James Montigny

iTrader: (13)

This has been driving me crazy for months.
At first I thought it was just poor quality lockup material in the Yank converter, but
even after switching to an ATI converter, S60 rear, Strange brakes and new CM driveshaft, the issue persists.

The car accelerates great at WOT (TC unlocked), but at part throttle over
42mph (Part Throttle TC lockup speed) I get a nasty shaking from the rear half of the car.
It goes away if you give it a healthy amount of throttle. (thus forcing a TC unlock)
It's not gradual, it's not there at 40, and all of a sudden there it is at 45.
I've had all 4 wheels rebalanced to make sure they were not causing the problem.

I don't remember having a problem when my H/C 350 in there in 07, but there have
been so many changes since then and so few miles (172 to be exact) that
I just can't pinpoint the source. I can say that none of the suspension components
have been changed or removed. But the tranny, motor, rear end, exhaust and brakes have all come off.
I also added SFCs, but they didn't seem to have any impact (+ or -) on the shaking.

Any suggestions? I sure would love to have this thing to a point where I can at least
make an appearance next week at the LTXshootout. As it is, I really don't even want to drive it
until I know what is causing the problem.

fasttagurl

iTrader: (12)

I believe I have the same issue after a track run and I am coming down the return road. I think mine's anywhere from 50-60mph. I thought my rear-end was coming apart, but it's not and I have a Moser. It would be interesting to see what others think. I have a Yank PT4000.

James Montigny

iTrader: (13)

Maybe I'd have more luck in the Auto Trans section.
Can a mod move this thread for me?

Firehawk441

iTrader: (41)

If your speedometer reads all over the place while this vibration is happening, you have a bad speed sensor or you broke the tailshaft housing which will effect your speed sensor, thus creating this vibration.

James Montigny

iTrader: (13)

No, the speedo works fine and the tailshaft looked fine when we had it up on the lift to install the rear end last weekend.

It's the drivetrain that shakes, not the needle itself.

91RS383

I installed a Fuddle 3400 RPM converter in my '02SS.

I had the same issue with mine. When the converter would first lock up it sounded like a jackhammer in the transmission tunnel. The guys at fuddle said it was the synthetic trans fluid I was running and that I should switch. After putting in conventional fluid it no longer does the jackhammer at lock-up, but it still whines when hot.

ssvert99

iTrader: (26)

had a very similar vibration with a customers car with one of my rearends... after looking at everything, different driveshaft, gear, mounts, etc., we actually found it was a engine harmonic vibration due to a broken rocker arm of all things... i was a noticeable vibration in the driveshaft area, but only with the tcc in lockup. car ran perfectly smooth going down the interstate and in town until the tcc engaged. this was a 98 t/a... h/c, ory/catback, built 4l60e and vig 3400 converter, Midwest fab 9 inch rear. last thing i woulda thought would cause this but it happened. may wanna check out your engine believe it or not!

tomcowle

iTrader: (5)

Check the run-out on the flexplate and both yokes.

James Montigny

iTrader: (13)

I run conventional fluid per just about every after-market converter manufacturer's recommendation

Interesting ... I recently switched to longer studs and reinstalled all of my
rockers, so I don't think that's the issue, but it's worth a check.
This issue has been around since long before that adventure.

I'll give that a shot as well.
The car will be up on the lift Thursday night to a going-over.

SSmoken

iTrader: (26)

i had this issue and before i knew it the hub on my converter broke and trans fluid went pouring out.

James Montigny

iTrader: (13)