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Automatic Transmission

Something Amiss with Planetary System

You may remember back in the early days of the 41TE transmission (A604), the sun gear was known to shear off the shell. The result would be no reverse; it would take off in 1st gear but when it shifted into 2nd it would neutralize. With 2nd gear being failsafe, it would default to a neutral gear. The vehicle would then have no movement both forward and reverse. Once the ignition was cycled off to on, you could once again take off in 1st and shift into a no-move condition.

Wayne Colonna
By Wayne Colonna
Published:

Technially Speaking

  • Author: Wayne Colonna, Technical Editor
  • Subject Matter: FS5A-EL/FNR5
  • Issue: No reverse, 2nd or 4th

You may remember back in the early days of the 41TE transmission (A604), the sun gear was known to shear off the shell. The result would be no reverse; it would take off in 1st gear but when it shifted into 2nd it would neutralize. With 2nd gear being failsafe, it would default to a neutral gear. The vehicle would then have no movement both forward and reverse. Once the ignition was cycled off to on, you could once again take off in 1st and shift into a no-move condition.

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The FS5A-EL/FNR5 has a similar power flow in that the rear sun gear is driven in reverse by the reverse clutch and held stationary by the band for 2nd and 4th. The 41TE used a 2-4 brake clutch instead of a band. One primary difference with the FS5A-EL/FNR5 transmission is that third gear is the designated default gear for failsafe. Should something occur with any part of the rear planetary assembly, the transmission would lose reverse, 2nd and 4th gear and failsafe to 3rd.

This is exactly what happened to Chuck at Curtis Transmissions. A 2010 Mazda CX-7 using the FS5A-EL transmission behind a 2.5L engine was brought in to the shop. The customer said the vehicle suddenly lost reverse, 2nd and 4th gear.

When the vehicle was road tested, the initial drive cycle felt like a 1-3 shift only before defaulting to third gear. A scan tool revealed the following codes: P0732 (Gear 2 Incorrect Ratio), P0734 (Gear 4 Incorrect Ratio) and P0757 (Shift Solenoid B Stuck On).

During the road test, the transmission range sensor and speed sensors appeared to be functioning correctly. There was no reverse even with the solenoid connector unplugged verifying an internal condition existed.

The pan was dropped showing a very clean sump along with no evidence of anything burning. When the unit was removed and disassembled to check for stripped splines or something broken, nothing appeared to be damaged. All friction components looked good as well. Knowing that something was not right with the planetary system, a closer look was made. It was not until a slight tap of a hammer did the rear internal ring fall off the front planetary carrier revealing the problem (figures 1 and 2). Although the pictures are blurry, they do tell the story. And now you can be “focused” when this problem is brought to your shop.

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