Posted to Technical Tips Forum on 9/19/2013
Nailing down a broken flywheel
Up until a couple of weeks ago we had never replaced or had
any problems with broken flywheels on the newer, to us, Gm
full size pickups.
A customer came to us with 04 2500 HD 6.0 with a 4l80e
trans. The complaint was a tick in the motor. When I first
heard it sounded like a lifter ticking away. Under the hood
though I could not isolate the noise to the top of the motor
and noted it was best heard behind the frt. tire in the
I also noted that the noise did not leave when dropped into
gear but when you power braked it did go way at about 1200
rpm. With it in neutral the noise was still clear at 1500
When we got into the shop the noise went away. The customer
was good enough to understand and took it home. He reported
the noise would come and go at will. Last I had talked to
him it had not bothered for two weeks.
I did note a bulletin about flywheels cracking. A peek on
iATN showed up some reports of them breaking also.
Enter truck number two, a 05 Tahoe with the 5.3 and smaller
auto trans. Again,exact same noise, same effect when power
loading it and this one did not go away. A stethoscope
picked the noise up best between the starter and the block
clear to the back. In the shop we pulled the little round
inspection cover off the lower bell housing and with a good
light were able to see a crack.
We replaced the flywheel, which was cracked clear around the
bolt pattern and when done I called the other customer and
told him I was now positive we had a cracked flywheel. He
got it right in and we replaced it also.
It is interesting to note that although both trucks sounded
and acted exactly the same they have different engines,
different transmissions and different part number flywheels.
Also the service bulletin only applied to the 3/4 ton, not
And the news you can use? Sounds like a lifter, maybe a bit
faster, hear it behind the frt. tires. In the air with a
stethoscope you pick it very strongly between the starter
and the engine block.
FWIW we used new GM parts, the new flywheel was slightly
different, also used new bolts, they came with a locking
agent on them, and the spacer.
Roy from Iowa
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24 Replies Received