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Go Back   ClassicBroncos.com Forums > 66-77 Ford Bronco > Bronco FAQ > Transmission FAQ's

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Transmission Talk - General Definitions Transmission Talk - General Definitions
Overview of terminology used to discuss transmissions relating to Early Broncos
Adapter - This is plate and/or shafts that will adapt a transmission to an engine with a different bolt pattern, or a transfercase with different input.

Bellhousing - This the the piece that mates a transmission to the engine. They come molded into the transmission itselt (one piece case/bellhousing), or as a seperate piece. The bellhousing houses the clutch assembly or the torque converter, and the flywheel or flexplate.

Bolt Pattern - This is the arrangement of holes on the bellhousing (either end), or the tail housing of the transmission. This is important to know, so you can determine if you can bolt a transmission either to a specific engine, bellhousing, or transfercase.

Clutch Assembly - refers to the clutch, pressure plate, and any necessary bearings. This is located between the flywheel and the transmission. There are hydraulic and manual versions. The factory bronco clutch is manual.

Cross Member - this is a brace of sorts for the transmission. It attaches to the frame on each side of the bronco, and helps support the weight of the transmission. Many transmission swaps require a modification or custom replacement to the factory transmission crossmember.

Dana 20 (D20) - This is the stock transfercase found on the bronco. It comes in a "J-shift" and a "T-shift" these refer to the shift pattern of the gear box. This is important in Transmission lingo, because you need to know what your transmission will output to.

Drive Shaft - These are the shafts that connect the transfercase to the front and rear axle. The importat aspect of these in transmission discussions is the length and clearance issues.

Fexplate - This is a thin metal plate with teeth around the outside of it found in automatic transmissions only. The Flexplate bolts to the crankshaft, and the torque converter bolts to the flexplate. The teeth around the outside edge are used by the starter to turn the engine over. There are different tooth counts (number of teeth around the outside edge) and bolt patterns (how the torque converter bolts to the flexplate).

Flywheel - This is a thin metal plate (can weight over 40 pounds), with teeth around the outside edge. It is found in Manual Transmissions only. It is bolted to the crank shaft of the engine. It allows a spot for the clutch to "grab" the engine. The pressure plate pushes the clutch into the flywheel as you let up pressure on the clutch pedal, which then in turn transfers the motion of the crankshaft to the input shaft of the transmission. As with the flexplate, there are different tooth counts available. The starter turns the flywheel during starting, which turns the crankshaft.

Gear Ratio - This refers to the ration of the number of teeth on two different gear wheels, usually expressed in decimal form (ie. 3.50 to 1 or 3.50). This is important to know for each gear in a transmission to determine how fast your vehicle will be moving at a given RPM. It is used to compare different transmissions and to help determine what you want for your particular application.

Input Rating - This is a rating, given in Foot Pounds of Torque. This tells you how strong the transmission is, and will give you an idea how much abuse the transmission can take. Another important factor to consider when looking at input rating, is what GVW (gross vehicle weight) it is measured at. The bronco is between 3000-4000 pounds, so a transmission rated to take 300 ft/lb of torque at 7000 GVW, can take even more torque output from a 3000-4000 GVW.

Input Shaft - This is the shaft that connects the transmission to either the clutch or torque converter.

Intermediate Housing - This is a housing on the rear of the transmission that adapts it to the transfercase. It also holds or houses the output shaft.

Kickdown rod/lever - This lever, rod, or cable causes the transmission to shift down into the next lower gear. This is activated by a throttle position. It is connected to the transmission and the throttle.

Modulator - This is a vacuum controlled device that regulates the pressure on certain lines in the transmission. Commonly referred to in discussions on the C4 transmission, and shifting problems.

Output Shaft - This is the shaft that connects the transmission to the transfercase. In 2 wheel drive transmissions, it is fitted with a yoke that connects to the rear driveshaft.

Shift Linkage - This is the linkage that connects the shifter to the transmission. It is found in Automatic and Manual transmissions with column shift. More modern Automatics usually have a Shift Cable that performs the same function.

Small Block - This is what was typicall found in the stock bronco. It refers to a Small Block Ford Engine of the 221-351W cubic inch displacement series of engines. The most common in the broncos are the 289 and 302, with the 351W being a common swap. Important in knowing the bellhousing bolt pattern that you need.

Spline Count - This refers to the number of splines cut into the output or input shafts. These are important to know if your transmission of choice can output/input to certain engines and transfercases.

Syncronized - This refers to a transmission that has syncros in it, which basically slow the gears in a manual transmission down so that shifting can be performed smoothly, and allow the gears to mesh without grinding.

Tail Housing - This is the housing at the end of the transmission. Usually referring to the housing on the end of a 2 wheel drive transmission that houses the output shaft.

Torque Converter - This is the "clutch assembly" of the automatic transmission. The operation of this, would require a tech article of its own, but it essentially is bolted to the flexplate, and as it spins faster and faster, it hydraulically transfers the motion of the crankshaft into the input shaft of the transmission. For transmission discussion you need to know the bolt pattern of the torque converter. Also, the stall range of the torque converter is important to the selection of a torque converter.

Torque Converter Stall - This refers to the RPM range at which the torque converter will force the engine to stall at, basically this is the equivalent of the clutch being fully engaged. If the wheels are unable to turn and the stall RPM is reached, the engine cannot rev any higher. The lower this number is, the less heat it will generate when operating below that stall RPM. Generally speaking a low stall RPM is preferable for off road and 4-wheeling.

Wide Ratio - This is refering to a transmission that has a slightly lower gearing in the first two gears, allowing the entire gear range to be wider.

OK, this is a very rudimentary list of definitions, if you see something that doesn't sound right, or can be improved upon, please feel free to let me know. Also, if there are other terms that you would like to see added to the list, please post below:  

Last edited by DebosDave'72; 07/19/06 at 03:41 PM..
BlackCat4 on 07/12/11, 07:51 PM
When driving do bouth driveshafts spin ,or is it just n 4wd That thay both spin?
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