2009 AWD question....

Technical info on the Pontiac Vibe and Toyota Matrix including do-it-yourself info
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Gumby
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Joined: Thu Dec 29, 2016 5:24 pm

2009 AWD question....

Post by Gumby »

Good Morning:

As the title says, I've got a question regarding the 2009 AWD system, but please allow me a moment of venting about the overall frustration of this situation.

I'm an entry level, professional mechanic. Although still inexperienced with many things regarding drive train systems, the basic, mechanical principles of operation are not a mystery to me. But sometimes the most obvious answers are right in front of us and we need someone else to point them out. That said, here's a shorter version of a long story:

A few years ago, my wife and I were looking at a 2009 AWD (2.4L) with just under 90K miles. It was in very good condition. On the test drive, I did notice a slight vibration from the rear end, but based on the sound, I thought it was a heat shield or something body-related and didn't give it its due concern, and we bought the car.

About 20K miles later, the vibration had gotten worse and is clearly related to the drive train as it changes depending on the speed and engine load. I found the rear most u-joint on the drive shaft had dried out and was "rough" when moved by hand. Since the u-joints are stamped in place, I had no way to replace them (I talked to a local shop that specializes in drive shafts and axles and they couldn't do anything with it) and installed a replacement drive shaft from a junk yard with good u-joints in it.

That didn't fix the vibration. :x

Just for the sake of exploration, I pulled the viscous clutch off the front of the differential and found that the bearing that supports the clutch coil (electromagnet) had been almost completely shredded. :shock: Since the metal shavings from that had destroyed the pinion seal, I decided it was best to rebuild the differential since there was most likely bearing damage inside the case.

I found a replacement bearing for the clutch coil at a local bearing supplier and got the remaining parts for the rebuild from the dealer.

Fast forward a couple years later, and that oh-so-identifiable vibration is back.

Here's my question: WHY is there a clutch coil in the viscous clutch? When looking back to earlier AWD models (compare with a 2006, for example), that clutch coil isn't there.

I've been doing a lot of research in trying to figure out why the clutch coil was added - I was hoping to find a TSB, recall or other info on earlier models stating something to the effect of "the AWD systems were having this issue, we think adding a clutch coil will solve it" but no such luck. I haven't been able to find anything more than generic info from GM on the 2009 system.

When you look at how the drive train is set up, the drive shaft hooks to the viscous clutch and the VC is splined directly to the drive pinion - there doesn't seem to be any practical purpose for the clutch coil to be there.

Can somebody please explain the purpose for this?

Thank you.
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vibrologist
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Location: Iowa

Re: 2009 AWD question....

Post by vibrologist »

That's an interesting question. Since I don't know much about this stuff myself I looked up this: http://auto.howstuffworks.com/differential5.htm
There it says:
this also highlights a disadvantage of the viscous coupling: No torque transfer will occur until a wheel actually starts slipping.
I suppose the electromagnetic coil is there to lock the viscous coupling when driving conditions require it.
Again, I don't have practical experience. Maybe there is a malfunction that keeps the coupling always locked or locked too often? Pure speculation on my part!!!
Good luck!
Vibrologist
'05 Vibe

"It is important to know the difference between 'accurate' and 'precise' even if you are neither!"

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Gumby
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Joined: Thu Dec 29, 2016 5:24 pm

Re: 2009 AWD question....

Post by Gumby »

Thanks for the link to the article, but it seems to have overlooked/omitted a basic point of VC operation - it only takes a speed difference of about 8% for the plates to start slipping, and once they do, it takes about 1/10th of a second for the fluid to heat up and expand enough to "lock" the plates together. (That's according to one of my books from school).

Let's see what that difference looks like (using simple numbers to make the difference easier to see) - if the output speed of the transmission is 1000 RPM (transferred directly to the drive shaft and, therefore, the VC), the speed of the drive pinion on the differential would only need to be 920 RPM for the plates to start slipping. Less than a quarter of a second later, the fluid is expanded and "locking" the plates together.

If I'm taking off from a stop, then for just the briefest of moments, the output speed of the transmission is greater than that of the drive pinion and the plates will start slipping. In other words, the VC would be "locked" by the time I drive from my garage to the end of my driveway.

If the clutch coil is there to lock the VC when driving conditions require it, then it doesn't make sense to me that the VC is there at all. By its very design, the VC will lock itself when needed.

It also doesn't make sense to me that the clutch coil would be there because the VC is locking up too often - because it's working on the principle of magnetism, if anything, it would cause the VC to lock up rather than release it because the "pull" its putting on the steel plates creates more friction within the VC.

Also, I can personally attest that the clutch coil has no impact on the traction control system - for the sake of experimentation, I disabled it a few months ago just to see if it would impact the driveability of the car. A couple weeks ago we got some ice on the roads and the TSC was working normally. Other than the AWD indicator light on the dash, it doesn't seem to have affected how the car drives.
jolt
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Re: 2009 AWD question....

Post by jolt »

This info may help; the Toyota RAV4, Matrix and the Vibe use the same type of drive couple. There are a lot of different types of viscous couplings, even a torque convertor in a automatic transmission is a type of viscous couple. Anyways check these links for more info on the type that is used in the Toyota.

"Here's a PDF file that gives a good overview of the rear differential and electric coupler:"
http://www.rav4world.com/pdf/2006/rav_diff.pdf

http://www.rav4world.com/forums/96-4-3- ... lutch.html

Ask yourself how does the clutch pack make friction to get the power to pass through the coupler. There are no springs to force the clutch disks together like the older Vibes had.
gtv237
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Re: 2009 AWD question....

Post by gtv237 »

Maybe it can electronically lock in certain conditions. You have to remember a viscous coupler still slips. It's incapable of supplying full torque to the rear wheels. Maybe this electronic locking system fully locks the coupler in certain conditions?
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vibrologist
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Re: 2009 AWD question....

Post by vibrologist »

Thanks to jolt for answering the question by providing the link to the overview of the rear differential and electric coupler.

The coil operates the CONTROL COUPLING. It controls how much driving force is transmitted through the MAIN COUPLING.
Vibrologist
'05 Vibe

"It is important to know the difference between 'accurate' and 'precise' even if you are neither!"

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Gumby
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Joined: Thu Dec 29, 2016 5:24 pm

Re: 2009 AWD question....

Post by Gumby »

jolt wrote:This info may help; the Toyota RAV4, Matrix and the Vibe use the same type of drive couple. There are a lot of different types of viscous couplings, even a torque convertor in a automatic transmission is a type of viscous couple. Anyways check these links for more info on the type that is used in the Toyota.

"Here's a PDF file that gives a good overview of the rear differential and electric coupler:"
http://www.rav4world.com/pdf/2006/rav_diff.pdf

http://www.rav4world.com/forums/96-4-3- ... lutch.html

Ask yourself how does the clutch pack make friction to get the power to pass through the coupler. There are no springs to force the clutch disks together like the older Vibes had.
FINALLY!!

Thank you for providing the links, and thanks to others for contributing to the discussion.

It was difficult for me to think of any set up other than a "traditional" viscous coupler - that is, alternating friction plates with silicone fluid that works on a purely thermal/mechanical basis. Thinking of it in those terms, I saw no practical reason for the clutch coil to be present (as previously stated :D ).

I had tried looking up info on the Toyota Matrix with the same limited results - I certainly didn't know the RAV4 used the same set up otherwise I'd of pursued that as well.

This is why good service info is so important - even if this wasn't a personal car for me, I'd have been asking the same questions at work had I run into the same problem.

I'll get the bearing replaced again and enable the clutch coil to get the car back in full working order.

Thank you!!!
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