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Discussion Starter #1
Hi all!
Lately I've been having a fairly new set of issues. And I am not sure if they're connected but I'm assuming they are.
I've recently been hearing a knock that raises in frequency and slightly in volume along with RPM's. Fairly certain I've isolated the noise at the bell housing.
I checked the flex plate, and outside of the TC thru the inspection holes, they dont appear to be obviously damaged or cracked. There are 3-4 bolts on the flexplate-TC accessible thru a hole in the front of the bell housing, they appear to not be loose (I didn't try to really crank down on them out of fear of cracking them.).
The truck DOES have a bit of a shudder most of the time in the range of 40-55MPH, from what I've read it's possibly the TC failing to lock in 4th/od.
What else should I check? I think the TC is on it's way out but I feel like it would be making a grinding or 'stripping' noise if it was..
Most recent repair was the trans filter and 2 shift solenoids, for stumbling and throwing codes.
Other known issues with the vehicle include a bad motor mount, and something going on with wheel speed sensors (indicated by ABS instance every time I slow down to ~3mph)
Vehicle info: 05 TB EXT 4WD ~165k miles
4.2 L I6
 

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2007 chevy
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How does the trans fluid look, is it fairly clean?

You may need to remove the trans to fully inspect the flexplate. I have seen small cracks around the bolt holes where it attaches to the crank, that would be hard to see with it still in the truck.
 

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Discussion Starter #3
How does the trans fluid look, is it fairly clean?

You may need to remove the trans to fully inspect the flexplate. I have seen small cracks around the bolt holes where it attaches to the crank, that would be hard to see with it still in the truck.
The fluid is clean. It's basically new. It wasnt that long ago that I did the shift solenoids, although I did not flush it, it was a drain, replace filter and solenoids, and fill.
I dont currently have a trans Jack, and if I was to pull the trans or at least pull it back, I would have to buy or borrow one,. From what i could see it didnt look cracked up there. Is there anything else I can rule out before I go assessing it by that means?
 

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2007 chevy trailblazer_ls
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Well I'm not sure yet but I think it spun a bearing. I unbolted the trans and it still makes the noise. I'm going to eyeball the flexplate one more time before I start looking for a used engine. It SOUNDS just like a cracked flexplate but those hopes may be crushed ☹
 

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Discussion Starter #7
The only thing is, in my case at least, I cant hear the knock at all in the engine bay.
 

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Discussion Starter #8
Well I'm not sure yet but I think it spun a bearing. I unbolted the trans and it still makes the noise. I'm going to eyeball the flexplate one more time before I start looking for a used engine. It SOUNDS just like a cracked flexplate but those hopes may be crushed ☹
If you think it's a bearing I suppose drop your oil pan and check the journals for excess play.. fairly simple to check, and if it's a rod bearing that's got crushed a bit, you might be in luck.. clean up the crank journals and throw near bearings in the one that's damaged.. it will inevitably break down if there is any damage to the cylinder bore, but you'll get a little more life out of the motor until you're ready for a new one.. it's what I'll end up doing most likely.. I paid less than 3 grand for the vehicle, and it's almost 15 years old, it just wont be worth the new motor especially since I'm having trans issues as well.
 

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2005 chevy trailblazer_ls
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It was the planetary gear that made that noise in my 05 Trailblazer with 4.2 motor. It looked like someone took a bite out of the teeth. I wound up buying a Jasper transmission and only got 800 or so miles out of the engine that blew a head gasket at 290,000 miles. By the way I took that Jasper transmission out when I purchased an 08 Trailblazer and junked the 05. If anyone wants the tranny I have all paperwork and receipt for $3200 installed by our local authorized mechanic shop. My price is $300 and I will palletize if you pay freight.
 

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Silver 007, or anyone, can you circle back and tell us what this rattle was? Your rattle sounds different from mine in the sense that yours fades at low RPMS, builds in volume and changes character of the clack and becomes more of a variable rattle, as you build rpms and gets a little louder and then fades again. My clack clack is as loud at idle as at higher rpms, but only the speed of the clack goes up and down evenly with RPMS. The character or nature of the clack is identical at all rpms
 

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I unbolted the trans, slid it back and still get the noise so it's definitely the engine. I've resolved that it's most likely crank bearing and am getting ready to replace the engine. It got louder just during my testing. When warmed up, it'll do it at idle and get louder as rpms increase under load. A crank bearing is apparently pretty common, and I was 3 quarts low when it happened. Soooo... 😁
 

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What is the process for replacing the crank bearing that makes it better to replace the engine? We are in the same boat it sounds, something that either is an expensive time consuming rebuild vs engine transplant. And how hard is it to get the engine out? Where do we find a suitable donor engine that is in better shape with low miles?
 

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This is really weird. No cracks on bell housing, its lugs or attachment points on engine block? Have you had the car up on a lift and tried to isolate source of the sound with a stethoscope? Noise could or should be louder under the vehicle. (Someone will have to be in the car to start it and operate the throttle.) Since it makes noise only when rpms decrease, I'm wondering if there's a thrust bearing issue. Check the harmonic balancer too because it damps out strong torsional vibrations transmitted all along the crankshaft, but it would be really odd if it only makes noise when rpms decrease. Check for noise from the transmission mount. Shine a timing light on anything rotating to see if something is randomly jerking when a plug fires. It's time to isolate the problem rather than throwing more parts at it.
snaptube vidmate
 
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