Other Articles - May - 2022

Snap, Crackle, Pop! A Look at Some Bellhousing Related Noises

Noises are typically something that many shops would prefer not to handle. In some cases, the noise is intermittent, so sure enough, the vehicle is not making the noise when the customer appears at your doorstep. The customer is typically quick to point out that the vehicle was making noise just before they pulled into your driveway, and they want to assure you that they are not making it up!

It is next to impossible to diagnose the cause without hearing the noise. In addition, the customer’s description generally adds to the confusion, as they are not sure if it occurs when the vehicle is hot or cold or if the concern is engine speed-related or road speed-related. Numerous other diagnostic indicators also come into play that the customer would not notice. Typically, the customer does not pay much attention, so their descriptions only add to the confusion.

Noise diagnosis is not for the faint of heart! You must duplicate the noise to diagnose the concern unless you have seen it before. With the noise present, locating the noise source can also be challenging, as noises can transmit through components leading to misdiagnosis. One of the best tools to help diagnose noise issues is a “Chassis Ear” (figure 1), and it is available in wired and wireless versions. Every shop should own one as they can be a lifesaver. The tool comes with a series of microphones that can be attached to different locations on the vehicle. A control box allows you to switch between the different microphones. An ultrasonic detector can also be used, even though it was designed for EVAP system diagnosis. These tools have replaced the old heater hose, or the long screwdriver mechanics would stick their ears on decades ago to isolate the noise.

So, what are some of the common noises we are seeing in today’s vehicles that can be a challenge? Let’s look at four common issues on GM vehicles that you should be aware of:

  • AFM/DFM engines have significant issues with engine valve lifters in many applications. The noise can either be a clatter like a lifter that has lost its prime or a sharp metallic snapping noise that may appear intermittent. Wear occurs in the lifter latching pins, which creates a sharp metallic noise. The wear allows the latching pins to pop out of their holes in the lifter body. You will hear a very distinct snap as the latching pins pop out of their holes. (figure 2).
  • A broken flex plate is typical on Duramax applications. You must inspect 100% of those applications when you have a transmission out for service.
  • Some Colorado/Canyon/Suburban/ Tahoe/Yukon/Sierra applications have developed a noise that emanates from the bell housing area. Sometimes the noise appears as a whirring noise that changes as the engine changes speed. Another noise might be described as a pop/snap/ clicking type that appears to be intermittent. If the noise occurs after you have just started the vehicle, locate and remove the starter relay from the UBEC (under hood fuse block) (figure 3).If the noise goes away, the relay is faulty. Issues with the relay not fully releasing are common on these applications, which will keep the starter partially engaged after start leading to the noise. Replace the faulty relay. If the customer has had the noise for quite some time, you may want to pull the starter so you can inspect the flexplate as damage may have occurred.
  • Silverado, Tahoe, Suburban, Yukon, and Sierra full-size truck applications may generate an intermittent snapping/popping/ clicking noise traced to the bell housing area. The concern may worsen when the vehicle is parked with the front of the vehicle elevated.

The issue is typically caused by a broken starter solenoid spring. The starter will function properly, but the starter drive may not stay in its released position allowing the drive to intermittently contact the flexplate when the engine is running, which will produce the noise. With the starter motor removed, rotate the starter motor, so the drive end is down. If the drive falls, the spring is broken (figure 4). Repair as necessary.

Noises will be around as long as vehicles are around, so it is something that a shop cannot avoid. However, having tools and an idea of where to look for the noise can give you a head start on your competition.

Until next time remember, “Always focus on the front windshield and not the rearview mirror.”