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Deoxyrybose

AWD to FWD Conversion

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I'm sure this has been covered 100 times, but the threads I've found don't have satisfying answers. What are your thoughts on an AWD to FWD conversion for a failing or leaking PTU? I simply don't have $1,500 to drop on a repair to literally have it happen again, which we all know is the case. Physically, this is my idea. Starting at the back, you could remove both axle shafts, the rear diff, the driveshaft and stop there. The problem with that method is eventually when all the fluid leaks out, the friction will cause the gears to fracture within the PTU, and honestly it's a crap shoot if it breaks the transaxle-side gear or one of the others. Potentially it could resolve itself (once it breaks, if the transaxle side continues to spin in the case, you've won the lotto, you're free!) but more realistically it could lock up and keep the transmission from spinning, and toast the transaxle.

 

Alternatively, if you were to remove all of the above components, and in addition the PTU as well... then pull one or all of the gears out of it and then reinstall it... you would just have the transaxle shaft spinning alone inside the PTU case. Mechanically this is sound, no danger to other components. Remember that the whole AWD system spins idling at all times until the rear dif solenoid engages it and puts an actual load on it. But, this is where the problems come in though... the ECU will likely notice the lack of input from the AWD system. How? I'm not sure. Maybe the Rear diff solenoid would have to remain hooked up to some extent,  just so the ECU is happy it can ground the circuit properly at will? How would the ECU know we've disconnected the system? The tires should all spin at the same rate for a given speed, so RPM signal would likely not be valuable feedback for if AWD is active or not.

 

I appologize for the rant, but I'm interested in salvaging the remainder of these wonder vehicles, despite the ONE glaring flaw of the PTU. So I guess one bit of homework is how does the Edge even differentiate the torque front to rear? If the AWD system right up until the rear diff solenoid is always active (spinning), and it's mechanically, permanently geared, to the transaxle, how does the car "split" torque? Some cars that have a center diff can split torque 20/80, 60/40, etc I don't see that happening here because there's no center diff. So would this even affect the driveability of the vehicle, and will this set check engine lights? (and how?). Thanks in advance, let the conversation begin!

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The clutch on the rear diff is electronically engaged via the solenoid when rear torque is needed.

 

I'm not sure if anything else in the FWD drivetrain is connected to the PTU.  If not then removing the gears and driveshaft seems like it would work.

 

But if you're going to do that much work why not put in a new PTU yourself, add a drain and change the fluid regularly?  Should be a lot less than $1500.

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You're correct. If you've gone that far, you might as well change it. But then I'm in it for the cost of a new PTU, and if the seals go, as SO many have, it's more hastle than it's worth to replace seals. My idea is a lot of work, I understand that, I was just looking for a wits-end alternative to dealing with poor engineering. My PTU is currently leaking out the tail shaft seal, and the passenger side seal (or at least it seems that way, maybe it's coming from above?) Another alternative I may take is to just let it leak but keep filling it. Always fresh fluid, and I don't have to tear half the car apart and use special seal drivers/pullers to fix it.

 

The problems add up and I start to wonder if it's worth keeping. The slam shifting has blown my engine mounts and cracked the old rusted exhaust. I tried replacing the mount, but snapped the first bolt right off at the bottom of the cat getting the Y pipe off. That's when I noticed the PTU leaking. Money pit.

Edited by Deoxyrybose

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If you just pull the electrical connector off the RDU (rear diff), the AWD system will fault to off.  You'll get a wrench light, but the clutches between the front and rear axle will remain permanently open and everything will just be free spinning.  That would take the load off the PTU, but it won't fix the leaks.

 

I haven't heard of any issues of seals leaking on the newer PTUs, I think that issue has been fixed.

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been seriously thinking about removing ptu/propshaft and installing intermediate shaft and right half-shaft from a fwd version. 

fairly confident it will work. 

btw, monitoring with forscan while driving casually (slow acceleration), the rear wheels are powered almost all the time, when starting from a stop or even slow coasting turn, as soon as you have any throttle pedal input, you get AWD on. so it's not just when there's wheel slip. turning off traction control seems to make barely any difference. (slight percentage less)

tho my plan might causing the ecm to freak out tho when the front wheels actually slip. 

just going to do this while to put off buying another PTU until a bit after Christmas

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8 hours ago, majorahole said:

been seriously thinking about removing ptu/propshaft and installing intermediate shaft and right half-shaft from a fwd version. 

fairly confident it will work. 

 

 

You'll have a big gaping hole in the side of your transmission where the PTU used to act as a cover.

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On 12/17/2019 at 10:15 AM, Waldo said:

 

You'll have a big gaping hole in the side of your transmission where the PTU used to act as a cover.

why? that's what the intermediate shaft from a fwd edge is for

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the fwd and AWD use the same transmission. AWD just has a PTU bolted to it. that's where the longer intermediate shaft goes in the FWD version. the the right half-shaft is a different length too. 

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That'd probably work. I'd still sjtu buy a new PTU and put it in if I was yanking the old one.  They aren't that expensive and if you change the fluid they will last.    You can wrap the exhaust pipes and/or make better heat shields around the cats to help preserve the seals.

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My understanding was that there is a "common wall" between the PTU and the trans, such that when you remove the PTU there is no longer a wall on the side of the transmission where the PTU used to be.  The internals of the trans are all the same, but the covers are different.  Maybe I'm remembering this from some other vehicle though.

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