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Ask GM Shane Your Own Question

GM Shane
GM Shane, Technician
Category: Car
Satisfied Customers: 27
Experience:  10 years GM experience, 20 years old car experience
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97 olds bravada: all wheel drive does not work..front wheels

Customer Question

all wheel drive does not work on 97 olds bravada,does not work to front wheels
Submitted: 6 years ago.
Category: Car
Expert:  GM Shane replied 6 years ago.
Hi Todd,
I'm a GM tech that worked at a truck shop for a decade with these and full size trucks.
Your s-series truck can have a few different transfer case setups that help your all wheel drive to work. The different systems work quite differently, so I'll need you to do some work with me to help me help you.
Do you have a selectable transfer case switch on your dash? By this, I mean a switch that allows you to pick 2HI or 4HI or Auto, or to select 2HI, 4HI, 4LO. If you have these as options then I would consider this a selectable shift AWD system. If you have one that seems to always have AWD with no selector levers or buttons, then I will call this a constant AWD system.
Please tell me if it's selectable or constant, then I can solve it with you.
Customer: replied 6 years ago.
my bravada has a constant awd.
Expert:  GM Shane replied 6 years ago.
So, if there's no selectability and it should work all the time, then you've now realized that the front wheels aren't helping along like they once were?
The transfer case behind the transmission should be putting out all the time then by means of the front driveshaft going up to the front differential. This shaft should be the diameter of a pop can, and will run from under your tailbone while you're driving up to underneath your brake pedal area. It will run parallel to your floorboards and be about 4-5" lower than your carpet underneath the truck.
I'll help you diagnose this step by step, starting at the source, okay?
Find something icy on an incline, such as a friends driveway or ease your bumper up against another vehicle in your driveway or something. Once you've figured out a way to see the driveshaft and you know what you're looking at, then get a friend that you trust to drive it SLOWLY in gear forwards so that the back tires are spinning like they'd be if you were trying to drive uphill. You'll see a larger diameter driveshaft heading off to the back wheels, and your front shaft should be turning the same speed. Don't let your friend run you over at Christmas Time!! You should be able to see the shaft at one end or the other without being under the truck completely.
Once you can tell me what's turning, or isn't, then I can tell you whether it is a driving member problem (transfer case, front driveshaft) or the driven member problem such as the front differential or one of your CV drive axles that go to the wheels.
When you do this test, you may see something grinding or slipping that you wouldn't have heard when you were actually driving. If you do, tell me roughly where it is coming from and that'd help me help you also.
Good luck, and please be careful, but you'll see that it's not that scary...
Customer: replied 6 years ago.
Expert:  GM Shane replied 6 years ago.
Sorry for the delay. My wife's aunt fell sick over the holidays and kept me from my work, and from helping you.
So, if the driveshaft is turning input power into the front differential, then you know the transfer case is fine.
The front differential is what outputs power to the front wheels. If you look in behind your front wheels you will see driveshafts that have black boots on either end of them. These CV joints allow for flex while your wheels are turning. If you have someone turn the wheels while in park you'll see what I mean. The boots look like an accordian...with ribs for flexing. The inner of these two CV joints attaches to the front differential and it is the differentials' job to transmit power to these shafts and also allow one shaft to turn faster than the other in times of turning or one spinning on ice or mud. The internal gears allow for this 'differential' in speeds and these gears should always be turning when your driveshaft is spinning unless you have had some terrible mechanical failure inside...
Now...on to the next thing I need you to check...
Your front differential has an engagement collar and cable that moves when you need the front axle engaged. I am somewhat confused about your 'full-time' 4WD, but all the other T truck platform vehicles have this cable system. Look behind your passenger side headlights and you'll find the battery. Underneath the metal tray that the battery sits on there is a vacuum powered actuator that pulls this cable. Think of a turkey baster ball mounted on a bracket. When the engine is running and 4WD is requested, engine vacuum will collapse this ball/diaphram and will pull this cable. The cable runs down from there below the cooling fan shroud, and connects to the differential. Please look for this actuator and confirm for me that you have it, and that you can find the cable. Watch for the engine fan if you're looking while it is running.
If you do have this actuator, you should be able to work the actuator with your hand and see if it moves the cable. Its' normal travel pulls the cable towards the passenger side fenderwell, and when it does pull the cable and actuate the front diff, you should find that the front wheels will now work.
Pretend you saw an earth worm crawling out of the dirt. If you pulled on it but let it go, it would pop back into the ground. Your cable will do the same. The cable slides in a black plastic sheath like the brakes on your pedal bike. Near the actuator bracket under the battery you should be able to see the cable coming out of its' sheath when you squeeze the actuator. If you pulled it all the way out, you could try to pinch the cable with some vice grips and keep it held there while you roadtest your truck.
Please try these tests, or at least confirm for me that you have these things there.
The only other thing I can think of...look at the CV axle shafts that go to the wheels and make sure that one of the four joints covered with the black boots aren't spinning. If the front differential is working properly but the shafts or the CV joints are broken you will hear a grinding or see one part of the shaft spinning but the rest of the shaft not spinning. It is possible for these CV joints to be damaged inside/under the boots but the boots will still look good.
In short, the whole front drive system needs to be intact to work properly. This includes the two shafts, and all the front gearset parts. If you cannot see either of the shafts working at all, but the driveshaft is spinning going in (like we tested first) then I would assume the shift collar or some member of this actuator driven shift assembly is faulty.
If we determine that the shift actuator/cable holding diagnosis proves that the mechanicals are good (the front wheels engage when held with vice grips on the cable...) then we can diagnose the vacuum system.
Get back to me.. Shane.

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