4R70/75W Mystery Bearing Noise

Ed Lee

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There have been a growing number of mysterious bearing noise complaints with 4R70/75W transmissions. The noise is often misdiagnosed as a converter bearing issue because it seems to go away when the transmission is in the lockup. This misdiagnosis can be avoided by qualifying that the noise is only present when the output shaft is turning. This qualification test works well to eliminate the converter as a possible cause, but it has also led many shops to mistakenly disassemble the differential, trying to pinpoint the noise.

The best tool for locating the source of the noise is a stethoscope. Generally, the noise will be loudest at the back of the case, just ahead of where the extension housing or transfer case adapter is bolted on. Upon disassembly, the source of the noise can be identified by examining the bearing between the output shaft and the case. A noisy bearing will have pitting or spalling on the rollers and both races.
Figure 1:
Visible race and roller damage

Drive configuration does not seem to matter when it comes to this problem. There have been an equal number of cases reported for both two-wheel and four-wheel drive vehicles.

Three generations of bearings have been used in this location dating back to the AOD transmission and only the third generation is having this issue. That points to a design defect as the probable cause.

The first generation bearing was an open faced bearing that used the output shaft as one of its races.

Figure 2:
First generation open-style bearing

The second generation bearing was a robust enclosed bearing.

Figure 3:
Second generation bearing with large, enclosed rollers

The third generation bearing was also an enclosed bearing, but had a lesser number and smaller rollers.

Figure 4:
Third generation with smaller, enclosed rollers

If the noise is diagnosed soon enough, the bearing can be replaced before the case or output shaft is damaged. The second generation bearing is the best replacement option as it is the most dependable due to the longer rollers and robust design.

Ed Lee is a Sonnax Technical Specialist who writes on issues of interest to torque converter rebuilders. Sonnax supports the Torque Converter Rebuilders Association.
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Subject(s) Included
  • General Diagnostics and Theory

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