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GM 3-Speed Auto

GM 3-Speed Automatic Truck/Motorhome

Roger Jamamura's, '56 Chevy

With the GEAR VENDORS dashswitch in “auto” you will have automatic overdrive just like the vehicle came with a factory system. The GEAR VENDORS will shift on and off without attention of the driver and can be used while towing up to combined weights of 30,000 lbs. An interactive floorswitch is positioned for the left foot (just like a headlight dimmer) to give manual control at any moment so that you can turn the overdrive on/off for performance and gear-splitting.

Performance while accelerating or climbing grade is greatly improved by the torque multiplication of 6 forward ratios (see Final Drive Ratios). With 1/2 the drop in engine rpm on each gear change, the engine, transmission, and torque converter stay in the power band running stronger and with lower exhaust gas temperatures.

Most importantly you are getting this horsepower and torque without modification in any way to the engine. Any other way of increasing power (chips, induction, exhaust, fuel) all put stress beyond the original equipment. With the GEAR VENDORS UNDER/OVERDRIVE™ you get this power because gears are multipliers of torque, plus the engine can be kept in a narrower (better performing) rpm range when power is needed. For this reason, if you have performance modifications the GEAR VENDORS also helps them work to their maximum potential. Not only do you get performance without engine modification but the overdrive will pay for itself in fuel mileage alone. Add to this the wear savings you get from slowing the engine down 22% so that the same rpms that currently take you only 500 miles will now take you 640 miles.

Rucker's, '66 Chevy Truck

Most vehicles will experience a mileage increase of 22-28% (the reciprocals of our ratio) if driven at the same speeds as they were without the GEAR VENDORS. No single change to your vehicle can increase mileage and reduce engine wear as effectively, which is why all vehicles today come factory with overdrive.

The GEAR VENDORS UNDER/OVERDRIVE™ will do more for this vehicle than any Underdrive or Overdrive ever offered. You will get all the features normally associated with an underdrive except a gear below first, plus all the economy of overdrive. Because GEAR VENDORS is the only product you can shift under throttle you will have far greater performance and economy. The GEAR VENDORS comes with the best warranties in the industry (2 years for noncommercial use) including a 30 day money back guarantee (see Warranty for details). It is without question the best item you ever bought for your truck or RV or your money back. This is our 27th year – we know you’ll love it.

GM/CHEVROLET FINAL DRIVE RATIOS

Gears Under/Overdrive

It is the gear under your seat that counts. Gearing is what you are buying when you purchase a Gear Vendors Under/Overdrive. If you take a few moments to study the gear chart for your transmission and rear end ratio combination you will se why this product is so popular. The Final Drive Ratio shows you how many times the engine turns for one complete turn of the tires. Gears are multiplier of torque. The mathematical equation for Horsepower is; Torque X RPM/5252 = HP. Close ratio gearing lets us work both the torque and rpm side of this equation for big gains in HP and performance. Notice for instance that 1st-over has a lot more torque multiplication than 2nd – now look how low you would have to go in rear end ratio to make your second gear have as much torque as 1st-over. Same with 2nd-over compared to 3rd.

Whatever your 2nd-over final drive number is – that is equivalent to having that ratio for a rear end torque multiplier. Of course, with gear-splitting we are keeping the engine rpm up from one shift to the next and further exploiting the ratio benefit.

There is not room here to cover all the details (like the benefit to passing gear and such) so call us at the factory to discuss your exact application – we have customer service guys on hand for you to ask these types of questions.

TH350 3-SPEED AUTOMATIC
  Axle Ratio 4.56 4.10 3.73 3.55 3.42 3.08
  Trans Ratio Final Drive Ratio
1st 2.52 11.49 10.33 9.40 8.95 8.62 7.76
Over 1.97 8.96 8.06 7.33 6.98 6.72 6.05
2nd 1.52 6.93 6.23 5.67 5.40 5.20 4.68
Over 1.19 5.41 4.86 4.42 4.20 4.06 3.65
3rd 1.00 4.56 4.10 3.73 3.55 3.42 3.08
Over 0.78 3.56 3.20 2.91 2.77 2.67 2.40
TH375/400/475 3-SPEED AUTOMATIC
  Axle Ratio 4.88 4.56 4.10 3.73 3.55 3.42
  Trans Ratio Final Drive Ratio
1st 2.48 12.10 11.31 10.17 9.25 8.80 8.48
Over 1.93 9.44 8.82 7.93 7.22 6.85 6.60
2nd 1.48 7.22 6.75 6.07 5.52 5.25 5.06
Over 1.15 5.63 5.27 4.73 4.31 4.09 3.95
3rd 1.00 4.88 4.56 4.10 3.73 3.55 3.42
Over 0.78 3.81 3.56 3.20 2.91 2.77 2.67

CHEVROLET / GMC Application Guide 4-Wheel Drive 3- Speed Automatic

  Application Price Code


Part # 3D0205A

Automatic NP-205 Cast Iron 3-Speed T-400 Mech Speedo

NP 205 Transfer Case with Fixed Yoke, Automatic Transmission.Replaces 1 1/8″ output case housing.If a slip yoke 205, requires output shaft replacement with GM #458499 (not included).

Price : $3,095.00

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Part # 3D0208A

Automatic NP-208 3-Speed T-350/400

NP 208 Transfer Case with Slip Yoke, Automatic Transmission.Replaces 9 1/4″ tailhousing with slip yoke.Vans & pickups with aluminum case and slip yoke.

Price : $3,095.00

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Part # 3D1371A

Automatic 3-4-Speed BW 1370L/400 Elec Speedo Std Cab 6-3/4 Tailhousing

Automatic 3-4-Speed BW 1370L/400 Elec Speedo Std Cab 6-3/4 Tailhousing w/fixed yoke.Replaces 6 3/4″ tailhousing.89-93 4×4 1 ton standard cab pickup. Check tail length and yoke to confirm.

Price : $3,095.00

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Part # 3D1370A

Automatic 3-4-Speed BW 1370S/400 Elec Speedo Ext Cab 2-1/2″ Tailhousing

Automatic 3-4-Speed BW 1370S/400 Elec Speedo Ext Cab 2-1/2″ Tailhousing w/fixed yoke.Replaces 2 1/2″ tailhousing89-93 4×4 1 ton dually standard & extended cab trucks. Check tail length and yoke to confirm.

Price : $3,095.00

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Part # 3D0242A

Automatic 3-4-Speed NP-241S/400 Suburbans 241S/400 1989 and Prior Elec Speedo

NP 241 Transfer Case for Suburbans.Replaces both 4 3/4″ & 3 1/2″ tailhousings totalling 9 1/4″.89 Suburban with cable speedometer.

Price : $3,095.00

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Part # 3D0243A

Automatic 3-4-Speed NP-241 Suburbans 241S/400 1989 and Prior Elec Speedo

NP 241 Transfer Case for Suburbans.Replaces both 4 3/4″ & 3 1/2″ tailhousings totalling 9 1/4″.91 – 93 Suburban, electric speedometer, passenger side front driveshaft.

Price : $3,095.00

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Part # 3D0241E

Automatic 3-4-Speed NP-241 3/4 Ton 241/700 Elec Speedo

NP 241 Transfer Case, 700R4 Transmission.Replaces both 4 3/4″ & 3 1/2″ tailhousings totalling 9 1/4″.88-newer 4×4 GM and standard and extended cab pickups with electronic speedometer.

Price : $3,095.00

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Part # 3D0241A

Automatic 3-4-Speed NP-241 3/4 Ton 241/400 Elec Speedo

NP 241 Transfer Case, TH400 Transmission.Replaces both 4 3/4″ & 3 1/2″ tailhousings totalling 9 1/4″.88-newer 4×4 GM and standard and extended cab pickups with electronic speedometer.

Price : $3,095.00

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Part # 3D1371F

Automatic 3-4-Speed BW1370L/4L80 Std Cab 6 3/4″ Tailhousing

Automatic 3-4-Speed BW1370L/4L80 Std Cab 6 3/4″ Tailhousing w/fixed yoke.Replaces 6 3/4″ tailhousing.89-93 4×4 1 ton standard cab pickups, check tail length and yoke to confirm.

Price : $3,095.00

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Part # 3D1370E

Automatic 3-4-Speed BW1370S/4L80E Ext Cab 2 1/2″ Tailhousing

Automatic 3-4-Speed BW1370S/4L80E Ext Cab 2 1/2″ Tailhousing w/fixed yoke.Replaces 2 1/2″ tailhousing.94-01 4×4 1 ton dually extended & standard cab trucks. Check tail length and yoke & provide axle ratio and tire size.

Price : $3,095.00

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Part # 3D0205E

Automatic 3-4-Speed NP-205/T-400

NP 205 Transfer Case with Fixed Yoke, TH400 Transmission, Electric Speedometer.Replaces 1 1/8″ output case housing.If a slip yoke 205, requires output shaft replacement with GM #458499 (not included).

Price : $3,095.00

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Part # 3D0205I

Automatic 3-4-Speed NP-205/T-4L80

NP 205 Transfer Case with Fixed Yoke, 4L80E Transmission.Replaces 1 1/8″ output case housing.If a slip yoke 205, requires output shaft replacement with GM #458499 (not included).

Price : $3,095.00

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Part # 3D0243E

Automatic 3-4-Speed Suburbans 241S/4L80-Elec Speedo

NP 241 Transfer Case for Suburbans.Replaces both 4 3/4″ & 3 1/2″ tailhousings totalling 9 1/4″.91 – 93 Suburban with 4L80E, passenger side front driveshaft.

Price : $3,095.00

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Part # 3D0241G

Automatic 3-4-Speed NP-241 3/4 Ton Pickup 241S/4L80

NP 241 Transfer Case, 4L80 Transmission.Replaces both 4 3/4″ & 3 1/2″ tailhousings totalling 9 1/4″.88-newer 4×4 GM and standard and extended cab pickups with electronic speedometer.

Price : $3,095.00

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Part # 3D1371E

Automatic 3-4-Speed BW1370L/4L80 Std Cab 6 3/4″ Tailhousing

Automatic 3-4-Speed BW1370L/4L80 Std Cab 6 3/4″ Tailhousing w/fixed yoke.Replaces 6 3/4″ tailhousing.89-93 4×4 1 ton standard cab pickups, check tail length and yoke to confirm.

Price : $3,095.00

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