Noise under load, cracked flex plate? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

powell72 · 04-20-2009, 10:30 PM

My truck has started making a tinging noise, almost like rocks rolling around, when it's under load. It occasionally does it at idle, it's coming from the very back of the motor/front of tranny. I can hear it very well underneath. It isn't consistent with rpm. Does not sound like a rod knock. I removed the inspection cover and didn't see any cracks, but I heard they crack around the mounting bolt holes. I put a new one in when installed the tranny four years ago. I've never encountered a cracked flexplate before, does this sound familiar to anyone who has had this happen? Am I one the right track?

low'n slow · 04-20-2009, 10:38 PM

That's where I would start. Check the bolts to the torque converter, my son had one that came loose there.

powell72 · 04-20-2009, 10:40 PM

Thanks, I forgot to mention the converter bolts are tight.

vasquezmrysvll · 04-20-2009, 11:27 PM

iv had cracks, and it did the same things you described. check it out

**Stocker** · 04-21-2009, 12:39 AM

Not sure what you have going on there -- it may be a cracked flexplate. But when mine was cracked (around the mounting holes), it sounded quite a lot like like a rod knocking -- a fairly loud, deep heavy knock. It was always there at idle and definitely followed engine rpm, though I don't recall it getting any worse under load. Maybe the cracks can be a bit different, making different sounds?

Longhorn Man · 04-21-2009, 05:41 AM

check it out... but every one I have heard sounded like a rod hammering its way out of the block.

powell72 · 08-19-2009, 06:49 PM

Sorry to bring this back from the dead, but I got a request to do so for people using the search.
The problem is gone after replacing the flexplate.
The week after I posted this I put a new SFI approved flexplate in from Summit. The Napa one I took out had nothing wrong with it that I could see, no cracks or anything. The only difference between the two I saw was the Summit one was welded to the ring gear on both sides as opposed to just one side on the Napa one (BTW the SFI one was no more expensive than the Napa one).
Was the old flexplate weakening from the locking and unlocking of my torque converter? Who knows, but at least that annoying noise is gone.

toddtheodd · 08-19-2009, 06:54 PM

Didn't know that would make a knocking sound...
hmmm...
maybe that's what that is. Oh well... I'm replacing the motor anyway because of the quart a week leak of 20w50 and the freeze plugs going out too... I'll just check the flex plate while I am at it.
Thank you,
Toad

**Jurassic-1** · 08-19-2009, 09:10 PM

I have had the same sounds from a loose front lower pully. Give that a look.

**FRENCHBLUE72** · 08-19-2009, 10:54 PM

I agree with andy when my flex plate cracked I though the motor was getting ready to grenade.

prostreetC-10 · 08-20-2009, 12:41 AM

That's interesting because the only problem I even had was no where near sounding like a rod knock. It was a light tinging. Was cracked from the crank bolt holes to the center.

**special-K** · 08-20-2009, 06:16 AM

Powell72`s truck wasn`t making a knocking sound.It was more suttle,as described at the beginning of the thread.

67-72trucks · 09-18-2009, 10:10 PM

my truck is making the same noise..never heard it before because it had just headers for exhaust.

texanidiot25 · 09-19-2009, 09:28 PM

I have it coming in my motor. It sounds a lot like a very light rod knock at idle, but doesn't sound like rod knock when revved. Just gets a bit faster. Comes right around the torque converter area on the lift, but I never remember to tighten the bolts when down their until it starts making the noise again!

*highperf4x4* · 09-19-2009, 10:08 PM

Generally a cracked plate will make a lighter noise unless it's pretty severely cracked. The "rod knock" sound will most often come from loose bolts. Just recently I had this problem and it started out sounding like a stuck lifter and then it quickly went to the hammering noise. I found that a loose converter bolt started hitting the dust cover on the inside where it was pushed in some and it caused the bolt to spin out and hit the bottom edge of the block. It happened pretty fast. Scared the crap out of me.

texanidiot25 · 09-19-2009, 11:07 PM

Funny you mention the lifter, that's what my neighbor mentioned listening to the truck run. But it comes way too low.

One of these days I'll get under and fix it.

*highperf4x4* · 09-19-2009, 11:27 PM

Yeah when it's the flywheel it's definitely louder under the truck.

04-20-2009, 10:30 PM	#1
powell72 Senior Member Join Date: Jan 2005 Location: Loveland Co. Posts: 3,098	Noise under load, cracked flex plate? My truck has started making a tinging noise, almost like rocks rolling around, when it's under load. It occasionally does it at idle, it's coming from the very back of the motor/front of tranny. I can hear it very well underneath. It isn't consistent with rpm. Does not sound like a rod knock. I removed the inspection cover and didn't see any cracks, but I heard they crack around the mounting bolt holes. I put a new one in when installed the tranny four years ago. I've never encountered a cracked flexplate before, does this sound familiar to anyone who has had this happen? Am I one the right track? __________________ Chris 74 Custom Deluxe SWB 350/350/3.73’s 99 2wd Silverado RCSB 5.3/4L60/3.90’s http://www.classictrucks.com/feature...short_bed.html

04-20-2009, 10:38 PM	#2
low'n slow Too Dumb To Know Better Join Date: Nov 2005 Location: Texas Posts: 882	Re: Noise under load, cracked flex plate? That's where I would start. Check the bolts to the torque converter, my son had one that came loose there.

04-20-2009, 10:40 PM	#3
powell72 Senior Member Join Date: Jan 2005 Location: Loveland Co. Posts: 3,098	Re: Noise under load, cracked flex plate? Thanks, I forgot to mention the converter bolts are tight. __________________ Chris 74 Custom Deluxe SWB 350/350/3.73’s 99 2wd Silverado RCSB 5.3/4L60/3.90’s http://www.classictrucks.com/feature...short_bed.html

04-20-2009, 11:27 PM	#4
vasquezmrysvll "the other guy" Join Date: Oct 2008 Location: Olivehurst California 95961 Posts: 901	Re: Noise under load, cracked flex plate? iv had cracks, and it did the same things you described. check it out __________________ God Said,"Building A 10 Second Import Is Like Coming Out Of The Closet, In The End Ur Still....."EXPLETIVE"

04-21-2009, 12:39 AM	#5
Stocker 20' Daredevil (Ret) Join Date: May 2003 Location: Jefferson State Posts: 13,618	Re: Noise under load, cracked flex plate? Not sure what you have going on there -- it may be a cracked flexplate. But when mine was cracked (around the mounting holes), it sounded quite a lot like like a rod knocking -- a fairly loud, deep heavy knock. It was always there at idle and definitely followed engine rpm, though I don't recall it getting any worse under load. Maybe the cracks can be a bit different, making different sounds? __________________ - Mike - 1972 K20 LWB 350/350/205 RIP El Jay

04-21-2009, 05:41 AM	#6
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	Re: Noise under load, cracked flex plate? check it out... but every one I have heard sounded like a rod hammering its way out of the block.

08-19-2009, 06:49 PM	#7
powell72 Senior Member Join Date: Jan 2005 Location: Loveland Co. Posts: 3,098	Re: Noise under load, cracked flex plate? Sorry to bring this back from the dead, but I got a request to do so for people using the search. The problem is gone after replacing the flexplate. The week after I posted this I put a new SFI approved flexplate in from Summit. The Napa one I took out had nothing wrong with it that I could see, no cracks or anything. The only difference between the two I saw was the Summit one was welded to the ring gear on both sides as opposed to just one side on the Napa one (BTW the SFI one was no more expensive than the Napa one). Was the old flexplate weakening from the locking and unlocking of my torque converter? Who knows, but at least that annoying noise is gone. __________________ Chris 74 Custom Deluxe SWB 350/350/3.73’s 99 2wd Silverado RCSB 5.3/4L60/3.90’s http://www.classictrucks.com/feature...short_bed.html Last edited by powell72; 08-19-2009 at 06:50 PM.

08-19-2009, 06:54 PM	#8
toddtheodd The oddest Todd around Join Date: May 2004 Location: Miami, Florida Posts: 1,418	Re: Noise under load, cracked flex plate? Didn't know that would make a knocking sound... hmmm... maybe that's what that is. Oh well... I'm replacing the motor anyway because of the quart a week leak of 20w50 and the freeze plugs going out too... I'll just check the flex plate while I am at it. Thank you, Toad __________________ "The greatest pleasure is to vanquish your enemies and chase them before you, to rob them of their wealth and see those dear to them bathed in tears, to ride their horses and clasp to your bosom their wives and daughters." Ghengis Khan IIOY???

08-19-2009, 09:10 PM	#9
Jurassic-1 Registered User Join Date: Jul 2007 Location: New River Arizona Posts: 1,180	Re: Noise under load, cracked flex plate? I have had the same sounds from a loose front lower pully. Give that a look.

08-19-2009, 10:54 PM	#10
FRENCHBLUE72 PROJECT 7DEUCE Join Date: Dec 2002 Location: GRANTS PASS OR Posts: 21,608	Re: Noise under load, cracked flex plate? I agree with andy when my flex plate cracked I though the motor was getting ready to grenade. __________________ GO BIG GREEN GO DUCKS MEMBER #6377 72 k-5 daily driver 6'' lift 35'' 350-350-205 slowly getting rust free. Project "7DEUCE" check out my build http://67-72chevytrucks.com/vboard/s...d.php?t=267665 Tim Powell..R.I.P EastSideLowlife..... R.I.P..

08-20-2009, 12:41 AM	#11
prostreetC-10 My Carbon Footprint Join Date: Oct 2008 Location: Orygun Posts: 5,527	Re: Noise under load, cracked flex plate? That's interesting because the only problem I even had was no where near sounding like a rod knock. It was a light tinging. Was cracked from the crank bolt holes to the center. __________________ A quick "pedalfest" *Still getting loose (carb test)* 496 Initial fire up video!

08-20-2009, 06:16 AM	#12
special-K Special Order Join Date: Nov 2004 Location: Mt Airy, MD Posts: 85,859	Re: Noise under load, cracked flex plate? Powell72`s truck wasn`t making a knocking sound.It was more suttle,as described at the beginning of the thread. __________________ "BUILDING A BETTER WAY TO SERVE THE USA"......67/72......"The New Breed" GMC '67 C1500 Wideside Super Custom SWB: 327/M22/3.42 posi.........."The '67" (project) GMC '72 K2500 Wideside Sierra Custom Camper: 350/TH350/4.10 Power-Lok..."The '72" (rolling) Tim "Don't call me a redneck. I'm a rough cut country gentleman" R.I.P. ~ East Side Low Life ~ El Jay ~ 72BLUZ ~ Fasteddie69 ~ Ron586 ~ 67ChevyRedneck ~ Grumpy Old Man ~

09-18-2009, 10:10 PM	#13
67-72trucks Registered User Join Date: Jun 2006 Location: Michigan Posts: 530	Re: Noise under load, cracked flex plate? my truck is making the same noise..never heard it before because it had just headers for exhaust.

09-19-2009, 09:28 PM	#14
texanidiot25 Eat My Rust Join Date: Jan 2007 Location: Cypress, Texas Posts: 3,362	Re: Noise under load, cracked flex plate? I have it coming in my motor. It sounds a lot like a very light rod knock at idle, but doesn't sound like rod knock when revved. Just gets a bit faster. Comes right around the torque converter area on the lift, but I never remember to tighten the bolts when down their until it starts making the noise again!

09-19-2009, 10:08 PM	#15
highperf4x4 Account Suspended Join Date: Apr 2009 Location: Oklahoma City Posts: 4,709	Re: Noise under load, cracked flex plate? Generally a cracked plate will make a lighter noise unless it's pretty severely cracked. The "rod knock" sound will most often come from loose bolts. Just recently I had this problem and it started out sounding like a stuck lifter and then it quickly went to the hammering noise. I found that a loose converter bolt started hitting the dust cover on the inside where it was pushed in some and it caused the bolt to spin out and hit the bottom edge of the block. It happened pretty fast. Scared the crap out of me.



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09-19-2009, 11:07 PM	#16
texanidiot25 Eat My Rust Join Date: Jan 2007 Location: Cypress, Texas Posts: 3,362	Re: Noise under load, cracked flex plate? Funny you mention the lifter, that's what my neighbor mentioned listening to the truck run. But it comes way too low. One of these days I'll get under and fix it.

09-19-2009, 11:27 PM	#17
highperf4x4 Account Suspended Join Date: Apr 2009 Location: Oklahoma City Posts: 4,709	Re: Noise under load, cracked flex plate? Yeah when it's the flywheel it's definitely louder under the truck.

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