Low-RPM "growl"

Hello all,

I have a 1996 Chevy Z28, LT-1 5.7L V8 engine, six speed manual transmission. The vehicle has 147k miles.

Ever since I've owned this car (since about 68k miles, in 2000), it has had a low-RPM "growl" coming from the engine/tranny. This generally occurs between

700-1000 RPM, and starts off low, with a crescendo to peak volume around 1000RPM, then tapers off as the engine revs up. It is a steady growl (no chittering, except when very, very low RPMs cause bogging down) that varies with engine RPM. It does NOT occur when the vehicle is out of gear.

Any thoughts on what this could be?

I've had the clutch replaced, along with throwout bearings, etc, and thus this is likely not the culprit. I have also had the differential replaced with a Jasper reman, as the original was noisy and had scored bearings/noisy gears. So I'm pretty sure these aren't the problem.

That leaves me with engine (worn rear main bearings?) or tranny (worn input shaft bearings or similar?). The car runs perfectly, does not burn oil, does not have low oil pressure (generally 50psi or so cold, 25-30psi hot, idling, according to the OEM dash gauge), does not shify roughly; but I have had to replace the rear main seal a couple of times (maybe 3) since I've owned it. Although I've been told this is a common need on the LT-1.

Any thoughts on this low-RPM growl? My spidey senses are saying "input shaft bearings to tranny," but I'd like to get some feedback. Lastly, any thoughts on repair for this item?

Thanks in advance, Josh

Reply to
Josh
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Just a WAG, based on no experience whatsoever with that particular combo... does it have a dual mass flywheel perchance?

nate

Reply to
Nate Nagel

I am not sure. I did a little googling and found that dual-mass flywheels are usually a corvette stock item, and that many corvette owners apparently replace them with single mass flywheels from camaros, which are supposedly lighter.

Thanks, Josh

Reply to
Josh

bearings to tranny," but I'd like to get some feedback. Lastly, any thoughts on repair for this item?

I would tend to believe it is _some_ sort of bearing problem with the transmission. Have you tried changing the transmission fluid and seeing if the sound changes at all?

--scott

Reply to
Scott Dorsey

bearings to tranny," but I'd like to get some feedback. Lastly, any thoughts on repair for this item?

That's a good thought. The tranny fluid on this vehicle is a b*tch to change - I'll get it changed this week by my trusted mechanic, and let you know how it turns out.

I have had it changed once before as regular maintenance, and did not notice a difference in the sound (but wasn't listening for it, either).

Thanks, josh

Reply to
Josh

The vehicle has 147k miles.

occurs between 700-1000 RPM, and starts off low, with a >crescendo to peak volume around 1000RPM, then tapers off as the >engine revs up. It is a steady growl (no chittering, except when

You could get a low frequency resonance like that from the exhaust system. It would be rpm related, audible at low speeds but disappear at higher revs.

is likely not the culprit. I have also had the differential replaced with a Jasper reman, as the original was noisy and had scored bearings/noisy gears. So I'm pretty sure these aren't the problem.

shaft bearings or similar?). The car runs perfectly, does not burn oil, does not have low oil pressure (generally 50psi or so cold, 25-30psi hot, idling, according to the OEM dash gauge), does not shify roughly; but I have had to replace the rear main seal a couple of times (maybe 3) since I've owned it. Although I've been told this is a common need on the LT-1.

bearings to tranny," but I'd like to get some feedback. Lastly, any thoughts on repair for this item?

Reply to
John S.

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