98 Blazer - Loud "Roaring" Noise at Highway Speed

I have a 98 4x4 Blazer. I've had this problem before and I THOUGHT I fixed it. :shakehead Okay, as I drive down the highway, all of a sudden I hear a loud "roaring" noise. I pull over and it quits. When my Blazer was doing this before, I was told to replace the actuator under the battery box. After looking, the bulb on the actuator was busted. I replaced it, and haven't had a problem for about a year. Now it is doing it again. I looked at that actuator and it looks fine. Any ideas?

I have a 98 4x4 Blazer. I've had this problem before and I THOUGHT I fixed it. :shakehead Okay, as I drive down the highway, all of a sudden I hear a loud "roaring" noise. I pull over and it quits. When my Blazer was doing this before, I was told to replace the actuator under the battery box. After looking, the bulb on the actuator was busted. I replaced it, and haven't had a problem for about a year. Now it is doing it again. I looked at that actuator and it looks fine. Any ideas?


Did you look at the actuator when the engine is running and the motor is producing a vacuum? Could be a bad switch on the Tcase.

You can jack up the right front tire and start the motor. Then try to turn the RT front tire, if it won't turn you are in 4x4.

I will try it this evening and see what happens...I will let you know what it does...:licka:

Could also be a bad bearing.

I'm pretty sure its not my bearings. I haven't had a chance to try what you suggested earlier. But, I replaced both front hubs, and to me, the noise I'm hearing is not even close to the sound of wheel bearings.

Could be the fan clutch. It's rather complex how and why it works, but in a nutshell.... When the engine is cold, the fan should turn, (by hand) but with some resistance. After driving and the engine reaches operating temp, shut the engine off and immediately check the fan, it should turn quite freely, (easier than when the engine was cold). If the engine overheats, the fan should turn with substantial resistance, (more than with a cold engine). More resistance, (harder to turn) equals more "roar" because the fan is moving more air. To replace the fan clutch, remove the upper fan shroud, loosen the nut on the water pump shaft by turning it counter clockwise. The nut is part of the fan clutch.

I replaced the vacuum switch on the transfer case and so far, that has seemed to fix the problem.

I replaced the vacuum switch on the transfer case and so far, that has seemed to fix the problem.



You should check the level of the fluid in the tcase. THe seal between the trans and tcase leaks and the level will rise in the tcase and cause the switch to malfunction.

After I got under the truck to replace that vacuum switch, I did notice that the transfer case is leaking. Is there only one seal that I should buy to replace? And my other question is: Is that seal difficult to replace? I have a Chilton book and it tells me step by step, but sometimes things are more difficult than they sound. I hoping to buy what I need tomorrow when I get the money.

After I got under the truck to replace that vacuum switch, I did notice that the transfer case is leaking. Is there only one seal that I should buy to replace? And my other question is: Is that seal difficult to replace? I have a Chilton book and it tells me step by step, but sometimes things are more difficult than they sound. I hoping to buy what I need tomorrow when I get the money.


Just one seal. As far as I know, you need to drop the tcase to get at the rear of the tranny and the seal.


Where was it leaking from?

You need to check the level at the fill plug on the case. Just make sure you have an oil pan under the tcase. Be careful, if the leak is bad you could drain your tranny of fluid before you get the plug back in.