Diagnosing Noise From a Manual Transmission

Updated on April 21, 2019
Dan Ferrell profile image

Dan Ferrell writes about do-it-yourself car maintenance and repair. He has certifications in automation and control technology.

Your clutch pedal can help diagnose transmission noises.
Your clutch pedal can help diagnose transmission noises. | Source

The most common sources of manual transmission noises include:

  • low fluid level
  • worn bearings
  • worn or failing synchronizer
  • worn or damaged shafts
  • worn or damaged gears

These issues don't show up suddenly, as a rule. They develop over time as the result of poor maintenance, abuse, or high mileage.

Then again, transmission noise can appear suddenly—a transmission component may fail early from a defect and become noisy—and some perfectly-operating transmission models may whir or growl in a low tone, even when new.

Is it Possible to Match a Noise to a Component?

Not all the time. When problems arise, a transmission's internal and external components can produce a variety of sound combinations (depending on the particular issue) under different driving conditions. This makes it difficult to isolate the source to a particular component.

However, there are certain noises that appear time and again, and, to some degree, have become symptomatic of common issues in a manual transmission.

Under this context, the following sections are divided into noises that happen under a particular driving condition or transmission state.

To make the most of the following sections, pay attention to the conditions under which your transmission noise appears. For example:

  • Does it happen in all gears?
  • Does it appear in a particular gear?
  • Does it appear only in neutral?

Use this information to better diagnose your manual transmission noise.

Before heading to the section that best describes your particular problem, though, do the following test. The test may help you confirm that the noise is actually coming from your transmission.

A Simple Transmission Noise Test

When your car is speeding down the road, there are many components moving at the same time: in the engine, transmission, and drive line mechanism. This can make it hard to isolate the source of a particular noise and tell whether it is coming from the transmission.

Here's a simple test that can help you confirm, most of the time, whether or not the noise is coming from your manual transmission.

  1. Engage the parking brake, start the engine and let it idle.
  2. Set your transmission to Neutral and depress the clutch pedal.
  3. If you have heard the noise at a certain engine speed, depress the accelerator slightly to rev up the engine.

If you can't hear the noise during the test, there's a good chance the noise you hear while driving is coming from the transmission. If your sound though is a "whirring" sound, and it disappears during this test, keep in mind that it could be caused by transmission bearings or by wheel bearings or even differential components. You most likely won't be able to hear the whirring unless the car is moving.

If you think you have a transmission noise, skip down to one of the twelve diagnostic sections below for the exact type of noise you have, or feast your eyes in the meantime on the diagram below.

Gearbox ZF 16S181 with opened transmission housing.
Gearbox ZF 16S181 with opened transmission housing. | Source

A Guide to the Parts of Your Transmission

A legend for the letters and numbers on the photo above!

I — input shaft
II — main shaft
П — countershaft
1 — input shaft
2 — splitter high gear wheel
3 — bearing
4 — splitter synchronizer
5 — splitter sliding sleeve
6 — IV gear wheel (broken)
7 — III - IV gears sliding sleeve
8 — II gear driven wheel
9 — rear gear shift rail
10 — III - IV gears shift rail

Index: Skip to the Section on Your Type of Transmission Sound

 
1. Transmission Makes a Growling Noise
2. Transmission Makes a Noise When I Step on the Clutch Pedal
3. Transmission Makes a Noise When I Let Off the Clutch Pedal
4. Transmission Makes a Grinding Noise When Shifting Gears
5. Transmission Makes a Humming Noise
6. Transmission Growls Except in Fourth Gear
7. Transmission Makes a Grinding Noise While Moving
8. Transmission Makes a Growling Noise in Neutral
9. Transmission Makes a Growling Noise in Forward and Reverse Gears But Not in Neutral
10. Transmission Makes a Growling Noise While Car is Moving
11. Transmission Makes a Clicking Noise
12. Preventing Manual Transmission Noise
Low fluid level is a common source of transmission noise.
Low fluid level is a common source of transmission noise. | Source

1. Transmission Makes a Growling Noise

If you suspect a transmission noise, don't forget to check the transmission fluid level.

Frequently, a low, growling type noise may appear because of low transmission fluid level.

Driving with low transmission fluid, will cause all kinds of transmission trouble later on. So start there, if necessary.

Low transmission fluid is a common source of manual transmission noise.

2. Transmission Makes a Noise When I Step on the Clutch Pedal

If the noise happens only when you depress the clutch pedal to change gears, the noise is probably coming from the release bearing in the clutch assembly, not the transmission itself.

3. Transmission Makes a Noise When I Let Off the Clutch Pedal

If the noise happens when you are letting your foot off the clutch pedal after engaging a gear and the car begins to move, probably the pilot bearing or bushing in the clutch assembly is faulty.

Watch the next video and see if you can hear the noise, possibly coming from the clutch assembly, when the driver releases the clutch pedal (engages the clutch).

4. Transmission Makes a Grinding Noise When Shifting Gears

Clash between gears may come from:

  • Low transmission fluid.
  • Transmission linkage worn, binding, or in need of adjustment.
  • A dragging clutch. When this happens, you may notice the grinding more pronounced when shifting from neutral into any gear. This may come from a linkage that binds, or that has a bent or broken component.
  • Worn or damaged internal transmission components can also cause a grinding noise, like synchronizers blocking rings, shift forks, and bearings.

A dragging clutch may cause noise when shifting gears.
A dragging clutch may cause noise when shifting gears. | Source

5. Transmission Makes a Humming Noise

The most common source for humming or whirring transmission noises is low fluid level or fluid contaminated with metal shavings.

Humming noise in all gears:

There could be a problem with a worn or damaged shaft, shaft end play spacer, or a bearing.

Worn transmission bearings are a frequent cause of transmission noise.
Worn transmission bearings are a frequent cause of transmission noise. | Source

6. Transmission Growls Except in Fourth Gear

This usually applies to transmissions, not to transaxles. In a transmission, fourth gear is commonly direct drive. When you are in direct drive, the input and output shaft provide direct rotational flow.

In this context, the growling sound may come from the output shaft pilot roller bearing. This may be the rear bearing for the input shaft, which supports the front of the output shaft.

7. Transmission Makes a Grinding Noise While Moving

This type of noise usually comes from a bad input shaft bearing. You may hear the noise in any gear, in any engine speed.

Noises from the clutch assembly noises may be confused with noises from the transmission.
Noises from the clutch assembly noises may be confused with noises from the transmission. | Source

8. Transmission Makes a Growling Noise in Neutral

This rough, growling noise happens with the engine running, the transmission in neutral, and the clutch engaged.

  • On a transmission, this could mean:

    • worn or damaged bearings on a countershaft, countergear, or input shaft.
  • On a transaxle, this could mean:

    • input shaft front or rear bearings worn or damaged

Initially, you may only hear the growling noise, but it can get worse over time. If so, the bearing may eventually fail.

9. Transmission Makes a Growling Noise in Forward and Reverse Gears But Not in Neutral

Possibly the fault is in the output shaft bearings.

10. Transmission Makes a Growling Noise While Car is Moving

This noise is usually heard in any gear while the car is moving.

  • On a transmission, this could mean:

    • Worn or damaged output shaft rear bearing.
  • On a transaxle, this could mean:

    • Worn or damaged output shaft rear or front bearings.

Worn or broken transmission gears can cause noise as well.
Worn or broken transmission gears can cause noise as well. | Source

11. Transmission Makes a Clicking Noise

The clicking noise may happen in any gear range.

  • On a transmission, this could mean worn or damaged teeth on a:

    • countergear or cluster gear assembly
    • output shaft gear
  • On a transaxle, this could mean damaged teeth on the:

    • input shaft gear

Worn gears may not represent a real or immediate problem. However, if a broken piece is moving around between gears and other components, it can cause more damage.

12. Preventing Manual Transmission Noise

Sometimes, noises can give you a clue about what is going on with your transmission. Pretty much, though, a noise is either a warning sign or an indication of impending failure.

The best way to deal with these type of transmission issues is not to allow them to happen in the first place.

There are three main things you can do to keep your transmission quiet:

  • Check the transmission fluid as necessary, and as recommended by your car manufacturer.
  • Change the transmission fluid as recommended.
  • Use only the correct fluid for your application.
  • Take a look under the car when you suspect fluid leaks.
  • Don't abuse your transmission.

Although you can't prevent your transmission from wearing away, following these suggestions can help your transmission age gracefully and have a good long service life.

Use the correct transmission fluid for your application.
Use the correct transmission fluid for your application. | Source

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

Questions & Answers

  • What causes popping noise in transmission when trying to move?

    Check the motor and transmission mounts. Also, a faulty axle can cause this popping noise sometimes.

© 2019 Dan Ferrell

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