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Worn Servo Bore solution for Ford 5R55W, 5R55S or 5R55N Transmissions

Posted by Andrew Smith on

Remember when the only way to fix a worn servo bore on our trusty Ford 5R55W, 5R55N, and 5R55S transmissions was to have them bored out and sleeved. A new product just came to market that doesn’t involve dropping the transmission, and can be done by an experienced mechanic in around 2 hours.

The OEM parts in this kit are the intermediate and overdrive servos/pistons. O-ring grooves were machined into them and viton o-rings installed and a patented assembly sleeve make it complete.

Worn Servo Bore Fix


  • Overdrive Servo Piston - Bell shaped 2.915" with installed O-rings and Sleeve
  • Intermediate Servo Piston - 2.815" with installed O-rings and Sleeve
  • 4 Spare O-rings
  • Instructions

Click on the link to order this product from our website:

Additional quote from the Manufacturer:

The bores in these transmissions reach limits of wear that cause loss in pressure to the top of the piston and that causes functionality issues in the 70,000 to 200,000 mile range depending on driving habits.

The secret to the longevity of the fix is the original design accounts for a percentage of fluid loss to the reservoir, and to the underside of the piston. The loss to the reservoir causes loss in pressure to the top of the piston and the loss to the underside of the piston causes back pressure. The o-ring above the cross bore seals the bore against loss and back pressure to the backside of the piston. The o-ring below the cross bore seals the loss of fluid to the reservoir. The exposed o-ring cross sections are under very little force, around 2-3 pounds. The top of the bore is mostly concentric with the pin and the bottom is where most of the wear takes place, causing an ob-round shape. The o-rings redirect all the flow to the top of the piston where it is needed.

This fix is not a permanent fix but we consider it a intermediate to long term fix. There are vehicles out there that have had this fix working in them for over 80,000 miles! The o-rings will eventually wear out and the servo will need to get pulled and o-rings replaced. But you can do that as many times as necessary. Not only do we machine the o-ring grooves, we smooth out the sharp edges that caused most of the wearing on the OEM machining which dramatically slows down the wearing.

U.S. Patent No. 9,121,418