Diagnosing Symptoms of a Bad Manual Transmission

Updated on July 18, 2017
Dan Ferrell profile image

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

Manual transmissions can develop problems after miles of service.
Manual transmissions can develop problems after miles of service. | Source

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.

  1. Odd sounds (whirring, squealing, bumping, or thumping)
  2. Grinding noise
  3. Transmission jumps out of gear (into neutral)
  4. Difficulty shifting gears
  5. Car stuck in one gear
  6. Car that can't get into gear
  7. 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.

Your noise may not be coming from the transmission; a bad CV joint can produce noises when you accelerate or make a turn.
Your noise may not be coming from the transmission; a bad CV joint can produce noises when you accelerate or make a turn. | Source

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.

  1. 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.
  2. 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.
  3. 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.

A bad synchronizer can cause a grinding noise.
A bad synchronizer can cause a grinding noise. | Source

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.

Shift linkage problems can cause your transmission to jump out of gear.
Shift linkage problems can cause your transmission to jump out of gear. | Source

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.

A worn out shift fork can make it hard to shift gears.
A worn out shift fork can make it hard to shift gears. | Source

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 wrong type of oil)
  • Misaligned transmission
  • Synchronizer problems

Low oil level can prevent gears' free travel.
Low oil level can prevent gears' free travel. | Source

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 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.

Inspect gaskets, seals, or loose bolts when looking for oil leaks.
Inspect gaskets, seals, or loose bolts when looking for oil leaks. | Source

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.

Questions & Answers

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    • Dan Ferrell profile imageAUTHOR

      Dan Ferrell 

      12 days ago

      Hi Chris,

      Make sure you got the rigth slave for the applicaton, and check the master cylinder. Usually both are replaced at the same time when one goes. Make sure you don't have a leak, probably a seal.

      Hope this helps.

    • profile image

      Chris martin 

      12 days ago

      Bought son 2013 dodge dart w 6speed Manuel, C635 im told, installed new slave, whent to bleed and realized no fluid getting to slave, just very small sauirts when you push pedal w hand, master is located near bottom of wall, how do i get fluid through it to the slave?? Then i realized the slave dont even have a bledder screw, jist a 1/4" nipple w rubber tip on it, alot money and time invested, dealers wont help and no parts store either, need halp bad please. College jyst started back, he really needs it. God bless.

    • profile image

      Dirtclustit 

      6 weeks ago

      @ Harold

      It sounds like you are referring to an automatic tranny (mention of putting the tranny in "park")

      This article is about manual transmissions, however your problem sounds like either a bad boost valve, broken sun shell, or band

    • Dan Ferrell profile imageAUTHOR

      Dan Ferrell 

      3 months ago

      Hi Finn,

      There could be some problems (damage?) with the high spining input shaft gears. Other then dissassembling the transmision for inspection, you may want to try drainig the oil and see if there are any metal falkes that may indicate wear or damage to some gears.

      Hope this helps

      Good luck

    • profile image

      Finn 

      3 months ago

      My car wont change into gear at high rpm. I move the shifter into position but it wont engage the gear and just stays in nuetral. When i drop back down to say below 4500rpm i have no problem other than second which takes a little while to come right. I have no problems while the car is in any gear only while trying to shift. Car is a 1999 toyota caldina gt-t 4wd turbo.

    • Dan Ferrell profile imageAUTHOR

      Dan Ferrell 

      3 months ago

      Hi Harold,

      If both transmissions seemed to have the same or very similar problem, double check the linkage. Also, there could be a problem with the gearshift lever (worn or damaged ) you may need to replace it.

      Good luck

    • profile image

      Harold 

      3 months ago

      I sent a question at the top where it says ask but didn't seem to go through. A Chevy 4×4 Silverado has has two rebuilt trans in it within a month. It has all gears working yet no reverse and no noise. Any suggestions. I also noticed shift linkage not right as it's only going as far as second to park. Any idea's. Something is telling me it's asimple fix. Thanks

    • Dan Ferrell profile imageAUTHOR

      Dan Ferrell 

      4 months ago

      Hi Wendy,

      The pilot bearing supports the front end of the transmission input shaft and keeps the crankshaft aligned. The shaft splines to the clutch disc to transfer engine power to the transmission. If the bearing is damaged, it's possible other components like the clutch and some in the gearbox are as well. But it's a good idea to get a second, and sometimes a third opinion to make sure you are only replacing what it's damaged. Some shops may be able to recondition the gearbox, if necessary.

      Good luck

    • profile image

      wendy 

      4 months ago

      we have a honda crv 2003 and the pilot bearing went the mechanic said we need to replace the clutch kit and a gearbox is this correct.

    • Dan Ferrell profile imageAUTHOR

      Dan Ferrell 

      5 months ago

      Hi JR

      Assuming the transmission was the original, there could've been some wear, but you might not know how the previous owner driving style. There can be several reassons for the transmission to slip out of gear, and preventing a shift into 3rd gear - damage or wear to gearshift internal linkage or shift rail assembly, sift rail detent plugner, a broke spring; gearshif lever, synchronizer sleeves or hubs damaged or worn. Ask your mechanic to see if he can detect any damaged (potential abuse) or wear on these items; and look at the condition of the lining on the clutch - signs of overheating - brittle spots, shattering.

      Good luck

    • profile image

      Jerry Robins jr 

      5 months ago

      Good day Dan

      If you have the time I would like to see what your opinion is on my current situation. I have a 2011 Camaro RS v6 manual transmission I purchased the vehicle almost a year ago and at the time I noticed that it was having some issues going into 3rd gear. I informed the dealer they looked at and said it was nothing!!!!!! Now it's in the shop and it will not even go in 3rd gear and slipping out of gear as well. At the time of purchase I did get the extended warranty that covers everything (I thought). They sent out someone to look at the failed part but what do you know he decided it to be because of the way I drive the car. I need to know what to look for when there is a failure part or abused driving cause I am having them send another adjuster and I want to be there. Thanks for your time.

    • Dan Ferrell profile imageAUTHOR

      Dan Ferrell 

      8 months ago

      Hi Tyler

      Assuming that everything was working fine earlier and only a worn out pressure plate-clutch was the issue, have you checked for a miss-adjusted shift linkage? Is the transmission correctly aligned? Oil level correct?

      Good luck

    • profile image

      Tyler 

      8 months ago

      Hi I'm working for a rather small towing yard and we do most repairs here at the shop. Our main mechanic just quit and they are now asking me to attempt to fix our service truck. But I am having trouble finding the issue. I have replaced the clutch pressure plate and slave cylinder but it still will not shifting when running. With the clutch pressed in trying to shift into any gear the truck starts creeping in the direction the gear carries it. Any help would be greatly appreciated

    • Dan Ferrell profile imageAUTHOR

      Dan Ferrell 

      13 months ago

      Hi H,

      Glad to hear you had a spare. Thanks for stopping by.

      Good luck

    • Hippie2000 profile image

      Hippie Untiet 

      14 months ago from Wisconsin

      Yeah I had a vibration coming from the from the front of my SM465. Turns out the needle bearings on pilot were gone. And it mushroomed the input shaft. I was happy just to have a spare SM465 to replace it. Now I have time to rebuild the old one and replace that shaft.

      So new clutch, new slave cylinder (I like the old rod and spring version better though) and replaced trans. Had it back on the road by night fall and readly to pull heavy hay wagons in the morning.

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