Rattle / harmonic - Low RPM in 3rd and 4th Gear (4l60e) under slight load

[m002922]

Hello,

1998 5.7 4l60e extended cab.

The truck runs and drives fine - no mechanical issues that I'm aware of.

I don't think this is a transmission issue, more of something being loose that reveals itself when the transmission is in 3rd and 4th, at low RPM, and then placed under load prior to downshifting. There is a rattling that is coming from the engine area or just behind, once the transmission downshifts it goes away. I had it in to a transmission shop for something else, and they said this was very common with these trucks (I think they may have even said it was specific to extended cabs - but I don't recall exactly) - but didn't have any insight in to what the issue is. It seemed to only be doing it in 4th gear at low rpm (before deciding to downshift), but now it seems to be doing it in 3rd as well.

Again, I think it might just be something loose (exhaust manifold heat shield for example), but wondering if anyone has had this problem and located the culprit.

Thanks.

 

[GMTNZ]

Hello,

1998 5.7 4l60e extended cab.

The truck runs and drives fine - no mechanical issues that I'm aware of.

I don't think this is a transmission issue, more of something being loose that reveals itself when the transmission is in 3rd and 4th, at low RPM, and then placed under load prior to downshifting. There is a rattling that is coming from the engine area or just behind, once the transmission downshifts it goes away. I had it in to a transmission shop for something else, and they said this was very common with these trucks (I think they may have even said it was specific to extended cabs - but I don't recall exactly) - but didn't have any insight in to what the issue is. It seemed to only be doing it in 4th gear at low rpm (before deciding to downshift), but now it seems to be doing it in 3rd as well.

Again, I think it might just be something loose (exhaust manifold heat shield for example), but wondering if anyone has had this problem and located the culprit.

Thanks.

Yeah I seem to have the same issue in my 93 RCSB. It kind of sounds as if the flywheel starter teeth scrape on part of the bell housing, maybe the crank migrates back and forth at certain rpm?
Though can't imagine it moving that much even with worn thrust bearings!
Must have a look one day.

 

[m002922]

A theory that I have read somewhere else is the exhaust heat shields rattling. That theory seems fairly reasonable (and consistent with the sound). I'm going to headers when I have the chance to install them (they're sitting in a box right now), so that will allow me to test that theory because it will eliminate the heat shields. I looked at just trying to detach the shields, but it doesn't look like that simple of a process - if I'm going to go through that trouble might as well throw the headers on.

My truck only has ~90k miles on it, and seems to have been pretty well cared for, so I hope the crank is moving back and forth, but who knows.

 

[someotherguy]

Each time I had a noise similar to that on a 700R4/4L60/4L60E-equipped vehicle, the trans went out not much later...sun shell failure

Just throwin' that out there...

Richard

 

[m002922]

Interesting. The trans shop I had it in didn't mention that, but I'll check it out. I wasn't familiar with that issue. Thanks for the heads up.

Each time I had a noise similar to that on a 700R4/4L60/4L60E-equipped vehicle, the trans went out not much later...sun shell failure

Just throwin' that out there...

Richard

 

[someotherguy]

If you can't find anything external making the noise, ya know? You're at the beginning range of mileage where many stock 700R4/4L60/4L60E croak, and the sun shell is one of the most common failures on them. So while it may not be your trans making the noise, wouldn't hurt to start saving up a few bucks for a rebuild with improvements (hardened sun shell, better 3/4 clutches, etc.)

Richard

 

[m002922]

Seriously, I really appreciate you pointing that out. I started doing some research on the 3/4 clutches problem and sun shell issue and started realizing that was a likely culprit. Ugh. At least now I know what to expect and can get ahead of the problem.

I thought I was getting a good a deal buying a low mileage truck, but this thing has been an unbelievable bag of hassles (made worse by the fact that I was moving and without my tools for a period when a lot of stuff was going wrong) - intake leak issues (which was the second time in the truck's life, as the intake manifold had been JB-cold-welded before, so I had to source a new one), unsolicited rear brake lock up issues that were almost impossible to trouble-shoot, the entire A/C system, then a weird ignition issue. I'm starting to wonder if the speedo wasn't unhooked on this thing for awhile (read: most of it's life), and the guy that sold it to me saw me coming a mile away (and he knew about the intake and transmission issues - because they both were not "new").

Bonus, I just pulled the oil plug and saw a fair bit of metal stuck to the drain plug . . . I don't recall seeing that last time, so I'm sending the oil in for testing (which I was going to do anyway after doing the intake manifold gaskets earlier this year). I'm getting scared that the "tick" that I hear mostly at startup might be something more serious . . .

And something is draining the battery slowly that I can't find . . . another weird issue.

I see you have a 2006 SRT8 . . . when I moved I sold my 2006 Magnum R/T (which I never had a problem with over 3 years) and kept this truck . . . really starting to question that decision

 

[someotherguy]

These trucks are usually rock solid for a good while (other than the expected trans failure, doesn't happen to all of them then, just fairly common) - but it may be that you got an abused one.

My current 06 300 SRT8 is just getting ready to turn 12K miles and it's still like new. Bought it with only 9K miles. Sold my buddy my previous 06 300 SRT8 at around 94K, still a great car inside and out. Also recently sold the 06 Magnum SRT8 my wife was driving, with about 100K on it, was still a great car but she wanted a truck (hence the 2nd Silverado SS.) The first gen SRT8's really are a lot of bang for the buck, can still be found with low miles for a fair price if you hunt a bit, and the 300 has all the gadgets.

Richard