Transmission 101 Options

[macavely]

Transmission 101

Manual transmission: is what change the cars drive wheel speed and torque in relation to engine speed and torque. An engine alone doesn’t have enough power to move a car from a stop.
In first gear the crankshaft turns several times to make the drive shaft and wheels turn once. This is done to increase the torque but keep the speed of the car down. After the car is in motion and the transmission is shifted into higher gears, the drive shaft and engine start to turn at the same speed. The makes the wheels and car move at higher speeds then that of the engine.

These are the things a manual transmission should do when in proper working order.
One.- Be able to increase torque to the wheels for quick acceleration
Tow – Have different gear ratios to go with different engine loads
Three – Have a reverse gear
Four – Give the driver an easy way to shift gears
Five – Work quietly with little power loss

Gears: are round wheels that have teeth machined on there rims. They transfer motion from one shaft to another. When two gears are touching and one is bigger then the other the output speed and torque (turning power) changes.

Gear Ratio: is the number of revolutions a drive gear must turnbefore the driven gear completes one revolution. The way to find a gears ratio is by dividing the number of teeth on the driven gear by the number of teeth on the drive gear. And example would be if the drive gear has 24 teeth and the driven gear has 48 the gear ratio would be 2:1 ( Two to One ). This would cause the drive gear to revolve tow times to turn the drven gear once. this would result in the speed of the larger driven would be half that of the drive fear. But the torque of the shafr of the larger fear would be twice that f the input shaft.

Each transmission manufacture used different gear ratios for different cars. but and approximate gear ratios are 3:1 in first gear. 2:1 in second gear 1;1 in third gear and so on .. and 3:1 in reverse

Gear Reduction: Happens when a small gear drives a bigger gear to increase turning power or torque. Gear reduction is used in the lower gears.

Overdrive Ratio: happened when the bigger gear drives a smaller gear. The speed of the output gear increases but the torque drops.

Gear Types
Manual transmissions normally use two types of gears spurs and helical gears.

Spur Gears: Or straight cut gears have their teeth cut parallel to the center line of the gear shaft. Spur gears aren’t used as main drive gears anymore but might be used sliding or reverse gears. Spur gears are also kind of noisy

Helical Gears: their teeth are machined at an angle to the centerline of the gear shaft.
This type of gear is strong and a lot quieter then spur gears.

Gear Backlash: the small clearance between the meshing gear teeth. This space lets gear oil in between the gears an cools the high friction area between the gears. Another reason for the space is to allow the gears to expand with our causing damage or grinding.

Manual Transmission Lubrication
The bearings, shafts, gears, and other moving, parts in a transmission are lubricated by oil throw off, or splash lubrication. As the gears rotate they sling off around inside the transmission case.
Normally 80W or 90W gear oil is used for a manual transmission. But it is best to read and use what ever your owners’ manual says to use for your transmission.

Transmission Bearings

Ball bearing, Roller bearing, Needle bearings are the three types bearings used in a manual transmission. They are used to reduce the friction between the surfaces of rotating parts in the transmission. Bearings are lubricated by oil spray from the spinning transmission gears. Normally antifriction bearings fit between the transmission shafts and the housing or between some of the gears and the shafts.

Transmission Case: This supports the transmission bearings and the shafts and keeps the parts surrounded by gear oil with our leaking. The case is made of either cast iron or aluminum. A transmission case must have a drain and fill plug, they drain plug is on the bottom of the case and the fill plug on top.

Extension housing: also called the tail shaft housing. It bolts to the rear of the transmission case. It enclosed the transmission output shafr and holds the rear oil seal.
The flange on the bottom of the extension housing provides a base for the rubber transmission mount. Or rear motor mount. A gasket normally seals the connecting areas between the transmission case and the extension housing.


Front Bearing Hub or front bearing cap: This covers the front transmission bearing and acts as a sleeve fo the clutch throw out bearing. This bolts to the transmission case. A gasket fits between the front hub and the case to prevent oil leakage.

Transmission Shafts
A manual transmission normally has four steel shafts mounted inside its case. They are the input shaft, a countershaft, a reverse idler shaft, and output shaft.

Input Shaft or clutch shaft: transfers rotation from the clutch disk to the countershaft gears in the transmission. The inner end of the sshaft has a gear machined on it. And the outer end of the shaft is splined. A bearing in the transmission case supports the inputshaft in the case. Anytime the clutch disc turns the input shaft gear turns.

Countershaft or cluster gear shaft: this holds the countershaft gears into mesh with the input gear and other gears in the transmission. The location is slightly below and to the one side of the input shaft. Normally the countershaft does not turn. It is locked in the case by a steel pin or a force fit or a lock nut.

Reverse idler shaft: a short shaft that supports the reverse idler gear. Normally mounts in the case midway between the countershaft and the output shaft. So the reverse idler gear can mesh with gears on both the countershaft and output shaft.

Main Shaft: or outer shaft” holds the output gears and synchronizers. The rear of this shaft extends to the back of the extension housing. It connects to the drive shaft to turn the wheels of the car. The output shaft is splined in the center. The gears are free to revolve on the output shaft but the synchronizers are locked on the shaft by splines. The synchronizer will only turn when the shaft itself turns.

Transmission Gears
Transmissions gears can be classified into four groups, input shaft gear, countershaft gear, reverse idler gear, and output shaft gears. The countershaft gears turn the ooutput shaft gears and reverse idler gears.

In accelerating a high gear ratio is provided by a small gear on the countershaft drives a larger gear on the output shaft. A larger countershaft gear drives an equal size or smaller output shaft gear in high gear. This reduces the gear ratio and the car moves faster. In reverse power moves from the countershaft gear to the reverse idler gear. Power is then transffed from the reverse idler gear to the engaged gear on the output shaft.

Input Gear
Is a machined part of th steel input shaft. The input gear drives the forward gear on the countershaft gear. A small spur gear is usually placed next to the main helical drive gear. This small gear is used for synchronizer engagement.

Countershaft Gear
Or counter gear turns the gears on the output shaft. This is actually several gears machined out of a cingle piece of steel. Some people also call this the cluster gear the countershaft gear rides on roller bearings. With thrust washers that fit on each end of the gear to set end play or case to gear clearance. When the input gear drives the engaged countershaft gear all the countershaft gears turn as a unit. But since each forward gear is a different size the countershaft gear unit is able or providing several gear ratios.

Reverse Idler Gear Assembly
Changes the direction of gear rotation so the car can be moved in reverse.

Output Shaft Gears
Or main shaft gears transfer rotation from the countershaft gears to the output shaft. Just one of the output shaft gears is normally engaged and locked to the shaft at the time. The inside bore of each output shaft gear is smooth so that it can spin freely on its shaft when not engaged. One output shaft gear will be provided for each transmission speed including reverse.

Transmission Synchronizers
It has two functions
One: prevents the rears from grinding during engagement
Two: locks the output gear to the output shaft.
When the synchronizer is away from an output gear the output gear spins on the output shaft. When the synchronizer slides against the output gear the gear is locked to the synchronizer and to the output shaft. Power is then sent out of the transmission and to the rear wheels.

Synchronizer Construction
consists of an inner splined hub. Inserts. Insert springs. And outer sleeve. And blocking rings. The hub is splined on the output shaft. Is is held in a stationary position between the transmission gears, inserts fit between the hub and sleeve. The springs push the inserts into the sleeve. This helps hold and center the sleeve on its hub. The blocking rings fit on the outer ends of the hub and sleeve.

Synchronizer Operation
When the driver shifts gears the synchronizer sleeve slides on its splined hub toward the output gear. First the blocking ring cone rubs on the side of the drive gear cone causing friction between the twon. This causes the output gear. The synchronizer and the output shaft to begin to spin at the same speed. As soon as the speed is synchronized the sleeve can slide somplyetly over the blocking ring and over the small spur gear teeth on the output gear. This locks the output gear to the synchronizer hub and to the shaft. Power then flows through that gear to the wheel.

Fully Synchronized Transmission
All the forward output gears use a synchronizer. This allows the driver to downshift into any lower gear while the car is still in motion.

Shift Fork
Fits around the synchronizer sleeves to transfer movement from the gear shift linkage to the sleeves. The shift fork fits into a groove cut into the synchronizer sleeve. A shift rail. Or a linkage rod. Connects the fork to the driver’s shift lever.when the shift lever moves. The rail moves the shift fork and the synchro sleeve to engage the correct transmission gear.

Shift Linkage – Shift Lever
Transmissions normally have two kinds of linkage: They external shift rod and they internal shift rail. Both do the same thing , they connect the shift lever with the shift fork mechanism. The external shift rod linkage fits into levers on the shift mechanism and fork assembly. Spring clips hold the rods in the levers. One end of each linkage rod is threaded so that the linkage can be adjusted. With the internal shift rail linkage, when the driver shifts gears.the bottom of the shift lever catches in one of the gates.

Basic Transmission Done ...



This post has been edited by macavely: Nov 4, 2005 - 12:55 AM