LS3 TRANSMISSION/CLUTCH

[dnelson]

I started noticed buzzing/vibrating going into 4th gear at lowish RPMs. The problem has since started talking to me in 3rd fear as well (only low RPMs).

Typically it is only for a few seconds until I get over 2500-3000.

This happened around 6 months after I dropped my trans and replaced the factory clutch with a McLeod RXT. I don’t think think there is any correlation but wanted to throw this out there. When I put in the new clutch, I put mobile 1 dex4 into the trans. One of my friends is a service manager at GM and said to put in the AC delco OEM fluid. I did and still no difference.

I’m out of ideas. The old fluid came out VERY clean with no glitter. The synchros feel fine as well. Another reason I don’t think it points to the synchros is because the buzzing will come back if I am cruising and drop down under 2500 without gear change.

Any help would be greatly appreciated!

[silversleeper]

Clutch - pressure plate.

[dnelson]

Then why does it only happen in 3rd and 4th? Also it’s after clutch engagement.

[TheFlyingBananaSS]

Resonance vibration of a loose part perhaps.

[fz4k98]

I had vibration ain the 1400 to 1700 rpm range after they installed a mcleod twin disk. They said it was trans. Gm said it was clutch. I eventually sent the mcloed down the road after having the trans professionally rebuilt by tremec and vibration was still there with the mcleod.

Now have a spec 3+ single disk clutch back in and the vibration was gone. Mcleod never saw the clutch pack but decided it was the trans? GM did see the car with the factory clutch back in and ran a vibration meter test and found no issue.

[Car Nation Videos]

I thought 5th gens recommends 2Dexos

[silversleeper]

Originally Posted by dnelson

Then why does it only happen in 3rd and 4th? Also it’s after clutch engagement.

I gave you the short answer free. If you want the long answer that will cost you $$$
All I know is back in the day changing clutches it's easy to bend the pressure plate trying to get the input shaft in the pilot bearing without an alignment tool or trans jack etc. And bent pressure plates or other issues, like warped clutch plate, springs etc cause weird issues that can mimic bad sycros in trans and whatnot.
Fz4k was kind enough to also add his experience in more detail being helpful to anyone having similar problems now of future searches. I was first but since he said it in more detail we should split the diagnosis consultation $$$ half and half.

[fz4k98]

In my case, gear changes either amplified or reduced the vibration but it was always in the same rpm range. In terms of transmissions, different gears create different speeds internally to the transmission and also run on different trans parts and shafts. Some internal transmission speeds may be sensitive to the vibrations.

If i had no vibration from the clutch system, there was none to input into the transmission. if there was vibration, it would transmit to the input shaft of the transmission. After the rebuild of the transmission, the vibration left me no choice but to address the clutch.

My experience may be unique but twin disk clutch system on my car amplified the vibration and factory single disk and the spec 3+ did not.

[dnelson]

Thanks for the info gentlemen, your insight is much appreciated. I really don’t want to drop the trans again. *sigh*

[fz4k98]

Originally Posted by dnelson

Thanks for the info gentlemen, your insight is much appreciated. I really don’t want to drop the trans again. *sigh*

The only other thing you might try is using a boroscope to check out the clutch system for anything loose etc. I used one and if you have patience you can check out quite a lot as long as you dont get it stuck somewhere. I got a cheap one at harbor freight and have used it several times.

Good luck, pulling the trans is definitely not fun.