Bravada smarttrac

[yamahog]

I've got an 02 bravada with the smartrac awd. Problem is the awd doesnt work. There's no light and no code. :) This is the time of year it would come in reaaal handy. Anybody have any ideas. I've checked all the fuses but have not climbed underneath to check things out. I'm not very familiar with this awd system.

[RayVoy]

How do u know it doesn't work?????????

[MTPockets]

I wish there was some info for you yamahog. You dont see too many AWD posts. Unfortunately the ones you do see are in regards to major problems. The GMT360 and previous chassis AWD system is a pricey and rare mofo.:worried: The transfer case and front diff are totally different than the PT 4x4 GMT360's.

Joel

[ScarabEpic22]

I wish there was some info for you yamahog. You dont see too many AWD posts. Unfortunately the ones you do see are in regards to major problems. The GMT360 and previous chassis AWD system is a pricey and rare mofo.:worried: The transfer case and front diff are totally different than the PT 4x4 GMT360's.

Joel

First, how do you know it is not functioning?

Joel- how is the TC and front diff different than the 4WD GMT360s? I was under the impression the AWD system was the exact same as the 4WD system except locked in A4WD mode all the time (and no selector).

[MTPockets]

Erik, on the GMT360 AWD setup, there is no front axle disconnect like the PT 4x4's have. The entire front axle and front prop shaft are live all the time on the AWD. The transfer case is also different, more like a fluid/viscous coupling rather than a mechanical clutch plate type like our PT 4x4's have.

Joel

[ScarabEpic22]

Erik, on the GMT360 AWD setup, there is no front axle disconnect like the PT 4x4's have. The entire front axle and front prop shaft are live all the time on the AWD. The transfer case is also different, more like a fluid/viscous coupling rather than a mechanical clutch plate type like our PT 4x4's have.

Joel

Really? Wow, learn something new every day.:cool:

[bkrhoades]

So does that mean my pt 4x4 is a more affective system than full time awd?:confused:

[madfx86]

So does that mean my pt 4x4 is a more affective system than full time awd?:confused:

In terms of off road capability generally 4x4 will be more effective than a comparable awd. Also I believe the awd bleeds more power than the pt4x4, but I'm not entirely sure.

[RayVoy]

How do u know it doesn't work?????????
yamahog, I don't think you've checked your thread, but I wanted to re-ask my question. As some of the posters have indicated, this tx box is different than the "normal" box. The Envoys and most TB have an AWD position on their selectors, but a computer switches the case into and out of 4WD. There is a clunk when this happens.
I have driven vehicles with yr type of case and I could not tell when power was being transfered to the front, if indeed it ever was, while I was driving. Therefore, my question. How have you concluded that your AWD is not working? Could you have a problem in the front dif maybe??

[mstazlee]

I've got an 02 bravada with the smartrac awd. Problem is the awd doesnt work. There's no light and no code. :) This is the time of year it would come in reaaal handy. Anybody have any ideas. I've checked all the fuses but have not climbed underneath to check things out. I'm not very familiar with this awd system.

I would check the tranfer case motor. I also have an 02 Bravada and had to replace the transfer case and motor. But I was locked into awd. And it cracked my tranfer case. Cost a lot of money to fix. Transfer case motor not too bad if you buy aftermarket.

[yamahog]

yamahog, I don't think you've checked your thread, but I wanted to re-ask my question. As some of the posters have indicated, this tx box is different than the "normal" box. The Envoys and most TB have an AWD position on their selectors, but a computer switches the case into and out of 4WD. There is a clunk when this happens.
I have driven vehicles with yr type of case and I could not tell when power was being transfered to the front, if indeed it ever was, while I was driving. Therefore, my question. How have you concluded that your AWD is not working? Could you have a problem in the front dif maybe??

Icy roads, gravel roads... front wheels do not pull, spin nuttin. there is only rear wheel drive. you can spin the rear tires all you want and with these torquey buggers, its real easy to do. Trust me its not working. Good news is (maybe) on the way to wyoming for our christmas trip I played in a snow covered parking lot a bit and actually got the service AWD light to come on for a few miles after that, but only for the few miles. So hopefully there will be a code now.

[Bravada_06]

Hey Guys,

Just wanted to add my two cents in about my O2 Bravada. At 64,000 i had to replace the Transfer case on mine, It made funny noises when you turn into a parking place or back up and turn. The aftermarket one was cheaper, but there was some part like a switch that costed another 400 for it as it didnt come with it. The GM part was only like 100 bucks more after that and it included the part the aftermarket one did not. Of course it could of been the service departments way of taking every penny from me :eek: In the end, Most of the cost was absorbed by the Extended warranty. Good luck with it.

[tehehodi]

are you talking about the transfer case motor encoder thinger ma bob? i forgot what it's called but it sounds like the same problem i have now with hard turning and backing up while turning. otherwise if i run straight it's fine. it could be teh transfer case sensor? theres a thread in here somewhere about it. it was a TSB.

[mstazlee]

are you talking about the transfer case motor encoder thinger ma bob? i forgot what it's called but it sounds like the same problem i have now with hard turning and backing up while turning. otherwise if i run straight it's fine. it could be teh transfer case sensor? theres a thread in here somewhere about it. it was a TSB.

I would replace the transfer case motor. Make sure you know if it is with opt4 or without. I had to get my transfer case from a salvage yard and had that put in and my awd was still locked in. So the garage asked me to get the transfer case motor from the same salvage yard. Well that worked for 4 days and then quit. The reason was they sent me the wrong one. my transfer case is with opt np4 and some come without.
You can find out which one you have from the glove box. It has a bunch of numbers and letters to tell you what you have for options. Hope this helps.

[tehehodi]

well i never really thought about that, my sensor comes in today. well i hope it works for more than 4 days. if it doesn't work i have to resort to getting a whole new transfer case?

[mstazlee]

well i never really thought about that, my sensor comes in today. well i hope it works for more than 4 days. if it doesn't work i have to resort to getting a whole new transfer case?

I hope it works too. If you have to get a transfer case good luck at that too. The only year that will fit is an 02. It took me a lot of searching to find one in a salvage yard. Unless of course you buy a brand new one.

[TrailBlazer LS]

I was going to post. But then i didn't know what the hell i was talking about!

[tehehodi]

well i just replaced the sensor today. The coldest day of the season. great day to work on a car. anyway, my wheels still do what it did before just not as bad, like it's 90% fixed. It makes an awful wowing type sound when turning, like my car is moaning. I thought i ordered a whole new transfer case motor but i guess not, it's just the sensor. should i get a whole new motor?

[mstazlee]

well i just replaced the sensor today. The coldest day of the season. great day to work on a car. anyway, my wheels still do what it did before just not as bad, like it's 90% fixed. It makes an awful wowing type sound when turning, like my car is moaning. I thought i ordered a whole new transfer case motor but i guess not, it's just the sensor. should i get a whole new motor?

I would. I got a new aftermarket one for $150.00. If I got a GM one then that would have been $450.00. I haven't hand any problems since.

[tehehodi]

Where can i get an aftermarket one?

[mstazlee]

Where can i get an aftermarket one?

I would say any auto parts store could find you an aftermarket one. I went through a garage that sells new and used auto parts. He ordered this somewhere in in PA.

[iDontKnow]

Erik, on the GMT360 AWD setup, there is no front axle disconnect like the PT 4x4's have. The entire front axle and front prop shaft are live all the time on the AWD. The transfer case is also different, more like a fluid/viscous coupling rather than a mechanical clutch plate type like our PT 4x4's have.

Joel
A lot of older Jeep Cherokee owners had issues with their viscous couplers failing in their transfer case (NP249). Symptoms of a failing viscous coupler were front tires chirping or binding. So essentially, the coupler seizes and locks the front drivetrain, kinda like a part-time 4wd system does, except you don't have the luxury of unlocking it, which doesn't fair too well on dry pavement.

But that doesn't seem to be the problem with yours.

[MichEnvoyBoy]

Or they could hurry up and trade in that Bravada for a 2007 Envoy/Trailblazer and help GM's sales! :D (I should be a sales rep for GM, LOL)

[iDontKnow]

Or they could hurry up and trade in that Bravada for a 2007 Envoy/Trailblazer and help GM's sales! :D (I should be a sales rep for GM, LOL)
If I were to get a new vehicle, I'd get a GMC Acadia. The Trailvoy is dated.

[TrailBlazer LS]

If I were to get a new vehicle, I'd get a GMC Acadia. The Trailvoy is dated.

:cry: Ouch!!!

[02-Bravada-88]

Well to tell the truth, when I first bought my Bravada. I took it mudding and found out I had full time rear wheel drive lol.

It turned out being that the front differential was cooked, and the bearings leading to the driveshafts had come apart. (According to the mechanic that wiggled them in front of my own eyes to show how loose they were).

Its all fixed now, but its not "full time" AWD. It is operative in RWD until major steering wheel input, yaw, or rear wheel spin is detected. It then transfers power up to the front wheels to compensate. In the snow earlier today I was sliding around during acceleration, only to find that the rear wheels were allowed quite a bit of slippage before you felt the center differentials lock and sent power up front. I will make videos to demonstrate this.

Could someone please explain how this system works to me??

And to the OP, I hope your problem wasn't as serious as mine.

[the roadie]

Could someone please explain how this system works to me?? As you found out, it requires slippage for the transfer case controller to take action. The controller is always looking for a difference between the front and rear output driveshafts. Once a difference occurs and the rear output shaft spins faster because one of the rear wheels is slipping, the controller tells the encoder motor to engage a multi-plate clutch pack to send some torque towards the front.

This encoder motor is like an electronic foot always pushing in on a clutch pedal unless the controller sees slippage, and then the electronic foot comes OFF the pedal and the transfer case starts to force the front and rear driveshafts to spin at the same speed. Normally they spin at the same speed because the road surface traction locks them together.

This speed detection and encoder motor and clutch pack activity takes real time (hundreds of milliseconds) to operate, which is why it clunks around compared to an always-running viscous clutch AWD system.

In Bravada and other AWD GMT360 vehicles that don't have a 4-position transfer case switch, the front differential is always actively connected to its input driveshaft. In TBs and Envoys with a 2WD position on the switch, this position also controls a disconnect fork on the passenger side of the oil pan. But none of the GMT360s have manual or automatic locking wheel hubs, so the CV half-shafts are always turning and never get any rest.

I could post more data from the service manual if it's really fascinating for anyone else.

[ghoster]

You always fascinate us!:D Thats the best description I have heard for it. Now explain why the GM's clunk and shake when it happens, and the Honda does it so smoothly that you wouldn't know it happened if the light on the dash hadn't flashed.:cool:

[the roadie]

Now explain why the GM's clunk and shake when it happens, and the Honda does it so smoothly that you wouldn't know it happened if the light on the dash hadn't flashed.:cool:If I had to guess, without knowing how the Honda does it, I'd guess that we actually can transfer significant torque to the front, and that the GMC design was optimized to leave the clutches significantly far apart until needed for less self-heating. So the clutch "throw" is longer.

The Honda, on the other hand, only has to transfer the torque from two out of its five struggling hamsters through the transfer case to the slipping part. Simpler design involving wire running wheels, rubber bands, and 87-octane hamster chow.

[ghoster]

If I had to guess, without knowing how the Honda does it, I'd guess that we actually can transfer significant torque to the front, and that the GMC design was optimized to leave the clutches significantly far apart until needed for less self-heating. So the clutch "throw" is longer.

The Honda, on the other hand, only has to transfer the torque from two out of its five struggling hamsters through the transfer case to the slipping part. Simpler design involving wire running wheels, rubber bands, and 87-octane hamster chow.

aha! I knew it involved hamsters!:D

[02-Bravada-88]

As you found out, it requires slippage for the transfer case controller to take action. The controller is always looking for a difference between the front and rear output driveshafts. Once a difference occurs and the rear output shaft spins faster because one of the rear wheels is slipping, the controller tells the encoder motor to engage a multi-plate clutch pack to send some torque towards the front.

This encoder motor is like an electronic foot always pushing in on a clutch pedal unless the controller sees slippage, and then the electronic foot comes OFF the pedal and the transfer case starts to force the front and rear driveshafts to spin at the same speed. Normally they spin at the same speed because the road surface traction locks them together.

This speed detection and encoder motor and clutch pack activity takes real time (hundreds of milliseconds) to operate, which is why it clunks around compared to an always-running viscous clutch AWD system.

In Bravada and other AWD GMT360 vehicles that don't have a 4-position transfer case switch, the front differential is always actively connected to its input driveshaft. In TBs and Envoys with a 2WD position on the switch, this position also controls a disconnect fork on the passenger side of the oil pan. But none of the GMT360s have manual or automatic locking wheel hubs, so the CV half-shafts are always turning and never get any rest.

I could post more data from the service manual if it's really fascinating for anyone else.

Please do! I'd like to learn as much about it as possible. I'm trying to tackle this big hill called Pilot's Hill with some other SUVs in the snow, and an 04 Envoy SLE 4WD made it up yesterday evening. My Bravada had no problem slushing around our off road course as long as you kept your momentum up, but as soon as I came to a sharp turn where you had to slow down to a crawl in order to execute it properly, it would get stuck due to the fact that I couldn't lock that center transfer case. The rear wheels would spin and it would jolt in an out of AWD, but wouldn't lock unless I stuck my left foot on the brake slightly, and used my right foot to give it gas. I could imitate front and rear locking differentials this way by stopping the wheels that weren't contacting the ground from getting the power that the contacting wheels should have done.

A little fidgeting back and forth got me freed, but I was laughed at when all the guys peered in the Oldsmobile and discovered no locking switch and they dismissed my Bravada as having a "p*ssy's 4WD". :mad: Even Honda makes a "locking" button for their VTM-4 system that seems to be pretty similar to mine. :rolleyes:

I want to prove to them that it can make it up the snowy incline like the GMC, H2, Yukon Denali, GMC Sierra HD, F-150, etc. that we had there yesterday..... I'm just worried about that delay between 2WD and AWD that will get me bogged down in the snow again. :undecided

Do you think I can make it up? Got any suggestions?

You always fascinate us!:D Thats the best description I have heard for it. Now explain why the GM's clunk and shake when it happens, and the Honda does it so smoothly that you wouldn't know it happened if the light on the dash hadn't flashed.:cool:

Yes I agree with ghoster. :yes:

[the roadie]

...but wouldn't lock unless I stuck my left foot on the brake slightly, and used my right foot to give it gas. I could imitate front and rear locking differentials this way by stopping the wheels that weren't contacting the ground from getting the power that the contacting wheels should have done.An excellent trick to know. I've used it on rocky trails that leave a front tire spinning in the air, since we have no front locker available due to the unique front differential. But the left foot braking trick doesn't actually affect the transfer case lockup, it's actually just reducing the torque leakage that happens with a totally spinning tire.A little fidgeting back and forth got me freed, but I was laughed at when all the guys peered in the Oldsmobile and discovered no locking switch and they dismissed my Bravada as having a "p*ssy's 4WD". :mad: Even Honda makes a "locking" button for their VTM-4 system that seems to be pretty similar to mine. :rolleyes: Some semi-trailworthy vehicles like the H3, Mercedes, and Lexus have AWD systems that still manage to control wheel spin by applying the brake on the spinning wheel only. The GMT360, for all its advanced systems, doesn't have that.
I want to prove to them that it can make it up the snowy incline like the GMC, H2, Yukon Denali, GMC Sierra HD, F-150, etc. that we had there yesterday..... I'm just worried about that delay between 2WD and AWD that will get me bogged down in the snow again. :undecided
Do you think I can make it up? Got any suggestions?If changing to a real 4WD trailvoy isn't an option, you might consider adding a control to force the encoder motor to full clutch engagement. I'll get the schematic out of the service manual for you and post it - then you can decide. It could eliminate the delay. But without the G80 Eaton rear automatic locker, you'll still be at the mercy of rear wheel spin. Members without the G80 have been stopped by 2" of snow on hills. Do you have it?

[yamahog]

ok sooooo... I've been living with this for a while now, and today while in line at the mcdonalds drive through, I feel a shudder as I'm creeping up...I watched the tach to see if it fluctuated while the shudders happend, nope. Look up and there is a "service AWD" light on... hmm I need to find someone who can run a diagnostic on her.

[garrinchilders]

"ok sooooo... I've been living with this for a while now, and today while in line at the mcdonalds drive through, I feel a shudder as I'm creeping up...I watched the tach to see if it fluctuated while the shudders happend, nope. Look up and there is a "service AWD" light on... hmm I need to find someone who can run a diagnostic on her.
01-22-2007 08:47 AM" Shuddering in the t-case is usually a sign of old abuse fluid (auto-trak ii fluid to be exact, its blue LOL) the shudder or slippage detected by the computer is what threw the CEL. See I can read the service manual too LMAO haha:D

[bust_ter]

I have a 2003 Bravada. There are some differences from 2002 to 2003 but the systems are very similar.
My old 91 Bravada had a true AWD with the Borgwarner TC it ran on a viscous clutch and always fed power to the front. A little or a lot depending on the conditions.
Starting in 2002 GM used a newventure TC. If you have a TB it has a 2 speed TC unit with a switch that allows you to choose 4L 4H auto 2h.
If you are a Bravada or Ranier you have a single speed TC that uses a computer to decide what to do. It will engage a clutch pack to send power to the front axel or not depending on the conditions like haveing the TB in 4H or auto. They just don't have a low range.
The big problem with the NV126 TC is that it might have a defect that will keep the power connected when it should not or a defective connector on the TC that makes the AWD service light come on.
If it is right you may never know if it is in 4WD or 2Wd unless you force it like finding a muddy spot and put your back wheels in to then pull out and see if the front end pulls out.
You may have a perfect Bravada.