There are many questions on various forums about the origin of a grinding noise that emanates from below the vehicle, especially when engaging 4-wheel drive. This article discusses the possible source as well as the solution to the strange sound. So why does my 4-wheel drive grind when turning?
When you hear a grinding sound when turning in 4 wheel drive means you are experiencing drivetrain binding. The binding of the drivetrain transfers high levels of torque through the drivetrain and transfer case resulting in difficulty turning, grinding noises, and wheel hop. Hearing a grinding sound when you are driving in a straight line when you engage 4WD means the gears inside the transfer case are partly engaged resulting in the teeth not meshing properly giving off a grinding sound. Stop or slow down your vehicle and attempt engaging 4WD again.
So now that we know what could cause the possible grinding noise from below the vehicle, there are other reasons why your 4-wheel drive could be making strange sounds while driving. One example is, it could be caused by the extreme suspension lifts. This severely alters the angles of the driveshafts into the transfer case which also gives off a grinding noise.
The next part of this article will cover why the grinding noise only happens when you are turning and not while driving straight as well as when it’s safe to engage 4WD and the phenomenon of drivetrain binding in more detail. Later we’ll cover the third reason that could be causing the grinding noise while driving.
If you’d like to find the answers to the above questions, continue reading…
Why is my 4 Wheel Drive grinding only when turning
So we’ve so far established that there are three instances that cause the grinding sound. It could be as a result of the following:
- Drivetrain Binding effect
- 4WD gears not engaged properly
- Driveshaft angles misaligned
So let’s look into when it’s appropriate to engage 4-wheel drive mode and under which driving conditions you need to exercise more caution.
When should you engage 4-wheel drive
For the purposes of this article, we will be referring to a part-time 4-wheel drive. Part-time 4-wheel drives need to be driven in 2H when not off-road or driving on a slick, slippery surface where traction is low. As simple as that. When you are driving on dry pavements and tarmac highways, you should always be driving in 2H. This mode safeguards your drivetrain from the binding effects, spares your tires, and returns the best MPG your 4-wheel drive can deliver. Even when the highway surface is wet and dry pavements are wet, it’s highly recommended to remain in 2H mode since the surface is a high traction surface and designed to offer sufficient levels of grip even under these conditions.
Engaging 4WD does not exempt you from the laws of physics.4wheeldriveguide.com
With that being said, many inexperienced 4WD owners are of the impression that as soon as the road surface is wet, it’s appropriate to engage in 4WD. NOT ALWAYS THE CASE! Unless the road surface is covered in snow or ice then yes, you can and should safely engage 4WD, otherwise, adjust your driving style, lower your speed, increase your following distance and leave the vehicle in 2H mode. Engaging 4WD does not exempt you from the laws of physics.
Why do we recommend the above? Well, it’s because, in order for you to safely engage 4WD, the driving surface needs to offer sufficient levels of slippage for it to work properly without risk of damaging your drivetrain. That means the driving surface must be slick, greasy, or muddy enough to allow the front wheels to slip a bit and rotate at dissimilar speeds to the rear wheels while turning. Straight-line driving is fine since both front and rear axles rotate at the same speed, but rather, it’s the difference in rotational speed and a wider turning radius of the front wheels which cannot be accommodated by a locked center differential when driving on a high traction surface. When that happens long enough and torque starts being transferred back up into the drivetrain system and finally the transfer case, is when you start hearing grinding metal sounds and other strange noises caused by the immense stress being placed on the internal gearing.
Now, this might sound strange, since the whole purpose of the 4-wheel drive is to improve traction, yet in order for it to work, it needs to slip? Exactly.
The 4-Wheel drive should only be engaged when:
- You are driving off-road i.e dirt roads
- You are driving in thick snow
- You are driving on sand
- You are driving in deep mud
Basically, all surfaces that allow for enough slippage and where maximum traction is required, are safe for you to engage.
Grinding could be an effect of driveshaft binding
So how can driveshaft binding be the cause of the grinding noise when turning?
Below is an extract from an article explaining the drivetrain binding effect.
4 Wheel Drive Locks Up When Turning
This effect causes your vehicle to under-steer heavily, gears to get jammed and makes steering very difficult and even jerky. This phenomenon is caused by the front wheels battling the rotational force coming from the front drive shaft as it tries to slow down the front wheels, causing the massive under-steer effect. You should avoid engaging 4WD on a high traction surface at all costs. The longer you drive in that mode, you risk serious damage to your drive-train components and you will find it increasingly difficult to remove it from 4WD mode and switch back to 2WD mode.
4WD Binding – How To Fix Transmission Wind-Up
If you have forgotten to take your 4WD out of 4H after heading back on to the tarmac you will definitely experience transmission wind-up after a while. One way to identify if you have transmission windup is, your vehicle being stuck in a gear. You can yank and hang on the gear lever but nothing will release that gear due to the immense forces and torque built up inside the transmission.
So how do you fix transmission wind-up? The easiest way to fix bind-up is by pulling over to the side of the road with two wheels firmly on the tarmac and the other 2 wheels on a slippery surface like grass, mud, snow or sand. This allows the wheels to rotate at altered speeds releasing the wind-up in the transmission box. Once the wind-up has been released you will then be able to use your gearbox/transmission properly again.
The other option is to reverse in the same direction you were driving. So if you were driving forward in a left direction, reverse in a left direction and allow the wind-up in the transmission to reverse itself naturally.Extract taken from the article: Why Your 4 Wheel Drive Jerks and Feels Hard to turn in 4WD
So that’s the one cause of the grinding noises that you are hearing. You are most likely driving the vehicle on a surface that has enough traction and the vehicle is begging (grinding) you to disengage 4H and select 2H instead.
Now let’s look at the second reason why grinding could occur, and this time it’s grinding while driving on a slippery surface that warrants engaging 4-wheel drive.
4 Wheel drive grinds when engaging 4×4 on-the-fly
Manufacturers are constantly trying to build smarter, sophisticated, more user-friendly vehicles. The traditional 4-wheel drives of decades ago involved a long tedious process to engage 4-wheel drive. This included bringing the vehicle to a complete stop, exiting the vehicle, and manually engaging the front hubs by physically turning the 4WD dials on the front wheel hubs in order for 4-wheel drive mode to be engaged. Next, you are meant to place the transmission in neutral, and then engage 4-wheel drive by yanking a short gear stick from inside the cabin. SERIOUSLY! By then I’d lost my desire to off-road… lol
Fast forward to modern day time, and we have intelligent, refined 4-wheel drives that offer on-the-fly 2H to 4H shifting. Manufacturers promise us, we can safely engage the 4WD at any speed. No need to even slow down or exit the vehicle anymore. Everything is becoming more automated and user-friendly. So that’s exactly what people do because that’s what the user manual and dealership salesman said they could. However, this is another reason why the grinding effect happens over time when you constantly engage 4WD while driving, especially when you are above the recommended speed to safely do so.
When the splines fail to mesh you hear a grinding noise
With certain 4WD trucks, when shifting into 4WD while accelerating, you will hear a metallic grinding noise and/or bang when it eventually engages. This is bad news since you could potentially break teeth off internal gears inside the transfer case. Engaging 4-wheel drive while driving essentially locks the front and rear driveshafts together while one is spinning at a few thousand RPMs and the other is basically stationary. In this instance, one of two things happens. By some freak occurrence, the splines in the TC mesh, and with the immense forces being applied once everything starts linking and turning together, that is when you hear a bang.
Alternatively, the splines attempt to mesh together and do not succeed. When the splines fail to mesh you hear a grinding noise. If the wheels are turning freely without you accelerating, then the splines mesh seamlessly and there is no bang or grinding noise.
Why grinding occurs inside the transfer case
So let’s try to isolate where exactly the sound is coming from first. If the noise is coming from the back it is your differential, if it’s more toward the front or middle it’s more likely the transfer case. You also need to use the process of elimination by isolating other possible components to confirm if it is the transfer case generating the grinding noise. Engage 2H and drive on a straight road under load and at varying speeds and listen out for any grinding sounds. This exercise is significant since 2H only propels the rear wheels and isolates the transfer case and front driveshaft. If possible, drop (remove) the front driveshaft to eliminate everything forward of the transfer case like u-joints, bearings, front diffs, etc.
Damaged Spline Teeth
If you’ve successfully established that it is the transfer case, the grinding is likely caused by the teeth of the spline that needs to engage with the transfer case failing to align 100% with the internal gears. The front output shaft bearing could also be in need of replacement in the t-case. These components all emit a grinding metal on metal noise once you attempt to engage 4WD.
Transfer case oil
You need to also make sure the transfer case fluid is topped up. When draining the TC, check for any metal filings. This will indicate excessive heat build-up caused by high levels of friction. If the lubrication levels are low, the friction will increase causing major wear on gearing components. This will also result in the transfer case not engaging properly when you are driving and attempting to switch to 4WD mode while driving.
Broken Clutch slider
The grinding noise coming from that area could also be caused by a broken chain, or the clutch slider could be stripped inside the transfer case. When the slider teeth are stripped, it will have trouble engaging 4WD on the fly, resulting in loud metal grinding noises being emitted.
Why the grinding sound disappears in 2-Wheel drives
Many 4-wheel drive owners continue to add that the grinding noise disappears when they select 2H mode. This is because when in 2H mode the transfer case and everything forward of that in the drivetrain system is disengaged and simply coasts along. The vehicle now operates as a rear-wheel-drive car by sending 100% of the power to the rear axle which splits it 50/50 between the rear wheels. The transfer case and all 4WD components are eliminated in 2H mode.
Grinding noises on Lifted 4-wheel drives
This is another reason why you could be hearing a grinding noise being emitted from your 4WD. Another common denominator is the fact that many drivers who experience grinding cannot seem to eliminate or even isolate the source of the grinding noises. Forums are filled with examples of 4WD owners replacing drivetrain components such as u-joints, draining differential oils, replacing transfer case oil, balancing driveshafts, all in an attempt to eliminate the grinding sounds. Many have taken their vehicles back to dealerships only to be told, it is normal for your 4-wheel drive to do that?
Bad Caster Angles
The grinding noise could be a result of a bad caster angle. The lifted truck extends the driveshaft further out of the yoke due to the bigger angle created by the lift kit. This also places more strain on the U-joints to function at an angle not parallel with the transfer case. In order for a driveshaft to operate correctly, the transfer case and the pinion need to be on parallel lines.
The difference in vehicle height places undue pressure on your pinion due to the angle it is at. The caster was not originally designed to function at the extreme angles created by high suspension lift kits.
So we’ve established a few possible causes of the grinding noise when 4-wheel drive is engaged as well as when attempting to shift into 4-wheel drive from 2H mode. There are a few processes of elimination exercises you need to do to isolate where the grinding noises are emanating from.
In summary, any of the below-mentioned components could result in a grinding noise when driving and turning in 4-wheel drive and they are the following:
- Drivetrain Binding effect in the transfer case
- Damaged Spline teeth
- Low transfer case oil
- Broken clutch slider
- Bad U-joints
- Bad Caster Angles