[blackbird83]

So I'm planning on having a new driveshaft (aluminum) made for my '83 T-Bird. Everything I've read so far says (center u-joint to center u joint)  the shaft is 48" well, mine is 48 7/16". 
Will this be an issue if I have it made 48"? One thing....My car originally came with the 7.5" rear, I replaced it with the 8.8 (not sure if that made a difference (as the 7.5 may be a bit shorter to the flange.) idk??? anyway... thoughts???? I want to get it right the first time.  
Thanks

[88TurboBird]

The best way to really know is measure it under the car. I just had an aluminum driveshaft made for my 88 and I needed to measure from the slip yoke hole centerline to the rear diff flange surface with the rear end loaded. If you were going stock for stock, I'd probably just send it but with the different rear end, I would personally measure to be sure.

[blackbird83]

Ok, Thanks. That's what they mentioned too (rubber transmission seal to rear flange) but I thought it was odd that my drive shaft was a bit longer, and I wanted a second reference dimension.

[TurboRay]

.
AFAIK, driveshaft lengths are always measured from center of u-joint cup to center of u-joint cup. I suppose one COULD measure from the face of the diff flange to the rubber dust shield sticking out from the trans rear seal....... and then the dr/shaft company COULD extrapolate the proper dimension, but I'm pretty sure that's not their normal practice and it might leave room for error, BUT...... I wuz wrong once B4!

For most RWD vehicles, the dr/shaft should be "shy" of bottoming into the rear of the trannie by about 1-inch, which leaves sufficient space for proper spline engagement throughout the full travel of the rear suspension. Sooo...... if that's what you have with your existing shaft, I would just take it to 'em and have it duplicated in aluminum.

OTOH, if it's too short or too long, figure out how much LESS or EXTRA length is needed. take the shaft to 'em and specify the added or shorter length needed . If a custom-length dr/shaft were needed and a "sample" wasn't available, I would get & install the front/splined yoke and rear flanged yoke, and measure the center-to-center distance of the u-joint bores with the front yoke "shy" 1-inch from bottoming.  My 2¢.......  <shrug>

[blackbird83]

Thanks Ray, I was hoping you'd chime in. Good info.
I'll install the yoke (back 1") and measure to the rear flange hole. (good idea)

[TurboRay]

.
I suggest consulting the dr/shaft company to make sure the 1-inch "out" dimension is correct for your application ~ but that's always been PDC (pretty darn close) in my experience. BTW...... it's difficult to measure from the center of one hole to the Center of another, BUT...... if you just measure between the FRONTS of both u-joint bores, it'll be the same as C-to-C. <thumbup>

[blackbird83]

Thanks again Ray, I took your advice and installed the yoke (1" back) and rear flange, took a measurement and came up with 48 1/2" (same as old one). So that confirms it. Thanks again.