Why Do Manual Transmission Gears Grind?

Written by tom lutzenberger
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Why Do Manual Transmission Gears Grind?
A handle for a manual transmission is often mishandled by inexperienced drivers. (Beautiful interior of the new modern car image by terex from Fotolia.com)

Depending on your type of car and its age, its transmission may be naturally noisy. For example, a diesel engine in idle can make an extremely loud racket, which is normal. However, unless your vehicle is a bulldozer or a wrecking ball, a grinding noise coming from your engine is generally not a good thing. Particularly when the noise is emanating from the transmission, it's usually a sign that something is going wrong. But what exactly is going bad is not always clear.

Simple Maintenance

A common yet cheap fix is to make sure the transmission fluid is topped off. Too little or contaminated fluid will reduce the necessary lubrication, causing friction within the metal gearing and leading to grinding. The noise and damage will get progressively worse without new fluid.

Human Error

Anybody who has driven or ridden in a vehicle with a manual transmission will wonder at least once what happens if you put the car in reverse too soon while moving forward. Don't. It's a bad idea. You will hear an awful grinding sound and a vibration that will shake the whole car. Do it too forcefully and the gears could break a tooth or two. The sudden, loud grinding is the last warning before you break the car badly, so stop trying to reverse if this happens. It usually occurs when the driver is shifting and not paying attention to where the shifter is going.

Intermittent Noise

Intermittent grinding is a sign of a problem that is gradually developing. This noise usually occurs while the vehicle is in motion and goes away when it is in park or idle. More often that not, the noise is caused by a loose part being thrown around inside the transmission and getting caught in the gears as they spin.

The Clutch

Those learning to drive a manual transmission will often hear a temporary grinding noise when shifting. This is a result of the driver still learning the timing of gear shifting and how the clutch engages and disengages. The cause is human error and will go away with experience and practice. Unfortunately, enough incidents can prematurely burn out a clutch. However, the problem is not the transmission itself.

The Clanging Grind

This situation is very uncommon and is more likely to occur in older vehicles with rudimentary straight-gear systems rather than modern transmission and hypoid gearing. What's going on here is that a gear is likely loose or has been installed the wrong way, causing it to bang against neighbouring parts as it rotates. The only fix is rebuild the transmission. Failure to do so will result in ongoing damage and an eventual breakdown.

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