Off Road Drving with AWD

[wwest]

I didn't know "broach" could refer to piercing, so if that's the case then no, the issue is not broaching. The seal is not getting pierced, it's getting compressed.

 

A PTU is not hermetically sealed, there is a breather vent and besides, it's not full.

 

Okay, concession time.

 

The seal is not being broached so much as being "melted", molecular structure compromised, due to the overheating of the PTO and 70 weight.

 

There's still plenty of air in there as the fill level is only about 2/3rds of the way up. Besides, the vast majority of the leaks are actually transmission fluid leaking out, not the PTU grease. That's the same transmission fluid that passes through the transmission cooler by the way.

 

The new Explorer will feature a specific off-road and hill descent mode, marketing specifically towards off roading. It also has higher ground clearance and beefed up suspension to meet Ford's off-road standards. If you want a non-off-road 7 passenger vehicle, Ford already has the Flex.

 

 

I suspect neither one of us can prove our point/position so I'll drop it here.

[EdgeNut]

"hill descent mode" simply uses, and OVERHEATS, the brakes automatically rather of one's own foot power.

 

Alright, definitely need to clear this one up, as you obviously don't understand why hill descent control is so helpful... Yes, the system uses the brakes, but automatically feathers the brakes to maintain a constant, slow speed. Otherwise, speed will often increase quickly due to changes in driving surface, causing the driver to need to press the brakes harder. As speed increases, and brake pressure increases, heat dissipation increases. Particularly on the grades this system is designed for, you are much MORE likely to overheat brakes left to your own devices, compared to when hill descent control is enabled.

 

You should consider learning more about these systems before you comment so vehemently about them...

[Waldo]

I suspect neither one of us can prove our point/position so I'll drop it here.

 

I've got a direct email from a Ford transmission engineer, what do you have? I also spent 10 minutes reading the 2010 Edge service manual and determined most of what you're saying isn't possible and the very detailed (including a specifically made video) repair instructions don't seem to line-up with your theories.

 

And about the hill descent control, are you saying that my parking brake is going to overheat if I park on a steep hill? As Edgenut points out, the slower you go, the less heat you generate - you disspate the potential energy of the vehicle over a longer period of time.

[ThinLine]

All I know is that my AWD Edge drives like a champ in the snow. Would anybody in their right mind by an Edge to go "off-roading" I really don't think so.

[wwest]

I've got a direct email from a Ford transmission engineer, what do you have?

 

Yes, and ALL of us have now seen the official press release from Toyota that indicated that the floor mat not being "hooked" inplace was the fault. Only to see a later official press release indicating that the gas pedal design was a contributing factor...

 

Next...??

 

I also spent 10 minutes reading the 2010 Edge service manual and determined most of what you're saying isn't possible and the very detailed (including a specifically made video) repair instructions don't seem to line-up with your theories.

 

"...isn't possible..."

 

Ford put a thermistor within the rear diff'l case because it was subject to overheating if over-used (mis-used..??). Are you questioning as factual that the ENTIRE driveline is under an extraordinary level of stress with the front and rear drive SOLIDLY, 50/50, coupled together..??

 

Why would the PTO not be just as subject to overheating as the rear clutch/differential with the rear clutch in non-slip mode...??

 

There goes my 50 years of driving and DIY experience out the window.

 

And about the hill descent control, are you saying that my parking brake is going to overheat if I park on a steep hill?

 

Yes, the parking brake will overheat to the same level as the parking pawl in the transaxle that I mostly use.

 

As Edgenut points out, the slower you go, the less heat you generate - you disspate the potential energy of the vehicle over a longer period of time.

 

Yes, I agree, intermittent braking, braking only after the downhill speed has "risen" will result in higher heat spikes than more even, constant, braking. That's NOT to say an experienced off-road driver wouldn't be just as good at modulating/moderating the braking as would the Hill-holding, Hill descent mode.

Edited November 27, 2009 by wwest

[Waldo]

First of all the PTU is connected to the engine 100% of the time, so it's load cycle is very different than the clutched rear end. I suspect it's actually the action of locking and unlocking the clutch, not the actual load transfer that creates the heat in the RDU anyway. Besides if Ford new about the temperatures in the RDU and put in a thermister, why wouldn't they do the same in the PTU?

 

But the real flaw in your theory is that even if the PTU grease was overheating, it doesn't touch the seal that's failing.

[wwest]

First of all the PTU is connected to the engine 100% of the time, so it's load cycle is very different than the clutched rear end. I suspect it's actually the action of locking and unlocking the clutch, not the actual load transfer that creates the heat in the RDU anyway. Besides if Ford new about the temperatures in the RDU and put in a thermister, why wouldn't they do the same in the PTU?

 

But the real flaw in your theory is that even if the PTU grease was overheating, it doesn't touch the seal that's failing.

 

Someone please correct me if I'm wrong. "The failing seal is the one for the inner side of the front halfshaft drive where is exits the PTO/PTU".

 

"Grease" = 70 weight.

 

"...so it's load cycle..."

 

There is virtually NO resistance to the PTO's ring gear turning the pinion that drives the rear driveshaft UNLESS the rear drive clutch is engaged. Engage, SOLIDLY engage, the RDU clutch on a highly tractive surface and the result will ALWAYS be driveline windup and/or tire scrubbing. Since there is no sensor or sensor set that can be used to sense, predict, that the engine torque can/will too easily overcome the roadbed coefficient Ford has chosen to be pre-emptive in engaging, most of the time NEEDLESSLY, the rear drive.

 

"...heat in the rear RDU.."

 

RDU clutch as the "weakest link" would be the result of SLIPPAGE, purely.

 

If the RDU clutch does not slip then the additional stress will show up elsewhere, say driveline windup and/or tire scrubbing are the most common. Driveline windup would obviously result in higher frictional losses in the PTO gearset teeth, along with many other points.