GM Truck Manual

GM 4, 5 & 6 – Speed Manual Transmissions

GM 4-Speed Manual Transmission Trucks

The Muncie 465 is a great transmission from a durability standpoint, but it is the widest ratio 4-speed of the Big Three. It has a granny low and so then just 3 normally usable ratios. See Final Drive Ratios and notice the extreme benefit there is to gear-splitting by using the GEAR VENDORS. After the installation – it’s just a whole different truck and you would not be able to stand driving the truck without the new gears.

GM Trucks auxiliary transmissions

You will have a 2-speed thumb switch on your shift lever to control the GEAR VENDORS (turning it on/off) while depressing your clutch. The .78 to 1 overdrive ration will increase your vehicle speed by 28.6%.

Fuel savings are guaranteed to be over 20% in both diesel and gas applications and are typically improved to right at 28%. The UNDER/OVERDRIVE™ will pay for itself while giving you tremendous performance gains in torque multiplication and horsepower.

You will climb hills, cruise, tow, do everything so much better with the Gear Vendors installed. A true 7 speed application. There is just no good reason to drive a Muncie Sm465 equipped vehicle without a Gear Vendors.

5-Speed Manuals

Look at the Final Drive Ratio charts and notice the great benefit in gear-splitting with the GEAR VENDORS. When you are climbing grades you will have a gear between 2nd/3rd and 3rd/4th that is ideal for keeping the engine in the power and the torque multiplication up. Look at the horsepower and torque curves and notice that by keeping the engine in the power you will gain 50+ horsepower and 60+ lb ft. of torque without any modifications to the engine.

The more heavily you are loaded the more you need the GEAR VENDORS and when you are heavy you would do best by not using 5th but instead use 4th + GEAR VENDORS (4th-over). This will keep your transmission temperature as much as a 100 degrees cooler (extending transmission life) and puts the stress on the GEAR VENDORS planetary gearing which is much stronger than 5th.

chevrolet axuliary transmissions

When you are running empty, 5th-over (double overdrive) will net you better fuel mileage and far less engine wear at today’s 75mph speed limits. Not only is the engine turning slower but so are all the engine drive accessories and this cuts down on parasitic losses (turning an a/c compressor or alternator slower greatly reduces the load on the engine).

For the empty truck which never tows and is never driven above 55 – 60 mph the stock transmission is good, but for everyone else the extra gears will give great performance gains that will actually pay for themselves many times over the life of the vehicle. Even the resale value of your truck will improve by more than the cost of the GEAR VENDORS because you will be able to point out that the engine has seen better care and effectively far less miles than other used trucks.

If you tow or run at speeds above 70mph there is just no good reason not to have a GEAR VENDORS UNDER/OVERDRIVE™.

Muncie M21/M22 (Also M20 and BW T-10)

Gear Vendors owes a lot to the Muncie close ratio trans. These words are very similar for the M20 and T10 but with some slight ratio differences depending on model. All M21/22 have the same 22% upshift and 28% downshift spread as the Gear Vendors.

Overdrive is the first reason you are going to add the Gear Vendors. 28.6% faster cruising speeds than you have now. Your 4.10 gears will cruise like 3.20s and your 3.55 will cruise like 2.77s. If you are normally aspirated expect 28% better fuel economy. If you have forced induction expect 50% better mpg.

Gil Palmer's, '55 Chevy

Performance is what the Gear Vendors is all about. This product is a very high-tech planetary overdrive. With our Auto-Launch circuit on you will leave the line in 1st and as the engine gains revs it will automatically shift clutchless to 1st-overdrive. This means you are 28% farther down the track or street before you have to clutch the car. This is key to acceleration as otherwise any manual trans car gives up big hunks of time to an automatic on the 1-2shift. Gear Vendors 1st-over ratio is only 7 hundredths different than having shifted to 2nd (not discernable and actually closer in ratio).

It is just 1st-over where you can use this clutchless shift. You can be in 2nd just boulevard cruising and show off by stepping on the throttle and hitting the Gear Vendors button on your sifter for 2nd-over which is identical (exact same ratio) as having shifted to 3rd but only clutchless (and with a nice bark of the tires). Most street guys will just grab a clutchless gear at whatever moment they start accelerating and then progress up through the gear box leaving the overdrive on so that each gear is just now up a step.

The bracket racers and serious street guys will flip the 3-4 side cover lever over so they can easily have two clutchless shifts in the ¼ mile with just one clutch depression. Flipping the 3-4 cover lever over lets them grab with a straight pull back because it moves 3rd to the 4th gear position on the pattern. Just awesome performance gains greater than a full second on the watch, increased mph and far more performance than any 5spd or 6spd tranny swap.

So you get a 5th gear overdrive and at least one clutchless shift to be used at any moment (we ship the kit with our 6speed car badges) and a huge performance gain plus get to retain your period correct transmission in the car and get the worlds strongest overdrive trans. Since your Muncie or BorgWarner is stronger than any non-race 5 or 6 speed, the Gear Vendors is just he right way to get overdrive in your GM manual performance car.

The Gear Vendors comes with a 30 day money back guarantee so you know you will be happy with everything you get from us and how it installs and drives. All our kits also have our 2year unlimited mileage, horsepower, and abuse warranty – you can go to the dragstrip every weekend and still be covered – no other overdrive can handle that.


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.

 Axle Ratio4.564.103.733.42
 Trans RatioFinal Drive Ratio


  Axle Ratio
 Trans RatioFinal Drive Ratio
5th Dodge O/D0.743.373.032.892.762.63
Double Over*0.582.632.372.262.162.06
*Note: Double Overdrive not to be used when towing or loaded.
M21/22 4-SPEED Close Ratio – showing clutchless options
 Axle Ratio4.884.564.103.733.553.42
 Trans RatioFinal Drive Ratio

CHEVROLET/GMC 2-Wheel Drive Manuals