Transmission-Shifts-Hard-When-Hot
Auto Engines,  Auto Parts,  Cars

Why Is My Transmission Shifts Hard When Hot?

A vehicle's transmission is able to transfer power from the engine to the car's tires. Its main purpose  is to control the speed at which the tires turn. It controls the power that flows from engine to the driveshaft. This particular part of your car goes through quite a bit of stress just like many engine parts of the car. The stress is due to the friction and heat generated because of the movement of different components.

Transmissions shifts hard when hot because their parts tend to get damaged, worn, and malfunction under high heat levels. Your transmission needs fluid to keep cool and if the fluid leaks then it may create more heat and pressure. The fluid may thickens and get burnt, and then it no longer functions to cool and lubricate, making the transmission shift hard. 

There could be several reasons for hard shifting, but a hot transmission may be one of the leading causes. To finding out what problem you have with your transmission we'll take a look a some common issues that lead to higher levels of heat and pressure in a transmission. Avoiding replacing the transmission may be important to you because it is quite expensive.

Some of the Most Common Transmission Problems

1. Low or Leaking Fluid

Leaking-Fluid

Whenever there is a leak, it can start damaging the transmission. Leaking transmission fluid is among the most common reasons (heat) behind transmission breakdown. Automatic transmission fluid (ATF) cleans, lubricates and the seals the transmission.

Checking the fluid level regularly (unless you have a sealed transmission) and changing it when the owners manual says will help prevent problems later. If you suspect a leak, find where it is leaking from (possibly because of a damage seal) and get help fixing it or replace the damaged seal yourself.

Reduced amounts of transmission fluid (or not changing the fluid) can create unhealthy condition for your transmission. Look for dark/burnt fluid when checking the fluid levels. If the fluid is light brownish or dark brown/black, it needs to be replaced.

Try wiping the fluid on a white paper towel to see what color it is. If you notice a pinkish color, then it's still in good condition.

If you have a leak try to fix it right away. If the color is dark try to replace it right away.

(Warning: If your car ran with burnt transmission fluid or low fluid for a while damage probably occurred to the clutch, even if you never noticed it. Changing the transmission fluid will clean out particles that may have filled in the gaps of a worn out clutch. The clutch will then start to slip because the particles aren't there to help grip. You'll need to replace the clutch parts that are worn and anything else that may have be damaged.) 

So, it is recommended to fill or replace the transmission fluid when needed. Fix any leaks or damage using a professional, unless you've got the skills needed. 

2. The Slipping of Gears

gear

The automatic transmission makes use of a series of gears that help transfer the right amount of power for speed, climbing hills, and going in reverse. A gear set consists of multiple small gears. Usually is has a sun gear at the center and three planet gears around the sun gear, and a ring gear surround the planets.


As the transmission changes from one gear set to another, a shift is performed. The shift can be automatic or manual.


If the transmission slips, then the gears are not engaged. It may seem like your in neutral. The reason may be because of a worn clutch or low hydraulic pressure. To find out more, check issues we talked about reason 1 above. Also, avoid driving with a slipping clutch since accidents could occur.

3. Dragging Clutch

Dragging-Clutch

A dragging clutch occurs when the clutch disk wont separate all the way from the flywheel. Since it wont disengage, changing gears will not work. 

This may happen when pressing the clutch pedal and the cable going to the transmission has too much slack. Adjusting the cable can fix this issues. If the clutch disk can't move away from the flywheel, it will just continue to turn providing torque to the gear.

If you hear a grinding noise every time you change the gears, this may be a dragging clutch that disengages almost all the way, but not quite.

In some cars the clutch only starts to drag when the transmission gets hot. This too is a cable adjustment issue usually. To repair these issues is usually inexpensive unless damage has occurred. This quick fix involves adjusting the cable, so the clutch can separate. 

4. Transmission Noisy in Neutral

neutral

When a transmission is noisy in neutral it might be time to consult a mechanic. Some of the possible reasons could be the transmission lost fluid and ran hot, causing damage to the clutch, using the incorrect transmission fluid, worn out gears, or a bad release bearing. 


First check the fluid and refill/change/flush if needed. Test the transmission by taking it on a road test. Any noises? (See: article for more info)


Next, pull over and put the car in neutral. Keep the clutch pedal to the floor and listen for any noises. If you hear noises, the release bearing could be the problem. Now, release the clutch pedal and listen. If you still hear noise in neutral with the clutch pedal released then the shaft bearing may be the problem. 


Last, if adding the fluid doesn’t work, get a professional to take a look. It may need replacement clutch parts, bearings, or gears.

5. Burning Smell

smokey

The burning smell mostly arises when the transmission fluid overheats. Transmission fluid works by keeping the parts cooled and lubricated so that they don’t get damaged. The transmission generally gets hot if there's not enough fluid.

The result could be damage and higher friction. Build up of debris and burnt fluid sludge in the valve body can create clogs. Clogs can make shifting more problematic and getting into gear more difficult. Flushing your system may make things worse, since the new fluid will clean the sludge and too much will clog the valve body.  (See: Video)

Flushing is a good idea when you have burnt transmission fluid, just make sure the valve body is cleaned also. A mechanic may be needed to check out what's going on. 

6. Checking the Engine Light

Checking-the-Engine-Light

The check engine light which is located on car’s dashboard will tell you if there is something wrong with the engine or transmission.


There are many sensors all around the engine and these sensors inform the car's computer of any unusual activity. The sensors on transmission can sense the slightest vibrations and jerks that we can’t even feel. Another sensor monitors the heat of the transmission fluid. If you see the light flashing or on consistently on, take time to check your fluids.


See a mechanic or get an OBD2 scanner to check what the check engine light means.

7. Does not go into a Gear

a-Gears

Sometimes the car does seem to want to go into gear. You might try going into reverse or other gears, but the transmission doesn't seem to respond at all. 

There could be a number of reason for the car not going into gear. Here are some reasons:

  • The thickness of fluid can be incorrect. The hydraulic pressure need to be correct to shift gears.
  • The linkage of the clutch. Adjusting the cable/linkage that attaches to the clutch pedal may help.
  • Heat and low levels of transmission fluid can create shifting problems.


Using a OBD2 scanner can be helpful in identifying the reason for the shifting problems. It can help identify the root problem(s).

8. Grinding or Shaking

Most of the time our cars run smoothly without any jerking, shaking, or grinding noises. These issues may be due in part to a problems with the car's gears. 

If you have a manual transmission and you hear grinding noises as you shift, the gears could be damaged. Another reason for grinding could be the clutch is damaged and is having difficulty helping the car to shift into gear. Heat can cause damage to the gear synchronizers, or they may have worn out due to age. An adjustment or replacement of the clutch might resolve this issue. 

An automatic transmission acts differently. In this, it may not make a grinding noise, but it may take time to shift into gear when compared with normal operation. When the problem gets worse the transitions into the next gear becomes shaky and more jarring. 


Consult your mechanic to help with diagnosis if your unsure what is going on with your car. Worn gears or clutch might be the reason for the vibrations your feeling and noises your hearing.

9. Whining, Clunking and Humming

Mechanical-Transmission

Transmission shifts hard when hot, and the sound varies between different models. The sound that you hear may be a whining, humming or buzzing noise. How the transmission fluid acts under extreme heat is different than normal operating temperature. 


Higher temperatures means higher pressure and although transmission fluid works well at high pressure, the heat may start to cause the fluid to burn if pressure and heat are not relieved. Under high pressure, shifting may be more difficult, so noises may occur.   


The sounds generated by a manual transmission may be more mechanical, abrupt and louder sounding. When you shift a gear, a clunking sound may occur. The differential or constant velocity joints may also be the source of these sounds, if the clunking is coming from the underside of the car.

10. Lack of Response

Sometimes while driving a car, it does not go into gear right away. What should happen is the moment a car shifts from park into drive, it should go into the proper gear immediately. 


For automatic transmission vehicles, a delay when the vehicle is shifting is usually a transmission-based concern. In a manual transmissions, there may be a similar response, but after shifting into gear, the engine RPMs will surge. The car remains still but the engine continues to rev.


This means you may have a clogged valve body. The clutch may also not be engaging for some reason, possibly temperatures are too high.  Low pressure could also result in delays when shifting. 


Check your fluid levels and do a scan with your OBD2 scanner to see if there's anything showing up that's creating this issues. 

Conclusion: If you want to know about transmission maintenance see: this article