Diagnosing A750E/F 2-3 Flare After Overhaul - Transmission Digest

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Diagnosing A750E/F 2-3 Flare After Overhaul

Diagnosing shift quality concerns can be difficult, especially after rebuilding the transmission. You have just invested parts, your time and expertise into repairing the transmission. You are emotionally invested, which sometimes makes it hard to think clearly. This can be the case when you have a Toyota/Lexus A750E or A750F that has a 2-3 flare after overhaul.

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By Jeff Parlee
Jeff Parlee is the Sonnax remanufactured valve body product support manager and member of the Sonnax TASC Force (Technical Automotive Specialties Committee), a group of recognized industry technical specialists, transmission rebuilders and Sonnax Industries Inc. technicians.
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Diagnosing A750E/F 2-3 Flare After Overhaul TASC Force Tips Author: Jeff Parlee Units: A750E/F 2-3 Issue: Diagnosing shift quality concerns

TASC Force Tips

  • Author: Jeff Parlee
  • Units: A750E/F 2-3
  • Issue: Diagnosing shift quality concerns

Diagnosing shift quality concerns can be difficult, especially after rebuilding the transmission. You have just invested parts, your time and expertise into repairing the transmission. You are emotionally invested, which sometimes makes it hard to think clearly. This can be the case when you have a Toyota/Lexus A750E or A750F that has a 2-3 flare after overhaul.

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First you drive the vehicle to try and relearn the shift adapts. If that doesn’t fix it, it is tempting to yank the unit and look for the problem. I would recommend taking the time to diagnose the problem first, then you have a better idea where the problem may be.

First, you can check the C3 clutch pressure during the 2-3 shift and compare it to the line pressure (figures 1-4).

The C3 clutch pressure should ramp up from zero to within 10% of line pressure over the course of about a half second. Line pressure must rise normally (see Figure 4 for line pressure specifications).

If C3 pressure is slow to rise or never rises completely, you could have a leak in the C3 oil circuit, a problem with the valve body or S1 Solenoid. If the pressure in the C3 oil circuit rises normally, you could have the wrong spring in the C3 accumulator (figures 5-7), damaged C3 accumulator seals, the wrong transmission fluid in the transmission or the aftermarket frictions in the overhaul kit are not applying (grabbing) as quickly as the OE frictions. I have had several instances where the OE C3 frictions were installed back into the transmission and the 2-3 flare disappeared.

Taking the time to diagnose the problem will usually help to decrease the repair time. I have not yet met the technician who wants to work on the same transmission a second time.

Jeff Parlee is the Sonnax remanufactured valve body product support manager and member of the Sonnax TASC Force (Technical Automotive Specialties Committee), a group of recognized industry technical specialists, transmission rebuilders and Sonnax Industries Inc. technicians.

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