Diagnosing the Screech on a Silverado LB7 Diesel Engine

by Karla Pestotnik


Any car can eventually get a pesky squeak coming from the drive belt area under the hood. For many 1999-2007 General Motors V8s, this has become an infamous issue. However, this common issue is often more than just a belt change; it can be a little bit more complicated. In our case with the LB7 diesel Silverado, it was multiple sources contributing to some head-scratching pondering. Since this is the dedicated tow vehicle for the Karla Pestotnik Racing team and a big event is coming soon, we needed to get to work to diagnose and fix the tow rig. 


To get started, we took the truck to our friend, Rob Choo from Chewerks. Most people think of fast racecars and alignments when they think of Chewerks in City of Industry- not beefy diesel trucks. This isn’t a typical job for the Chewerks shop, but we know that he can fix almost anything. Let’s get started!


First things first- finding the source of the squeak. Since the accessory drive belt was replaced a year ago, we knew that it was more than just that. Rob brings out the trusty WD-40 to easily find the source.

By spraying each pulley one at a time, the source can be found easily. If a pulley is sprayed and the screech stops, you have found the winner! Rob had a feeling that one of the drive belt idler pulleys was the issue, so we ordered both ahead of time. Since they are relatively inexpensive, we went ahead and purchased both to replace at the same time. The last thing that we want to have happen is to just replace the bad pulley, and then a few months later the other one fails as well. While we were already in there, it was the perfect opportunity to do both at the same time. Sure enough, the squeak quieted briefly after spraying them. 


Sure enough, one of the two black idler pulleys was a source of the squeaking. Don't mind the WD-40 overspray. 
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Wednesday, February 15, 2017 7:18 AM
Very good news about the crankshaft, as there is 1100 posts on the "broken crank register" on the dmax forums, it seems like a very common problem.
Wednesday, February 15, 2017 9:42 AM
I have same truck and same engine and had the alt squeek. Easily diagnosed by putting a long screwdriver tip to the case, and your ear to the handle.

Did the idlers and tensioner at the same time while in was in there. They are so inexpensive that there is no reason to only do half the job.
Wednesday, February 15, 2017 1:29 PM
That right there. That's a good mechanic. Those are the jobs that drove me nuts years ago when I worked as an auto mechanic.
I may sound preachy. But remember this article the next time your car has to go back a few times to get all the little squeaks and grumbles fixed.
Thursday, February 16, 2017 4:10 AM
My first thought the moment I saw the article title was, "Belt, idlers, tensioner, alternator. Do it all. It needs it all." A/C compressors seem a little more robust, unless they've been replaced with cheap junk before. A belt system on (what I assume is) a higher mileage engine should usually be treated as everything being broken, and working your way backwards to verify what IS good. Chances are high, very little is good anymore. Take the belts off, verify the noise is gone, and inspect every pulley by hand. Anything not silky smooth WILL be a noise. And it gets new belts, every time unless you know for a fact it's brand new. When your fixing the truck owned by a guy who doesn't know an LB7 from Apollo 7, 4 phone calls asking for more money isn't the way to win his confidence.
Friday, February 17, 2017 9:55 PM
Your car is way too far forward on the trailer, a little Honda shouldn't squat a 2500 like that. With something of a 60/40 bias, you could probably center it over the axles and be good especially when that tire rack is loaded.
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