HELP!!!
I was driving down the highway, and all of a sudden I hear a loud whining sound, sort of high pitched coming from under the truck. I pulled over and as I was slowing down, the whine got lower in pitch, then as I came to a stop there was a slight clunk. I checked everything over as best I could while on the side of the highway, and since I couldn't see any thing out of place, I decided to limp the thing home since I wasn't that far from the house. When I got going again, everything seemed fine. No noise at all.
But it happened again a couple of miles from the house. Again, I pulled over and as I was slowing down this time, I shifted into nuetral to see if that made a difference. It didn't have any effect at all. It made that slight clunk again as it came to a stop. I shifted into reverse and backed up a few yards, then I took off. Nothing... like it was back to normal again. Made it home without any trouble.
It sounded like gears trying to mesh, but not able to do so all the way. And I'm not sure if it was coming from the front end or the transfer case. I don't think its the tranny, since it was shifting fine and shifting it into nuetral while the truck was making that noise didn't make a difference.
Does anyone think that the thing was partially going into 4WD or something like that? This truck has the electronic 4WD control. Maybe the control motor isn't holding the T-case in one position, and its slipping into 4wd... who knows!!!!
I did have a front bearing go bad two weeks ago, so we took care of that. But It doesn't seem to be related to that. But like I said... I couln't tell where from under the truck the noise was coming from.
Any ideas? Please help... Thanks!!!

[quote=duster340;5934614]HELP!!!
quote]

If it were the drive train I would expect the whine to vary with a load/no load change...

this is more like a bearing...

my 2000 S10 P/U is doing the same thing going on two months now. i was told that a tell tale sign of front wheel bearings going bad is if you turn sharp you should hear a clicking and grinding noise. i dont think this is correct. what if the bearings havent got to that point? dont you think they would start whining first before they completeley blow up?


also, do you have to re-align the front end after replacing a wheel bearing?


by the way duster340 welcome to the site.

I would pull the rear differential cover and look for metal chunks. Wheel bearings grind when they fail and this does not sound like a wheel bearing issue. Also chech U-joints and the rear yoke on the differential.

I do not agree with the 2 posts above mine since the noise rises and falls with speed it is almost certainly a u-joint/differential issue. Also, does this truck have the 4 button 4WD with Auto? Could also be a sloppy/bad chain in the transfer case as well since the front driveshaft is always spinning on these trucks if they have the Auto transfer case.

I believe we have the same unsolved problem. I have a 2002 ZR2 Blazer with an automatic transmission, and 4x4 (electronic transfer case). It makes the same noise as the one you described. It sounds farther forward than transfer case, though. In addition to the pitch falling as you slow down, does it get quieter if you speed up? Does the noise itself slow down as you come to a stop?
The noise started two months ago for me. A few days before, the vacuum control switch that controls the AC/ Heat settings stopped pulling a vacuum and would leaked air on all settings (including off). After taking the A/C switch apart and getting it to seal again, the "bad whine" didn't come back. That said, the switch is leaking and the noise is back as of yesterday. Maybe you have a similar problem.
It is going to the shop tomorrow morning. Hopefully it will be fixed for good this time.

Did you ever find the problem. I have a 2000 Blazer with exactly the same issue. I cannot find a Transfer case vacuum switch as described many times on this forum.

Followed the vacuum line under the battery tray right down into the Transfercase connected to the front right wheel. The line did not go to the supposed switch on top of the Transfer case.

2000 Blazer
3 button (No Auto) 4x4

Ok I have the same problem is it a vacum leak or somithing else?
I changed an the axel but that did not help. It does not do it all the time and if I switch it into 4wd it stops grinding.

HELP!!!!

barnettmkb@yahoo.com

Ok I have the same problem is it a vacum leak or somithing else?
I changed an the axel but that did not help. It does not do it all the time and if I switch it into 4wd it stops grinding.

HELP!!!!

barnettmkb@yahoo.com

Sounds like your 4wd is not disengaging completely.

Did you ever find the problem. I have a 2000 Blazer with exactly the same issue. I cannot find a Transfer case vacuum switch as described many times on this forum.

Followed the vacuum line under the battery tray right down into the Transfercase connected to the front right wheel. The line did not go to the supposed switch on top of the Transfer case.

2000 Blazer
3 button (No Auto) 4x4

I have heard that after 98 there is no vacuum swtich on the TC, but an electric switch that controls a vacuum valve located on the fire wall, passenger side.

Check if that is true, if not please post back here...
/F

I have heard that after 98 there is no vacuum swtich on the TC, but an electric switch that controls a vacuum valve located on the fire wall, passenger side.

Check if that is true, if not please post back here...
/F

That is definitely not true. Mine was a bad Vaccuum Switch. As well as a bad Vacuum line. There was a corroded vacuum line that was on the drivers side near the windshield that went into the canister in the fender. Had to unmount but not disconnect the Fuse box and ABS system to get to it. Not too hard but a pain the a$$. The get under your blazer on the drivers side look on the Transfercase at the end of the Tranny. If you look on top from the passenger side of the transfer case you will see the vacuum switch. In the bottom of that switch, there is a bearing like ball. on my bad one, the ball would not full extend to the end to close. Swapped that and havent had a prob since. I couldnt get to it with a socket, but I could using one of the wrenches I had (I tried two and the shorter one worked) A little tricky to get off but not undoable. Make sure to check the vacuum under the battery box just to be sure. But most likely it is that switch on the transfer case.

Rock Auto has em for about $15, I got back doored locally for about $45 at Napa. I couldn't wait though cause the wife was going out of town.

The vacuum line took me about an hour and the switch about 20 mins. I am not a pro mechanic.

Good luck bud!

2000 Blazer 4x4 LT
195k miles 4.3l

So the vacumn switch is the solution?

So the vacumn switch is the solution?


It was for me! Go ahead and pull the Switch if your not sure. If the little bearing looking ball at the end is stuck halfway, then you know you have a bad switch. This is so common that they even put a different color stripe on the switch to denote the one that was known to fail.

See the ball on the end, Mine was stuck about halfway in. It is easy to do and if you order the part from Rock Auto, you can get one for about $20.

http://www.s-10crewcab.com/og1/modinfo/stockspecs/tcswitch/ts3.jpg

Most likely. These have a tendency to fail, and when they do, they will allow tranny fluid to get sucked into the vacuum lines, the front diff actuator diaphragm, the accumulator bulb mounted under the hood, and even come out of the tranny breather tube. With the fluid in there, any residual vacuum is retained and the 4wd system work erratically.

The switch is not difficult to replace and is not expensive ($15 Dorman HELP! part at the parts store), but I do remember having a tough time getting it threaded back in...had to buy a big bolt the same size & thread from McMaster to clean the case threads and see the angle that it went into the case. Then had to blow out all the vacuum lines, actuator, and drain the vacuum bulb by drilling a hole in it & resealing after it was empty of tranny fluid. PITA.

Hope this helps!

I believe we have the same unsolved problem. I have a 2002 ZR2 Blazer with an automatic transmission, and 4x4 (electronic transfer case). It makes the same noise as the one you described. It sounds farther forward than transfer case, though. In addition to the pitch falling as you slow down, does it get quieter if you speed up? Does the noise itself slow down as you come to a stop?
The noise started two months ago for me. A few days before, the vacuum control switch that controls the AC/ Heat settings stopped pulling a vacuum and would leaked air on all settings (including off). After taking the A/C switch apart and getting it to seal again, the "bad whine" didn't come back. That said, the switch is leaking and the noise is back as of yesterday. Maybe you have a similar problem.
It is going to the shop tomorrow morning. Hopefully it will be fixed for good this time.



So did you find the problem?

Sounds like your 4wd is not disengaging completely.

Just the opposite its trying to engage for no reason I have also changed the transfer case. That did not help.
any other ideas?