5R55E Reverse Servo Piston Length | Ford Explorer Forums - Serious Explorations

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5R55E Reverse Servo Piston Length


September 10, 2006
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City, State
Greenville, SC
Year, Model & Trim Level
1998 XLT
I bought a replacement reverse servo piston from the Ford dealership. They told me there was only one replacement servo piston they sell for the 5r55e transmission now. Apparently there used to be like three different sizes. Now when I compare the original servo piston with the new servo piston, the new one is shorter, but it appears to engage the reverse band when I press down on it.

Does anyone know if there was a design change. I'm thinking that maybe the shorter length places less stress on the reverse band when it's not engaged to lengthen the life of the reverse band?

Will the transmission still engage reverse with a shorter reverse servo piston? Should I send it back? Replace with an exact match?

Any advice would be greatly appreciated.

How many beveled grooves do you have on each one? A dial indicator gauge will tell you which one is the correct one. They make a part called an extendo tip from Sonnax, but it has to be ground down to get the exact fit. If it's too long, it will cause the band to be engaged all of the time. If it's borderline, it will cause the band to drag, and cause friction. This will cause glazing of the drum surface with wear on the band.


The original servo piston had 1 beveled groove, but the new one has two beveled grooves. The original piston length is approximately 2-1/8" long and the new one is approximately 2" long. Not much difference. I'm wondering why Ford only offers the one piston length? Did they change the band to fit this different length?

Originally I bought a new reverse band from www.transmissionpartsusa.com, but because I was concerned about it being relined, I ordered one from Ford at the same time I ordered the reverse servo piston.

Does anyone know this answer or where I can find out. I'll probably check with the Ford place and see if anyone knows the answer to this.