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wolfpack219

PTU issues..... possible long-term solutions

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So after hours upon hours of research it's come to my attention that there is a solution to failing PTU units. The more expensive way appears to be a flush and change of oil between 20-30k miles, lesser end if hard usage occurs. It appears that the oil breaks down under immense heat and also can wear the seals due to heat once the oil is turned to paste. Now the dealership will change it for you, but it will be on your dime (around 110.00). Other solutions from Ford mechanics has been to add their own drain plug to the unit. It it important to not over fill the unit however as it will overflow and leak from the exhaust tube and could leak onto the exhaust causing bad odors. Just thought I would put this here to let Ford owners know you can extend the life of the PTU but it will require more maintenance than suggested in the user manual. Also the over seas explorer is said to have the drain plug installed from the factory and is recommended regular changes with off road use.

 

Has anybody been doing this already?

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Yes, this is known over at least over at FordFlex.net and Yes people are changing PTU fluid over there on their own derived maintenance schedule. Clearly as you note Ford fluid service life has been greatly overrated on these...

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The difficulty with this, is some require removal of the catalytic converter to access fil plug. I agree that fluid changes would be good preventative maintenance. All the PTUs I have changed and dismaltled, the fluid is congealed. Most of them have over 80k miles. This problem is accelerated by uneven tire wear. When tires aren't rotated properly, the circumference difference becomes significant making axles spin at different speeds creating excess heat into the PTUs.

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Ford definitely isn't the first to have problems with PTUs. Basically, viscous couplings in full time awd/4wd systems are just trouble, period. It seems like the industry would figure out a better way to do it.

 

I always preferred part-time systems as they don't have viscous couplings. I guess the downside is that you have to be smart enough to use a part-time system effectively which is apparently something the driving American public struggles with.

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Ford definitely isn't the first to have problems with PTUs. Basically, viscous couplings in full time awd/4wd systems are just trouble, period. It seems like the industry would figure out a better way to do it.

 

I always preferred part-time systems as they don't have viscous couplings. I guess the downside is that you have to be smart enough to use a part-time system effectively which is apparently something the driving American public struggles with.

The American public struggles with anything requiring even the slightest amount of thought

 

And therein lies the problem

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Well I think it's a good thing to change fluids on the vehicle regularly regardless of what the manufacturer suggested. It can never be a bad thing to replace fluids, other than cost of course. If your like me though and keep your vehicles for 10 years or more it's worth it.

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I changed the PTU lube in my MKS at about 50,000 miles. For what it's worth, the fluid I sucked out still looked pretty good with no evidence of become sludge. That is not to say that it would have remained that way forever. In the forums where I am active, other owners of SHOs and MKS ecoboosts have had sludging issues. My MKS is tuned and I take it to the drag strip occasionally so I think keeping the lube fresh is particularly important for me.

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That's good to hear about your MKS. As far as I've seen, that's the only real issue customers have had. The vehicles ford is producing now days seem pretty reliable.

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The vehicles ford is producing now days seem pretty reliable.

 

Except for the Ford Edge gas tanks. And leaking body seams. And cooled seats that burn your back. These don't affect long term reliability but they're having far too many of these problems on too many vehicles lately.

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The PTU is not a viscous coupling. Its basically a ring and pinion bolted to the transaxle. The viscous coupling is attached to the rear axle.

 

To go along with fordtech1's uneven tire wear comment I have seen uneven tire wear (front to rear) prematurely break down the lubricant on utility interceptors in as low as 30,000 miles.

 

I just wish they had a higher lube capacity. Its only .56 quarts! I'm no engineer, but I feel a higher capacity may help. It won't help if the rear tires are bald and the fronts are new though.

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The PTU is not a viscous coupling. Its basically a ring and pinion bolted to the transaxle. The viscous coupling is attached to the rear axle.

 

To go along with fordtech1's uneven tire wear comment I have seen uneven tire wear (front to rear) prematurely break down the lubricant on utility interceptors in as low as 30,000 miles.

 

I just wish they had a higher lube capacity. Its only .56 quarts! I'm no engineer, but I feel a higher capacity may help. It won't help if the rear tires are bald and the fronts are new though.

Duff is correct. It's very simple ring and pinion design. I agree more fluid or at least fluid replacing intervals. Not sure if some better type of synthetic fluid would not break down as easily from heat.

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The PTU is not a viscous coupling. Its basically a ring and pinion bolted to the transaxle.

It has to be more than that ! An "open" differential transfers all power to the axle/wheel that has the LEAST amonunt of resistance/traction. This would be useless on an AWD PTU.

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Does this recommendation apply to 4WD units on F150 and Expedition ?

 

No - completely different system and components.

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Coming up on 60K in my MKX....looking to get the transmission fluid changed, I will ask about changing PTU fluid and the rear differential unit fluid as well.

Edited by twintornados

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Wizard It IS a ring and pinion gear to turn the torque 90 degrees to the driveshaft for the rear axle. The rear axle uses a coupler to transfer torque from the driveshaft to the rear axle input. Therefore potentially in situations where the front wheels are spinning, all torque can be sent to the rear axle as it (the PTU) is splined directly to the case transaxle differential case, not to the side gears. The rear axle and the transaxle both are open style diffs, but that is what traction control is for.

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I know there are issues with the D3 and CD3 PTUs, but what about the earlier gen Escape? My wife's Escape has 125K on it and knock on wood I haven't seen any PTU issues with it. Guess I should get the transmission fluid flushed on it.

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Wizard It IS a ring and pinion gear to turn the torque 90 degrees to the driveshaft for the rear axle. The rear axle uses a coupler to transfer torque from the driveshaft to the rear axle input. Therefore potentially in situations where the front wheels are spinning, all torque can be sent to the rear axle as it (the PTU) is splined directly to the case transaxle differential case, not to the side gears. The rear axle and the transaxle both are open style diffs, but that is what traction control is for.

 

Just wanted to add that the PTU on the D3 (Taurus/Explorer/MKS/MKT/Police Interceptor Utility/Sedan) is apparently the same used on the Edge/MKX and CX-9. The PTU is working 100% of the time, always spinning the driveshaft. There's a JTEKT electronic coupler mounted at the Rear Differential Unit (RDU) that controls whether power is sent to the rear wheels or not. If you look at the AWD intelligent monitor on Fords that have it enabled, hard acceleration basically sends almost 100% of the power to the rear wheels - and by hard acceleration I mean like 30% or more throttle not necessarily WOT. Once you're at speed, the power is almost all to the front. On deceleration, I notice power going to the rear wheels, with nothing or low power to the front.

 

My guess is that the helical cut gears inside the PTU, combined with the low fluid quantity, and the proximity of the catalytic converter probably shears the fluid very quickly and then overheats it, causing it to thin and then thicken within 20k miles. Looking at the transfer cases on other AWD systems, their designs aren't much better and use about the same amount of fluid.

 

The transfer case on the pickup trucks and truck-based SUVs are a chain based system, looks like the timing chain setup on an OHC engine, and generally use something like transmission fluid (Dex VI, Mercon LV, etc...)

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I actually had 3 vehicles with PTU leaks with a couple thousand miles, 2007 and 2011 MKX. My mother also had a PTU leak on her MKZ. At the time, Ford didn't have a solution in 2007 so I ended up waiting 6 months with the occasional scent of burning transmission fluid in the winter. I know it took them a long time to sort it out but I haven't had any issues in newer vehicles. I generally tell people to avoid buying used AWD Fords for this reason, I specifically told my Sister to stay away from one when she was looking for her used Edge. PTUs and ACC are guaranteed trouble on the Edge, but otherwise they are great solid products.

Edited by BORG

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Supposedly the fluid is binary - it's fine for 150K if it stays below 340 degrees (or thereabouts). If it goes over it's toast and failure is imminent.

 

There is plenty of heat shielding from outside sources. A common theory is that manufacturing tolerances on the gears result in some units generating too much heat.

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What heat shielding is there? The rear cat and downpipe sits right below the transfer case. I was burning my arms after driving the car onto ramps, all of 2 or 3 minutes after a cold start at 60F.

 

I think Ford knows about this issue. They are specifying a 75W-140 when other transfer cases with hypoid gears (not the chain transfer case from pickups which generally use ATF) are using equivalent to 75W-90 or 75W-85 gear oil (Borg Warner 4474 in the ATS and CTS, as an example or the Mitsubishi Evo).

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There seems to be a huge variation with the number of issues and the service life of these PTUs. Many of us who are active on Ecoboost specific forums change the lube on a regular basis. Some report that the lube is the consistency of tar after 25,000 miles and that their PTUs appear to have been underfilled. Others report that the lube looks great after 50,000 miles or more and is at the proper level. How the car is driven or the area in which it is driven doesn't seem to matter.

 

Most dealers in my area as well as other areas will not exchange the lube as a regular maintenance item. With the proper suction device, it is relatively easy to suck the old fluid out and replace it with new. I have done it twice on my MKS, the first time being at nearly 50,000 miles. Actually, the fluid looked just fine and would probably have lasted another 50,000. I changed it again at 60,000 since I had been taking the car to the track and it looked nearly as good as when I replaced it a year earlier. For me, it is annual maintenance whether it "needs" it or not.

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Uneven tire wear adds to the overheating of the fluid from what I have seen. As with any all wheel drive, different tire circumstances adds stress to the system.

I think the ptu taking a crap is caused by a multitude of things. Driving habits, tire wear, manufacturing issues, and possibly just luck. To the people that think he ptu was overfilled, it wasn't. It's puking out the vent on top because the fluid has turned to sludge. Unless fluid was changed and overfilled, factory filled units I highly doubt overfilled.

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Uneven tire wear adds to the overheating of the fluid from what I have seen.

 

So have to ask this question, just noticed my front tires are significantly more wore down then the rears on my SHO...I got new tires about 2 years ago and due to several different things going on at the same time, I forgot to rotate them, which I'm assuming lead to the additional wear. Can I get away with rotating the tires for the time being (maybe for another 6 months) till I can get funding for 4 new tires?

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I don't quite buy the argument about uneven tire wear contributing to the PTU overheating. The reason being is that the PTU is constantly working (100% of the time) spinning that driveshaft. The helical cut gears are churning that oil whether you need power to the rear wheels or not, plus you have the catalytic converter and both exhaust pipes running underneath the aluminum casing. Coupled with the fact it has only 18 oz of oil for cooling and lubricating.

 

I think plain and simple is that the PTU design/placement is flawed on the Ford AWD system. They could have installed drain plugs and fill plugs (like every other PTU/transfer case on the market) to help with the maintenance, but chose not to probably for cost cutting reasons. After watching the Netflix documentary, A Faster Horse, I can understand where that cost cutting guy is coming from - but sometimes you have to step in with a maintenance perspective as well.

 

A drain plug with a remote fill port would have been nice. Allow us to drain it, then fill it with 0.56 qt of fresh 75W-140. It'd be simple enough to do every oil change, rather than have us finagle a suction hose between all of those gears inside the PTU, try to suck out molasses, then get our arms covered in gear oil while some of it drips onto the exhaust. Nevermind that even running the engine for 2 minutes will result in my arms getting burned on the catalytic converter.

 

The Cadillac ATS/CTS uses a Borg Warner 4474 transfer case that looks like the transfer case from a pickup, but understandable given the ATS/CTS platforms are RWD-based, so the driveline is longitudinally mounted. Ford chose to cut corners by using the same transverse setup on the bulk of its platforms.

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