HELP!! Gear swap trouble

[four55cibird]

I'm trying to help my friend do a gear swap in his cobra. It's a '97 cobra, 8.8 rear. i know it had 3.55's stock, but the previous owner put in 3.27's. He bought a set of "brand new" Ford performance parts 3.73's off E-bay. I've spent 3 days trying to get these gears set up right. I can't get the pinion depth right. I've changed shims(from .030" up to .090") and the tooth pattern is saying the pinion is too shallow. I'm thinking the gears aren't a matched set like they should be. If anyone has done this swap could you please help us out?

 

[COBRA90GT]

FWIW, factory gear ratio was 3.27.

 

[missouri_guy197]

Take them out, wrap them up and send them back and get some 4.10's or 4.30's instead...3.73's aren't a good gear for N/A Cobra's...