semi truck repair

Complete Semi Truck Transmission Repair Guide

July 13, 2022

Keep your semi-truck's transmission running smoothly and your truck on the road

Heavy-duty semi truck transmissions are built to last, but even the toughest gearboxes eventually need work or replacement. If you’re experiencing problems with your transmission, or an OEM defect, don’t panic. There are many qualified diesel technicians who can help get your truck back on the road asap. This semi truck transmission repair guide will teach you everything you need to know about diagnosing and repairing heavy duty transmissions.


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What causes a truck transmission repair, rebuild or even a complete transmission replacement?

You probably expect a lot from your heavy duty truck. After all, your truck is the vehicle that takes you across the highway to deliver on time to your customers. But over time, your truck will experience general wear and tear requiring repair and maintenance that all heavy duty trucks need.

Even when it comes to completing your heavy duty truck inspection, scheduling service for your truck on a regular basis is a good idea, but more on that later. Problems with transmissions are one of the most costly expenses that truck drivers must deal with. Long-haul trucks will typically require transmissions to be repaired or rebuilt and will require downtime at some point during the life of a truck.

Factors that cause a transmission repair, rebuild or replacement in a truck.

There are many factors that can cause a truck’s engine and parts to need repair, rebuild or even a complete transmission replacement. The most common reasons include:

  • General wear and tear
  • Manufacturer defect
  • Improper maintenance
  • Accidents or collisions
  • Overheating

Each of these causes can result in serious damage to your truck, requiring costly repairs, or in some cases, a complete replacement. Let’s take a closer look at each of these causes:

Wear and Tear:

The most common cause is simple wear and tear. Over time, the internal components of your transmission will begin to wear down, causing it to function less efficiently. This can lead to shifting problems, diminished fuel economy, and eventually, complete failure.

Manufacturer Defect:

Another common cause is manufacturer defects. In some cases, the transmission may be faulty from the factory, or it may develop problems over time due to a manufacturing defect. If you think your transmission may be defective, it’s important to have it checked out by a qualified technician as soon as possible.

Improper Maintenance:

Your truck is a complex piece of machinery, and it needs to be properly maintained in order to function correctly. Failure to change fluids on a regular basis can cause serious damage to the internal components of the transmission, leading to shifting problems, diminished fuel economy, and eventually complete failure.

Accidents or Collisions:

If your truck is involved in an accident, the impact can damage the internal components of the transmission, such as being able to shift correctly.


Overheating is another common cause. If the oil level gets low, or if the cooling system isn’t working properly, the transmission can overheat.


How do you know if there are issues with your heavy duty vehicle?

Low fluid levels or leaks can be signs of transmission trouble

Symptoms of Trouble

While you may not be able to predict when your tranny is causing you trouble, there are a few things you can consider to help determine if there is a problem with your heavy duty vehicle. Some key factors include checking the transmission fluid level, looking for abnormal noise, and monitoring the temperature of the transmission. If you notice any of these issues, it’s important to have your truck checked out by a qualified technician as soon as possible.


Is it possible for you to diagnose and even service or fix your engine? Maybe. You can consult a technical help page for troubleshooting tips. Depending on the transmission problems as well as the make and model of your truck, it might be something as simple as ordering replacement parts that you can install yourself. Or, it could be something more serious requiring a brand new transmission.

Common repairs and transmission parts

  • Replacing the fluid and filter
  • Replacing the torque converter
  • Rebuilding or replacing the transmission

Other transmission parts and semi truck transmission repair may include:

Faulty transfer cases

Transfer cases are crucial to your truck. Transfer cases are part of the drivetrain of four-wheel-drive, all-wheel-drive, and other multiple powered axle vehicles. If the transfer case is not transferring power from the engine via the transmission to the front and rear axles, it could cause the truck transmission to overheat or fail. One cause for transfer case failure could be low fluid level caused by a leak or lack of routine service. A symptom of a bad transfer case would be gear shifting troubles.


Clutches are an essential part of a transmission. It allows you to shift between gears and help channel the engine’s power to move the wheels of your vehicle. Signs of a bad clutch could be weak acceleration, grinding gears, a loose or sticky clutch pedal, and problems moving into gear or even staying in gear.


O-rings are small, circular seals that help keep liquids and gases from escaping various opening. These are often used to help keep the fluids inside while preventing leaks. A leak could be a sign of a faulty o-ring. But many o-ring kits are available online and in local stores where you can get quality parts.


Bearings are important because bearings support rotating shafts and decrease friction between moving parts. These are found throughout the transmission and play an important role in overall function and optimal performance. A damaged bearing could cause gear oil to leak and therefore cause damage to the entire unit.

How do you know when to repair transmissions versus replace?

A skilled diesel technician can help diagnose transmission problems and whether a repair or replacement is needed

The answer to this question depends on a number of factors, including the severity of the problem, the cost of repairs, and the age and value of your truck.

Repairable problems

Some issues can be fixed relatively quickly and can extend the life of your transmission. If piping leaks and/or is insufficiently lubricated, it could be as simple as replacing or topping off fluid. Should you notice any of the common problems and let them go unchecked, you could be facing more expensive repairs such as having to have your transmission rebuilt.

If you think you have a problem, it is usually best to take it to a mechanic for a diagnosis. They will hook up a diagnostic machine to your truck and run some tests to see if there are any issues. If they find a problem, they’ll be able to tell you what it is and what needs to be done to fix it.

Transmission Rebuilt Vs. Remanufactured Transmissions

If your truck has transmission problems, the diesel technician can check the fluid among many other things. If dirty transmission fluid is not a problem, the tech may perform manual testing and drive it, but they’ll usually connect a device to a diagnostic system and find out what codes they throw. In some cases, it will be necessary to replace the transmission.

How mechanics rebuild a transmission

Generally, reconstructed or remanufactured transmissions involve a lengthy and labor-intensive process. Diesel mechanics need to disassemble the transmission and fix defective parts. Mechanics then identify the transmission parts that caused the failure and may help determine if a brand new transmission is actually needed.

What to consider when fixing transmissions?

Know warranty and estimated costs before you start any transmission repairs.

When rebuilding or replacing a semi-truck transmission, you need to consider the cost of the transmission parts, the cost of labor, and the warranty. The cost of transmission parts can vary depending on the make and model of your truck, and the cost of labor can be expensive, especially if the transmission needs to be completely disassembled.

First, check if the warranty is valid

If you are looking at a rebuilt transmission or replacement, you need to check your truck’s warranty and any other warranties you may have. Warranties vary widely depending on make and models, and the OEM. OEM coverage can be up to 24 months, but transmission parts covered may vary and be dependent on other warranties purchased such as an unlimited mileage warranty. Additionally, the warranty on remanufactured transmissions may not be as long as the warranty on newer transmissions.

Average Semi Truck Transmission Repair Costs

The cost will vary depending on the severity of the problem, the transmission parts needed, the wear and tear or mileage on your truck.

It can be costly for mechanics to work on transmissions. Ultimately, the transmission problems and the associated transmission parts needed will determine the cost.

Transmission repair costs guides indicate average repair costs for a transmission replacement range from $1,800 to $3,400. Used and remanufactured transmissions range from $1,000 to $1,500. The labor cost of removal and replacement of transmissions ranges between $500 and $1,600. Transmission parts vary from several hundred dollars to thousands.

So is it better to rebuild or replace? Rebuilding can cost as much as a replacement based on damage severity. That said, it’s important to find a heavy-duty repair shop and diesel technicians with experience.

How do you find a qualified heavy duty repair shop and diesel technician?

Reference heavy duty repair shop listings like BigRig411 and customer reviews to find reliable repair shops & mechanics.

Considerations and factors for finding the right repair shop

The diesel mechanics handling working on your truck may make the difference between a cost-effective and expensive repair. As a rule of thumb, you should get an estimate before any work is done. It is best to gather several quotes, ideally three different transmission repair quotes to compare prices, value and quality work.

When you compare prices, also consider the cost of repair parts, replacement parts and whether the shop uses quality parts.

You should also consider does the shop work on medium duty and heavy duty vehicles only, and what models of trucks are they most familiar with.

Location may also be a factor. Is the location, close or will you need to have your truck towed to the shop location. Do they offer mobile repair services? Do they have parts or overhaul kits in their shop? Have customers left good service reviews?

Find shops that have excellent reputations on the web and user your local BBB. You can also leverage popular heavy duty tow and repair directory listings like BigRig411.

Future preventive maintenance measures

Employ routine check-ups for your truck to minimize wear and tear and catch problems early.

Semi truck transmissions and engines need routine check-ups in order to prolong their life . Here’s a lit of some of the most common preventive tips to follow going forward:

Fluid changes

Transmission and differential fluid, and engine oil, etc. should be changed on regularly according to the manufacturer’s recommendations. This will help remove any dirt, debris or built-up deposits that could potentially cause damage.

Filter changes

Along with regularly changing your fluids, you should also change your filters (air, fuel, oil, etc.). This will help keep your engine running smoothly and efficiently.


Periodically inspecting your transmission (and engine) for signs of wear and tear can help you catch problems early on before they become major issues. Pay attention to things like strange noises, leaks, fluid levels, etc. and have them checked out by a professional if you notice anything out of the ordinary.

By following these simple tips, you can help keep your semi truck’s transmission in good shape and avoid significant costs down the road.


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