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3-1 Downshift clunk

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3-1 Downshift clunk

2010 Sierra 4x4

427" Engine with 4L whipple

Yank 3200 converter

This unit is just rebuilt. It was originally built by Century Transmission. Customer brought it in nuked badly. All clutches were gone. The oil pan had been caved into the filter restricting flow. 

Rebuild is essentially the PATC Level 4 kit. Using the billet planetary. Alto clutches throughout and the sonnax 6l80 zip kit which has a boost valve and increased pressure spring. 

The unit drives well under acceleration and basic crusing. Maybe a little bit agressive as far as shifting goes but not too bad. It has a very defined clunk coming to a stop on the 3-1 down shift. It actually feels as if the truck gets rear ended. 

A couple points to note, the unit will not do this clunk unless it accelerates all the way to 4th gear. It also doesnt seem to do it cold. 

Logging with the scanner the current gear selecion will make the change from 3 to 1 and then a slight delay before the bang. The vehicle is almost stopped or completely stopped when it happens. 


Any thoughts are appreciated. 


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