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  #11  
Old 05-16-2009, 08:24 PM
Human
 
Real Name: Pete
Location: Ogden,UT
Hybrids: Ford Escape AWD
Posts: 4
Default Re: Bad PTU-Am I the first?

Thanks for the feedback. I guess I should've mentioned that the car is already at the dealership-and I assure you I will be driving it home with a $0 bill. I put it up in the air and ran it to diagnose , u joints, cvs' bearings all sounded good. I figured at that point it's not my job, I'll let ford fix it. Local dealer had no clue but the guys 15 miles away got it got it in right away and gave me a loaner till it's done. Old school, small town dealership (McFarland in Brigham City, UT). You gotta walk into the shop to get to the service desk, service guy rides with me to hear the problem, the way it should be done (and seldom is nowadays). Should have the new PTU in by tues.-I think that's pretty quick. I was really wondering if this was a weak point in these cars, but I can't find anyone who's had one replaced yet. Love the car and hope this was just a fluke. I'm just glad it didn't happen at 61,000 miles or I would've been doing it myself.
Thanks again for the input,
Pete
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  #12  
Old 05-16-2009, 08:42 PM
Imported from Detroit
 
Location: Michigan
Hybrids: none
Posts: 992
Default Re: Bad PTU-Am I the first?

Quote:
Originally Posted by wwest View Post
The way it works as I have been given to understand it is that the rear driveline is engaged under only two circumstances. First, when moderate to heavy acceleration is "called for", and then only in at lower roadspeeds.

Second, the other instance, is if front wheelspin/slip develops due to too much engine torque being applied, even with light throttle openings, for roadbed conditions. In which case the initial plan of action is to engage the rear driveline.

Remember that as much as 1/2 of the engine, HSD system, torque can be routed to the rear. If that doesn't work and wheelspin/slip persists then I have little doubt that TC braking and engine dethrottling would quickly follow. probably 200-300 milliseconds total timespan.

My guess is that like many other TC systems if it is disabled the rear driveline will still be engaged in the same way, manner, and you will be allowed to initentionally use wheelspin to get unstuck and/or initially up and going.
What does that leave out??

Articles I linked to in other threads say that under heavy throttle, the front wheels are left to steer, instead of doing both chores. That sort-of implies 100% torque to the rear. If it's only 50% possible that would be the reason my brand new SG-II is showing much higher than my test equipment.

I have to agree from my monitoring the torque control solenoid, a light throttle applies torque to the rear wheels

.

Bill

09 Ford Escape Limited, 3.0L, 4WD
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  #13  
Old 05-16-2009, 09:58 PM
Ridiculously Active Enthusiast
 
Real Name: willard west
Location: Beautiful Pacific NW
Hybrids: 2003 Prius
Posts: 1,678
Default Re: Bad PTU-Am I the first?

Quote:
Originally Posted by Bill Winney View Post
Try replacing the U-joints first. I have had u-joints go out on cars over the years and the first one kicked my butt in diagnosing it because of the very symptom you describe: worse when coasting and speed dependent.

There are two u-joints between the PTU and the rear axle.

Roger that the rear axle should not be engaged when on a dry hard surfaced road, but a failing element in the drive line just might kick in the AWD feature by increased resistance...

U-joints are maybe $15-45 each and are not difficult to replace yourself with certain tools. Worth a shot and cheaper than a PTU.

PS wwest's musings on TC, the rear clutch, and so on are off the mark, musings of a guy that doesn't even own an FEH nor have the manual.
But I do have full and complete access to the Toyota Venza and the 2010 RX350 factory documentation (techinfo.toyota.com) both of which use EXACTLY the same electromagnetically controlled clutch design to couple the rear drive to the front PTU.

But why don't you help us all out by telling us where my "musings" have gone awry.
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  #14  
Old 05-17-2009, 08:57 AM
Ridiculously Active Enthusiast
 
Real Name: Bill Winney
Hybrids: Escape
Posts: 767
Default Re: Bad PTU-Am I the first?

So long as its under warranty let them problem solve it...

But keep in mind for later, that a key indicator of a bad u-joint is the load/no load noise thing. When I first had this happen, years ago on an old Plymouth Duster, the only way I could find to diagnose it was to put the rear end up on jack stands, engage the drive line, and crawl under it and listen. Once I did the problem was obvious.

Since then every time I have had that kind of noise there was indeed a bad u-joint around.

I hope that Ford made the PTU strong enough not have a problem in the first 60k of life.
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  #15  
Old 05-17-2009, 10:10 AM
Ridiculously Active Enthusiast
 
Real Name: willard west
Location: Beautiful Pacific NW
Hybrids: 2003 Prius
Posts: 1,678
Default Re: Bad PTU-Am I the first?

"..I hope that Ford..."

The early indications of that are not so good.."

An indicator to let the driver know the electromagnetic clutch and rear differential is overheating, has overheated, is NOT a good omen.

The later addition of cooling of the PTU would indicate that the electromagnetic control of the rear driveline has been "stiffened", made more robust, moving the higher stress point to the PTU. Obviously water cooling of the PTU would be an easier design change than cooling the clutch and rear diff'l.

Insofar as I can tell neither Toyota nor Lexus nor Porsche have made any attempt to cool any portion of this drive system. In the case of Toyota and Lexus their efforts insofar as F/awd implementation often stop at simply sale sand marketing, no real functionality of F/awd required.

In Porsche's case it's a rear engine R/awd system so the stress level, actual useage, need not be so high.

Kudos to Ford for at least trying to build a fully functional F/awd system.

Last edited by wwest; 05-17-2009 at 10:14 AM.
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  #16  
Old 06-13-2009, 10:21 AM
Enthusiast
 
Real Name: John
Location: Yonkers, NY
Hybrids: 2007 Mercury Mariner Hybrid
Posts: 7
Default Re: Bad PTU-Am I the first?

I have a 2007 and have the same symptoms a low speed 0-5 mph. It is like a "surging". Took it to the dealer and they diagnosed a faulty transmission and replaced the eCVT. That did not solve the problem completely and now they are waiting for a PTU. Fortunately their doing it under warranty and gave me a loaner for the 2 weeks they had the car to replace the eCVT. Told me that it was safe to drive until they receive a PTU.

Problem is that there had been issues with leaking seals in the PTU and initially they were replacing entire PTU units, until they realized that they only needed to service the seals. That has resulted in no PTU units being immediately available. It has been a week but I think it will probably take a month for the dealer to get a unit (I hope not longer).

There hardest stress I put on it is when I accelerate onto a highway, otherwise I am pretty good with it. Could this stress out the PTU?
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  #17  
Old 06-13-2009, 04:02 PM
Ridiculously Active Enthusiast
 
Real Name: Bill Winney
Hybrids: Escape
Posts: 767
Default Re: Bad PTU-Am I the first?

First: on a dry hard surface road I wouldn't even think the rear axle would kick in, even under heavy load.

But Second: This is kind of sounding like a bad constant speed unit to the front wheel(s). I just would have thought that Ford would have been able to recognize this (particularly when they made a decision to replace the transaxle).

Don't know, just my thoughts.
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  #18  
Old 06-13-2009, 05:44 PM
Imported from Detroit
 
Location: Michigan
Hybrids: none
Posts: 992
Default Re: Bad PTU-Am I the first?

Quote:
Originally Posted by Bill Winney View Post
First: on a dry hard surface road I wouldn't even think the rear axle would kick in, even under heavy load.
That's what this thread was all about: http://www.greenhybrid.com/discuss/f...uage-ii-21592/. You do get rear wheel torque on dry pavement.

.

Bill

09 Ford Escape Limited, 3.0L, 4WD
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  #19  
Old 06-13-2009, 09:23 PM
Ridiculously Active Enthusiast
 
Real Name: willard west
Location: Beautiful Pacific NW
Hybrids: 2003 Prius
Posts: 1,678
Default Re: Bad PTU-Am I the first?

I can't think of any reason for the rear driveline to be engaged beyond ~5% (95/5)(if even that) on a dry hard-surfaced road in any circumstances other than a way to shorten the life of the drive train, PTU/(PTO) and/or rear electromechanical clutch.
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  #20  
Old 06-14-2009, 06:20 AM
Imported from Detroit
 
Location: Michigan
Hybrids: none
Posts: 992
Default Re: Bad PTU-Am I the first?

Quote:
Originally Posted by wwest View Post
I can't think of any reason for the rear driveline to be engaged beyond ~5% (95/5)(if even that) on a dry hard-surfaced road in any circumstances other than a way to shorten the life of the drive train, PTU/(PTO) and/or rear electromechanical clutch.
That's what I first thought when seeing SG-II pictures showing 47.6% rear wheel torque under good driving conditions. My testing in the link I provided aboved proved otherwise.

I'm not sure why Ford even refers to it as a "on demand" system when torque is so easily sent to the rear wheels!

That one sentence from a '09 shop manual about the 4WD system says it all: Under normal driving conditions "most" of the torque is sent to the front wheels.

.

Bill

09 Ford Escape Limited, 3.0L, 4WD
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Old 06-14-2009, 06:20 AM
 
 
 
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