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2004 chevy trailblazer_lt
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Discussion Starter #1
Here is an update to this thread: http://www.forums.trailvoy.com/showthread.php?t=49335
Because I'm everyone was on pins and needles to hear what happened. ;)

I took the TB into the dealership on Friday (Yesterday), they changed the transfer case fuid and that took care of rough engagement when in A4WD, but it was still whining. They opened up the front differential and found that a bearing had been "shredded" and replaced that and took it for a test drive. It was still had the whine and drag, but was different. They swapped the rear tires/wheels for a new set (from a nearby Envoy) and say that the sound/symptoms went completely away. And recommend that I get 2 new tires. The service Manager stated that the small difference in tire size was putting excessive load on the differential bearing when in 4WD, causing the previous damage, and that it would happen again unless the tires were replaced.

I picked it up today. The engagement is smoother, but the whine and drag persists - but it is different. It almost seems as if there is more resistance. (I suppose it could be due to a new bearing).

Does this make sense? I had two tires replaced in July - due to grossly uneven wear. And those had been rotated into the front in the last month. So, two tires on the front, roughly 5 months old, and two tires on the rear of undetermined age - but are not badly worn, and still have fairly decent tread left.

Does this sound legit, or is the dealership trying to meet a quota for tire sales? I suppose I won't be using 4WD soon until this is sorted out.

Any thought? Similar experience?

Thanks,

db
 

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2007 chevy trailblazer_lt
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So were the tires the same size all arond before? A slight differance in tire size due to tread wear will not cause a Diff to blow up. If it were a matter of inches then possibly. I would say they are just throwing out a best guess solution.

Which bearing was it that failed exactly?

A new bearing will not cause any drag or resistance. Its just a band-aid on the source of the problem.

The badly worn tires: How were they worn? Normal tread wear or worn in a certain area?
 

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Discussion Starter #3
Thanks for the reply brendan.

The old worn tires just had normal tread wear.

I just went back to the dealership to chat with the service manager.
The replaced bearing was "differential actuator bearing" and it was "fried". He took me back and showed it to me, but to be honest I'm not sure what I saw - but whatever it was looked worn and messy. He also stated that the 4WD is engineered so tightly that even a 1/4" difference in tire diameter will make a "big difference".

On the way back home, I played with the air pressures - lower in the newer tires to possible simulate decreased diameter as well as higher in the newer. No change in the sound.

Me thinks I should call a different dealer/shop???

Thoughts?

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Interesting.

I would suggest you keep at the dealer who did the work, as you are probably paying out of pocket for the repairs, and a trip to another dealer will only cost you more. I would try another place for any future repairs if your not happy with this place. For instance, Im a mechanic, so dealer visits are strictly for warranty, but the local Chev dealer pi$$ed me off so much in one visit, that after said problem was repaired, I went across the street to the GM dealer, and have had no issues at all.

Since they claim that they swaped 2 tires and the problem went away, and thus sold you 2 tires to fix the problem, which in turn did not "fix" the problem, I would be after them as to why their solution did not infact correct the problem after paying the cost of the repair.

If they give you the run around, GM's customer care center is pretty effective, though not always quick, and may be of some help if the Service manager is an idiot.
 

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Discussion Starter #5
I think I misunderstood the service manager when I first spoke with him, and then was confusing in my message.

Earlier today, he clarified that they tried my TB with 4 new tires (from an Envoy) - and had no problems/no noise. They then put the original tires back on the TB and the noise/symptoms persisted. I have not purchased any new tires yet as I am just not sure if that is the best solution to all this. I guess it just doesn't make sense to me.

So far all this dealer has done is to change the transfer case fluid and replace the differential actuator bearing.

I suppose I could get the tires and then try to raise hell if that doesn't fix things, but I don't want to try that just because they don't have any better ideas.

db
 

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Ah, ok. Still does not sound right to me, for what you describe and what they suggest.
Where are our Trailvoy 4WD experts?
Roadie????
Anyone???
 

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2003 gmc envoy_slt
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I think I misunderstood the service manager when I first spoke with him, and then was confusing in my message.

Earlier today, he clarified that they tried my TB with 4 new tires (from an Envoy) - and had no problems/no noise. They then put the original tires back on the TB and the noise/symptoms persisted. I have not purchased any new tires yet as I am just not sure if that is the best solution to all this. I guess it just doesn't make sense to me.

So far all this dealer has done is to change the transfer case fluid and replace the differential actuator bearing.

I suppose I could get the tires and then try to raise hell if that doesn't fix things, but I don't want to try that just because they don't have any better ideas.

db
It seems like they did spot the problem. Even tires that have the same number size can be different in actual size depending on manufacturer. I think any 4x4 or AWD vehicle should have all tires replaced at one time when ever possible. :m2:
 

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Discussion Starter #8
Wooluf1952...

It seems like they did spot the problem. Even tires that have the same number size can be different in actual size depending on manufacturer. I think any 4x4 or AWD vehicle should have all tires replaced at one time when ever possible. :m2:
The newest tires on the vehicle have ~10k on them (rated/guaranteed for 60k), do you think I would be safe to just swap out the two oldest tires?

For some reason, I'm just skeptical of that, but I guess that is the only major equipment difference I have from last season to this season. Do you think the tire difference would also cause the feeling of being in midst of a "downshift"?

Thanks WOOLUF,

db
 

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I'm stumped so far. If only they had let YOU drive it with the loaner set of tires. :undecided

I've neither read nor experienced anything that says that the GMT360 4WD system is engineered "tightly" or that it should be sensitive to 1/4" tire diameter differences. But I rotate often enough that any uneven wear would not develop to the point that only 2 tires would need replacing.

You should be able to measure the exact diameter difference of your tires with string or something. Just measure the circumference of all four and let us know what they are. I suspect the noise, assuming you're rolling in 2WD mode, is due to tread design - also assuming the dealer's hearing response is similar to yours and he's really hearing no noise with the loaner set. If only they had let YOU drive it with the loaner set. ;)

In any event, you would only have been stressing the bearing by that method if you were in 4HI mode on a lot of dry pavement. How much have you used the 4HI or 4LO modes, and what sort of mileage have you put on the system on slippery and dry conditions? Out of my 70,000 miles, I've probably been in 4LO for 1000 miles or so, and 4HI for 3000 miles, without any diff or transfer case problems. Not that it proves anything, because all of that driving was on surfaces with slip.
 

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2003 gmc envoy_slt
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I would think 10K would be OK if they weren't beaten on or smoked to much :x. Try calling or emailing a tire dealer that you trust. Maybe Tire Rack could help. I can't really help with the "downshift" feeling. Have you tried jacking it up and spinning the wheel to see if you can feel any dragging or bearing noise?
 

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Earlier today, he clarified that they tried my TB with 4 new tires (from an Envoy) - and had no problems/no noise.
db

DB, it would have been nice if the stealership called you to come take a test drive when they put the tires from the Envoy on your TB....then they would have proved their point, and you would have known 100% what to do to fix it.

As of right now, your just having to take their word for it, and possibly buy a set of tires you don't really need.

I know this will be a PIA, but you could jack up the TB and take the thinnest tape measure you have, and measure the circumference of all 4 tires. I would say that would give you more information and help you make an informed decision.
 

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Discussion Starter #12
roadie,

I just ran outside and did a quick check with a length of string, but I didn't jack the wheels off the ground, so its more of a side-circumference - and all 4 tires were very close. When it is light out (and hopefully warmer) in the A.M. I'll lift 'em up and get exact measurements.

The whining only occurs in 4HI or when A4WD is "fully engaged" and its part of the feeling of being "downshifted". Its obvious that nothing has down shifted, but its that same kind of "drag" when stopping with a down shift and it occurs as soon as 4WD is engaged.

I haven't run too much on dry pavement, only here and there recently to try to check out this dang problem, never for more than ~5-10 seconds. and I have been experiencing the noise ever since the first time I engaged 4HI this season, and I was on snow. I actually only use the 4LO rarely or when testing it and infrequently use 4HI. I just don't want it to fail if/when I really need it.


WOOLUF1952,
I haven't smoked the tires too much. When gas prices went up, so did my lap times. ;)


I agree with all about being able to test drive it with the new tires. I am tempted to have the others put on, just to see what happens, but I don't want to drop the coin for a sketchy solution. I will get good measurements of all four tires tomorrow and post them here. I'll also try spinning the wheels with the front off, unfortunately I don't have a full lift to see if the whine continues with absolutely no load.

Thank you everyone for your suggestions so far, hopefully this can be solved sooner rather than later.

db
 

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Discussion Starter #13
OK everyone, I jus finished up measuring the tire circumferences - I measured each tire 3 times.

The rear tires (old tires) are between 94" and 94 1/8"
The front tires (new tires) are between 92 7/8" and 93"

Anyone else a little shocked?

I did jack the front end all the way up and spin the tires. They spin fine in 2HI. In 4HI they spin fine, and when I spin the left forward, the right spins backward and vice versa - but that is normal?

The service manager may have been onto something, but I'm still not sold.

Is that evough of a difference?

db
 

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The backwards rotation is normal for the open differential in front.

I did more of a search in other forums just now. Your circumference difference implies about 0.3" diameter difference. I'm not sure I'd blame that amount of difference in a 4WD vehicle for problems, but it seems in an AWD it would be a worry:

http://www.automotiveforums.com/vbulletin/t557596.html

As a guy who replaced a transfer case in a Bravada because some goof drove it a few miles with the spare on with 3 different size tires I think you should be VERY careful with this. The comments about rolling diameter are right on. If everything doesn't turn at a 1 to 1 ratio something has to give that something is the clutches in the transfer case. When they are gone. there is no getting them back. Look at the Subaru site and search for Subaru specific data. The word on the GMC AWD is tire diameters as little as .100 different will kill the TC in short order. Good Luck.

http://www.gminsidenews.com/forums/f53/awd-tire-size-mismatch-safety-sales-training-68760/

I own a 2005 Buick Rainier. The Vehicle was sold to me with over 30k of wear on the front tires and the rear tires are new. The vehicle had various TC problems. Hopping, locking, whining and tremendous banging durinig slow down to stop. I have read by on a non-GMC post that the differnce should never be more then 0.100 of an inch. I replaced the front tires and all the problems stopped.

A discussion from Tirerack:
http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=18

I'm as skeptical as you that it would be a problem on your 4WD system to have tires that much different. If the dealer changed the TC fluid, did they *(or you) also check the front diff level? The actuator side bearing doesn't get oiled from the differential, so its damage shouldn't have thrown metal into the diff, but they should have checked the level while they were working in the vicinity, as a troubleshooting measure.

In 2WD, there's no torque being sent forward by the driveshaft from the TC, so it doesn't spin. In 4HI, it does. Any chance the whining can be heard by somebody outside the car as you drive past them? Could they help localize it? Or do you have four jack stands you can borrow to put the whole thing in the air to try it out?
 

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Discussion Starter #15
the roadie,

That was certainly a wealth of information. I greatly appreciate it.

Sorry I didn't respond earlier, my wife informed me that "we" were not yet finished Christmas shopping - and then I had to replace a battery...yea!

Reading through those links, maybe I sold the service manager/department short with this theory. Maybe I should also be upset with the shop that sold me just the two tires before.

I did have my wife drive by me in 4HI, and it sounds like engine braking, but seems to be much more noticeable when in the TB.

On the link to the gminsidernews.com thread, in the long post by GMCSonoma there was a section that stated:

"PART-TIME 4WD
Part time 4WD refers to vehicles equipped with a transfer case to split power between the front and rear axles of the vehicle. This traditionally is a 2-speed selectable transfer case that can be shifted into 2HI, 4HI, 4LO and usually a Neutral position. The 4WD modes of Part time systems do not allow for a difference in speed between the front and rear axles while turning. This system effectively locks the front and rear propeller shafts together. When turning, the tires must allow for the different turning radius of the front and rear axles, which is why this is intended for low traction or off-road use. These systems have low range gearing for the transfer case. An example of a vehicle with this style of transfer case would be a Silverado with a manual shift transfer case (a shift lever on the floor) (RPO NP2) or a Colorado with a push button transfer case with a 2HI, 4HI, 4LO and Neutral position (RPO NP1). The RPO codes for this style of transfer case are NP1 (NVG 233, 243, 263, and T-150 push button) or NP2 (NVG 231, 241,261, BW 4401, 4470 shift lever)."

To me, the bold/italicized section means that a difference in tire circumference can be a bad thing in the 4WD that my TB has. The front and rear are supposed to be turning at the same speed, but my tires aren't letting it do that.

I think I'll be heading out later this evening to drop my vehicle off for tomorrow. Hopefully I'll be able to make it back to them before they close tomorrow evening.

Thanks again roadie and Wooluf, hopefully I'll have good news in a day or so. ;)

db
 

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To me, the bold/italicized section means that a difference in tire circumference can be a bad thing in the 4WD that my TB has. The front and rear are supposed to be turning at the same speed, but my tires aren't letting it do that.
Only on dry pavement will you get crow hopping or driveline binding. On gravel, snow, sand, etc - low traction surfaces, the tires will slip (1" slippage on the front or rear would be required per revolution) and relieve the stress in the driveline. Since you weren't in the habit of running in 4HI on dry pavement, that's why we don't trust the dealer's explanation of the bearing failure.

I did a long explanation a couple of years ago, using the drawing below - to explain how the effective turning radius of the front and rear diffs causes extreme driveline binding in 4HI in a parking lot - due to the effect of the turning point of the vehicle being in line with the rear axle and much farther away from the front diff. The effective RPM of the front wheels is a lot higher than the rear because they have farther to go in a turn. Since the transfer case locks them together - stress buildup is inevitable.

 

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Discussion Starter #17
I remember seeing that picture in other posts when I searched, it makes more sense the more I look at it. ;)

I am not sure what to think about the bearing failure, especially since I'm not sure what the differential actuator really does. It could be that the two issues aren't related, and they just happened to stumble onto a failed bearing during exploration of the initial complaint...?

I did notice that it was much harder to turn on dry pavement the very few times that I did try it. I also noticed that changing lanes on the street with 4HI engaged took a little more effort, even though it was a much less severe arc of travel.

I never really experienced any crow hopping or vibrating, just a feeling/sound that there was excessing friction/resistance somewhere in the front of the drivetrain. It may have happened, but I refrained from any sharp turns with 4HI on pavement - seeing as its not good for the system.

Given all the info so far, I'm curious as to what you think the outcome of the new tires will be? Solution, or no difference?
I'm sure if the two don't fix it, then it will be "you need a whole new set". Ehhhh. :(

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Assuming the dealer can't supply an exact match tire to your 93" circumference rear tires, can your tire store? I'm afraid I never replaced just two tires at a time on the Envoy, and I certainly wouldn't mix brands/models, so I really don't have any experience there.

In 25 years of my wife owning Subaru 4WD wagons, we tried replacing a pair by mixing tire models only twice. Both experiments were miserable failures, with the steering dynamics (not even in 4WD mode) being so horrible that it was downright scary. Subarus are different beasts, but the concept is similar. Tires matched for stiffness and other dynamic characteristics enhances safety. Proper rotation should never allow a pair of tires to look bad enough to replace while leaving the other pair looking OK to get by with.
 

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Discussion Starter #19
The dealer is actually able to supply the same brand and style of tires (Firestone Destination LE - which I purchased at a Firestone shop), and actually about $100 cheaper for the pair - go figure...

I actually just got a call from the dealer, the service manager says they tires are on and the noise in 4WD is gone - I asked specifically. I guess we will see what happens when I pick up in the morning. *fingers crossed*

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This doesn't make sense.....unless the front axle is engaged, the fact that the front tires are a bit newer (ever so slightly taller) than the rear tires, shouldn't make a difference. (Both fronts are the new tires, you didn't put one on the front and the other on the back.....this would result in a problem). If the whine occurs in 2HI, it can't possibly be the problem, the transfer case shouldn't be applying any TQ at all to the front wheels in 2HI. - Now if it occurs only in A4WD, 4HI or 4Lo, yes it might be the issue, however in 4HI/4Lo, the conditions should be so bad as to not make a difference due to the poor traction conditions.

Have you driven the vehicle since the fluids were changed? If so, could the noise just be the annoying hum that some tires make on certain pavements? The Goodyear GTII tires I had for a while, made this very annoying hum, which could be described as a whine, on some pavement......you could hear the whine slow or change pitch as you applied the brakes to stop. Just wondering if it could be normal tire hum.
 
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