[encantotom]

here is a web site at allison that if you put your serial number in, it will tell you all about your tranny.

http://www.allisontransmission.com/myall.../index.jsp

here is what spits out for mine in my 2002

Serial Number 6610087423
Model Name HD4000MH

Engineering Groups
Component Number Description
RSN NO REAR SUPPORT BRKT.
01-807 MAIN HOUSING HD/B500
02-628 FILL TUBE & DIPSTICK
05-600 MAIN SHAFT MODULE (CR)
08-774 1710 FLANGE RETARDER
10-609 FRT SUPT & OIL PUMP (STD)
14-1005 P1 PLANETARY MODULE
15-511 P2 PLANETARY MODULE (CR)
16-1739 4"SUMP,W/OLS
20-540 REAR RMT PROV
21-928 TC541 CONVERTER GROUP
24-799 TRNS SE DDC V92 & S50/6O
25-543 ROTATING CLUTCH HD NO PTO
34-543 CONVERTER HSG MOD (STD)
39-816 HD,REAR COVER,CR,NO TACHO,1BOLT,O/N