Automatic Transmission Grinding Noise When Put In Gear

An automatic transmission has many moving parts that all need to play together in a mechanical symphony to go into gear and switch through gears as it shifts up and down. This is usually a relatively silent process. So, when you start hearing grinding noises when you put it into gear or as it shifts up or down, it’s a sure sign that something is wrong inside the transmission itself.

This could be as seemingly simple as low or old transmission fluid losing its lubricating properties. However, some grinding noises when going into gear can be from a more serious mechanical fault, such as a bad torque converter.

To figure out why your automatic transmission is making a grinding noise when you put it into gear and how you might be able to fix it without an astronomical repair bill, we need to shift our focus to other symptoms to clue us in.

How Does An Automatic Transmission Go Into Gear

When you put your foot on the brake and move the gear selector on an automatic transmission from Park or Neutral into Drive or Reverse it, the TCM (Transmission Control Module) sends an electronic signal to shift solenoid A, which also affects the fluid pressure in the valve body. This hydraulic pressure activates the clutch packs and bands that shift the gears.

At this point, the forward clutch engages while simultaneously locking the input ring gear or the input sun gear to the input shaft. Then, the transmission goes into first gear. At this point, the shift solenoids and valve bodies continue to respond to the signals sent by the TCM to activate clutch packs and bands, shifting gears up or down the tree according to the RPMs and the driving conditions.

Common Reasons Why a Transmission Grinds When Putting It In Gear

The most common reason a transmission makes a grinding noise when you put it in gear is low transmission fluid or degraded/contaminated transmission fluid. However, there are undoubtedly other mechanical faults that could be causing the grinding sound, such as a worn-out shift linkage or a worn-out torque converter.

1. Low Transmission Fluid

Low Transmission Fluid

Low transmission fluid makes it hard for the valve body to smoothly engage the clutch packs and bands while also robbing the gears of the lubrication they need, causing a grinding or whining noise as the first gear engages. This is usually accompanied by hard shifts into second gear where the engine revs high for a long time before the gear finally catches.

If the transmission fluid is severely low, it might grind going into first gear, travel a few hundred feet, and then suddenly slip out of gear when the valve body can’t maintain sufficient pressure. Low fluid can eventually cause the transmission to overheat, which is more likely in stop-and-go commuter traffic.

How to Diagnose Low Transmission Fluid

Finding out if it’s low transmission fluid is as easy as checking the dipstick when the transmission is warm. However, if your car has a sealed transmission without a dipstick, you’ll have to check it via the inspection plug.

How to Fix Low Transmission Fluid

If your transmission is making a grinding noise due to low transmission fluid, the easy answer seems to be to add more. You can do this in small doses while the transmission is warm until it reaches the correct level.

The problem is that automatic transmissions don’t use or burn transmission fluid. They’re engineered to be sealed systems. This means you leak somewhere, and finding it can be tricky.

The most common places you’ll find a transmission leak include:

  • The pan gasket
  • A puncture or crack in the oil pan
  • The O-ring on the dipstick spout
  • The transmission lines to and from the radiator
  • A crack in the housing
  • A leak in the seal with the torque converter bell housing
  • A leak in the axle seals

Unfortunately, most of these leaks need to be handled by a professional mechanic. This could be as simple as replacing the pan gasket or replacing a leak in a transmission line, which will only set you back $100 or so.

If it’s a more serious leak, such as the seal with the torque converter or a leak in one of the axle seals, the floor for the repair cost will start at $300 and go up from there. These more serious leaks are usually best handled by a transmission specialist rather than an everyday mechanic.

2. Degraded or Contaminated Transmission Fluid

Degraded or Contaminated Transmission Fluid

Transmission fluid that’s lost its lubricating properties as it degrades or has become contaminated with debris can also cause an automatic transmission’s gear to grind when shifting gears. This first starts to show up when putting the car in first gear (Drive) or reverse when the load on the gear is the heaviest. However, you’ll gradually notice the grinding noises when it shifts into second and third gear.

When you check your transmission fluid, and it looks dark or smells like burned rubber, it’s a sure sign that it’s started to degrade. Though the even bigger concern here is if you see debris or fine particles suspended in it, which is a sign that a leak or something is allowing outside material into the system.

Fine metal flakes suspended in the fluid are also a serious worry. This is a sign that the grinding of the gears is causing untold internal damage, and the car needs to be parked to prevent more serious problems.

If the fluid is dark but has no signs of contamination, it might just be that it’s gotten old, or you might have unknowingly overheated the transmission recently. If you’ve been doing a lot of towing or stop-and-go driving, the excess strain and heat on the transmission could have caused the fluid to break down.

How to Fix Degraded/Contaminated Transmission Fluid

If your transmission fluid is degraded, you need a complete flush and fill.

If you’re a reasonably capable DIY mechanic, you can do this on your own for around $100 or so. It will consume much of your Saturday afternoon but save you another $100 to $150 on a mechanic’s labor time.

If your transmission fluid is contaminated and/or you see metal flecks suspended in it, you’ll still need a complete flush and fill. The wise move here is to take it to a transmission specialist. They’ll diagnose what caused it. They can also assess if the internal gears and mechanical components have been compromised and must be fixed.

However, these repairs are often expensive, as most transmission specialists will charge you $300 or more to open the transmission case. The repair bill then starts to skyrocket further if the sun, ring, or planetary gears need to be replaced.

In this scenario, you can expect a partial transmission rebuild to set you back at least $2,000 to $2,500.

How to Prevent Degraded/Contaminated Transmission Fluid

Routinely changing your transmission fluid every 30,000 to 50,000 miles or, according to the manufacturer’s specs, will help prevent degradation. However, it would help if you were also mindful not to overheat your transmission, which can also rapidly degrade the fluid.

If you do a lot of stop-and-go driving or frequently tow within 80% of the maximum tow rating for your car, you might want to consider installing a transmission radiator. It’s a separate device that augments the transmission lines’ cooling to and from the radiator.

3. A Clogged Transmission Filter

A Clogged Transmission Filter

A transmission filter that clogs over time or particulate matter can make it hard for the gears to get the proper lubrication they need, causing them to grind in the low-end gears like first and reverse. You might even find the car grinding into first gear and traveling ways before mysteriously slipping back into neutral even though you have the gear selector in Drive.

In a scenario like this, you might check the transmission fluid only to find it looks full on the dipstick. Yet it acts just like the transmission fluid is low because sufficient fluid can’t make it from the oil pan through the filter to the valve body and the gears.

How to Fix a Clogged Transmission Filter

Fixing a clogged transmission filter is usually part of changing the transmission fluid. Though chances are good, there’s probably a bunch of silt or lingering particulate matter sitting in the oil pan itself.

The wise move here is to take the pan off as part of a complete transmission fluid flush and fill, especially if you’ve gone over the manufacturer’s recommendations for replacing the fluid.

However, one thing to be careful with is putting the pan gasket back on. If you over-tighten the bolts, it can deform the flange. You’ll end up trading a clogged transmission filter for a transmission leak that leads to low fluid symptoms.

4. Bad Transmission or Engine Mounts

If the support structure provided by a transmission or engine mount fails, the deviation in the relationship between the input shaft and the output shaft can cause a grinding noise when the transmission goes into gear. This will be more pronounced in the lower gears at first, but as the mount degrades, you’ll likely hear grinding noises and clunking sounds throughout all the gears.

A bad transmission mount will also transmit vibration to the steering wheel or the gear selector. You might have the engine running in the park or neutral, and everything feels normal. Then, when you put it in Drive or Reverse, the steering wheel starts shaking with the force of the transmission engagement.

They’re just robust pieces of heavy-duty rubber with metal fastener hardware.

How to Fix Bad Transmission or Engine Mounts

If you’re a capable DIY mechanic with the right tools, you might be able to replace your own transmission or engine mounts. However, you’ll need to get creative with jacks to support the transmission. You need to be extra smart about safety, and it’s wise to find a way to block the car off.

The part cost for new transmission mounts is usually less than $40 each. However, if you have one that’s bad, you might as well replace them all.

If you’re uncomfortable with jacking up the transmission or feel like replacing the mounts is beyond your skill level, there’s no shame in having a mechanic do it.

A mechanic’s labor costs usually add another $50 to $75 per mount to the final repair bill.

5. A Torque Converter Problem

A Torque Converter Problem

Any time there’s a problem with the torque converter, there will be a problem transferring power from the engine to the rest of the transmission, which can cause delayed gear changes with grinding noises. In a scenario like this, the transmission will often hesitate to shift gears, or it might make an overly loud clunk after grinding as it slips into gear when the engine is revving too high.

If the disparity between the torque converter and the engine’s RPMs is too high, the car might finally grind into gear and then suddenly stall. You’ll probably also notice that the car feels down on power, even though the engine seems to be running properly. Many torque converter problems will also cause transmission fluid leaks at the seal where the bell housing joins to the transmission housing.

Sometimes, a bad torque converter will trigger a transmission or check engine warning light. When it does, it will throw a code you can read.

  • Code P0740 is a blanket code for Torque Converter Clutch Circuit Malfunction.
  • Code P0741 is for the Torque Converter Clutch Circuit Performance stuck-off.

How to Fix a Bad Torque Converter

There isn’t a good way to tear into a torque converter and repair it. When you have a torque converter problem, the wise move is to replace it as soon as possible. The longer you let the shifting problems persist, the more likely you will suffer damage to other sensitive transmission components.

The good news is that the torque converter is separate and can be replaced without the horrendous costs of opening the transmission housing. This is a job that calls for a transmission specialist.

The part cost for a new torque converter can range wildly from $175 to $500, with a real-world average of around $225.

Having a transmission specialist install the new torque converter will add another $225 to $375 to a final repair bill of around $450 to $600.

6. A Dirty or Clogged Valve Body

A Dirty or Clogged Valve Body

If dirt or contaminants have made it into the transmission’s valve body, it won’t be able to rapidly divert fluid pressure, causing delayed activation in the clutch pack leading to grinding noises as first gear or reverse finally engages. Problems with a transmission’s valve body tend to show up early in the low gears where the most pressure and force transfer is called for. In time, you’ll start to notice hesitation in all the gear changes.

In short order, you’ll probably also notice things like the RPMs jumping up when the transmission shifts up. Gears can start slipping and/or clunking as they engage. The grinding noise persists as clutch packs and bands fail to keep up with the lag in demand.

Since the valve body works with the TCM to act as the “Brain” of the transmission, you’ll eventually get a check engine or transmission warning light. When you do, it might throw one of the following codes.

  • Code P0700 is a blanket code for a transmission problem and will occur in conjunction with pretty much any valve body problem.
  • Code P0783 means the PCM has detected an irregular signal from the transmission’s input/turbine speed sensor.
  • Codes P2707, P0829, &P0751 are codes for a problem with the various shift solenoids. If you get more than one of these codes, it could be an issue with the valve body affecting the performance of the entire shift solenoid pack.

How to Fix a Bad Transmission Valve Body

The average DIY mechanic cannot clean or replace a transmission valve body. It’s probably best to bring it to a transmission specialist. However, the good news is that with most models, you don’t have to completely open up the transmission housing, which always adds a ton of labor costs.

If it’s just that the valve body is clogged or part of it is obstructed by particulate material due to something like contaminated transmission fluid, the transmission specialist might be able to clean it without replacing it.

The labor to have the valve body cleaned and tested will cost you between $250 and $500, with a real-world average of around $350.

If the transmission valve body is severely clogged or physically damaged, the wisest move is to have it replaced.

The part cost for a new transmission valve body will run you between $275 to $600, with the real-world average being around $400 for most domestic models.

The labor cost to have a transmission specialist install the new valve body will add another $250 to $500 to a final bill of $425 to $1,000.

7. A Worn-Out Transmission Pump

Transmission Pump

If the transmission pump is worn out or dying, it won’t be able to effectively circulate the lubricating transmission fluid, leading to grinding noises from excess friction between the moving parts. Since first gear and reverse bear the most force, you tend to hear the grinding noise the loudest when you first put it into gear.

As the transmission pump continues to die, you’ll also start hearing whirring and whining noises. The grinding sound will also be prevalent at every gear change until it’s constant whenever the car moves. You’ll probably also notice a massive lag in acceleration, and the transmission will start to overheat in stop-and-go driving.

How to Fix a Worn-Out Transmission Pump

Replacing a transmission pump is another one of those repairs that’s beyond what a DIY mechanic can handle. You’ll need a transmission specialist. However, some models won’t have to open the transmission case itself completely. They might be able to open the bell housing to pull out the old pump and install a new one.

The part cost for just the transmission pump will only cost you around $160 to $350. However, some foreign and exotic models might cost more.

The labor cost to replace it will easily add another $300 to $500 to the final repair bill.

NOTE

Another big problem is that when the transmission pump goes out, it often puts so much strain on the torque converter that it’s also compromised. Since the mechanic likely already has to take the bell housing off to replace the transmission pump, replacing the torque converter might also make sense.

8. Worn-Down Gear Teeth

Worn-Down Gear Teeth

Worn-down teeth on the sun, ring, or planetary gears can easily cause a grinding noise, which is most prominent in first gear and/or reverse. This is when the gears are first engaging, and the stresses on the gear teeth are the highest, causing them to grind and slip.

In a scenario like this, you’ll usually see a lot of metal flakes suspended in the transmission fluid from tiny bits of the gears wearing off. Overall transmission performance will also be sloppy, with the car feeling like it’s down on power. Depending on how severe the wear and tear is, the transmission might slip when accelerating.

How to Fix Worn-Down Gear Teeth

This is a worst-case scenario for a problem like this, as you’ll need at least a partial rebuild from a transmission specialist. This will automatically tack $350 to $500 onto the repair bill to have them open the transmission housing to inspect the damage to the teeth.

The part cost of a partial or complete rebuild can vary wildly. Sometimes, having them completely replace the transmission makes more sense, so you’re starting from a clean slate. The costs are often the same, ranging from $2,500 to $5,000 depending on the make and model.

If your car is over ten years old, and the engine has at least another 50,000 miles of life left on it, it might make sense to have them do a partial rebuild. If your car is less than ten years old and you plan to drive it for a long time, the clean slate of installing a new transmission might make more sense.

Frequently Asked Questions

How Often Should I Check My Transmission Fluid?

You should check your transmission fluid at least once a month, as the state of the fluid might help you catch a problem in the early days. If the fluid looks dark, has debris floating in it, or you see metal flecks in the oil, you might be able to correct the problem before the transmission suffers more damage.

Why Does My Transmission Grind Most in Drive and Reverse?

Drive and reverse are the two gears where the transmission is under the most load. It’s also the point where the transmission is engaging. Fluid pressures change in the valve body, clutch packs activate, and gear teeth start making contact. The shift to higher gears tends to be smoother, and the torque converter often requires more assistance.

Conclusion

If you’re lucky, your transmission makes a grinding noise when going into gear because of low-end transmission fluid or a partially clogged transmission oil filter. These problems can usually be addressed by a reasonably cheap transmission flush and fill. Then, you might also need to chase down and repair a hidden leak.

If the grinding noise when putting it into gear is due to a physical defect or a bad motor mount, you might get away with a cheap repair bill.

From there, the potential reasons your transmission is grinding when you put it in gear are expensive and usually require a transmission specialist to confirm and complete the repair. If you’re lucky, this might call for replacing a clogged valve body or replacing the torque converter completely.

If you’ve got buzzard luck and see metal flecks in the transmission fluid due to grinding gears, you’ll have to shoulder the massive cost of opening the transmission housing. Depending on the car’s age, completely replacing the transmission might make more sense here than a partial rebuild.

Jason Farrell

Written By

Jason Farrell

Jason Farrell is a certified master technician, the editor of Mechanic’s Diary in Pittsburgh, Pennsylvania. He is ASE (Automotive Service Excellence) certified and earned a Bachelor’s Degree in Automotive Technology from Pittsburg State University. With nearly 18 prior years of experience in the automotive field, he has extensive knowledge about Domestic, European, and other foreign makes and models of cars and light trucks. Jason’s experience working as a technician and service manager at dealerships, gave him the experience and know-how of most aspects of inspection, diagnosis, and repair from engine and drivability to electrical, HVAC, brakes, steering and suspension and everything in between.

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