So, the next steps for this truck are getting the rest of the fluids changed. I think the brake fluid is next. Transmission, oil, coolant, and power steering are complete.

As for the other fluids. This is where I have no idea, no experience. This is the first truck I have ever owned, and seemingly a complicated one at that. So what else do we have here? Differential fluid and transfer case fluid? How often do they need changed? I assume the previous owner didn't do anything. This 2000 Bravada has the Smart Trak which is on-demand automatic AWD. I have no switch to manually control the 4x4. So I'm not sure how this changes things. Some kind of expensive, special transfer case fluid I bet?

Now, there are some odd noises going on and would hate to spend money on expensive fluids only to have to dump it out to change a worn component. So, what's the best way to diagnose these noises?

One of the noises occurs as I'm first starting to accelerate it kind of sounds like a bit of a grinding noise, it seems to go away after I pick up a little speed.

The other noise sounds like a rubbing noise. For instance if you are on a highway and maybe the road is not perfectly level, not bumpy or rugged, but there is a gradual rolling unevenness that causes your car to raise and lower gently while going 45 - 60 miles per hour. So that at the bottom of the "dip" your truck has to squat a bit, then at the top of the "dip" your car raises a bit. At the bottom part of this, the sound is most obvious, again like a rubbing.

Thanks in advance.

 

Your transfer case takes GM AutoTrak II. Just bought it yesterday for my '99 Safari; it was $9.50/qt at the GMC dealer. You need 2 quarts. The case has a drain plug and a fill plug on the back - iirc, they're both 18mm. Pull the fill plug first and make sure you can get it out. Once you do, have a drain pan handy for when you pull the drain plug - the stuff shoots out pretty good and it's kinda stinky, so you definitely don't want it on you.

Look at the fluid in the pan. Does it shimmer? Are there noticeable metal flakes? Does the fluid smell burned (or just like nasty synthetic fluid)? If yes, you probably have an internal problem. If no, you're probably okay.

The fill plug on the front differential faces the front of the truck, the drain plug faces the driver's side wheel. The fill plug is 15mm and the drain is 13mm. Again, pull the fill first, then the drain and have the pan ready. Again, burned, metal, shimmery - these are bad. Just dirty is normal.

While you're under there, bring your grease gun and grease every grease fitting you can find - and look hard, some point away from you. There are lots. Check the condition of all the boots. If the boots are cracking/leaking grease, it's time to replace that component.

For the rear differential, there is only a fill plug. You loosen the bolts for the cover and pop it loose at the bottom to drain the fluid. Have a replacement gasket ready and, if the cover's rusty, a new cover too. The usual chain autoparts stores carry the cover and gasket as a set - it's a Dorman part and not expensive.

For both differentials, you want normal gear oil - 80w90. I happen to prefer synthetic 75w90 (seems to work better/longer, stay cooler and give slightly better gas mileage). I use Mobil 1, personally.

 

go to harbor freight, walmart, or Oreillys/autozone. What ever is near you and buy a fluid pump, it will make it so much easier for these fluids, for filling and removing, for the rear differential you dont have to remove the rear cover you can pump the fluid out of the fill plug! Make sure the car is warm because the fluid is hella thick when its cold! Hope this helps, here is the link to the pump, and you only need to fill them until they start coming out of the fill hole, also my 97 blazer 4x4 uses ATF in the t-case and 80w90 gear oil in the differentials.

Multi-Use Transfer Pump

^^^^^^ MUST HAVE!!!!!!!!^^^^^^

 

Your blazer doesn't have the same 4x4 system as the Bravada's do, dj00140.

 

Just to further support Leeann's post, all of the 98+ NV236 (2spd w/ auto) and NV136 (single speed AWD) transfer cases need to use AutoTrak II fluid from GM. Anything else could result in damage to the preloaded clutch pack ($$$) in the transfer case.

 

Thanks for the replies. This helps a lot. I've never had to purchase differential fluid before, it's pretty pricey stuff. Is AutoTrack II available at the stealership only? I actually own that little pump from Harbor Freight already. I purchased it awhile back for a project on my other car, but didn't end up needing it. So I haven't even used it yet, I was wondering how well it was going to work. But if you can confirm it works good I might go that route.

Some more information on the one noise during acceleration. It seems to occur at all speeds, when accelerating you get the noise. I found a quiet road and was able to hear it accelerating at even 40mph. It doesn't do it when coasting, it doesn't do it while standing still. For instance if I put it in drive and apply the brake and give it a little gas, no noise. It only happens when you move under power. Does this sound like the Transfer Case?

 

Yes, it's only available at the dealership.

Someone else will come along and answer your other question - I'm not sure.

 

I thought I would stop by for a good ole' fashioned .

 

More information on this noise: I rode as a passenger last night and the 2nd noise you can feel through the floor on the passenger side. So it makes me think it's on that side. It's kind of a pulsing rubbing noise with a slight vibration. It's more obvious the faster you go.

Then I'm still wondering about this other noise:
Thanks again in advance, hope you don't mind the

 

The first noise sounds like a wheel bearing or a CV joint issue. Do you hear any change in the noise while turning?

What kind of noise is the one that occurs on acceleration? Could be the u-joints in the rear driveshaft.