In this issue of Keep Those Trannys Rolling we are going to take a look at a special tool that enabled me to easily locate and isolate a clank type noise on a 2010 Isuzu NQR. I’m using this as an example but consider that same approach, no matter what you’re working on.
Our story begins with a phone call from one of our local produce distributor dispatcher. The dispatcher was looking for a transmission shop that was willing and able to work on their medium-duty fleet of trucks. The dispatcher said they had close to twenty medium-duty Isuzu trucks that needed repair work, but was having problems finding a shop willing or able to work on them. The dispatcher indicated that they’ve had one of their trucks in a local repair shop for the last three months, trying to fix a noise concern and asked if I could take a look at it for them. Naturally, I agreed to take a look at the truck for them.
Truck Arrives at Shop with a History:
A couple of days later, a tow truck arrived at the shop with a 2010 Isuzu NQR in tow. I contacted the produce distributor dispatcher to discuss their concerns. According to the dispatcher, the truck was experiencing a clank type noise during accelerator tip-in and tip-out. The dispatcher went on to say that the previous repair shop had first replaced the driveline u-joints, then the driveline assembly and then the differential ring and pinion gears. Unfortunately, this did not fix the clank type noise concern. The repair shop then contacted the dispatcher and recommended replacing the entire rear differential assembly in an attempt to fix the clank type noise concern. That’s when the dispatcher decided that it was time to get another opinion. I explained to the dispatcher that noises and vibrations are one of the most difficult repairs to diagnose. I then assured the dispatcher that I would be able to locate the clank type noise, knowing I had a special tool designed to locate and isolate noises and vibrations.
As always, before working on any vehicle, I performed an initial vehicle inspection. This 2010 Isuzu NQR was equipped with a 4HK1-TC diesel engine and an Aisin Seiki A460 transmission. During the inspection, I noticed that the driveline assembly had been replaced, and the rear differential had signs of silicone on the carrier assembly, which indicated a differential repair was performed. I inspected the vehicle for leaks. I checked the engine oil level, transmission fluid level and the rear differential oil level before heading out for the initial test drive.
Duplicate to Diagnose:
Before heading out for the initial test drive, I checked for codes in the transmission control module, there were no codes present. I then headed out for the initial test drive. I drove up and down city streets, ranging from 10 mph to 45 mph. Just as the vehicle started to warm up, I noticed that there was an intermittent clank type noise during tip-in and tip-out of the accelerator pedal. The warmer the vehicle got, the more noticeable the clank type noise had become. After duplicating the clank type noise during the test drive, it was time to head back to the shop and diagnose this concern.
With the vehicle back at the shop, I lifted the vehicle on the rack. I began inspecting the drivetrain for any signs of worn parts. I found excessive backlash in the differential and excessive backlash in the axle to differential side gear splines. All of which could be causing our clank type noise during tip-in and tip-out driving conditions. I inspected the differential housing mounting components and found no problem there. As I rotated the driveline assembly back and forth, I notice a slight clank type noise coming from the middle of the transmission. With excessive backlash in the differential and noise coming from the transmission, it was time to locate and isolate this clank type noise.
Locating and then isolating noises in a vehicle can be quite difficult at times. One of the best tools for locating and isolating noises is a tool called “Chassis Ear” (figure 1). You may be asking yourself, “What is a Chassis Ear”? “Chassis Ear” is a unique diagnostic device specifically designed to pinpoint squeaks, rattles, and any other troublesome noises or vibrations across a vehicle’s engine, transmission, axles, and chassis. They are ideal for diagnosing faulty fuel injectors, bearings, gears, suspensions, transmissions, differentials, and CV joints, and underhood noises. Chassis Ear is available from your local tool supplier.
Locate and Isolate:
I installed two Chassis Ear transmitters on the rear differential, one transmitter (#1) near the pinion bearing, and a second transmitter (#2) near the carrier side gear area. I installed a third transmitter (#3) on the middle of the transmission case. With the Chassis Ear transmitters installed, it was time to head out for another test drive and see if I could locate and isolate the clank type noise.
With the Chassis Ear transmitters installed on the differential and the transmission, I headed out for another test drive. During the test drive, I switched the Chassis Ear controller to each of the individual transmitters. While selecting transmitter #1, I could hear the pinion bearing turning and a load thud type noise during tip-in and tip-out. When selecting transmitter #2, I was able to hear the carrier bearings rotating and the same thud noise during tip-in and tip-out. The pinion and carrier bearing rotating noise and the loud thud noise seemed to be fairly normal for a differential. I then switched the Chassis Ear controller to transmitter #3, which was located on the transmission case. While listening to transmitter #3, I heard a very distinct clank type noise coming from the middle of the transmission during tip-in and tip-out. This was the noise I was looking for. I had located the noise, and it was coming from the transmission. Now that I had located the noise, I needed to isolate what section of the transmission was making the noise. I removed the transmitters from the rear differential and placed them on the transmission case. Transmitter #1 was placed near the bell housing/pump area, transmitter #2 was placed on the middle of the transmission case, and transmitter #3 was moved to the rear section of the transmission. With the transmitters relocated, it was time for another test drive to try to isolate our transmission noise.
With the Chassis Ear transmitters relocated on the transmission, I headed out for another test drive. During the first part of the test drive, I selected transmitter #1. Transmitter #1 was producing a swirling type noise, which was a typical noise for a hydraulic pump. I could slightly hear the clank type noise during tip-in and tip out. As the test drive continued, I then selected transmitter #2. Transmitter #2 was producing the same loud clank type noise, I had previously heard during tip-in and tip-out operation. I then selected transmitter #3, which was located on the rear section of the transmission. Transmitter #3 was fairly quiet. I could hear the output shaft rotating, and I could barely hear the clank type noise during tip-in and tip-out operation. With transmitter #2 producing the clank type noise I was looking for, it was obvious that the clank type noise was coming from the middle of the transmission. With the help of “Chassis Ear,” I was able to locate and isolate the clank type noise to the middle of the transmission, and it was time to remove, disassemble and inspect the transmission.
Transmission Removed, Disassembled & Inspected:
With the clank type noise being located and isolated to the middle of the transmission, it was time to remove, disassemble and inspect the transmission. I removed, disassembled, and inspected the transmission. I found small chunks of metal in the pan and fine metal particles throughout the transmission. I found the planetary carrier had been damage allowing the planet to rock back and forth in the shell (figures 2 and 3), causing a clank type noise during tip-in and tip-out operation.
After a brief discussion with the produce distributor’s dispatcher, it was determined that the best course of action would be to replace the transmission assembly with a rebuilt unit and get this vehicle back on the road. I installed a rebuilt transmission assembly, test drove the vehicle and delivered it back to our customer.
Well, there you have it. I was able to locate and isolate a clank type noise using “Chassis Ear.” With a little bit of patience and a special set of “Ears,” you should have no problem “Keeping Those Trannys Rolling” down the road.
Tip: There are several different models of “Chassis Ear” available from your tool supplier. Some models come with wired clips to attach to the components you are checking, other models come with wireless transmitters that attach to the components you are checking. Some models come with headphones (illegal in some states) or a speaker to listen to the noise/vibration. Whichever model you decide is right for you, I would recommend purchasing an FM transmitter (figure 4) and attaching it to the Chassis Ear controller, so you can hear the noise/vibration through the vehicle stereo system. You can find the Chassis Ear through various sources on the internet. You might even want to check with your local parts supplier. Thanks for listening!