98 Bravada Service AWD light

I just bought a 98 Bravada with some problems.

First the Service AWD light is on. Durring the test drive I believed the AWD kicked-in in the snow and pulled very hard to the right. It seemed like just the right side was pulling and not the left. Is this possible? The next time I drove it tracked straight down the road (I assume the AWD was off). I see where the tranfer case fluid changing helps some models - my owners manual says this one takes ATF fluid. How do you know exactly if you can put the GM blue fluid in? Put the code reader on it and there are no DTC codes. Any ideas on trouble shooting the pulling?

Second the former owner recently had brakes worked on and the front pads look new. The brake light comes on when you press hard on the pedal then goes off when pedal is released. The brakings seems weak like they have air in the lines.

is the vehicle under anykind of warranty??? some problems that the bravada's have is the encoder motor going bad, and those can give you a hefty repair bill. but i may be wrong since u said that the steering wheel pulled to the right

Sorry no warranty. I am a mechanic and pretty good trouble shooter and bought this rig cheap with the intent to fix and drive. This forums supplies a lot of information that is useful and I am looking for someone who has simular problems with their 98 Bravada who is willing to share info on the AWD and braking systems.

Ok, I talked to former owner. The Service AWD light came on when she put some used tires on the front (installer claimed the sevice light was a msimatch thread issue on used tires)- been on for 3 months. I would guess he distrubed something and didn't feel obligated to fix it (understandable). Can mismatch tires cause the light to go on?

The pulling to the right when the AWD engages is a recent issue. I am not convinced that it could be related to a transfer case service (maybe low or dirty fluid). I am looking for someone who knows the transfer case on a 98 to tell me that it is possible to drive just one front tire?? When the AWD comes on how does it dive the front tires - is it mechanical linking or hydraulic to both the front tires individually??

The front differential is the normal ring gear & pinion setup with no posi.
The transfer case is solid mechanical when activated.
As you can reason, unequal diameter tires will eventually try to lock up the drivetrain.
Pulling to the side may be due to the taller front tires out running the back or even wheel alignment.
All help gratefully accepted.

Thanks Chris!
Sounds like it wouldn't hurt to get a good set of tires put on, replace the ball joints and get an alignment.

Stopped snowing so I went out and spent some more time checking the girl out. Turns out the used tires that were put on are two different size tires. 235-75R-15 on the left rear and 235-70R-15 on the right rear. The fronts are both good 235-75R-15. I'm no tire expert but from what Chris said about the transfer case I would guess the 70R is somewhat smaller in diameter and that is why the front right wheel is driving so hard when going into AWD. I'll leave a post and let you know when I get new tires put on if this cures the problem.