Street Smart - March - 2017

5R55N with Wrong Gear Starts and Bindups? Look for a Faulty Servo

In 2000, Ford introduced the 5R55N. It was only used in the 2000-2002 Lincoln LS, 2002 Thunderbird, and 2000-2002 Jaguar S-type. It’s a lot like the 5R55W/S, but the N model has an intermediate clutch; the W/S models don’t.

Ford introduced the 5R55W/S in 2002 and, by now, you’ve probably become pretty familiar with the ins and outs of this unit. Some common problems include slipping in 2nd and 5th gears, or binds on the 2-3 shift. For these conditions, check the servo pin bore for wear (figure 1), and, if it’s worn, repair it with a pin bore repair kit.

Then there’s the famous no engagement, slow engagement, or pump noise. For that problem, check the blow-off valve in the pump and replace it or update it with an aftermarket kit (figure 2).

And, of course, who can forget the ever-troublesome multiple codes and missing gears? Look for a broken circuit in the solenoid block (figure 3).

But there are a couple other problems that can sometimes send you wandering in the wrong direction: wrong gear starts or bindups.

When faced with one or more of these conditions, the first thing you need to check is what gear the transmission control module (TCM) is commanding. You can check the range commands with your scan tool or a signal monitor.

There are a few things that can cause the (TCM) to command the wrong gear:

  1. Diagnostic trouble codes (DTCs) in memory, putting the transmission in failsafe.
  2. Manual Lever Position Sensor (MLPS) is out of adjustment.
  3. Vehicle speed sensor picking up a stray signal from the charging system or ignition system.

But if you’ve verified that the TCM is commanding the correct gear range, you can move on to the transmission.

Begin with this test:

  • Start the engine.
  • Raise the car into the air.
  • Shift the transmission into gear.

With the transmission running and in gear, have another tech see if he can turn either of the band adjustment screws in.

In drive, both bands should be off. You should be able to turn both band adjustment screws in without any problem. And this is where things usually go wrong. If one of the band adjustments is tight, that’s a problem.

Now, you might jump to the conclusion that you’re dealing with a valve body problem. But, after replacing the valve body, you have the same problem. So now you’d think it’d have to be a faulty solenoid block. And, after replacing the solenoid block, the servo adjustments are still tight.

How can this be? The computer is issuing the right command, the valve body and solenoid block have been replaced. What can be causing the band to be tight when it should be off?

What a lot of techs don’t realize is that both servo pistons use release oil to push them off when they aren’t supposed to be applied. They have springs that help, but they require release pressure to remain off.

The release pressure applies to the big side of the piston. If the piston is hard, has a tear in the seal, or even if it becomes delaminated (figure 4), the release oil leaks across and becomes apply oil, applying the band when it should be holding it off.

On many of these units, we hear that the servos air check fine. They do, because the apply side of the piston isn’t the problem; it’s the release side that’s damaged.

Depending on how bad the leak on the release side is, it can create different types of problems:

  • A bad leak can cause a bind in reverse and manual low, and wrong gear starts.
  • A small leak can cause wrong gear starts, or a clutch or band failure after a short time, with gear ratio codes.

So, whether it’s a new job or a comeback, if you have wrong gear starts or a bindup, always check the commands from the TCM. If they’re okay, perform this quick test on the bands.

The problem could be as simple as a bad servo… and that’s not just smart… that’s Street Smart!