★★★★★
September 29, 2025
good bearings
nice fit
Replaces
Part Details
Specifications
About TRQ:
TRQ is a trusted brand dedicated to making every repair a success story by combining premium parts with easy installation. Each TRQ part is engineered by a team of automotive experts to meet or exceed OEM standards, delivering enhanced performance and maximum longevity. With rigorous in-house testing, the brand ensures superior fit and function across every product line. TRQ also provides customers with best-in-class, step-by-step installation videos—so you can complete repairs with confidence, whether you're a first-time DIYer or an industry professional.
Attention California Customers:
WARNING: This product can expose you to chemicals including Lead and Lead Compounds, which are known to the State of California to cause cancer, and birth defects or other reproductive harm. For more information, go to www.P65Warnings.ca.gov.
Lifetime Warranty
This item is backed by our limited lifetime warranty. In the event that this item should fail due to manufacturing defects during intended use, we will replace the part free of charge. This warranty covers the cost of the part only.
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Brought to you by 1AAuto.com, your source for quality replacement parts and the best service on the Internet.
Hi, I'm Mike Green. I'm one of the owners of 1A Auto. I want to help you save time and money repairing or maintaining your vehicle. I'm going to use my 20-plus years experience restoring and repairing cars and trucks like this to show you the correct way to install parts from 1AAuto.com. The right parts installed correctly: that's going to save you time and money. Thank you and enjoy the video.
In this video we're going to show you how to replace the idler pulley on this 2004 Trailblazer with a 4.2 liter engine. Tools you'll need are a 3/8 drive ratchet handle, either a long one or one with an extra piece of pipe for some leverage. You'll also need a 15mm socket with a ratchet or a 15mm wrench.
The first thing you want to note is how the serpentine belt is on your vehicle. You see it goes across up there to the alternator and down to an idler pulley, then down around the AC pulley way down there, then up and around the water pump and fan. Then it wraps back down and around the crank and back up to the tensioner right there.
I'm going to place the camera over here. What you want is a ratchet with a 3/8 drive end on it. There's a square hole in our tensioner here. Here's a shot of it from the other angle of my ratchet in the tensioner. Now take your ratchet and you're going to want to push it clockwise as I push down on the tensioner. That loosens the belt. I can remove it up here from the alternator and then slowly let my wrench back, being careful not to pinch my hand in anything. Now my belt can come off.
Your engine idler pulley is right down here underneath the alternator. Put a 15mm socket and ratchet on it. We'll just fast forward removing that bolt. The bolt and the pulley come off. Make sure you retain this washer here.
Here's the new pulley from 1A Auto. The shape is slightly different than the original but the function will be the exact same. Put it down, just push the bolt in and start it a little bit. A little bit of fast forward again as I tighten, by hand, and then most of the tightening with a wrench here. Just make sure that, before I tighten it all the way, just make sure that washer is in there correctly. You want to make sure it's nice and tight.
Check the condition of your belt. Our is in pretty good shape. You can see there's a little bit of cracking on the ribs but that's not too big of a deal. You want to check the whole length. Where they sometimes can get bad is where they're joined together. If it's getting bad there you'll know it because you'll see it. I don't see it, so this one is okay. If you do need a new belt we carry them at 1AAuto.com.
I can't really film putting this on too well, but I'll try and put it together in detail as best I can. I'm putting a loop down and around the crank pulley, which is the largest pulley at the bottom of the engine. Loop it down there. Then I'll bring it back up and over my water pump right here on top, then way down and around my A/C pulley, which is a smaller pulley at the bottom of the engine. Then up and around my idler pulley here. Then on this side around my tensioner pulley and then around my power steering pulley. Now basically I have the whole thing routed except for having it on the alternator. Here's my belt and I've got a piece of pipe actually you can see it at the top of the camera there. Put it on to my ratchet that is in my tensioner. That just gives me a lot more leverage. Pull my tensioner over, put the belt onto my alternator there, let the tension back. Take out the pipe. Take out the wrench. Make sure everything is routed correctly, and it appears to be. We're all set.
We hope this helps you out. Brought to you by www.1AAuto.com, your source for quality replacement parts and the best service on the Internet. Please feel free to call us toll-free, 888-844-3393. We're the company that's here for you on the Internet and in person.
BPA03850
nice fit
Installed it in my 2007 Chevy Trailblazer LT with the 4.2 I6 a couple months ago and so far so good. No more whine noise when accelerating.
This diameter will be 70mm.
