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5R55S Transmission Rebuild – Taking It To The Next Level

Written by Staff. Posted in How To Tutorials

Published on May 10, 2016 with No Comments

Ford rolled out a completely new Mustang in 2005 with stellar looks, an outstanding engine package, and a new automatic transmission that impressed even diehard stick-shift guys. We instantly saw people throwing tunes in the ECU and adding nitrous, cold-air kits, exhaust systems, turbo kits, and supercharger systems.

The quest for more power pushed the aftermarket into overload, and now we’re left with a skewed sense of reality as 500 rwhp from stock engines is expected every time a wrench is spun. The 4.6L Mustang Three-Valve engine program lasted six years, and we can confidently point to the supercharger as being one of the most popular upgrades. Going mid-11s is as simple as a blower, custom tune, and sticky tires.

Anthony Giagnacovo can certainly attest to the simplicity of it all. His ’06 Mustang GT benefits from a Saleen twin-screw supercharger (10 psi), JDM Engineering tune, Kook’s headers/ X-style midpipe/axle-back exhaust, and 17-inch Mickey Thompson drag radials. The car was modified in 2008 with just 5,000 miles on the ticker.

Once the mods were done, Giagnacovo wasn’t shy about racing the car hard, as he attends three NMRA events a year, plus local Mustang events at Englishtown and Atco Raceway, countless test-and-tune sessions, as well as a lot of cruising at the Jersey Shoreyes, we said the Jersey Shore. Best time to date has been an 11.24 at 120 mph, and the car cranks out 469 rwhp through the automatic transmission that is relatively untouched. He added a hardened input shaft and trans cooler, otherwise, the transmission is the same as it rolled off the assembly line–including the torque converter.

All too often we proudly display performance gains on these pages, but rarely do we speak of long-term endurance of the parts. Unfortunately, it is just too hard to track the progress of each install, and every owner treats his or her equipment differently. For Giagnacovo, it took 25,000 miles and who-knows-how-many dragstrip runs, but the stock trans threw up the white flag and surrendered. The car wouldn’t move, so JDM Engineering yanked it out and sent the 5R55S to Level 10 Performance Transmission in Hamburg, New Jersey. He smoked Second, Third, Fourth, and Fifth gears, comments Pat Barrett of Level 10.

The company isn’t a stranger to the pages of MM&FF, as it was responsible for delivering a bulletproof 4R100 transmission for our former project vehicle, The Fridge, a low-10-second Gen 2 Lightning that was driven daily and whipped often. Barrett and his Level 10 shop did the same thing to Giagnacovo’s trans since more dragstrip abuse and street fun are on the agenda.

Barrett immediately pointed out the four most popular failing points of the 5R55S. The first is an issue with the input shaft–it will bend and snap under hard use, including some aftermarket ones. “The shaft can break two ways, locking the torque converter up at the wrong time, or from excessive wheelhop,” states Barrett. “The input shaft was never designed to lock up under WOT, but you know racers–they love to get the mph out the car by locking it up. Our shaft is designed to withstand that abuse. The wheelhop will shake the shaft and snap.”

The next issue on the list is a cold start valve failure. According to Barrett, there is a special circuit in the valvebody that restricts fluid flow to and from the trans cooler. This is done to bring the trans up to operating temperature quickly.

It was designed for extreme cold weather startups, like 20-30 below zero. In a perfect world this valve works perfectly, but we don’t live in a perfect world, adds Barrett. Level 10’s overhaul eliminates the valve to prevent any problems because 99 percent of these cars aren’t going to be fired up in that extreme weather.

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Fords Magazine Staff is a group of car lovers, editors, and writers who have a passion for Ford Motors. Besides being all around car nerds and proud owners of Fords, our staff is dedicated to providing you breaking news, reviews, and tutorials.

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