates that distribute torque, probably in order to handle the enormous torque, and clutch plate uses carbon material to reduce heat problem etc.

if you look back at Celica GT-Four's system, it had viscous coupling and locking center diff, more like (at least closer to) rally car
 

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Looks like the coupling is completely separated from the rear diff and doesn’t share fluid between the two. Additionally, the temp sensor is measuring air temp around the unit, and not the fluid.
That is a very interesting read. I expect the temperature sensor is buried up in there enough that it is measuring right next to the unit, but it is a bit of a strange choice to make it external.

The expanded Cusco diff cover (which may or may not help much) also seems to be a side plate, interestingly enough; it's not a back cover like I'm used to seeing on differentials. (Though Banks Power has a great video or two on how differential back covers can really mess up the oil flow if not designed properly, so the side cover design should help.)
 

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I'm very much looking forward to the savagegeese in depth review with the car in the shop on the lift. I like engineering explained, and he does a very good job explaining it, but I feel like I get more out of a savagegeese video. Maybe it has something to do with the way he explains it or shows it through video editing. Also as far as reliability, I'm sure it will go for decades if not track abused. I know the celica gt 4 s viscous coupler wasn't serviceable, but there was a guy in the UK at one point who was able to somehow take it apart without ruining it and replace clutches. I wonder if the grc will be serviceable or not?
 

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I'm very much looking forward to the savagegeese in depth review with the car in the shop on the lift. I like engineering explained, and he does a very good job explaining it, but I feel like I get more out of a savagegeese video. Maybe it has something to do with the way he explains it or shows it through video editing. Also as far as reliability, I'm sure it will go for decades if not track abused. I know the celica gt 4 s viscous coupler wasn't serviceable, but there was a guy in the UK at one point who was able to somehow take it apart without ruining it and replace clutches. I wonder if the grc will be serviceable or not?
SavageGeese (Mark and Jack) are very similar to us. Just car enthusiasts that like to get down with the nitty gritty.
 
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