Diagnosing Transmission Noise

mechanic working on transmission

When you're diagnosing transmission noises, often the drivers input or description of the noise is the most helpful piece of information.

However, keep in mind that a noise complaint the customer thinks is an automatic transmission problem can actually be traced back to something else in the drive-line.

Things like a bad CV joint on front drive cars, universal joints on the drive-shaft for rear wheel drive cars, front and rear wheel bearings and even some brake system problems like a binding caliper or brake pad that's hanging up can generate a noise that may seem to the driver like a transmission problem.

Automatic Transmission Noises

When you have eliminated all of the other possibilities and the noise is really coming from the transmission, focusing a lot of attention to the speed and the conditions at which the noise is most evident is very important to nailing down the transmission problem.

If a whining or grinding noises is heard that increases with the engine speed and is present in all gears including park and in neutral the most probable source would be from the transmission front pump.

This is because it rotates whenever the engine is running regardless of what gear is selected. Nevertheless, if you're diagnosing transmission noises and the sound is evident in all gears, but not when it's in park or neutral then the most probable cause would be internal parts rotating in all of those gears.

On a front wheel drive vehicle the drive chain can cause noise such as this. In addition,  transmission parts like the input shaft, it's bearings and the torque converter can also create strange noises under these conditions.

Nailing Down the Transmission Noise

When you get to the point where you eliminated all of the easy stuff and you're now searching inside the transmission for the cause of the problem, careful inspection and disassemble of the transmission will be needed to pinpoint the problem.

Fortunately, as you begin to take the automatic transmission apart you may run across signs of the problem. This can often begin when you remove the pan. You may find flecks of metal or even pieces of bearings or bushings laying in the bottom of the pan. What the material is made of can help you identify problem areas.

Brass shavings point towards bushings, friction material and steel chips point to clutch packs and chunky looking metal chips point towards gears and planetary assemblies. I have mentioned this before on many other pages, but often when you're having a specific problem with your transmission this may not be an isolated incident.

When you are diagnosing transmission noises it's also a good idea to check for technical service bulletins. In fact chances are that other mechanics have identified this sound and might provide insight on what is wrong with your automatic transmission. Case in Point: Pictured below is the 4l60E transmission from my 2004 Chevrolet Blazer.

They had a problem with the sun shell breaking on a few model years. When this happens the vehicle loses reverse only and all forward gears work fine. GM dialed back the line pressure to take the stress off the defective part, but this didn't help my Blazer. I didn't even bother taking it apart. I purchased a remanufactured unit with a 3 year/30,000 mile warranty and just swapped them out.

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4L60E Chevrolet Blazer Transmission4L60E Chevrolet Blazer Automatic Transmission

For a short lesson on automatics and additional pages that cover specific problems visit my automatic transmission pages.

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