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Old 05-25-2022, 09:33 PM   #1
truckster
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Torque Converter Rattle?

I have a new (less than 6000 mile) 5.7 Vortec in my 72 Blazer. I balanced and blueprinted the engine and assembled it myself, so I'm confident that's not my problem. I mated it to the existing TH350 transmission and reused the torque converter, because it was working fine before I pulled the engine... seven years ago (I probably should have thought that one through better). I should mention that I used a new Jegs SFI heavy-duty flexplate.

In the past few weeks it's picked up a rattling sound when I first start it. My first thought was to check the torque converter bolts and the bellhousing bolts - they're all good and tight. I also have what I would describe as something like a squealing sound around 2000 RPM, and it seems to only occur in a narrow RPM range.

I crawled under it again today, and I'm pretty sure it's coming from the torque converter. Two questions - does my diagnosis seem accurate, and how long is it likely to last before it strands me or does some serious damage?

Thanks!
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Old 05-26-2022, 06:18 PM   #2
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Re: Torque Converter Rattle?

Flexplate torque to back of crank? flexplate installed correctly? yes I've seen them backwards
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Old 05-26-2022, 07:11 PM   #3
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Re: Torque Converter Rattle?

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Flexplate torque to back of crank? flexplate installed correctly? yes I've seen them backwards
The engine has been in for over a year. The noise only started a few weeks ago. The flex plate was installed and torqued to specs. I mark each bolt as I torque it and then go over them again. I'm kind of obsessive when it comes to proper torque.
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Old 05-26-2022, 08:00 PM   #4
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Re: Torque Converter Rattle?

Typically it's the torque converter to flex plate bolts that make the sound you described.
IMHO the torque for these bolts is low.
Betting you find them loose as the description, you gave, of the sound matches perfectly.
A drop of LocTite will keep them place.
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Old 05-27-2022, 12:21 AM   #5
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Re: Torque Converter Rattle?

That was the first thing I checked. I wish it had been that because it would have been an easy fix.
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Old 05-27-2022, 12:55 AM   #6
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Re: Torque Converter Rattle?

Then check the flex-plate for cracks. Not a lot of other possibilities that I can think of.
Shouldn't have speed read this and I would have know you checked them.
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Old 05-27-2022, 12:57 AM   #7
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Re: Torque Converter Rattle?

I'd narrow down to exactly where the noise is coming from then. Maybe something in the starter? heat shield? just throwing things out until they stick
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Old 05-27-2022, 11:53 AM   #8
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Re: Torque Converter Rattle?

It's definitely a head-scratcher. I checked all the bolts first, I checked for loose exhaust components, and laying underneath it when it's running, it's definitely coming from the torque converter area. I considered the possibility of a crackd flex plate. I would just be really surprised if a new SFI-rated flexpte cracked.

Either way, it looks like I'm going to need to separate the trans from the engine. I was hoping to avoid that, but at least I have a transmission jack to help me with a very heavy transfer case. I'll inspect the flex plate and replace the converter and let you all know what I find.

Thanks for your help.
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Old 05-27-2022, 12:49 PM   #9
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Re: Torque Converter Rattle?

I had a vehicle once that sounded like the torque converter was rattling, like it had a ball bearing rolling around inside or something. I can't remember if I ever solved it or what vehicle it was right now. Sorry I can't help but I remember the sound and the dilemma.
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Old 05-28-2022, 10:42 AM   #10
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Re: Torque Converter Rattle?

Go buy a pair of 5" grade 8 bolts and install them in the two upper bell housing bolt holes. Drop the drive shaft and pull the trans mount bolts, take the converter bolts out and you can slide the trans back hanging from the two bolts far enough to inspect and change out the flex plate if necessary. If that converter came apart on the inside it most likely contaminated the whole transmission with metal.
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Old 05-28-2022, 01:28 PM   #11
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Re: Torque Converter Rattle?

Lots of good ideas here. Drop the pan first and look for metal etc.
If that looks bad then you know what you have to do.
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Old 06-01-2022, 09:30 AM   #12
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Re: Torque Converter Rattle?

I don't know f I can add this.

https://www.facebook.com/groups/4468...42426835835639
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Old 06-01-2022, 03:19 PM   #13
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Re: Torque Converter Rattle?

Quote:
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All that came through was a set of rules for the group.
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Old 06-01-2022, 07:52 PM   #14
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Re: Torque Converter Rattle?

Sorry that's a bummer. It's a 73-87 chevy truck group on facebook. A guy posted a video of his rattling TC and everybody swears it's a cracked flexplate. I have had a couple cracked flex plates and they knock more than rattle. Oh well, it looks like yours is coming apart anyway for further investigation.
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Old 06-01-2022, 07:55 PM   #15
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Re: Torque Converter Rattle?

Depends on where they brake at. If it's at the hub it's a very different sound.
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Old 06-01-2022, 09:55 PM   #16
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Re: Torque Converter Rattle?

I might get to it this weekend... if I finish my daughter's sheetrock and my wife's floor and have time left over.
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Old 06-03-2022, 11:11 PM   #17
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Re: Torque Converter Rattle?

OK, so I'm an idiot...

I know I torqued the flex plate bolts to 65 ft/lb... but there they were, mocking me. It became really obvious when I separated the transmission from the engine and started the engine.

My apologies to all those who mentioned the possibility.

Sometimes having a 4WD sucks, like when you have to get to the back of the crank. It was pretty much an all-day job. I did take advantage of the opportunity to replace the rear main seal, because I must have nicked it when I installed it - there was a small drip leaving spots on the pavement when I parked.

Oh, and I re-torqued EVERYTHING under there, and this time I applied a decent amount of Loctite blue.

Thanks again for all the suggestions, and I'm almost full now with my meal of crow and humble pie.
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Old 06-04-2022, 02:33 PM   #18
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Re: Torque Converter Rattle?

Hey you admit to your mistakes and learn from them. We have all been there no shame at all!
Thank you for sharing.
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