AWD weirdness in 02 Bravada - or "Stupid Questions, part 1."

TequilaWarrior

Original poster
Member
Dec 5, 2011
577
Central Pennsylvania
So, I have (2) 2002 Bravadas. Both with AWD. If I jack up one front tire on "mine" I can not spin the wheel (truck in park). If I jack up one front tire on "hers", I can spin that wheel with ease. Both drive perfectly fine. "Mine" squeels tires in turns but doesn't "crow hop" hers doesn't squeel tires and doesn't crow hop. Dealership just told me that mine is working as designed - I'm confused. I know her AWD works perfectly (many snow trips tell me that). Hers also gets almost 3 mpg better than mine. We both have the same RPO for the AWD (np4, I think). Reason would seem to tell me that my front diff is somehow locked in, and hers is not. I don't however, have a deep understanding of the individual components of the AWD in these - so I don't know if that's even possible. Mine behaves like my old '75 GMC used to when I'd forget to unlock the lockin/lockouts while not in 4wd.

So, I guess my questions are these: Should I be able to spin my wheel or not? Could the front diff be somehow engaged? What should I be looking for, if anything? What is the meaning of lif... never mind different thread.
 

strat81

Member
Dec 29, 2011
399
TequilaWarrio said:
So, I have (2) 2002 Bravadas. Both with AWD. If I jack up one front tire on "mine" I can not spin the wheel (truck in park). If I jack up one front tire on "hers", I can spin that wheel with ease. Both drive perfectly fine. "Mine" squeels tires in turns but doesn't "crow hop" hers doesn't squeel tires and doesn't crow hop. Dealership just told me that mine is working as designed - I'm confused. I know her AWD works perfectly (many snow trips tell me that). Hers also gets almost 3 mpg better than mine. We both have the same RPO for the AWD (np4, I think). Reason would seem to tell me that my front diff is somehow locked in, and hers is not. I don't however, have a deep understanding of the individual components of the AWD in these - so I don't know if that's even possible. Mine behaves like my old '75 GMC used to when I'd forget to unlock the lockin/lockouts while not in 4wd.

So, I guess my questions are these: Should I be able to spin my wheel or not? Could the front diff be somehow engaged? What should I be looking for, if anything? What is the meaning of lif... never mind different thread.

Have you checked your front differential for the proper amount of fluid? If it has never been changed, I'd change it. It's a simple job and requires only 1-2 quarts of gear lube. Get a synthetic such as Mobil 1 or Valvoline Synpower. Should be about $10 a quart. Pop the front driver's side wheel off, remove the fill bolt, remove the drain bolt, drain the fluid, replace drain bolt, fill with fluid until it flows out of the fill hole, replace fill bolt, put wheel back on.

How about your transfer case? How long has it been since that fluid was been changed? Two quarts of Autotrak II from the dealer will get the job done.

Was the squealing a sudden occurrence, or did it progressively go from a whine to a squeal? I'm curious if you have a toasted wheel bearing.

Do some searching here and on TOS for "transfer case encoder motor". See if you're having similar problems.
 

TequilaWarrior

Original poster
Member
Dec 5, 2011
577
Central Pennsylvania
strat81 said:
Have you checked your front differential for the proper amount of fluid? If it has never been changed, I'd change it. It's a simple job and requires only 1-2 quarts of gear lube. Get a synthetic such as Mobil 1 or Valvoline Synpower. Should be about $10 a quart. Pop the front driver's side wheel off, remove the fill bolt, remove the drain bolt, drain the fluid, replace drain bolt, fill with fluid until it flows out of the fill hole, replace fill bolt, put wheel back on.

How about your transfer case? How long has it been since that fluid was been changed? Two quarts of Autotrak II from the dealer will get the job done.

Was the squealing a sudden occurrence, or did it progressively go from a whine to a squeal? I'm curious if you have a toasted wheel bearing.

Do some searching here and on TOS for "transfer case encoder motor". See if you're having similar problems.


Both diffs had fluid changes within the last 10k miles (bought the vehicle in October 2011 - full service including front wheelbearings and passenger cv shaft). TCase had the 2 flush tsb done to it 2 days after I bought it as it crow hopped so bad I thought I snapped something. Wheel bearings are good - no ABS codes and no whining.

The squealing reminds me of when I had my '75 GMC with lockin/lockouts on a dana 44. If I locked in the front without it being in 4wd - it would stear ok, but the tires would squeal in a very tight turn - no binding, no pushback. This is almost the same. I don't have the crowhop I had before (that was obvious, it shook the whole damn car).

I guess my problem is this: why are the two cars different? They're both '02 Bravadas, both awd, both 4.2, both 4l60e - identical in every way. Jack one front tire up on mine - no spin. Jack one front tire up on hers - spins freely.

Dealership just called - said everything is working as designed. Fluids are correct, full, and clear in diffs and tcase. They don't see a "binding" (I never said it did), but state that you should never be able to spin just one wheel if the opposite wheel is on the ground. So - could the wifes have snapped something in the frontend?
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
The dealer is wrong. (What else is new?) The transfer case is engaged when it shouldn't be, locking the front driveshaft when you try the spin-the-tire trick.

Look more closely when you spin a tire. On hers, turning a tire will cause the front drive shaft to rotate freely, unless she does indeed have something broken in the differential or the passenger side bearing assembly (where vehicles like mine have a splined disconnect and your AWD is supposed to be permanently connected).

On yours where the tire doesn't spin, your transfer case is resisting the front drive shaft's need to turn. With a tire in the air, try to manually turn the front drive shaft and see the difference between the two vehicles.

Pre-2005, there was a weak bearing support inside the transfer case that could break during the shock of transfer case clutch activation when the TCCM detected wheel slippage. That, and premature clutch wear, is a reason many of us with selectable 4WD advise against using the A4WD mode. You're stuck permanently in that mode by design, and it's hard to understand why the dealer couldn't just duplicate your spin-the-wheel test. Sigh...
 

strat81

Member
Dec 29, 2011
399
TequilaWarrio said:
Dealership just called - said everything is working as designed.
My local dealership told me that too. When I got it home I pulled the wheel off and found a wheel bearing that felt like it was filled with gravel and a front differential leak.

I don't know what's worse - the dealership "fixing" things that aren't broken or not fixing things that are clearly broken.


Anyway, let's wait for Roadie to chime in. (ETA - I was too slow.)
 

TequilaWarrior

Original poster
Member
Dec 5, 2011
577
Central Pennsylvania
the roadie said:
The dealer is wrong. (What else is new?) The transfer case is engaged when it shouldn't be, locking the front driveshaft when you try the spin-the-tire trick.

Look more closely when you spin a tire. On hers, turning a tire will cause the front drive shaft to rotate freely, unless she does indeed have something broken in the differential or the passenger side bearing assembly (where vehicles like mine have a splined disconnect and your AWD is supposed to be permanently connected).

On yours where the tire doesn't spin, your transfer case is resisting the front drive shaft's need to turn. With a tire in the air, try to manually turn the front drive shaft and see the difference between the two vehicles.

Pre-2005, there was a weak bearing support inside the transfer case that could break during the shock of transfer case clutch activation when the TCCM detected wheel slippage. That, and premature clutch wear, is a reason many of us with selectable 4WD advise against using the A4WD mode. You're stuck permanently in that mode by design, and it's hard to understand why the dealer couldn't just duplicate your spin-the-wheel test. Sigh...

Roadie, thanks for the reply.

I had a 15 minute conversation with the service manager - known him for years. He explains thus:
The front diff in an awd bravada acts just like a rear diff. All four wheels in the air, spin one front, opposite front spins. 3 wheels on ground, can't spin one front. TCase in awd bravada always sends some (30%) torque to front diff. That's why you have to tow with all four wheels off the ground. When I asked why my wifes doesn't act that way, he suggested maybe a midyear change in design where they may have added a disconnect to the system - or something broke in hers - bring it in, I want to look at it.
I like the service manager, he does well, me means well - but he's part of the dealership culture, too. All the checking they did today they did for no charge. He's done this before for me. He knows if he finds something there's a 75% chance I'll just have them fix it right then and there - so there's no real incentive to hide a problem. He also knows if the repair is ridiculously expensive that I'll trade the stupid thing right then and there.

I'm beginning to think that the wifes is working as designed, and that mine is somehow stuck with less than complete disengagement. I know theoretically that it's all or nothing - but still, I wonder.
I wonder if the 2 flush tsb didn't actually free up the tcase in mine - but why would my crowhop all but disappear?
I'll have to check her diff when I get home - see if there's a disconnect (i suspect there isn't - I'm pursuing an untamed ornithoid here).
How can I forcibly disengage my awd if that's the problem?

EDIT - Checking ALLDATA was not much of a help. It did describe the operation in detail and noted that the system is designed to have some engagement from 0 to 20 mph (engagement of 0 to 32 inchlbs of clutch force) and more engagement at higher speeds. Would 32 inch/lbs of clutch be enough to keep the output shaft from spinning? Would it keep that pressure even if the car is off?
The fact that the range includes 0 may explain why my wifes spins and min does not, but I'm still concerned. Anyone out there with a AWD Bravada or AWD Rainier want to chime in?
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
The no-wheel-slippage, at rest, not moving torque bias is only 5% IIRC.

There was never a disconnect on the AWD models.

You can command full disengagement of the transfer case encoder motor with a Tech II, which is how the dealer should have confirmed your proper operation. You can also pull the encoder motor and manually rotate the control shaft, but that's work.

Will be interesting to see if your wife's vehicle allows the driveshaft to spin when one wheel is rotated.

With a Tech II, all things are possible. :yes:
 

RayVoy

Member
Nov 20, 2011
939
GM has built a lot of vehicles; however, the techs and the service manager are expected (by the customer) to have some knowledge of the vehicles.

I know the manager is a friend, but to make a statement like "maybe a midyear change in design where they may have added a disconnect to the system" shows that techs and service managers DO NOT KNOWN about their products.

To the best of my knowledge, unless engaged, the transfer case sends about 5% of the torque forward. This 5% could be sufficient to cause the wheel to be difficult to turn.

Jack up both fronts. the diff is open, if one wheel is trying to turn the front driveshaft, the other will not. If one wheel is hard to turn, the other should turn freely.

Then try the other vehicle for comparison.
 

TequilaWarrior

Original poster
Member
Dec 5, 2011
577
Central Pennsylvania
So... on the way home last night I decided to exercise the AWD TCase a little. First stop/start - no wheel slippage at all (this was gravel, btw). Next stop/start... a slight delay. Do it in reverse... no delay. Do it again in reverse... slight delay. In all, I must've done this at least 2 dozen times. Now it seems that the tcase takes a second (less than that probably) to kick in, where the first time it seems it was already locked in.

So... I get home, jack up one side and LO' and BEHOLD - the wheel spins free! Try the other side - yep, free too. Check the tcase front output shaft, yep - spins when wheel spins while other wheel is on ground.

So... lesson learned? I think I might have a sticky clutch pack in my tcase. Apparently the wife's is in good shape - her awd has always worked well. Hers was a VERY well maintained specimen when we bought it.

Next time I take mine in for an oil change I'll have them flush/fill the TCASE just to see if it helps a little. The dealership I bought it off of (not the one I usually go to) had to do the double flush tsb because the tcase was bound up. I'm thinking that was the first time the tcase was ever done and the car had over 100k on it! Maybe she just needs an extra flush or two.

I'll have another talk with the service manager - explain what I found. We rap about problems / solutions I've found, it helps him - it helps me. As an example: My wife's ABS was kicking in constantly - they couldn't find anything wrong with it. Poking around on here and the OS I surmised it was probably a wheel bearing or the VSS. I asked him to sell me time with a technician with a tech 2 - $89/hour. No problem. Twenty minutes later we roll back in and the tech sheepishly says to him - wheel bearing. (Passenger side abs sensor was dropping tone - causing abs to engage). While glaring at the tech the service manager says - "you want us to change it, no labor cost?" I declined as their parts prices are outrageous (duralast works for me). I walk away without a bill. Tech didn't find it when he should've, so - no charge.

In fact, yesterday's time was free-of-charge and he offered to take a look at the wife's to compare free-of-charge. I usually get most of my service done there - they treat me well and they always have some sort of special running. Thanks to everyone for the replies - I may update the thread if I find anything else ( especially after the flush ).
 

HARDTRAILZ

Moderator
Nov 18, 2011
49,665
Hopefully it continues to function well. May let them take that free look just to have some eyes looking in case they find some other issue...
 

TequilaWarrior

Original poster
Member
Dec 5, 2011
577
Central Pennsylvania
strat81 said:
Why not change the transfer case fluid yourself? It's just two bolts. Only use GM AutoTrak II in your transfer case. You'll need two quarts.

10 years ago, before I was married, had kids, and worked 50+ hours a week - that would've been the second or third thing I did (the first being to pull the actuator, disassemble, clean, and reinstall it - then maybe a beer). I've reached a point where with a 19 month old daughter, a 2 month old son, a cranky wife (understandably so, we're both cranky, my son doesn't sleep) and little free time that I just can't justify sliding under a car for any amount of time unless it saves me an enormous amount of money ( dollars trump hours - orders from the wife ). I've done the fuel pumps in both cars myself - $800+ at the dealership vs $78 rockauto replacement parts and about 2 hours under the rig each time. Similarly, I've done both tie-rods, both wheel bearings, spark plugs, fuel filters, belts, and at least 2 coils each, in both vehicles; water pump and thermostat in mine, rear brakes and battery in hers - all because the rate at the dealer was just astronomical compared to doing it myself. I figure my time is worth about $35 an hour (I am an amateur after all). If I can save a few hundred bucks after factoring in my own labor rate, I'll do it - otherwise, probably not. I had the wife's second wheel bearing and a tie-rod done at a local shop(not the dealer) - with the alignment minus parts cost the total was $200 and change. I'll never do that again. I found that the dealer's charge for an alignment and the local shop were $5 different (less at the dealer on special). I did both of my wheel bearings and both tie-rods and had the dealer do the alignment at my next oil change - thanks to the special and by combining services the alignment cost me around $30 - and I get dropped off at work in a limo, picked up in a limo and they even washed my car (detail it every now and then, too ). Heck, before the economy tanked, the dealership would take each and every service customer - regardless of work being done - up to the local restaurant for breakfast or lunch in the limo. They're was always a wait to get in for service - I sort of miss those days.

I need to take a very close look at my a/c compressor - they won't diagnose anything beyond the compressor, but I believe it to be the clutch coil. Pressures and levels are good, all connections ok, just no engagement at clutch when signaled to do so. Their estimate $800 to change the whole compressor and recharge. If it is the coil and I can find one, it should be less than $50 if I do it myself.

I know most people like to bash their local stealership, and most deserve it. I have a pretty strong bullcrap filter and weigh everything the dealership says carefully. I know they want to make money, they know I can do my own work (when I choose to).

That being said - if they want more than I'm willing to pay to change it at the next oil change, I'll change it myself. I usually come away from an oil change at around $35 - $45 if they do a tire rotation and brake/suspension inspection. Worth it in my book... but that's just me.
 

TequilaWarrior

Original poster
Member
Dec 5, 2011
577
Central Pennsylvania
HARDTRAILZ said:
Hopefully it continues to function well. May let them take that free look just to have some eyes looking in case they find some other issue...

Definitely will let them. It's funny - I simply call and say "Do you have time to fit me in, you can have it all day." That's usually how I get away with the "free" stuff - they use it for filler between other service jobs knowing that if they find a real issue, they'll have something worth charging for.
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
TequilaWarrio said:
... I believe it to be the clutch coil. Pressures and levels are good, all connections ok, just no engagement at clutch when signaled to do so. Their estimate $800 to change the whole compressor and recharge. If it is the coil and I can find one, it should be less than $50 if I do it myself....
A few discussions recently have revolved around weak coils being fixable by just removing shims to reduce the pull-in gap. Free!

You sound like you have a rare kind of relationship-building dealer who's thinking long-term. Congrats!
 

TequilaWarrior

Original poster
Member
Dec 5, 2011
577
Central Pennsylvania
the roadie said:
A few discussions recently have revolved around weak coils being fixable by just removing shims to reduce the pull-in gap. Free!

You sound like you have a rare kind of relationship-building dealer who's thinking long-term. Congrats!

It seems I may have hijacked my own thread :undecided:. The shim fix is the first thing I'll try - just need time to do it. Thanks again, Roadie! (and everyone else that commented, it does help to discuss these things).

Yes, this is a rare kind of dealer indeed. I know the body shop manager, service manager, sales manager, and the financing manager.
When I bought the wife's Bravada here, I told the sales guy - "You want me to buy here, knock $1000 off what it's listed at, have Donny (Body guy) debadge the whole thing and I'll be here on Friday to pick it up." I got a call about an hour later from the body shop - "I can do all of them but the front emblem, it'll need filled and painted if I pull it. How 'bout I black out the logo on the mudflaps, instead." When I went to pick it up and there was one of those dealership stickers on it, I looked at the sales guy for a second, his eyes lit up and he says, "Shoot, I'll have Donny take that off for you." Sale made.
 

strat81

Member
Dec 29, 2011
399
TequilaWarrio said:
10 years ago, before I was married, had kids, and worked 50+ hours a week -
I hear you - I'm in the same boat. Time is precious.

I'm just cynical - too many rip-off dealers and guys that do bad work out there. A local dealership wanted $115 to change the rear differential fluid in my Honda - a job that calls for less than two quarts of fluid and loosening two bolts (easier than an oil change on that car!). Yeah... I'll buy the fluid for $15 and do it myself.
 

TequilaWarrior

Original poster
Member
Dec 5, 2011
577
Central Pennsylvania
strat81 said:
I hear you - I'm in the same boat. Time is precious.

I'm just cynical - too many rip-off dealers and guys that do bad work out there. A local dealership wanted $115 to change the rear differential fluid in my Honda - a job that calls for less than two quarts of fluid and loosening two bolts (easier than an oil change on that car!). Yeah... I'll buy the fluid for $15 and do it myself.

Heh. Valvoline Instant Oil Change wanted $75 to install a new cabin air filter in my old silverado, even refused to put the old one back in as it was loaded with debris and what looked like a mouse nest. After my oil change, I shook out what I could, reinstalled it and drove across the street to Advanced and bought a new cabin air filter for $12. Never used Vioc again.
 

RayVoy

Member
Nov 20, 2011
939
TequilaWarrio said:
Heh. Valvoline Instant Oil Change wanted $75 to install a new cabin air filter in my old silverado, even refused to put the old one back in as it was loaded with debris and what looked like a mouse nest. After my oil change, I shook out what I could, reinstalled it and drove across the street to Advanced and bought a new cabin air filter for $12.
One of the Canadian TV networks did an expose on cabin filters. The price (same vehicle) was all over the map.
 

cliffordg

Member
Feb 24, 2013
1
I had a similar problem with my 03 Bravada. From everything I had read it sounded like I needed to replace the front differential (front carrier). I came across a GM tech bulletin (20-04-21-008A), it suggested looking at the transfer case encoder motor.
I took mine off and opened it up. I found one of the planetary gears had broken the the pin that it rides on. I drilled out the old one and replaced it. Put the motor back together and my problem is gone. No more crow hop.
Even if I replaced the motor with a new or rebuilt one it is a much cheaper and faster fix than the differential swap.
Only four bolts and a wire to unplug.
Hope this helps someone else.
 

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