First decent snowfall of the year and the 4X4 on my '99 4-door Blazer is acting a little strange. I've had no problems with it since last winter, when it failed to engage consistently. With this forum's help, I found and replaced a length of degraded (crunchy) vacuum hose. That corrected the problem. I used the drive on and off the rest of the winter and over the summer with no issues.

Today, I had no problem engaging 4-wheel drive, but it seems as if something is not quite right. While moving at less than 15 MPH, I pressed the 4-High button on the dash. There was a single muffled mechanical "bang" feeling transmitted through the frame of the vehicle, and I could feel the front axle's engagement slow down the vehicle noticably. There was also a low mechanical whine/noise that accompanied the drive engagement. It wasn't exactly the gear gnashing and crunching that denotes a catastrophic failure, but it was definately a gear-train noise. I had no problems disengaging the front axle at this point.

I have yet to get the truck in the garage and check out the driveline components, so until I can do that (hopefully tomorrow), I just wanted to see if anyone else has run into some similar symptoms.

 

Hopefully it will check out OK. If you were driving on snow for the first time this season it may have made the normal noise level a bit less letting you hear the normal FW drive train noise better then before.

 

Yes I agree its normal for you to hear a light wineing noise comeing frm the front drive train...

 

maybe ur trans case is low on fluid?

 

Make sure all of the tires are exactly the same size, preferably the same tire manufacturer. Also make sure the tire pressure is equal in all tires. Check the front differential and transfer case fluid quality and level. 80W90 gear lube in the differential and DexronIII in the transfercase. Keep in mind that 4WD should not be used on dry pavement or pavement that is just wet.

 

Well, so far I've gotten to the transfer case and it appeared to have the correct amount of fluid in it. I did drain the case just to see if there were any metal flakes present, and all seems well. I refilled it and topped it off with some of the Auto-Trak II fluid I bought several years ago. I find it interesting that the facltory fluid is red and the purpose-bought Auto-Trak stuff is blue. GM charges a premium for this stuff and I probably could have used the Dexron III you mention instead, right?

While I have the truck up on the stands, also I put on my snow tires. I noticed that it does take some effort to rotate the front axle, even when the brakes are not rubbing on the rotors. I canot see/feel anything actually binding.

I'll get to the front diff next. I did replace the lube in both diffs last Summer, so I don't expect any issues here. That leaves all the drive shafts and whatever bearings hold them in place. On a side note, how long are the U-joints in all the drive shafts supposed to last? I'm leery of any moving part that is "lubed for life". This is Wisconsin. Everything is exposed to salt, water, and dirt.

Thanks for the replies....

 

The NV233 two speed selectable transfer case uses DexronIII. There is no reason to use the [expensive] auto-trak fluid in it. It was designed to use in the single speed auto-trac cases.

When the transfer case is in 2WD, raising only the right front wheel off the ground, it should spin quite easily. If it doesn't, the actuator under the battery may be operating the axle clutch for the right front wheel.

Turn the shaft so the cross is level, grab the shaft with both hands close to the joint and push/pull up and down, there should be no movement. Rotate the shaft 90 degrees and check again. That will check for looseness, it's always best to remove the shaft to check the joints for binding. As for how long they last... until they are loose or binding Always install joints with grease fittings and lube them at each oil change.

 

Ok, there is plenty of lube in the front diff. It looks as clean as the day I installed it. The front axleshafts appear okay but are rusty. I know the driver's side is okay as I removed that about a year and a half ago to repair the CV boot. It also came out again last summer the same time I changed the lube and that side's axle shaft seal. Both bearing hubs were replaced then too. The passenger side axle shaft has never been touched. I take it is one solid shaft from the diff to the CV boot, right?

I could have sworn that the aluminum plate screwed to the t-case said it was an 236GM (new process??) I'm pretty sure this uses the same fluid.

I don't quite understand what you mean in your latest comments by "the cross". Is it the metal U-joint cross (+)? Also to which shaft are you referring below:

"Turn the shaft so the cross is level, grab the shaft with both hands close to the
joint and push/pull up and down, there should be no movement. Rotate the shaft
90 degrees and check again. That will check for looseness, it's always best to
remove the shaft to check the joints for binding. As for how long they last... until
they are loose or binding Always install joints with grease fittings and lube them
at each oil change."

How big of a deal is it to replace the U-joints in these things? One part of the U-joint has bolted on retainer, the other part has nothing. I imagine I will need some kind of bearing press to get these apart. The last time I dealt with U-joints was with my old Bronco II and it had retainer clips holding the bearings in. Much easier to work on. I think this is turning into something much bigger than I can do today. Besides, what auto parts store is open on Christmas eve....

One more thing. When I look at the front drive shaft (the one from the transfer case to the front diff), it appears to have U-joints on only one end. The t-case end has some kind of one-piece sealed unit. It looks like it can only be removed with the t-case. Am I missing something here?

 

The driver side inner CV joint connects to the differential. The passenger side has an inner axle that connects to the differential. The inner CV joint connects to the outer axle shaft. There is a clutch mechanism that connects the inner with the outer axle shaft when 4WD is selected.

If you have a 3 button switch on the dash, it's a NV(New Venture)233 two speed selectable transfer case and uses DexronIII. If you have the 4 button switch on the dash, it's a NV236 two speed selectable/automatic transfer case. It has a clutch pack inside and requires Auto-trac fluid.

Yes, the cross + of the driveshaft universal joints in the front and rear driveshafts, (not the CV joints in halfshafts).


Unbolt the front yoke and remove the straps holding the rear end of the rear shaft to the differential yoke. IIRC there is a slip joint in the rear driveshaft. Piece of cake, MUCH more substantial set up, [and easier to do] than the BroncoII.



The front drive shaft has a combination slip joint/CV joint inside the rubber boot. Unbolt the front end of the driveshaft from the differential yoke. Push the shaft rearward until it clears the front yoke. Pull it out of the transfer case.

 

Hello I just had the same thing happen to me about 40 min ago, I was coming home from visiting family doing 80 km with the cruise control on, when all of a sudden I hear the wineing noise of the front diff but I wasn't in 4HI I was in 2HI, as I slowed down to get off onto a side street the noise started sounding like a tire rubbing then once i got down to about 40km it just stopped, I have a 1997 blazer 4X4 4 door LS

Just wondering is there any way a bad 4X4 dash switch could cause this or is it more likely that it's a bad electronic switch on the transfer case?

Sorry to be thread jacking just didn't want to start a thread about the exact same thing

Any and all advice is greatly appreciated Thank You