Hi, I have a front end issue that I just can't figure out. I have a 99 Blazer that randomly pops in the front end. I can be going straight or turning, slow or at speed, and feel and hear a loud POP from somewhere in the front end. I have replaced the following: upper and lower control arms with new ball joints, both wheel hubs, steering box, pitman and idler arm, tie rods, front tires, and had an alignment done. It still pops randomly. It usually only happens after I've been driving for a while, not right away. I can also hear a slight rattling sound when I drive next to a wall or line of bushes or something like that when going down the road. Any ideas what I should look for NEXT? Thanks, Neal

 

Check all of your heat shields and skid plates if you have them. Sometimes a loose heat shield will rattle a bit and if it gets caught on one of the teeth on a bolt then pops off it can cause a good bit of noise. Sounds crazy but I've seen it a ton especially on the 90's fords!!

 

Ok just got under it again. no skid plates so thats out. Heat shields all look fine. What I did notice the other day is that the noise is NOT present when I'm in 4x4. I have 4 buttons in the 99. I just pulled the battery tray and tested the vacuum to the actuator under the tray. It expands and closes as it should and hold vacuum just fine. Any ideas? Thanks, Neal

 

I think I might have just solved the issue...turns out the person who had it before me must have replaced the solenoid driving the actuator for 4x4. When they did, the vacuum lines were installed backwards. The actuator was pulling on the 4x4 cable ALL THE TIME. I just drained the oil from the diff and it looks ok. I switched the vacuum lines and voila! It works as it should. I'll test drive it soon to see if the noise is actually gone.