Manual Transmission

Manual transmissions preceded automatics by several decades. In fact, up until General Motors offered an automatic in 1938, all cars were of the shift-it-yourself variety.

From the most basic four-speed manual in a car from the ’60s to the most high-tech six-speed in a car of today, the principles of a manual gearbox are the same. The driver must shift from gear to gear. Normally, a manual transmission bolts to a clutch housing (or bell housing) that, in turn, bolts to the back of the engine. If the vehicle has front-wheel drive, the transmission still attaches to the engine in a similar fashion but is usually referred to as a transaxle. This is because the transmission, differential and drive axles are one complete unit. In a front-wheel-drive car, the transmission also serves as part of the front axle for the front wheels. In the remaining text, a transmission and transaxle will both be referred to using the term transmission.

The function of any transmission is transferring engine power to the driveshaft and rear wheels (or axle halfshafts and front wheels in a front-wheel-drive vehicle). Gears inside the transmission change the vehicle’s drive-wheel speed and torque in relation to engine speed and torque. Lower (numerically higher) gear ratios serve as torque multipliers and help the engine to develop enough power to accelerate from a standstill.

Initially, power and torque from the engine comes into the front of the transmission and rotates the main drive gear (or input shaft), which meshes with the cluster or counter shaft gear — a series of gears forged into one piece that resembles a cluster of gears. The cluster-gear assembly rotates any time the clutch is engaged to a running engine, whether or not the transmission is in gear or in neutral.

All modern transmissions are constant-mesh type transmission, which means that all the mainshaft gears are in constant mesh with the cluster gears. This is possible because the gears on the mainshaft are not splined to the shaft, but are free to rotate on it. With a constant-mesh gearbox, the main drive gear, cluster gear and all the mainshaft gears are always turning, even when the transmission is in neutral.

Alongside each gear on the mainshaft is a dog clutch, with a hub that’s positively splined to the shaft and an outer ring that can slide over against each gear. Both the mainshaft gear and the ring of the dog clutch have a row of teeth. Moving the shift linkage moves the dog clutch against the adjacent mainshaft gear, causing the teeth to interlock and solidly lock the gear to the mainshaft.

To prevent gears from grinding or clashing during engagement, a constant-mesh, fully "synchronized" manual transmission is equipped with synchronizers. A synchronizer typically consists of an inner-splined hub, an outer sleeve, shifter plates, lock rings (or springs) and blocking rings. The hub is splined onto the mainshaft between a pair of main drive gears. Held in place by the lock rings, the shifter plates position the sleeve over the hub while also holding the floating blocking rings in proper alignment.

A synchro’s inner hub and sleeve are made of steel, but the blocking ring — the part of the synchro that rubs on the gear to change its speed — is usually made of a softer material, such as brass. The blocking ring has teeth that match the teeth on the dog clutch. Most synchros perform double duty — they push the synchro in one direction and lock one gear to the mainshaft. Push the synchro the other way and it disengages from the first gear, passes through a neutral position, and engages a gear on the other side.

Clutch & Manual Transmission – Trouble Symptoms

Clutch Fails To Release

  • Master or slave cylinder leakage
  • Clutch disc warped or damaged
  • Pressure Plate failure
  • Pilot Bearing worn

Clutch Slips

  • Clutch disc oil soaked
  • Clutch disc worn thin
  • Clutch disc not seated
  • Pressure plate worn

Hard Going Into Gear

  • Pressure plate is not releasing disk completely
  • Linkage damaged or out of adjustment.
  • Hydraulic system malfunction

Clutch Chatters

  • Oil on clutch disc
  • Broken or loose mounts
  • Spline on clutch hub stripping
  • Warped pressure plate or flywheel
  • Drive lines loose or damaged

Squeals When Clutch Is Engaged

  • Worn release bearing
  • Release bearing is binding on support

Pops Out Of Gear

  • Shift linkage interference or binding
  • Worn or loose pilot bearing
  • Bearing retainer broken or loose
  • Misaligned or debris between the bell housing & engine
  • Worn bearings & synchronizers

Noise In Neutral W/ Engine On

  • Worn or damaged input shaft bearing
  • Worn or damaged pilot bearing
  • Worn or damaged anti-lash plate
  • Worn or damaged bearings or shims

Noise In Reverse Only

  • Worn or damaged reverse idler gear.
  • Worn or damaged reverse idler bushings.
  • Worn or damaged reverse counter gear

Noise In All Gears

  • Low or no lubrication
  • Worn or damaged gears.
  • Worn or damaged bearings
  • Worn or damaged anti-lash plate

Noise In Any One Gear

  • Worn or damaged bearings
  • Worn or damaged synchronizers
  • Worn or damaged gear

If any of these symptoms are present, call or bring your car into Clutch Mart today for a free adjustment / evaluation / diagnostic test.

Manual Transmission Rebuild

Manual transmission are significantly less complex that their Automatic transmission counterparts. When a transmission requires an overhaul, there are generally two options that you may have. The first is to remove your existing transmission and overhaul it, then put the same, newly rebuilt unit back in your car. The second option is to replace your existing unit with another unit that has already been or rebuilt or remanufactured.

For a Manual transmission rebuilt below is an overview of the standard process:

Rebuild Standard Transmission

All parts in our rebuilt manual transmissions, gears and transfer cases meet or exceed all original manufactures specifications, and most of the time are purchased from the same suppliers who supply the original manufacture.

Rebuild Transmission Process

Our rebuilding process includes soft parts are replacement. Soft parts include clutches, bands, lip seals, sealing rings and gaskets. We also inspect all hard parts. The hard parts must meet or exceed specific standards or they are replaced with new or remanufactured parts.

Additional Manual Transmission Information Link

http://auto.howstuffworks.com/transmission.htm