Here you go, Marc, I hope the upload works... What I'm seeing from your measurements is that your engine/trans is offset 4mm from centerline, which certainly isn't worth talking about, BUT, since the rear axle is apparently off by 10mm (12/32=3/8=10mm, roughly), there is some angular error in there somewhere. You did measure a 4mm variance in your wheelbase length, which may be part of it. Did you happen to measure FLCA to RLCA on either side, AND across? That could be instructive. Additionally, when you did the measurements, did you ballast the front seat, how much gas did you have in the tank, and did you have your "normal" load of junk in the trunk? As you know, weight changes in the rear will affect ride-height, which in turn will affect the left-to-right center of the pinion shaft. Also, measure the rear LCA length. When you put the car up on the ramps, did you jack it up or drive it up? If there was some bind from the ramp, it could be skewing your measurements. Last question: What would you consider your margin of error to be in your measurements?

About all I can see is measurement error, compounded by normal manufacturing variance yielding a slight angle in the engine/trans combo that over the length of the car is exaggerated by 6mm... Hardly earth shattering in the end, and doubtful the cause of any noise or vibration. That said, if you confirm that, for example, one of the LCAs is longer than the other, and you swap them side-for-side, that may just cure your angular issues...

 

yes the engine tranny seems to be off centerline by ~4 mm, but also at a slight angle, whereby that becomes the 10 mm at the rear. In my post immediately above yours i reported that the hum is less and happens at at higher speed now...so I think there is some correlation of the hum to the thrust angle (any angle in that vertical plane would add to the true operating angle of the U-joints).
No I didn't measure FLCA to RRLCA and voce versa...I guess I should have. I did drive the car up on the fron ramps, then jacked the rear up by placing a floor jack under the pumpking to keep it loaded, and lowered it onto the rtear ramps, and I had slightly more than half a tank, but I didn't have any ballast on the drive's side. As far as measurement error, I had my wife under the car holding the tape measure up to the plumb line at one end while I did the same at the other, so I'd say +/- 1mm on the bolded measurements...the others I did by myself and may have more like +/- 2 or 3 mm...
Swapping the right and left LCA's huh? Interesting idea. I'll have to wait till next weekend to raise it again and measure the LCA's and do the cross measurements you suggest.

 

Sorry the upload didn't work! I would do the cross measurements and perimiter measurements just to ensure that your chassis is square, then work on locating the drivetrain components in that squared chassis.

X-------X
| \ / |
| \ / |
| \ / |
| \/ |
| /\ |
| / \ |
| / \ |
| / \ |
X-------X

The "X" marks would be FCA and RLCA mount bolt holes. Fill in side-to-side, front-to-back, and cross measurements, and that'll tell you how close to square your chassis is. THEN, you can plot the drivetrain component locations on that grid, and you'll be able to tell how much, and where, you're off-kilter. FWIW, I would closely scrutinize the LCAs. Granted, I have adjustable LCAs and UCA, but I have my wheelbase set to within 1/16", appx 1.5mm, within the margin of error for hand measurements. On a Hunter alingment rack, it was verified to be less than 1/16", with a thrust angle of 0.0*. I also have my rear axle completely centered fore-aft and side-side at 1/2 tank with 150lbs (yeah, I'm a stick) in the driver's seat. No drivetrain issues whatsoever with the Spydershaft.

 

Dave,

Thanks again for your patience with this matter. I will do as you suggest. Do the engine and tranny have any room for play in the mounts? I guess what I'm asking is, if i take it to an alignment shop, and verify the chassis is fundamentally square, can the engine/tranny be moved over to be exactly in the center?

Hunter alignmenmt rack you say? I guess I need to find someone in Houston that has one...

 

I'm also looking for a place in Houston that will do a proper alignement...i've already swapped out springs for ultralites. This weekend i'm replacing shocks/struts with Tokico D-Specs, LCAs with J&Ms, and the panhard bar with an adjustable J&M one. If anyone can recommend a place in Houston to get the car properly aligned after all of that i would really appreciate it.

 

Being 1300+ miles away, I can't help you with a local shop... Another thing to remember, is that I would ALWAYS take the final result of an old-timer with a spirit-level over a MORON with a computer. GIGO still applies. If one of the wheel clamps aren't installed properly, it can throw things off, and if the tech doesn't know enough to question the results of the reading, then your alignment will be off.

You might try what worked for me... Google local road-course racing clubs, and look for any shops that act as sponsors, and then look for shops listed as accredited tech inspectors. Those guys will know race cars, and alignment is CRITICAL for road-course cars... The owner of the shop I use races open-wheel, and just bought a used Craftsman Truck rolling chassis to play with...

THAT SAID, I think there is definately slop in the trans crossmember, and probably in the motor mounts. I would ensure the car is aligned and square before re-measuring your driveline. I would also start with the rear axle set to match the chassis, then work the driveline in from there.

 

Good advice...thanks again.