tranny/torque conv/gears guestion
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Junior Member
Joined: Sep 2004
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From: Persia, IA
tranny/torque conv/gears guestion
I have a 03 f-150 screw xlt 4x4 and i am wondering what gears i have or of my torque converter is not locking up like it should. My rpm's at 75mph is 2.1k i have 265 tires on my truck. im not sure what else i can say about it but can anyone help me out. ooh i have the 4.6 with an auto trans
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Joined: Mar 2004
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From: SoCal
Originally Posted by Viper5035
axle code is 26 is there a formula to find out what the rpm's should be at at a certian speed
http://www.f150online.net/forums/sho...ight=axle+code
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Joined: Feb 2005
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From: San Diego, CA
Originally Posted by Viper5035
axle code is 26 is there a formula to find out what the rpm's should be at at a certian speed
DGR = Diff Gear Ratio
TGR = Trans Gear Ratio (1st=2.71, 2nd=1.54, 3rd=1.00, OD=0.71)
D = Tire Diameter in inches
DGR = RPM*D/336.09/MPH/TGR (not exact but can tell 3.55, 3.73, 4.10, etc)
Viper has 265 tires so D=30.5", MPH=75, RPM=2100
DGR = 2100*30.5/336.09/75/.71 = 3.58 so Viper has 3.55 diff gears
or
RPM = 336.09*MPH*DGR*TGR/D
RPM = 336.09*75*3.55*0.71/30.5 = 2083 RPM
BUT 26 axel code says 3.73 so I must have guessed wrong on the tire dia. Viper, are the tires 31.8" or 32" tall? If I got the tire size right then the RPM should have been 2200 at 75MPH. The best way is to use 3rd, get accurate RPM and tire dia.
Last edited by fasterhorses; Oct 31, 2006 at 02:04 AM.
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Joined: Sep 2006
Posts: 292
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From: North Pole, Alaska
Originally Posted by fasterhorses
YES...formulas....have fun
DGR = Diff Gear Ratio
TGR = Trans Gear Ratio (1st=2.71, 2nd=1.54, 3rd=1.00, OD=0.71)
D = Tire Diameter in inches
DGR = RPM*D/336.09/MPH/TGR (not exact but can tell 3.55, 3.73, 4.10, etc)
Viper has 265 tires so D=30.5", MPH=75, RPM=2100
DGR = 2100*30.5/336.09/75/.71 = 3.58 so Viper has 3.55 diff gears
or
RPM = 336.09*MPH*DGR*TGR/D
RPM = 336.09*75*3.55*0.71/30.5 = 2083 RPM
BUT 26 axel code says 3.73 so I must have guessed wrong on the tire dia. Viper, are the tires 31.8" or 32" tall? If I got the tire size right then the RPM should have been 2200 at 75MPH. The best way is to use 3rd, get accurate RPM and tire dia.
DGR = Diff Gear Ratio
TGR = Trans Gear Ratio (1st=2.71, 2nd=1.54, 3rd=1.00, OD=0.71)
D = Tire Diameter in inches
DGR = RPM*D/336.09/MPH/TGR (not exact but can tell 3.55, 3.73, 4.10, etc)
Viper has 265 tires so D=30.5", MPH=75, RPM=2100
DGR = 2100*30.5/336.09/75/.71 = 3.58 so Viper has 3.55 diff gears
or
RPM = 336.09*MPH*DGR*TGR/D
RPM = 336.09*75*3.55*0.71/30.5 = 2083 RPM
BUT 26 axel code says 3.73 so I must have guessed wrong on the tire dia. Viper, are the tires 31.8" or 32" tall? If I got the tire size right then the RPM should have been 2200 at 75MPH. The best way is to use 3rd, get accurate RPM and tire dia.
I found your error. You used 30.5" for the tire diameter, a 265/75/16 tire is 31.6", substitute 31.6 and it works out. I would say his TC is locking up correctly.