[tomslik190]

68 GTO, fresh 455, new tremec TKO 5 speed, 3.42 8.5" non-c-clip posi rear, PS, PB, new driveshaft (part of the Keisler 5 speed conversion kit). Car rides great, but when I get on the freeway and hit 60 MPH or higher, there is a vibration that seems to shake through the car for a second and then smooths out. This cycle repeats every few seconds. It is not RPM dependent as putting the car in a different gear or in neutral doesn't change anything. There is no vibration through the steering wheel. The front bumper and hood visibly shake with this cycle. wheels are 17" year one cast rally IIs with new tires, just balanced. What could be causing this odd vibration cycle? Could it be the driveshaft or rear end? I'm stumped. Any input is greatly appreciated. thank you!

[MilesM]

I've got same problem. Drives me crazy.

[Formulajones]

Probably one of 2 things.

Installing the TKO, depending on the crossmember and mount used, may have changed the working angle of the driveline. So that needs to be checked.

The other I've run into on these swaps is that Keisler as well as others use Inland Empire for their supplier to build these driveshafts, and the ones I've received were less than perfect. 2 of them I had to send into the driveline shop up the street from me for a rebalance (one was even bent!!) and they were new pieces. From that point on I've had the driveline shop build all my driveshafts now, and he has nothing good at all to say about Inland Empire. He was fixing a lot of their stuff in the off road desert racing stuff around here.

In any event, what you describe, the resonance in and out vibration type of thing, is almost always directly related to the driveline and it's working angles.

[Troy_forman]

My old bird had a bad vibration at highway speed and the slip yoke going into the tranny was loose . I replaced the tailshaft bushing and the slip yoke and now it's smooth to top end

[north]

I'd be inclined to look at the yoke of the diff and the angle the driveshaft comes into it.

[heups1629]

When I first bought my LeMans, the car started to shake on the freeway (I pulled over, thought I had a flat tire). Didn't see anything wrong (the tires were fairly new), continued on a side road towards home, and it happened again. As I was examining the right front tire, a bubble started to grow in the tread, expanding to softball-size before it burst with a bang (it was like watching a cartoon). Turns out the tire was defective.

[tomslik190]

Thanks guys. I'll check the driveline angles and will likely have the driveshaft checked.

[tomslik190]

So I found an app for my phone - Tremec Toolbox. Takes three measurements (engine/trans angle, driveshaft angle, rearend angle) and tells you if the numbers are in spec. Turns out my drivetrain is almost dead straight which is not good. I'll make some adjustments to get the desired angle for the u-joints and see what happens. If that doesnt work, I'll have the driveshaft checked for balance. Fingers crossed.

[Formulajones]

Yep, dead straight is most certainly a cause for vibration. In order for the u-joints to work properly they need a slight working angle.

Usually trans pointing down 2-3 degrees and the rear doing the opposite.

In your case, since the trans is the only part of the equation that has been changed, then just moving the trans angle may be enough to cure your vibration, so no cost and fairly easy fix.

[gtohunter]

[QUOTE=Formulajones;5786735]Yep, dead straight is most certainly a cause for vibration. In order for the u-joints to work properly they need a slight working angle.

Agree with that....the lubrication is an issue as well if joints have no misalignment. Rolling elements never move relative to their trunnions and the rollers will flute them.