01silvercoupe

I have my torque tube out right now because I'm replacing the rear main seal/rear timing cover gasket. When i spin the drive shaft in the torque tube, I notice a very slight wobble. The shaft spins easily and freely, has no side to side play but does have that slight wobble. It's so slight that I had a hard time filming it with my cellphone but i can see it if I look hard enough. I took the drive shaft out and the torque tube couplers look perfect (no cracking or tearing). My question is a small amount of wobble acceptable? If you would like to see a video, I can get my camera with a tripod out.

Also, I have vibration in the motor at 2k and 4k rpm. It persists in all scenarios that I could test.
Driving normally in all gears
revving the motor with clutch depressed and transmission in neutral
revving the motor with clutch depressed and transmission in 1st
revving the motor with clutch engaged and transmission in neutral

I kind of figured that would be a motor mount issue because revving with clutch depressed and transmission in first means the drive shaft isnt spinning. Also, the harmonic dampener is new and not wobbling.

Thanks!

Bill Curlee

Have you ever had your clutch and or flywheel replaced??

Sounds to me like a HOT BALANCE issue..

You could also have a slight vibration if the Harmonic Damper has been replaced. Is yours original??

BC

01silvercoupe

Yep, both have been replaced. Clutch assymbly has been replaced with a luk OEM kit (about 30k miles ago) and the harmonic balancer was replaced without weights (about 14k miles ago). The original balancer had no weights in the holes either.

Bill Curlee

Was your OEM flywheel replaced? If so, did you take into consideration the off set balance of the OEM flywheel (any pins installed in the rim) and when you reinstalled it, was it properly clocked back onto the crank??

Bill

01silvercoupe

I did replace the flywheel with the one in the kit. I was under the impression that no flywheels were hot balanced on the ls1. Just internal and harmonic dampener? It is a recent vibration. The clutch kit was in the car years before it started vibrating.

Bill Curlee

ALL,,, C5 & C6 LS Engines that powered a manual transmission were HOT BALANCED!

That being said,, what would have changed to cause a NEW vibration??

Thoughts:

1. Pilot Bearing
2. Damaged pressure plate
3. Torque Tube Bushing/s
4. Torque Tube Bearings
5. Cracked Bell Housing (Mine was cracked but didn't know it. Hair Line)
6. Loose or missing bell housing or torque tube bolts. (Seen that a few times)

= Yes,, if the prop shaft is bent/wobbles, it could flex and cause a weird vibration.

Bill

01silvercoupe

I have the old flywheel and it does have two pins with a blue paint over them. I guess it would be a good idea to transfer? Reading about the transfer of those weights has given me grey hairs

thbwlZ

You said the clutch was in for a long time with no vibrations, correct?? If yes, don't transfer weights. If you have your original pressure plate ALONG WITH your original flywheel, you could see what the COMBO balances out to. The hot balance is done AFTER the pp and fw are BOTH installed to the engine. Weights are sometimes added to the fw. Due to the fw and pp own starting imbalances, that creates a unique fw/pp combo that works with your engine. Not just a fw alone. All components have their own balance tolerances. Put them together, you get tolerance stackup. Don't just transfer weights. Early service manuals instructed to transfer weights, then was changed. There is a reason!

thbwlZ

Want to know a secret?? The new LT1 and LT4 are ALSO hot balanced!! For manuals. This aint going away anytime soon. You'd think after 19 years it wouldn't be such a flipping mystery! Nah, that's just crazy talk!

Bill Curlee

I had a strange feeling that you were going to reply. I didn't have a 100% confirmation that the procedure was still being conducted.

Thanks

Bill

thbwlZ

Yes sir, 100% confirmation from a current engine builder at bowling green. They are very willing to help if anyone wants to educate themselves about the actual processes being used. Like maybe clutch manufacturers or shops who claim to want to help customers address this issue.

Paul 75 L82

C5 Z06 forum, it's where the experts live.

01silvercoupe

I gotta tell you, for an engine that has such a high reputation for reliability and ease to work on, this has to be the most frustrating back-and-forth reading I've ever done.

I guess I'll hold off on installing the weights. I do have the original flywheel/PP (my hoarder instinct is paying off) so I may look for a machine shop that can compare the two and make adjustments if needed. I'll get a video of the drive shaft wobble to see if anything looks off to anyone.

lionelhutz

The input shaft wobbles? To me, it seems rather pointless to check for runout when the one of the bearings that supports the shaft is missing. The input shaft is supported by the throwout bearing in the front and a single roller bearing in the rear. A single roller bearing itself won't hold the shaft straight and a rubber coupler has little chance of holding it straight either.

01silvercoupe

There's one up front that supports it in the torque tube too

thbwlZ

I know you may not have read it during your searching, but I have said this over and over; this is NOT AN ENGINE BALANCING PROBLEM.
The engine balance is fine AS ASSEMBLED without any further external balancing. The build tolerances on all components are all tight enough to make as built engine balance very good for engine reliability and operation. LS engines going in to automatic vettes ARE NOT HOT BALANCED.

HOWEVER

Due to the different vibration transfer paths inherent to the manual transmission vette's design, and its NVH impact, LS engines going into manual transmission vettes ARE further externally balanced via the hot balance procedure. It is to get TOTAL engine assembly balance DOWN EVEN BETTER than what is required for engine reliability, strictly for NVH purposes, to minimize vibrations transmitted into the cabin. This is unique to vettes because of the split engine/transmission design, connected with the rigid torque tube.

You are in good shape if you have your stock FW/PP. Keep them. Put them together see what their state of balance is, as the COMBO. That will give you a starting point, as far as balance goes.

As far as the propshaft wobbling, I'm not clear what you are describing. Just the elastomeric couplers and length of the shaft will allow a little "flex". The shaft guide at the center of the propshaft ( I don't know what it is actually called) helps keep the spinning propshaft from flexing too much. If you have "play" in your bearings, that's a whole different ballgame.

PS: when I CAPITALIZE words, I am not yelling, I'm just trying to highlight important sections. So as not to tick anyone off.

lionelhutz

That is exactly what I wrote. One roller bearing on the input shaft.

thbwlZ

Hey Bill,

CHECK THIS OUT.

https://www.corvetteforum.com/forums...ndbuilt-2.html

post #26 is a video of the hand build LT4 and LS7, current procedure.
timestamp 8:56 shows the hot balance, and balance weights. Notice the entire engine ins in the balance stand, WITH BOTH the flywheel and pressure plate installed.

Yet, there will still be people who won't believe it is done.

01silvercoupe

Woops, missread it. I thought you meant at the rear of the driveshaft. I guess since the shaft felt so solid in the torque tube (no side to side play) I figured that pilot bearing wasn't much of any additional support. Everything is probably ok and I'm just nit picking. I'll get the pilot bearing replaced this weekend and hopefully that helps.

01silvercoupe

I gotcha