Why Do Monster Trucks Diff Glow?

Image editorial credit: BW Press / Shutterstock.com

When driving a monster truck, you might suddenly find yourself in a situation with you see smoke, and suddenly, when you look beneath your car, you might see that your entire differential is glowing red. There are many things you do not want to happen whilst driving a monster truck, and having a differential that is looking a little off-color is not one of them. So the question is: why do monster trucks’ diff glow?

Monster truck diffs glow because of heat build-up in the diff. When a monster truck does a lot of turning, the diff works hard to transmit the right amount of torque to each wheel. Sharp turns, or even ‘drifting’, make the diff work hard, which generates a lot of heat, causing the diff to glow.

So now we know overheating is one of the causes why a monster truck’s diff glows, but are there any other problems that to watch out for when it comes to the truck’s diff? What are symptoms that the truck’s diff might start to fail, and how can you prevent it from failing? We explore all of this!

What Does A Monster Truck Diff Do?

The diff in a monster truck works on the same principles as a diff in any other vehicle. A differential (or ‘diff,’ as some motorists call it) is the system in a vehicle that transmits the torque of the engine to the wheels of the motor vehicle.

The function of the differential is to take power produced by the engine and split it between the wheels, which allows the wheels to spin at different speeds. It achieves this by having many gears of different sizes connected to one another that spin at different speeds that turn wheels at different speeds.

Why does a vehicle need a differential, or why do wheels need to turn at different speeds? Well, simply because all the wheels are connected to the same axle. If a motor vehicle only has to drive straight, there is no problem, but if a vehicle turns at a corner, the speed of each wheel is different because the distance each wheel has to travel is different.

The reason that the diff in a monster truck has to work so hard is because of the size of the wheels that the diff has to drive and the inertial weight of the vehicle that the power from the diff needs to overcome.

Why Do Monster Trucks’ Differentials Glow?

So now that we know what a differential is and what it is supposed to do, we can figure out why it might glow. First, there are various types of differential gear sets, most of which are made of steel. One thing we know from iron and steel is that it glows when it is heated to very high temperatures.

Often, what can happen is that your vehicle gets stuck, and you want to get it unstuck immediately. If you are stuck and you find yourself in a situation where only one wheel is spinning while one or more of the other wheels are not spinning, the little gears inside the differential gear set get extremely hot.

Furthermore, because monster trucks are larger and require more power than ordinary automobiles, the loads on these gears are also larger. They require more torque to do the ‘monster truck stuff they do; thus, the gears in the differential gear set work harder – especially if the monster truck gets stuck. Once these gears become very hot, they can reach temperatures such that the steel of the differential gear set starts to glow.

The fact that monster trucks often ‘drift’ and engage in extreme and aggressive turning gives more insight as to why the ‘diffs’ are very overworked. After merely a couple of minutes of severe turning in completely opposite directions, the differential has worked extremely hard by putting out massive amounts of torque to swing this monster truck around – the gears experience such a heavy load that the differential becomes extremely hot and starts to glow.

Experts assign other possible causes to your differential overheating to either:

  • You used the wrong oil in the differential
  • The fluid levels in the differential are low
  • Seals on the differential have either reached their life expectancy or are damaged

Image: Shutterstock.com

Symptoms Of A Differential Potentially Failing

When your differentials are starting to give problems, it will become difficult to turn, and there are various parts in your differential that will start experiencing severe strain.

Differentials are expensive on normal motor vehicles, but the prices of monster truck diffs are comparative to the size difference between the vehicles. That is why it is important for monster truck owners to take note of signs that the differential is showing signs that it needs maintenance, additional care, or repair.

Here are some symptoms that the differential of your machine is starting to fail and that you should probably have a professional take a look at your vehicle.

Tires Show Signs Of Damage

When you notice that there is damage on the outer tread and sidewall of the tires of your vehicle, it can be because your differential is experiencing failing components.

The reason why your tires will be damaged is that the tires cannot spin in the way they are supposed to spin while turning at a corner. These speeds at which vehicles spin while cornering can cause damage to the tires.

While this symptom is unlikely to show on a monster truck due to the size of the tires, and because they spend less time on asphalt, the tires could start to show some wear in these locations, which would be an indication of a pending diff problem.

Increased Handling Difficulty

For reasons already explained above, if you experience difficulty in turning or going around corners, you most likely have a failing differential. This is because the differential cannot perform the only function it is meant to: help your car turn by adjusting the speed of your wheels.

Monster trucks are already difficult vehicles to control, so any reduction in their handling is magnified. A failing diff in a monster truck, therefore, is very noticeable when the handling becomes affected.

Experiencing Vibrations In Your Vehicle

There are many joints in your differential that become worn. If this happens, your driveshaft will most likely start vibrating. This vibration is much more apparent when one starts to rapidly accelerate.

This vibration would be magnified on a monster truck as it rapidly accelerates towards a jump or a mud pit.

Gears Of Your Vehicle Grind

If the gears are worn, and the fluid inside the differential is low, it results in a grinding noise that comes from the differential. This is what most likely contributes to the overheating and potential glowing of a differential if taken to extreme measures.

Your Vehicle Makes Whining Sounds

The largest indicator of a failing differential is the whining noise it makes. There are a couple of reasons as to why this might happen, but it can often be attributed to improper lubrication of the differential, which means your differential has a fluid leak.

How To Make Sure Your Diff Is Properly Cared For

To replace a differential might cost a lot of money, and it would be wiser to take preventative steps that ensure you don’t end up with a vehicle without a functioning differential.

  • The most important maintenance aspect you can do to ensure that you always have a functional differential operating on your motor vehicle is to change the differential fluid regularly. The oil found in a differential is thicker (or denser) than the oil found in a motor vehicle. Depending on the particular differential your machine is operating, it may require a fluid change every 30 miles (at the least) or every 50 000 miles (at the most).
  • Another thing you can do to prevent your differential from malfunctioning is to drive properly! The differential is located at the bottom of your car, and, thus, if you hit rocks or debris with the bottom of your car, you can hit your differential. This can cause damage to the housing of the differential, which can lead to oil leaks or destroy the differential entirely.

What To Do If Your Differential Requires Reparation

There are, broadly speaking, three types of repairs your differential can receive:

  • Replacement: If the differential is completely worn out or if the housing is broken, you might want to consider replacing the entire differential with a new functioning one.
  • Rebuild: If only the gears and other internal parts are worn out, they can be replaced with new parts. This will leave your old housing with a new unit inside.
  • Swap gears: This is similar to rebuilding since you remove old gears and replace them with new ones. The only difference is that you install new gears with the aim of changing the differential ratio, which will have an impact on your driving performance and your fuel economy.


The long and short is that your monster truck requires a lot of power to turn it and to transmit the right amount of power to each wheel to ensure that it turns exactly as you want it. The more you turn, the more the differential has to work and spin those gears! Overworking your diff like this might cause it to overheat and make that steel glow red!

To ensure that you do not break differential, stop turning and drifting so aggressively and always make sure that it has the right amount of oil in to lubricate it.