caldercay

(originally posted to the LT1 forum, with no responses).

A few months ago, I installed Kooks headers, Yank SS3200 T.Q., and
FLT (Level 3) auto tranny to a standard rubber tranny mount. Just prior
to that, the only other things I've done is add a Meziere electric pump,
ignition wires, plugs, MSD cap/rotor, new Yokohama tires all around.

A couple of months ago, I replaced the broken stock rubber tranny mount
with a poly mount and noticed an increase in vibration. But in the last
month, or say, 1,000 miles, I've noticed a fairly "violent" vibration. I've
rotated the driveshaft 180 degrees with no improvement.

The vibration occurs mostly between 1,800-2,000 RPM, and seems to be
most apparent in 3rd gear - if i manually shift through the gears, it's not
so noticeable in 1st or 2nd, but is most noticeable when i shift into D. In
fourth, (circle D), it's not as apparent.

I have also noticed one other thing. Let's say I'm running at 50+ MPH and
above 1500 RPM and I let off the gas. When the RPM's hit 1500, the tranny
downshifts to 3rd VERY noticeably (never did this before). Also, if I mash
on the gas (say, from a stop) conservatively, the tranny shifts into overdrive
prematurely, at around 1500 RPM at 45 MPH, which it never did before.

So here's my question - and I'm mostly interested in determining the
vibration problem now. What is the best method to determine where the
vibration is coming from? Could it be the flywheel, harmonic balancer,
torque converter, tranny, or driveshaft components? How can I reliably
eliminate where the problem could be coming from?

performabuilt

iTrader: (25)

First I would absolutely get rid of the poly mount . The only area really that the trans itself would be likely to be able to make a vibration would be the tail housing bushing. When a trans vibrate internally they generally fly apart there not much room in there for error. I would say likley your issue is going to be the drive shaft IMO ,As for the downshift and early upshift i would have to say a sensor or tuning issue there

Ntimid8r7

iTrader: (9)

Do you have any noise or whine from the rear end? I had a vibration in my Blazer at certain RPMs and when I slowed down it would shake the whole truck. I eventually had to replace the rear. I found 1 ring gear tooth and 6 off the pinion. No problems after that. Just a thought. I could be way off.

caldercay

Actually, the poly mount isnt bad, except during that 1800-2000 RPM spread.
In the last 2 years, I've replaced the tranny mount 3 times, which is one reason
why I used the poly (it came as a set with the poly engine mounts).

I've checked the tranny fluid - looks and smells fine and is at the proper level.

It's as if the engine is shaking badly - as if it's running on 4 or 5 cylinders and
out of balance. it's a crazy thought, but I want to say the flywheel or torque
converter is out of balance. (No codes are set).

If I drive along and put it in neutral, and rev the engine to the RPM's where
the shake occurs, I feel the shake a bit, but it's not near as bad and when
it's in gear.

When I rotated the driveshaft 180*, I checked the u-joints and they are fine.
The only thing I could not do is check the driveshaft for balance, which I'll
have done if nothing else pans out.

I should also mention that the FLT 4L60E tranny and SS3200 torque converter
have somewhere in the neighborhood of 5,000 miles.

As far as the rear end goes, I'll have to go for a spin and listen specifically for
any roaring / whine noise.

FLT

iTrader: (1)

With poly mounts on the motor and trans it is going to vibrate. Try to swap just the trans mount out. I bet it is much better. Poly mounts are much less forgiving over the factory mounts. Vince

caldercay

Understood. I know there will be *some* extra vibration, but not a "shudder" as
violent (violent might seem like a strong word to use to describe the shake, but
it seems appropriate).

However, I think I've discovered an issue *because* I switched to the poly tranny
mount. If I go to the dentist because of a toothache and he simply gives me pain
pills, the real problem hasnt been fixed, but only masked by the pain pills.

Ok, so, I put on a stock rubber mount and the vibration goes away, but eventually,
this stock rubber mount will break, no doubt because of this odd vibration.

I've yet to hear anyone say, "all LT1 based F-Body automatics shake violently
between 1800-2000 RPM".

BTW - I'm not claiming it's the tranny - I posted in this forum because I dont see
a generic "Driveline" forum ... I posted to the general LT1 forum with no responses.

Ntimid8r7

iTrader: (9)

Did you get a chance to open the diff up? You would have had to do something pretty major to the d/s for it to be out of balance IMO. Hopefully you find it before you go crazy.

LS1TXGuy

I am having the same problem... hmmm LS1 Car

Joshiedoom

iTrader: (4)

Same problem. Ive got a new performabuilt waiting for the first snow. I CANNOT find a stock 1le mount for my car anywhere, im going to be getting a new DS as well .