Tremec, aka TTC, bought out Borg-Warner a couple of years ago. They started using different housings, and a few other parts. It threw a lot of Mustang owners for a loop, since the housings on the stock transmission had 'Tremec' stamped on them. The poor guys thought they already had Tremec HD transmissions.
If you want to surf their site, goto
www.ttcautomotive.com
According to the info posted, here are a few differences between the current T-45 and the Tremec 3550:
Needle bearings:
T-45: has them under gears 1-4
3550: has them under gears 1-5
Tapered roller bearings:
T-45: on main and countershafts
3550: on input, main and countershafts
Reverse gear:
T-45: synchro, 3.22 gear ratio
3550: no synchro, 3.01 gear ratio
Rated Torque Capacity:
T-45: 250-325
3550: 350
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Moxie Racing
[This message has been edited by Moxie (edited 01-06-2001).]