Freddie's Back on the Road!

[MacDee]

Here's one idea I happened to run across for the shoulder belt, for a mustang...it uses a part from a ford van.

Nice setup! Of course, my hardtop doesn't have a convertible top well to provide the attach point used in that installation. I still think I'll need a loop on the seat or attached to the interior quarter panel to position the loop above the sill line (sort of a pseudo-B pillar).

[MacDee]

We took Freddie out for some "speedometer calibration" runs the other day. You know, drive past one of those "Your Speed Is" signs and compare to what your speedometer says. The speedometer is way off since swapping in the C4. We have a pretty accurate chart now that we'll use until I get around to swapping in a different speed-o drive gear.
We then just went for a drive along a higher speed highway. At about 45 [actual] mph, she seems to begin to produce an acoustic "beat", and it seems to get worse as speed increases. It's really annoying, and it didn't do this BEFORE the rebuild! I'm wondering if she maybe lost a wheel weight....
Any ideas?

[Jeff W]

Did your rebuild guy spin balance the rotating assembly?

Did the shop hack jack up the car using the drive shaft as a lifting point?

Did they forget to reinstall or tighten the transmission mount?

Hope it is something easy. You deserve a break today

[MacDee]

So we got the wheels balanced at the Goodyear place in Woodinville yesterday. We took her for a "high-speed" drive again this afternoon, and, alas, the "beat" is still there. It's very prevalent at about 50 mph, but here's a hint: The FREQUENCY of the "beat" is dependent on LOAD, not speed. The frequency increases significantly when we go up a slight grade or accelerate, and slows down to almost going away while coasting downhill.
Could it be something to do with the torque converter? The relative speeds of the turbine and stator in the torque converter vary by load, don't they?

Oh, and, yes, the engine was fully balanced. The shop, I'm sure, did not jack the car up on the drive shaft!
Forget to tighten the transmission mount? Hmmm... Or the flex plate?

[Luva65wagon]

Same U-joints? Maybe all this new "Saturn 5" launch torque has made one of them fail? They would vary with load as well.

What's the frequency?

[Jeff W]

I carefully read your posts again and can't see the specifics...

Do you FEEL anything or is it strictly "noise". I know it's hard to tell the difference sometimes.

[MacDee]

Same U-joints? Maybe all this new "Saturn 5" launch torque has made one of them fail? They would vary with load as well.

What's the frequency?

I carefully read your posts again and can't see the specifics...

Do you FEEL anything or is it strictly "noise". I know it's hard to tell the difference sometimes.

It is definitely FELT, but it acts like an acoustic dissonance.

While cruising along at about 50 mph, there is a vibration that sort of grows and subsides, grows and subsides, over and over, continuously, at about 1 cycle per second. If I feed a little more throttle, as when going up a slight grade, the frequency of the vibration rise-and-fall cycle will increase to... I dunno... 3 or 4 cycles per second without any significant change in road speed.

This is why I'm suspecting it has something to do with the torque converter. The torque converter has within it a Stator and a Turbine which spin on a common axis, one driving the other. Because of slippage, their relative speeds will always be slightly different. However, the more load you have, the more speed difference there will be between the Turbine and the Stator. I'm not sure, exactly, how this relates to the vibration, but it's the only thing I can think of that would have two components spinning out-of-synch. Maybe the converter isn't quite centered on the flex plate so the turbine is slightly off-center?

Or am I just over-thinking this...?

I'm going to take Randy Long for a ride. It will be up to him to fix it!