Manual Transmission Assemblies

A typical manual transmission has an input shaft, an output shaft, and a countershaft that rotate on ball bearings and roller bearings inside a cast aluminum case. The input and output shafts are in-line with one another, with the countershaft below them. The gears on the input/output shaft and countershaft are in constant mesh and rotate with one another, but the gears on the output shaft can rotate freely on the shaft until locked in position. Power flow is from the input shaft, through the countershaft to the locked gear and the output shaft. Between gears on the output shaft are hubs that are splined to the shaft. Over the hub is a slider that is connected to the shift linkage. When the driver selects a gear, the shift fork moves the slider toward the gear, locking it to the hub and output shaft. Each gear has a coned surface that works with the cone on a synchronizer ring. When the slider forces the synchronizer against the gear, it quickly brings the gear to the speed of the shaft to prevent gear clash.

First gear is the largest gear on the output shaft and when locked to the corresponding countershaft gear provides approximately a 3:1 gear ratio, where the input gear turns 3 times to the output gear’s one rotation. This supplies the torque multiplication needed to get the vehicle moving from a stop, however if this were the only gear the vehicle would have a very low top speed. Successive 2nd and 3rd gears are progressively smaller but continue to supply torque multiplication so the vehicle can continue accelerating. Fourth gear is often a 1:1 ratio, with power flow directly from the input to the output shaft.

That 1:1 ratio was common on the 3rd and 4th gears in the 3 speed and 4 speed transmissions in older vehicles, where those gear ratios were the “high” gear in the transmission. However, the 1:1 top gear ratio could still require the engine to turn at a high rpm at highway speed, especially if the differential gear ratio was numerically high, reducing engine life and fuel economy. For this reason, separate overdrive units that attached to the transmission were often included or available as optional equipment, to reduce engine rpm and increase fuel mileage. The 5th and 6th gears in modern manual transmissions incorporate overdrive within the transmission, with typical ratios of 0.7:1 and 0.5:1. In overdrive the driven gear spins faster than the drive gear. Of course, a reverse gear is required for backing up, and for this purpose an idler gear is included between the countershaft and reverse gear on the output shaft.

A clutch assembly, consisting of a flywheel, clutch disc, pressure plate and release bearing, is positioned between the engine and manual transmission. The clutch allows the engine to be disconnected from the transmission so the vehicle can come to a stop while in gear with the engine running, and so the driver can make gear changes. The clutch is housed in a bell housing that is mounted to the engine. The bell housing may be part of the transmission case or a separate component to which the transmission is attached. The front of the transmission input shaft is supported by a pilot bearing or bushing in the end of the crankshaft or the center of the flywheel. The clutch disc is splined to the input shaft and the release bearing rides on a hollow shaft that encircles the input shaft. On most modern transmissions the shift mechanism and rods are internal components, but some manual gearboxes still feature externally mounted shifters and shift linkage.

Manual transmissions can suffer fluid leaks, noise, and poor shifting performance. Before condemning the transmission, the transmission and other components should be carefully inspected to ensure a leak is not coming from somewhere else like the engine rear main seal. A tailshaft seal can usually be repaired while the transmission is in the vehicle but repairing other leaks will usually require some degree of removal and disassembly. Noise can be due to worn bearings or gears. Shift through all the gears to determine which gear is faulty. Noise from worn gears and bearings will get louder as speed is increased and bearing noise will sound like a growl. Jumping out of gear can be caused by shift linkage that is worn or out of adjustment, worn synchronizers, worn shift forks, or a transmission or bell housing that is misaligned. Hard shifting can be caused by a worn or misadjusted clutch, worn or misadjusted shift linkage, and binding synchronizers.

No matter what you’re working on or what kind of transmission problem you’re having, we have the replacement manual transmission assembly needed to restore proper shifting and transmission operation. We offer new and remanufactured 5 speed and 6 speed manual transmissions that are assembled according to original equipment specifications, so when repairs are completed you can count on the transmission performance your vehicle was designed to deliver. Our new transmissions are brand new assemblies that are manufactured to meet or exceed OE quality standards. Our remanufactured transmission assemblies undergo numerous quality inspections throughout the remanufacturing process. All reusable parts are cleaned, inspected and measured to ensure they meet specifications and replaced with new parts if they don’t, and all seals, bearings, and other common wear components are replaced. Finally, all remanufactured manual transmissions are dynamometer tested to ensure they function perfectly.

A performance manual transmission assembly will be a great upgrade for street, towing and competition applications as it significantly increases the amount of power that your vehicle can support. What benefits are you getting with an aftermarket transmission box? First of all, it's high quality materials used in the construction that are much stronger than stock. Dependable housing allows for more robust gears and high quality components ensure a higher torque-handling capacity. Improved fuel economy and extended engine life complete the list of performance manual transmission gains. We offer manual transmission assemblies from renowned companies that manufacture transmissions for racing and off-road use. Usually such transmissions are full of improvements, like a reinforced case that protects high stress areas from premature wear. Shop at CARiD and you are sure to get the manual transmission assembly that will help you get your engine's power to the ground.