4K videos of Maverick FX4 in deep sand.

[Phimosis]

One revelation from this trip is that if you work the awd very hard, like doing 3-4 back to back steep climbs with lots of wheel spin, you’ll start to smell clutch pack from the PTU or RDU, then if you keep pushing it further, you’ll soon find yourself in 2wd and a message on the dash saying “awd temporarily unavailable”

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[Tbone289]

There isn't a clutch pack in the RDU on an FX4 is there? I thought the base (non Tremor, Lobo) RDU is an open differential with only the brakes controlling the L/R bias. AFAIK, PTU only has a clutch pack, to engage/disengage AWD, and I would assume the Tremor and Lobo would fare better with the liquid-cooled PTU.

 

[Phimosis]

There isn't a clutch pack in the RDU on an FX4 is there? I thought the base (non Tremor, Lobo) RDU is an open differential with only the brakes controlling the L/R bias.

If there was no clutch in the RDU, the rotation of the rear tires would drive the differential and drive shaft, increasing parasitic drag.

By putting a clutch at the front PTU and rear RDU, it allows the drive shaft and rear differential to come to a stop, when AWD is not needed.

The tremor and lobo have 2 clutch packs in the RDU: one to disengage the AWD and one to lock the rear differential.

 

[Tbone289]

That makes sense, thanks!

 

[Snox801]

As stated it the brakes you are smelling not clutches
I’ve had my awd turn off a lot. But not nearly as much now that I’ve got the sand mode.
im curious if disabling the stability control in forscan would help. I was climbing a hill stock and knew it was not the sand. As soon as the awd disabled I got into the throttle and in fwd it went up.
It’s better now. I am actually heading to the sand box tomorrow to test out the new rdu fluid I did from redline.
it sure seems to move power around a bit differently.

 

[mavhopefull]

There isn't a clutch pack in the RDU on an FX4 is there? I thought the base (non Tremor, Lobo) RDU is an open differential with only the brakes controlling the L/R bias. AFAIK, PTU only has a clutch pack, to engage/disengage AWD, and I would assume the Tremor and Lobo would fare better with the liquid-cooled PTU.

I was wondering the same thing. Also how can you smell something completely sealed and bathed in Oil?

 

[Tbone289]

I was wondering the same thing. Also how can you smell something completely sealed and bathed in Oil?

That's a very good point. It most likely was hot brakes as @Snox801 suggested.

 

[Headcase650]

If there was no clutch in the RDU, the rotation of the rear tires would drive the differential and drive shaft, increasing parasitic drag.

By putting a clutch at the front PTU and rear RDU, it allows the drive shaft and rear differential to come to a stop, when AWD is not needed.

The tremor and lobo have 2 clutch packs in the RDU: one to disengage the AWD and one to lock the rear differential.

Are you sure there is a clutch in the PTU? Most haldex systems do not. If the front wheels are turning so is the PTU and the drive shaft. There is normally a clutch between the drive shaft and the RDU.

 

[Phimosis]

I was wondering the same thing. Also how can you smell something completely sealed and bathed in Oil?

The Dana Spicer Advantek RDU is not sealed. It has a vent tube. As air gets hot, it expands. Without a breather tube, the differential would become pressurized, which would then blow all of the lubricant out through the seals for the axles and drive shaft.

The smell that I was smelling, was the smell of hot ATF at the smoke point. It was not the acrid smell of burning electronics that hot brake pads give off. Hot brakes is a very different smell than hot oil.

I have an FX4 that has sand mode. I had the traction control turned off.

I had no stability control braking interdiction before the “AWD not available notice”

braking interdiction is very noticeable when doing a big power slide, doing donuts, or even a u-turn with lots of throttle.

When the AWD shut off, I was doing very steep climbs in soft sand, straight up a hill. Again, no braking interdiction.

When the AWD shut off, I immediately lost power to the rear tires and the front started to spin wildly and my front tires started to sink, so I got off the power and came to a stop, it until it sorted out the rear wheel drive situation.

The message that I received was “AWD temporarily unavailable”, not “stability control unavailable”. The disc brake activated stability control was still working just fine. The problem was no power transferred through the PTU or RDU.

 

[mavhopefull]

The Dana Spicer Advantek RDU is not sealed. It has a vent tube. As air gets hot, it expands. Without a breather tube, the differential would become pressurized, which would then blow all of the lubricant out through the seals for the axles and drive shaft.

The smell that I was smelling, was the smell of hot ATF at the smoke point. It was not the acrid smell of burning electronics that hot brake pads give off. Hot brakes is a very different smell than hot oil.

I have an FX4 that has sand mode. I had the traction control turned off.

I had no stability control braking interdiction before the “AWD not available notice”

braking interdiction is very noticeable when doing a big power slide, doing donuts, or even a u-turn with lots of throttle.

When the AWD shut off, I was doing very steep climbs in soft sand, straight up a hill. Again, no braking interdiction.

When the AWD shut off, I immediately lost power to the rear tires and the front started to spin wildly and my front tires started to sink, so I got off the power and came to a stop, it until it sorted out the rear wheel drive situation.

The message that I received was “AWD temporarily unavailable”, not “stability control unavailable”. The disc brake activated stability control was still working just fine. The problem was no power transferred through the PTU or RDU.

Thanks for the additional info. I would do a fluid replacement to see what condition it's in. Both the front PTU and the Rear Disconnect Unit.

 

[Tbone289]

The smell that I was smelling, was the smell of hot ATF at the smoke point. It was not the acrid smell of burning electronics that hot brake pads give off. Hot brakes is a very different smell than hot oil.

Well, that rules out the PTU and RDU. Hot ATF smells very different than hot gear oil. Did your transmission burp ATF out of the vent hole on top as it tends to do when it gets hot?

 

[Phimosis]

Are you sure there is a clutch in the PTU? Most haldex systems do not. If the front wheels are turning so is the PTU and the drive shaft. There is normally a clutch between the drive shaft and the RDU.

It’s not a Haldex system. It is a Dana Spicer Avdantek disconnecting AWD system.
When it is not using awd, the driveshaft and RDU stop spinning. This is achieved by a clutch pack in the PTU in front of the driveshaft, and then a clutch pack inside of the RDU, after the driveshaft, pinion gear, ring gear and spider gears, but before the rear axles. When both clutches are disengaged, the driveshaft, pinion gear, ring gear and spider gear carrier all come to a stop, to reduce parasitic drag.

https://driving.ca/features/feature-story/deep-dive-2022-ford-mavericks-awd-system-explained

 

[Phimosis]

Well, that rules out the PTU and RDU. Hot ATF smells very different than hot gear oil. Did your transmission burp ATF out of the vent hole on top as it tends to do when it gets hot?

The Dana Spicer Smart Connect PTU and Advantek RDU don’t use gear oil. They use a “ultra low viscosity” lubricant that has been described as being similar to 5w20 with an added friction modifier.

Could the smell have been ATF? Yeah, that is a possibility. However, if the ATF was overheated, it should have sent a transmission temp warning and put the power delivery into limp mode, not simply disabling the AWD, while leaving power production at 100%

Also, I didn’t mention this in the discussion above, but when the AWD unavailable message popped up, it would go away in as short as 30 seconds after stopping and sitting with the engine idling and letting the oil pumps and coolers do their magic. If it was overheated brakes, that are normally cooled by high speed airflow, I would expect it would take more than a few seconds for the brakes to cool down sufficiently, when sitting at a dead stop.

 

[Tbone289]

The Dana Spicer Smart Connect PTU and Advantek RDU don’t use gear oil. They use a “ultra low viscosity” lubricant that has been described as being similar to 5w20 with an added friction modifier.

The transmission uses ULV ATF. The PTU uses 75w-80 Hypoid gear oil, and the RDU uses 75w "rear disconnect drive unit fluid". I changed all three Motorcraft/Ford-specified fluids in mine two weeks ago, and I can tell you for certain that the transmission fluid looks and smells like ATF (basically hydraulic fluid), and the oils in the PTU and RDU look and smell like sulpher-y gear oil. Granted, they're not as viscous as some gear oils, but they're much more viscous than ATF, and certainly wouldn't ever smell anything like ATF, hot or cold.

Also, I didn’t mention this in the discussion above, but when the AWD unavailable message popped up, it would go away in as short as 30 seconds after stopping and sitting with the engine idling and letting the oil pumps and coolers do their magic. If it was overheated brakes, that are normally cooled by high speed airflow, I would expect it would take more than a few seconds for the brakes to cool down sufficiently, when sitting at a dead stop.

Now that you've mentioned the ATF smell, I don't believe it was brakes either. They do smell different, and we didn't have that tidbit of info to go on at the time that @Snox801 mentioned it.

 

[Headcase650]

It’s not a Haldex system. It is a Dana Spicer Avdantek disconnecting AWD system.
When it is not using awd, the driveshaft and RDU stop spinning. This is achieved by a clutch pack in the PTU in front of the driveshaft, and then a clutch pack inside of the RDU, after the driveshaft, pinion gear, ring gear and spider gears, but before the rear axles. When both clutches are disengaged, the driveshaft, pinion gear, ring gear and spider gear carrier all come to a stop, to reduce parasitic drag.

https://driving.ca/features/feature-story/deep-dive-2022-ford-mavericks-awd-system-explained

Good deal, that's a much better system than the haldex system in my 2013 equinox.

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