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Below are parts of articles on torque converter shudder. This posting is provided as a review of information available about torque converter shudder in automatic transmissions. Note that these articles are general in nature, and are not specifically written about CVTs. Note that any text in italics were noted by me, and not in the original article.


What is Torque Converter Shudder?
Life Automotive Products - Smart Blend Synthetics, Trans Flush, ATF Products

Torque Converter Shudder occurs when the clutch inside the converter on an automatic transmission is being applied and the transition from slipping to locked up does not occur smoothly. The clutch locks up for a brief moment and then slips, or breaks away, because it could not hold enough torque to complete the lock up. The ability of the clutch to hold torque is the converter’s torque capacity, which is a function of the oil pressure applied to the torque converter clutch combined with the friction characteristics of the oil and friction surfaces. This process of locking up and breaking away repeats itself rapidly, typically 30-50 times per second, until the engine RPMs are reduced and the clutch finally locks up. Torque converter shudder can be both felt and heard as these rapid vibrations are transmitted to the drive line.

Customers will often complain about this shudder after a transmission service because the friction in the new fluid is different

AGCO Automotive Repair Service - Baton Rouge, LA - AGCO Automotive

Torque converter shudder and diagnosis

Driving about 45 MPH there is a sudden shutter in the vehicle. It almost feels like running over a rough spot in the road or a cattle guard. As quick as it appeared, it is gone, until the next time it occurs.

Many people describe this feeling as running over a rough spot in the road. Very often the problem is a torque converter shudder. A torque converter shudder is a brief shake or shudder in the vehicle when internal clutches apply inside the torque converter. They refer to this application of clutches as 'lock-up." Often this problem is misdiagnosed and sometimes they needlessly rebuild transmissions as a result.

On many vehicles, one way to identify a torque converter shudder is lightly touching the brake pedal, while carefully maintaining vehicle speed with the other foot. If the shudder immediately stops, with brake application, the problem is likely the torque converter clutch. When the operating system sees brake application, most vehicles release the torque converter clutches. A trained transmission-service technician can also test for torque converter lockup using a specific vehicle scan tool.

What causes torque converter clutch problems?
Torque converter clutch lubrication is one reason for so many automatic transmission fluids (ATF) on the market. Without the additives in these fluids the clutch may chatter when it engages, causing the shudder sensation. If allowed to chatter, we may damage the clutch arid material from the clutch can ruin the automatic transmission.

Time, heat and mileage also cause the additives in automatic transmission fluid to become depleted. Without these additives, clutches may chatter and wear. If we find excessive debris in the transmission pan or if the shudder persists after a proper service, we may have to replace the torque converter. In other cases, we might need a transmission-rebuild. Continuing to drive with the shudder can result in automatic transmission failure. When this occurs the transmission will need to be repaired, replaced or rebuilt.


Things to note about these articles:
1) The ability of the torque converter clutch system to lock up properly is dependent upon the hydraulic system and the pressure it needs to work properly.
2) The transmission fluid has to have the right characteristics and additives to allow the torque converter clutch to work properly.
3) Take the warnings about transmission failure due to shuddering with a grain of salt. These articles were written by companies that either sell transmission fluid or make a living by servicing transmissions, so their predictions might be slightly overstated.
 

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Thanks for posting this. As someone who is just starting to experience the CVT shudder issue, it really helps to hear that the torque converter chatter is really not that out of the ordinary. I'll be keeping an eye and an ear out to make sure it doesn't get worse, but if it only happens once in a blue moon, I guess I'm not that worried anymore.
 
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