Eric Brumley

I have read just about everything there is to read on this forum on drivetrain vibration and still have no luck correcting my vibration.

Ok... Here goes...
87 GTA, LB9, 700R4, 90,000 miles, motor and trans stock as possible

What I've replaced/done:
Harmonic balancer
Motor Mounts
Distributor, cap, rotor, wires and plugs (I think all of them were original)
Trans mount
U-joints and swapped out drive shaft
Rear axle seals and bearings
Tires and checked balance twice
TPI (and its adjusted correctly)
Idle air solenoid
Belts run hot, straight and normal
Engine does not vibrate in neutral regardless of RPM
Nothing binding in drivetrain or touching body
Trans bellhousing bolts tight and present
Bolts present and tight in flywheel and torque converter
No cracks in flywheel
TV cable is adjusted correctly. It wasnt when I bought the car and I have no idea how long or how many miles were driven with it like that.

Now... having said all that, I STILL have a vibration. Its less but its still there. Instead of it being nearly undrivable at 60 MPH, it becomes undrivable at 75 MPH. If I "sneak up" on the speed, meaning very light throttle inputs, I can get up to 80-85 before I feel any vibration. If I hit it hard, the vibration is worse.

Can it be possible that the torque converter is causing the vibration?

Heres why I think that:
The vibration is coming from the center of the car. It doesnt seem to be on any corner of the car.
It vibrates between 2000 - 3000 RPM and is RPM dependant (goes up and down) and is not MPH effected. Vibration is the same at 70 MPH or 30 MPH.
While the RPM does drop when the converter locks, the vibration goes away. It returns when the converter unlocks (or when I think it unlocks). But if thats the case, why does it vibrate at 75 MPH? Supposedly the converter is locked at 70 MPH right?

To refine the question, could it be possible that the stator inside the converter be either off balance or cracked?

I would have replaced it sooner but if I do that, I'm going to get the trans rebuilt too. It shifts ok but with the TV cable issue from the previous owner, I'd rather be safe than a pedestrian.

Any further insight would be greatly appreciated.

Bob88GTA

iTrader: (2)

Try to get the car to vibration speed, whatever that is. Then put the trans in neutral and let it coast. Does it do it on de-cel also in drive? Sounds like TC to me

RedLeader289

iTrader: (2)

How are all of your bushings? (front and rear, but mostly the front).

I would go with replacing those before I messed with the torque converter. because- I had similar vibration issues with a past vehicle (96 cherokee sport). It was commonly referred to as the "xj death wobble" and was caused by issues with how the bushings in the suspension wore. Once they were all replaced with poly bushings it drove like a Cadillac at all speeds. It too was almost undriveable at certain speeds before doing the swap(and that's with multiple tire balance jobs, different tires, etc etc).

just a thought, hope you figure it out!

Eric Brumley

I think it was Sherlock Holmes who said "If you eliminate everything that is possible, whatever is left, no matter how improbable must be it.
So after thinking I saw a crack, driving more and feeling it out, I decided to replace the flex plate. I get it. I look at the flex plate closer and cannot find a crack at all. In fact it looks nearly new. So I decide to clock it again. 2nd position reduced it some (at idle). Then I noticed the catalytic converter vibrating up and down. Not much but enough to me seen. So I replaced the cat with straight pipe. HUGE difference. That is the only time that that vibration has been effected.

Now that begs the question what caused it to vibrate? The holders were present and serviceable. No holes in the pipe or loose connections. I'm thinking there might be something in the engine after all. But what? Any ideas? The engine starts first time nearly everytime, no misses, idles perfectly, no loss of power at any speed, alt pumps out 14.7, no burned plug wires, all plugs are new, etc. Ever once in a while I'll feel a miss at highway speed but it's once in a weeks time and it's only once.

Eric Brumley

Sort of. I'm not sure if it's just the car decelerating or if it's the vibration I feel. I've got a sensitive butt.

Eric Brumley

I think I have it almost figured out. I changed the timing and set it back to 0* (base timing). It seemed to smooth out quite a bit. Its almost smooth at 70 mph plus and hasnt changed the performance at all. I do hear a bit more clattering (like from the rockers). So that makes me think that the timing chain is either stretched too far or the nylon broke off. I'm going to advance it 2* at a time to see where it starts to really vibrate. I'm slow but I'm steady.

Thoughts??

87IROCBOOTH

I have an 87 IROC. I went through everything you have done and still had a vibration at the same rpms that your getting the vibration. I just replaced the torque converter and the car runs smooth as silk all the way to 120mph. I replaced it with a stock converter from oreillys. Turns out the converter had a bent or broken vain in it causing the vibration at those rpms in park or while driving. Hope that answers your question.

Eric Brumley

87IROCBOOTH

Thanks. I've been noticing that it seems to get worse when the converter locks and smooths out when it unlocks. I'll let you know when I replace it.