The M-SU model is the economy model M with fewer options. I believe it stands for Special Utility. mdelmarcelle and Native Son both have the M7040SU, so they can tell you more.
The MX is smaller than the M and the biggest you can get is the MX5100.
http://www.tractorbynet.com/forums/...73485-m7040-variations-getting-ready-buy.html
This was posted by another member, but I don't remember who:
DT-1 = Dual Traction 4wd, ROPS model with IC/Shuttle Transmission (M7580/M9580)
DTL = Dual Traction 4wd, Low Profile (for orchards)
DTM = Dual Traction 4wd, MUDDER (for specialty, row crop and vegetable)
DTN = Dual Traction 4wd, Narrow (for vineyard/orchard tractor)
DTN-B = Dual Traction 4wd, Narrow wheel tread with Bi-Speed Turn
F = Two Wheel Drive
F-1 = (-1) = Larger two pump hydraulic system
FC = Two Wheel Drive Cab Model
F-CS = Two wheel drive with Creep Speed (Ag. tires or as Turf Special)
HC = High Clearance (2wd M7950 only)
HD = Hydraulic Shuttle, 4wd
HDC = Hydraulic Shuttle, 4wd, Cab
HDCCS = Hydraulic Shuttle, 4wd, Cab, Creep Speed
L = Low Profile
ML = Mechanical shuttle, Low profile
MDT = Mechanical shuttle, Dual traction 4wd
MDTL = Mechanical shuttle, Dual traction 4wd, Low profile
MF = Mechanical shuttle, Two wheel drive
OC = Orchard model
S = Synchro-Shuttle, 2wd
SD = Synchro-shuttle, 4wd
SCS = Synchro-Shuttle, 2wd, Creep Speed
SDN-B = Synchro-Shuttle, 4wd, Narrow with Bi-Speed Turn
SDNBC = Synchro-Shuttle, 4wd, Narrow with Bi-Speed turn, Cab model
SDNBF = Synchro-Shuttle, 4wd Narrow with Bi-Speed turn, Foldable mid-mounted ROPS
SU = Special Utility, 2wd
SU-R = Special Utility 2wd, Rigid ROPS
SU-F = Special Utility 2wd, Foldable ROPS SU-TF = Special Utility 2wd, Turf Special
SUD-R = Special Utility, 4wd, Rigid ROPS
SUD-F = Special Utility, 4wd, Foldable ROPS
SUMDT = Special Utility, Mechanical Shuttle, 4wd
SUDT = Special Utility, 4wd
W = Wide Row
H = 2WD, ROPS (Note: All H-Models are Std. Swing Shift 16F X 16R speeds)
HC = 2WD, CAB
HD = Swing Shift, 4WD, ROPS
HDC = Swing Shift, 4WD, CAB
DS = Dual speed, ROPS (Note: All Dual Speed models are 32F X 32R speeds)
DSC = Dual speed, CAB
SDSCC = Dual speed, CAB, cold weather w/high amp alternator and creep speed and second remote valve
SDSC = Swing Shift Dual Speed, CAB DSDF = Dual Speed, 4WD, ROPS
SDSL = Dual Speed, 4WD, Low Profile
M-Series Notes:
Suffix "1 models are the second generation "Wide Cab tractors. Cab is 5.7 inches wider than first models.
Suffix "2 models are factory equipped with 540 / 1000 RPM PTO kits. M95S and M105S:
The "S represents the model/tractor class in general is no specific meaning, however it can be applied to "Swing Shift as the base transmission on all "S models.
