In the article “A Transmission That Gives a Hoot,” Ford described a noise problem with their 6F35 transmission where it produces a “hoot” sound at low rpm’s. Audi say their S6 vehicles using the ZF6HP26 transmission.
A grunt sound is described as being guttural, sort of like when James Brown sings. Ironically, the James Brown band produced an instrumental piece called “The Grunt” in 1970 where he didn’t sing! But when it comes to automatic transmission, a grunt sound typically is produced by fluid to friction incompatibility issues, compromised clutch apply pressure, and/or incorrect friction plate clearances. Interestingly enough, Audi sites one of these possibilities as being the primary cause of the noise as follows:
Grunting noise when changing down from 6th to 3rd or 5th to 4th is due to manufacturing tolerances in clutch A and B; in other words, they have clutch clearance issues.
Their fix: Optimized software to improve gear changing. In other words, they reprogram the computer with calibrations that is consistent with the factory tolerances.
They also clarify that the fluid level and condition be checked first. If servicing is required that it is necessary to use the correct fluid otherwise transmission damage will occur.
Software Version Management (SVM) Update Instructions:
1. Follow all instructions per TSB 2011732 SVM operating instructions.
2. Update the Transmission Control Unit (J217) using SVM action code as listed in the update Instructions.
For those of you who are rebuilding these transmissions, be sure to maintain proper manufacturer clearances. ZF is known for having loose clutch clearances. Tightening these clutch clearances will produce shift quality issues that will not be compensated with shift adapt strategy. It will also produce a grunt of your own, guaranteed!
The manufacturer clearance specifications are as follows:
Clutch A - 0.062 inch to 0.080 inch
Clutch B - 0.055 inch to 0.073 inch
Clutch C - 0.054 inch to 0.072 inch
Clutch D - 0.082 inch to 0.106 inch
Clutch E - 0.072 inch to 0.093 inch
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