Hi All:

I have a 98 blazer 4x4 4dr 4.3L.

I have had a problem that has been intermittent for about a year. It happened 2 times in the last year, now about every other day.

While driving to work in the morning, after about 10 miles I get a high pitch whine from the front right wheel area (at about 65mph). When I slow down to stop at the first stop light the front area (wheel, or wherever), starts to grind, like something is stuck in the rotor, it slows with the truck. When I start moving again the sound increases into a whine again (grind to whine).

If I change into 4wd, the front area thumps hard once every 3-4 seconds and the whine/grind goes away. When I take it out of 4wd, I get a huge thump (like a hit a small speed bump) after about 2-3 seconds. The thump happens every time I change from 4wd to 2wd now. The grinding is somewhat hit or miss.

Does anyone have any ideas?

Thanks,

Glenn

 

as for the grinding, try cleaning your brakes, I've had crap stuck in there before and the sound is HORRIBLE. could also be a bearing that went to hell. your 4x4 problem sounds pretty serious, id get it checked out by a certified mechanic before i used it again.

 

I had the wheel off, brakes are clean, with nothing stuck. The grinding/whining goes away completely in 4wd. Usually stays aways once I take it out of 4wd, until the next time it starts again (not usually the same day)...... odd.

Glenn

 

Sounds like you have a vacuum leak that's causing your 4x4 to partially engage (your loud clunking). Check the vacuum lines around the master cylinder for excessive wear (see pic below of the lines i'm talking about)

Vacuum lines

 

It sounds like you are not totally disengaging out of 4WD to 2WD. Check your cable coming out of the front diff, might need to be lubed. Also have the front diff checked to see if the fork that engages and disengages the 4wd is hanging because something inside the front diff is broken.

 

20Blazer00,

Mine is an Automatic, and has the electronic switching from 2 to 4wd. Will mine have the same components you are talking about?? How would you check to see if the fork is disengaging? I have not had the diff or transfer case apart.

I am planning to r&r front diff fluid tonight. But my understanding is that I cannot open the diff, other than to r&r fluids.

I have neglected to mention that the repeating thumping sound doesn't happen all of the time, only after hearing the grinding sound. The thump when disengaging the 4wd happens all of the time now.

After reading what you said, I wonder if the grinding is the 4wd partially engaged? Which is why the grinding goes away in 4wd.

Can you explain which parts engage the 4wd? Does the diff get soemthing engaged, or is it the transfer case that has the engagement? I understand that the axles turn all of the time. Does the Differential turn all of the time (with the axles) and the drive shaft from transfer case to diff spin free at the transfer case end? When 4wd is engaged, the drive shaft at tx case end is engaged? Is that correct? If so, you are saying that there is most likely a throwout style fork in the tx case that is not engaging/disengaging properly..?

Not trying to be stupid, just not all too familiar with this engagement system. I have only had 1 other 4wd and it was a ford (much different).

Glenn

 

Here is an exploded view of the front differential. Items 15 (cable) through 22 (fork) are what engage 4hi to 2hi operation. The transfer case controls 4Hi to 4Lo operations.

It is possible to remove the cable housing into the front diff to check cable operation but the firts thing you need to do is to determine wether the acuator under the battery is functioning properly if it is not then replacing that part may fix this problem. Some people have replaced the actuator with a "Posi-Lock" cable, it is tedious work to install and sometimes that system has its own pitfalls.

Here is what you can do, remove the cable when you are changing fluids in the front diff try to move it back and forth if it moves then the cable is not the problem, follow the cabel up to the battery box find the actuator and check it by using either a vacuum checking tool or clean off the line and suck vacuum the old fashion way (cheaper/faster) hold the vacuum hose with a finger or sharp pencil/golf tee. If the vacuum does not hold then the diaphram is ripped/cracked and needs to be replaced. You can either find a used one in the wrecking yard or new one from a local parts store???

[IMG]local://upfiles/1127/91969C1CA9344500949AEE5FA3784506.gif[/IMG]

 

Thanks so much.... The exploded view makes all of the difference.

I understand what you are saying, I will see what I find tonight. I hope the gear the the throwout engages, isn't damaged to badly. The strange thing is that I hear the grinding sounds from the front right, not left where the diff is located.

Glenn

 

Over the weekend I changed the Front Diff Oil, it was pretty dirty (my diff has a drain plug, that made it easier).

I cannot say if that helped the grinding, since it is intermittent (joys of intermittent problems). However, the thump as it leaves 4wd is still there. I tried to check the actuator cable, but it doesn't come out. Obviously it is attached to the arm inside the diff. I tried removing the housing where the cable is attached, same issue. Any ideas on how to check this cable. I did not try to get under the battery to remove it from that end, or check the vacuum issues, I ran out of time.

I assume that when diff is in 2wd, the actuator is in its relaxed state. Meaning that if I lost all vacuum to the actuator, it would be in 2wd. So that being said, the clunk (thump) would most likely not be a vacuum issue?

Glenn

 

My 96" Blazer is doing the EXACT same thing. Let me know if you find out what is causing this problem.