Diagnosing Symptoms of a Bad Manual Transmission
Manual transmission problems can develop due to high mileage, abuse, or lack of proper maintenance. But they are rather rare. Most manual transmission issues originate not with the transmission itself, but from related components like the clutch assembly, linkage, or driveline: the components that transmit turning power from the transmission to the wheels. Also, as we discuss below, symptoms that seem to be coming from the transmission can come from unrelated parts of the car.
The key to diagnosing your manual transmission problem is to gather detailed information about the particular problem. For example, does the problem appear in only one of the gears, only at a certain speed, only when turning, only when downshifting, or after having serviced the clutch or another transmission component? Can you feel a vibration? Can you hear a clunking or grinding noise?
Symptoms of a Bad Transmission
Here are some symptoms that can indicate a worn-out transmission, each one of which we discuss below.
- Odd sounds (whirring, squealing, bumping, or thumping)
- Grinding noise
- Transmission jumps out of gear (into neutral)
- Difficulty shifting gears
- Car stuck in one gear
- Car that can't get into gear
- Leaking transmission oil
This guide will get you started on identifying the source of these problems. You'll need to investigate further and remember that manual transmission configurations can change from one model to the next.
Remember that this guide only deals with symptoms coming from the manual transmission (or transaxle) itself. Some symptoms that may appear to originate in the transmission actually come from the clutch (or another system), and vice versa. To get a more accurate diagnosis, take a look at the Bad Clutch Symptoms guide as well.
1. Odd Noises That May Come From the Transmission
The most common cause of a noisy transmission is insufficient oil, causing the gears or internal assembly to hum or whir. If a noisy transmission does have enough oil, the lubricant may be contaminated with metal shavings or particles.
Insufficient or contaminated oil may cause the transmission to become noisy in some or all of the gears. But if you hear noises in a specific gear, that gear's teeth or synchronizer may be worn or damaged.
Sources inside the transmission that can cause noise:
- A worn-out synchronizer
- The gears on the speedometer drive
- Misaligned transmission
- A worn or damaged input shaft bearing, if your transmission makes noises only in neutral (sometimes a bumping sound)
- Worn-out gears
- Output shaft pilot bearing problems
- Metal shavings in the oil
Sources outside the transmission that can cause noise:
Some noises that seem to come from the transmission are actually coming from an outside though possibly related source. For example, if you hear a thumping noise when you accelerate or decelerate, check first for these problems before you blame the transmission:
- A loose or damaged engine or transmission mount
- A worn or damaged drive axle inner CV joint
- Problems with the differential case
Noises that manifest when turning could point to a problem with the CV joint. Knocking noises when driving at low speeds could come from the differential case or the CV joint.
A Three-Step Test for Transmission Bearing Noises
That noise you keep hearing may come from a bearing. This three-step test is simple and can reveal problems with one or more transmission bearings.
- Fire up the engine and set the transmission to neutral. If you can hear a noise in neutral, suspect a worn-out input shaft bearing. Watch the video at the bottom of this article to see how internal problems can affect input shaft operation.
- Now, with the engine running, depress the clutch pedal just enough to remove the free play, to the point where you feel you need to apply force to the pedal to push it down further. You may need to push the pedal a little more. If you hear a squealing noise, you may have a worn out release bearing.
- Fully depress the clutch pedal to release the clutch. If you hear a whirring sound then, you probably are dealing with a bad pilot bearing.
2. The Transmission Makes a Grinding Noise
Problems with the transmission can also be revealed through a grinding noise.
A grinding noise may come from clashing gears. The clashing may happen because of linkage problems like wear or need of adjustment.
Other potential sources could be a worn or damaged synchronizer, shift fork, or rail and bearing shafts.
If you can hear the gears clashing only when downshifting, the problem may come from the synchronizer (too much play at the output shaft end).
However, a grinding noise may also come from a dragging clutch.
3. The Transmission Jumps Into Neutral
This seems to be a common problem on worn-out transmissions. You shift into gear, and the transmission jumps out of gear.
Once again, there could be other several causes for this problem, besides a worn-out transmission:
- A common problem is a worn out, stretched, or maladjusted shift linkage. A stretched linkage can be caused by a damaged engine or transmission mount. An external linkage can wear out or become loose and maladjusted, causing the transmission to jump out of gear. Look for rust and binding. You can try to adjust the linkage. But in most cases, you'll have to rebuild or replace that part of the assembly.
- You may be dealing with a weak or broken spring in the shift rail. In an internal shift linkage, the spring is part of the spring-loaded ball that locks the transmission into gear. If the ball slips out of the notch, the transmission will jump out of gear.
- Also, you may be dealing with a worn-out pilot bearing (the gap causes the input shaft to vibrate, which causes the shift forks or synchronizers to move).
- You may have problems with a worn synchronizer or shift fork assembly or other internal components.
Other potential causes to keep in mind:
- Loose or misaligned transmission (possibly after service)
- Misaligned clutch housing
- Loose shifter cover
- Worn-out gear teeth
Note: When the transmission only jumps out of a high gear, check the clutch housing bolts for tightness, or the transmission for misalignment.
4. It's Hard to Shift Gears
This problem happens when you find it hard to move the shift lever from one gear to another. Usually, this points to a problem with a loose linkage, worn shift cables or worn bearings.
Check the linkage. You may need to raise the vehicle and safely support it on jack stands or remove a component in order to make the inspection, depending on your vehicle model. You may need to remove a shift lever boot.
Get the help of an assistant to operate the linkage while you inspect the linkage, if necessary. Look for problems like binding, poor lubrication, misaligned components.
To remove components for inspection, consult your vehicle repair manual. Haynes is a good aftermarket manual: get the manual for your exact model.
Other causes for a hard-to-shift manual transmission include:
- Worn or loose internal components (shift fork, levers, shafts)
- Low oil level (or the wrong type of oil)
- Misaligned transmission
- Synchronizer problems
5. The Transmission Is Stuck in Gear
You may find that you can't get the transmission out of gear. This symptom may indicate:
- Low oil level or the wrong type of oil
- Problems with the linkage or shifter assembly. Look for maladjustment, or wear or damage to rods, bushings, or shifter arms.
- Internal components: shift rail, detents, forks or a stuck synchronizer sleeve
- Worn-out or broken drive gear teeth
- A stuck shift rail
- Misaligned transmission
6. The Transmission Won't Get Into Gear
When you have trouble getting the transmission into gear, inspect the shift linkage for adjustment, looseness or damage.
However, remember that failure to get into gear can also be caused by the clutch, if the clutch isn't fully releasing or has other problems. The clutch might need adjustment. Check my article on bad clutches. Also, consult your vehicle repair manual.
7. Leak From the Transmission
Manual transmission leaks can be caused by:
- bad or worn-out seals or gaskets,
- a damaged case or component,
- or even loose bolts.
To verify that a leak exists, first, check the transmission case and oil level. If it leaks after you just replaced the oil, you may have put too much. Consult your vehicle repair manual.
Locate the source of the leak. Inspect the transmission oil seal and the O-ring in the vehicle speed sensor.
Consult your vehicle repair manual for the proper procedure to replace seals, bearings, or gaskets. Some of these repairs don't require much work, and you may be able to do the job in your own garage with a few common tools.
Knowing about common manual transmission problems can help you diagnose your problems sooner, and possibly save money. This guide helps you identify and explore those common and not-so-common areas. Still, manual transmissions vary between models, so once you have an idea of the possible problem with your transmission, consult your model's vehicle repair manual to troubleshoot that particular issue. You may be able, in some cases, to do the repair yourself.
This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.
Questions & Answers
There is a clunking noise coming from the right side axle. And when I jack up the car, put it in gear with the motor running only the left wheel turns. What could be the problem?
The CV joint (the part of the axle that slides into the splined hub on the wheel) is probably busted.Helpful 2
Why has my 99 Nissan Frontier lost 4th gear?
There could be several reasons for this, like a damaged synchronizer sleeves or hubs; a worn gearshift lever; a problem with the shift rail or internal linkage; or a worn shift rail detent plunger (something like this: https://www.youtube.com/watch?v=H48OY-QYYSU).Helpful 1
My 2008 Chevrolet Cobalt is having problems going into first and second gear. It will start in 3rd, slowly, and not a huge deal but as a woman, I now have callouses on my right-hand pads from trying to get it into gear (first and second gear- reverse at times, but mostly when it is cold). No grinding noises or any other abnormal noises. Is it the clutch or transmission? Perhaps something else?
The problem might be in the fluid. Make sure there's enough fluid and in good condition. Another possibility is the synchronizer assembly. This will require a better diagnostic before committing to any major transmission work.
My 2011 Camaro is a V6 manual transmission but when the engine is running it will not shift into first. But, if started in first the car creeps forward; I've been using second for now. What could the issue be?
This could be several things, cable in need of adjustment, leaking cylinder (hydraulic models), a linkage problem.Helpful 2
I have an 2008 Jeep Compass Limited 4x4 5 speed manual. My reverse gear will occasionally engage then jump to neutral. If I feather clutch to keep it from neutral it is jumpy like it’s missing teeth. I’m trying to figure out if that would be the idle gear or some other problem. All other gears work perfectly as well as the clutch. I let a friend learn to drive and he rev dumped neutral. What parts should I plan on ordering? This is my daily drive and want minimal downtime.
© 2017 Dan Ferrell