LS6427

iTrader: (2)

So if I slowly accelerate to 50mph I get this ridiculous vibration from under the console. Like an earthquake rumble.

I pop it into "OD" and its 100% gone.

What could that mean....?

.

01ssreda4

iTrader: (96)

OD with the converter locked or not? Have you tried both ways? Seems like I've heard of other 4L60Es vibrating in third also, especially after they are built.

homemade87

If you put it in 4-O/D and bring it up to the same rpm as it was in 3rd does it do it then. If so It may be t/c or a harmonic balancer ( engine side related ). Would not hurt to rule this out .

01ssreda4

iTrader: (96)

Neutral would be easier and probably more accurate for ruling out engine vibes.

mrvedit

A few people have reported that their built 4L60E vibrated a bit in 3rd, and the culprit was "The Beast" sunshell. However, the complaints are relatively rare and the vibration modest.

Sounds like the vibration is tied to engine RPM. Transmissions rarely vibrate strongly unless completely broken. As suggested, I would also consider the flexplate and torque converter.

Tell us what kind of engine mount, trans mount, flexplate and converter you have.

savage388

Mine has done the same thing since I bought it, I've put 15k on the car since with no issues so I just stay out of third unless I'm racing. My trans is built with unknown parts so I can't sat if it's the sunshell or not.

LS6427

iTrader: (2)

Well....I bought this tranny back in 2002 from FLT. It was an FLT IV. I've had my friend rebuild it over the years like 4 times since then. It has a Vig 3200, a factory flexplate and a new factory tranny mount. It has never vibrated at any speed, any gear. Always been very smooth all the way to 180mph.......for the past 13 years.

This started after my new engine went in about 1 1/2 years ago. I thought the tires were flat-spotted from sitting for 6 months waiting for the new engine to go in. Got new tires and new 18" rims and the vibration is still there.

SO...today just 20 minutes ago driving around all day.......sometimes it was smooth in "3" up to about 55mph. But its still happening almost always. Its like a deep humming sound and it has that long wah-wah-wah frequency sound........if I change speed up or down it goes away for a second but then comes back.
The whole console vibrates.

At first I thought it was coming from the rear end or maybe driveshaft u-joint in the rear.......but its hard to pinpoint, its like everywhere from the tranny to the rear end.

Does a driveshaft need to be rebalanced after its been removed...?

.

01ssreda4

iTrader: (96)

The vibe happens at 55mph? What rpm is that? Try that rpm in neutral and see if it will do it sitting still....to test tires and driveshaft pinpoint the speed say 55, accelerate past it, then flip the trans in neutral and let the car coast down and pass that speed again and see if the vibe changes. You need to see if you can make it disappear or get worse. If the car sat a long time, you could have a bad tire on the rear.

LS6427

iTrader: (2)

I have 4 brand new tires and 4 brand new rims from OE Wheels.

I'll have to take it out later tonight or tomorrow and try some things while driving on the highway.

The vibration generally starts to come alive at 48-50mph and is in full roar around 50mph....in "3". As soon as I pop it into "OD". It smooths right out. But then a matter of 5-10 seconds later I start getting the WAH-WAH-WAH crap that just hums right into my brain....its ridiculous.

I'll try some things to figure it out.......but I think I need to bring it to a powertrain place here and see if they can find anything out of balance.

.