Driveshaft length... how do you know if it needs to be shortened?

[SadbutTrue]

(I tried these follow up questions in my last driveshaft thread but it fell by the wayside after I tried to bump it, so here goes part 2)

I swapped a C4 to a T5 last summer. Used the NPD swap yoke and didn't shorten the driveshaft. Its been like that for about a year, roughly 2,000 miles (max).

There have been no problems except that my rear main seal is leaking (it was a used transmission to start with, so I'm not sure if the driveshaft length had anything to do with it).

Questions:
1) If the driveshaft has been in that long without any issues, my gut says getting it shortened is a waste of time and money. Is my gut right?

2) Could a slightly too-long driveshaft cause a rear main seal to leak? My gut says that if the driveshaft is too long, you'd have a much more obvious issue than a leaky rear seal.

On a semi-related note... does anyone know a good place to get a 1989 World Class T5 rear main seal?

Thanks!

 

[Tim65GT]

When I swapped in my AOD I was able to install the driveshaft without shortening it. I took it for just a short drive (about a half a block) and when I did a U-turn, there was a definite banging noise that i noticed when i got on it a little. So I took it out and had it shortened. I was told by a driveshaft shop to have between 3/4 and 1" of additional slip into the yolk. In other words, if you unbolt the u-joint from the axle flange and slid the driveshaft forward, it should go about an inch before bottoming into the tailshaft.

 

[RogerC62]

I was told by a driveshaft shop to have between 3/4 and 1" of additional slip into the yolk. In other words, if you unbolt the u-joint from the axle flange and slid the driveshaft forward, it should go about an inch before bottoming into the tailshaft.

X2