bad vibration

**97ws6** · 11-24-2009, 06:28 PM

ok so when im driving in my car and i speed up to between 3500 and 4000 rpms i have a terrible vibration i push in the clutch and it imeadiatly goes away does anyone know what this could be i have an lt1 with a t56.
now i can just rev the engine to 3500-4000 rpm with it in neutral and there is no vibrations only when it is between those rpms and the trans is engaged.

please tell me somone has had this problem...

**pajeff02** · 11-24-2009, 06:35 PM

Could be a u-joint that has gone bad.

**Skippy** · 11-24-2009, 06:54 PM

I had a similar problem once with an old car of mine. It turned out to be several broken fingers on the clutch pressure plate. It was setting it off balance but I only felt it under load. I found it by pulling the inspection plug and looking into the bellhousing.

**clovenhooves** · 11-25-2009, 09:41 PM

It could be the transmission mount. On my car, it was visible from the underside.

**Sweet Chops** · 11-28-2009, 05:59 AM

My bets are u-joint.

**97ws6** · 11-28-2009, 07:17 PM

well u joints were my first guess as well those are now new the trans mount is new(prothane) so im thinking maybe driveshaft out of balance???

**c5z28** · 11-28-2009, 07:26 PM

Originally Posted by 97ws6

well u joints were my first guess as well those are now new the trans mount is new(prothane) so im thinking maybe driveshaft out of balance???

If you have poly tranny mount and stock motor mounts the tranny mount could be the vibration. I changed my tranny mount and got vibrations so I went back to stock.

**35th-ANV-SS** · 11-28-2009, 07:30 PM

Originally Posted by 97ws6

well u joints were my first guess as well those are now new the trans mount is new(prothane) so im thinking maybe driveshaft out of balance???

If your tires are turning wouldn't your drive-shaft still be spinning regardless of whether your clutch was engaged or disengaged???

Thus, if a DS was out of balance, you would feel it all the time while moving and it would feel like a tire out of balance I would think.

Sounds from your description that you have a BAD vibration. Maybe a motor mount?

**Sweet Chops** · 11-29-2009, 10:45 AM

Originally Posted by 35th-ANV-SS

If your tires are turning wouldn't your drive-shaft still be spinning regardless of whether your clutch was engaged or disengaged???

Thus, if a DS was out of balance, you would feel it all the time while moving and it would feel like a tire out of balance I would think.

Sounds from your description that you have a BAD vibration. Maybe a motor mount?

Yes, if it was the driveshaft you would feel it at a certain speed not RPM.

Did it start happening right after you installed the poly trans mount?

**97ws6** · 11-29-2009, 07:07 PM

well i did a lot of work at the same time new clutch new front suspension and full bushing kit except motor mounts all at the same time and that is when it started... but idk what it would be i put a duralast clutch in it from autozone and i hate it want to replace but it cost $$$$ and im broke...

**02WS6dream** · 11-29-2009, 07:35 PM

I'll tell ya I had a terrible vibration after goin poly trans mount. so bad I bought a new stock mount and sold the poly on ebay. its a trade off--you want stiffness or smoothness??

**02WS6dream** · 11-29-2009, 07:37 PM

I had also installed a new, balanced driveshaft trying to remedy the vibration before deciding to replace the mount again. think a lot of guys like the poly mount and just adjust to the vibration--but it is very noticeable and not worth it to me. maybe better with new motor mounts, Idk???

**autotrix** · 11-30-2009, 04:55 PM

Originally Posted by Skippy

I had a similar problem once with an old car of mine. It turned out to be several broken fingers on the clutch pressure plate. It was setting it off balance but I only felt it under load. I found it by pulling the inspection plug and looking into the bellhousing.

+1 I agree with Skippy. There is a problem with the rotating assembly in the trans, although checking and replacing the mount is an easier/cheaper/faster thing to consider look at first.

**402 Guru** · 11-30-2009, 09:57 PM

yes could be 1 of 3 things a flyweel going out or your u joints going out Just Get under the car ( dirt doesent do anything but put hair on ur chest haha)and check your u joints jack the car then put it up on jack stands and rotate a single back wheel when lifted off the ground watch your u joints and it they are tapping agianst something then they are going out . after the wheels stop spinning hold your driveshaft and pull IT HARD up down left and right if it moves like easly you have a bearing out in your diffrential . did u hit a bump recently or drift a turn if so u threw your driveshaft out of wack/balance if u bottomed out

plus if youre short on cash go with a new z06 assembly they are a sloid clutch with a steel flywheel and GM tested them for 100,000