Gear Vendor Under/Overdrive Hot Rod Applications - Terszich, Camaro 1300HP
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GM Muscle Car / Street Rod / Restoration
2-Speed / 3-Speed Automatic

Chevrolet / GMC Auxiliary Transmissions At about 2600 dollars (depending on model) the GEAR VENDORS is not the cheapest way for you to get overdrive but is by far the best. A Gear Vendors will handle more horsepower, deliver bigger performance gains, give you guaranteed trouble-free performance, and install easier than any other overdrive available. A GEAR VENDORS will handle 1200+ horsepower reliably and is under warranty even at the dragstrip. This is why you have seen GEAR VENDORS in 7 & 8 second ¼ mile cars in publications like Hot Rod and National Dragster. This is also why all GM Callaway Twin Turbo Corvettes with automatics came with a TH400 and GEAR VENDORS instead of the 700r4 which was the base Corvette trans.

Auto Drive Electronics You are also going to actually make more horsepower and enjoy overdrive cruising better with a GEAR VENDORS. For cruising you will have a dashswitch that allows both manual and automatic operation. With the switch in "auto" the vehicle will act just like it came from the factory with overdrive. The overdrive will kick in at 47mph or whatever the eprom is set for in our electronics and turn back off at slower speeds without attention of the driver. The ratio is .78 to 1 (see the final drive ratio chart below). This equates to 28% faster vehicle speed at the same rpm. Or, take your existing rear gear multiplied by .78 (ie 4.10 rear X 78 = 3.20). In this example a vehicle with a 4.10 has the same cruising rpm as it would with a 3.20 rear when the overdrive is engaged. The 3.42 rear gear will net a 2.67 final and yet have a 6.72 1st-over gear which is nearly as strong as a 4.56 rear car in 2nd (Awesome!). Plus with this step in overdrive you can still ran a 3,500 stall converter and cruise efficiently (see converter discussion in our "common questions" section) you're good with any torque converter you choose for performance. Your high stall converter will hook better from gear to gear with less drop when gear-splitting but also since the gears are closer there is not as much need for high stall and so stock converters perform to new levels of performance when Gear Vendors equipped.

Year One's '67 Chevelle Gear-Splitting is that feature which has made Gear Vendors so popular. Our 1:1.286 ratio brings the same close ratios found in a close ratio Muncie to your automatic. You will have a full 6 forward ratios and torque multiplication that will have even taller rear gears like 3.20 and 3.42 comparing to 4.10s. When you switch to manual on our dashswitch you control the overdrive. Pull into low, hit our button (on the shifter or the floor) this activates our Auto-Launch feature (a red LED light up on your dash), as you accelerate the car will rev in 1st and then shift automatically to 1st-overdrive which is a gear ratio right between 1st and 2nd and the green light appears indicating overdrive. You are now 28% farther down the track or road before you shift to 2nd. When you move your shift lever to 2nd turn us off. Then rev back up and hit the button for 2nd-over (this will also be a much higher torque multiplier than shifting to 3rd - see Drive Ratios). Then 3rd and 3rd over. You have never had this much performance, tire barking, and just plain fun driving your car. Even at just throttle it performs, and at full throttle is just plain awesome. Look at the final drive ratios for each gear. Notice with your rear gear in 1st-overdrive how low you would have to go in a new rear gear to make 2nd gear have that much torque multiplication. A 3.55 rear Th350 will grab 1st-over like 4.5s in 2nd.

The equation for Horsepower is: Horsepower = Torque X RPMM/5252
Gear Splitting gives you more torque multiplication and higher rpm on shift = more HP!


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.

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 people who are car enthusiasts and they are here to give you any information you could want. Look at the ratio charts here and then check out the Magazine Articles tab. See also - See also some discussion of 700R4 lower on this page.


  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


  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


Why you don't want a 700R4 in your muscle car or truck!

James Kryta's, '71 442 Oldsmobile There are good places for a 700R4 and bad places. Fortunately the Gear Vendors Under/Overdrive can handle all the bad places. High horsepower, heavy car, or heavy footed driver, and guys who love performance will all go the Gear Vendors route. A 700R4 is ideally suited to a fuel injected, stock motor, in a light car with a very moderate driver. This is because that trans is hyper sensitive to throttle cable adjustments on carburated vehicles so it is really only decent with a computer (4L60E) that typically coincides with a late model swap. Also the 700R4 has a huge step between each gear and a very tall overdrive gear that requires a lockup converter (another irritation and failure point) that will have many motors with a sizable cam and carburetor lugging (besides sounding bogged down and resonating).

It is not that the trans isn't decent — it is just meant for the astro vans and gently driven camaros to get good EPA fuel mileage. Imagine you have a little two seater like a 32 Ford that is scary to go fast in anyways. Simple light little car that goes fast enough for you — the 700R4 is a good cheap alternative to the Gear Vendors. A Gear Vendors would still be more fun, and outperform and out-last the 700R4 but in this case the 700R4 is a decent choice.

On the other hand if you have a heavy full bodied car and enjoy performance through the gears. Maybe even struggle with the idea of having a manual because you like to shift — here the Gear Vendors is the only choice. You get six forward, close, performance ratios in a bulletproof package that will last you a lifetime of abuse even on the dragstrip. There is no 700r4 guaranteed for two years of dragstrip use. You put the Gear Vendors behind a powerglide, TH-350, or TH400 and you have a trans package that stays in the car. The money you saved on a 700R4 is out the door if you ever have to work on it again. Do the Gear Vendors and your done with this part of the car.

Check out the Magazine Articles tab and the Racing tab. These race cars run the same exact product we sell to all our street customers. Get one — you will love it — guaranteed or your money back (see warranty for details).

CHEVROLET / GMC Application Guide
2-Wheel Drive 2/3- Speed Automatic



GEAR VENDORS, INC. 1717 North Magnolia Avenue, El Cajon, CA 92020
Toll Free 800-999-9555 • Telephone (619) 562-0060 • Fax (619) 562-1186