It’s the Little Things That Matter - Transmission Digest

It’s the Little Things That Matter

Whenever a transmission fails to work correctly after a rebuild, a small error like cross-connecting speed sensors can cause a major headache. It does not take much to correct this error if you know it occurred, but when you do not, a small error turns into a giant monster. Without a doubt, when it comes to many things in life, little things can matter.

Figure 1

A little thing that “could” have caused a bit of a headache for Darrell at ACE Transmission occurred with a 2011 Kia Forte using the A6MF1 transmission.  On the initial test drive the technician that test drove the vehicle experienced what felt like a bind up on the 3-4 shift. It literally near put him through the windshield. When the transmission was disassembled, only the L/R clutch was found to be damaged. The question is, why? Looking at the clutch application chart in figure 1, how could the L/R clutches come on in fourth? Something very odd hydraulically would have to cause it. If the L/R clutches were stuck on, a bind-up would have occurred on the 1-2 upshift.

Figure 2

When the valve body was being disassembled, they discovered that one of the tabs on the solenoid retainer bracket had broken off (figure 2).  When the bracket was put up against the solenoids, the tab that had broken was between to two black solenoids as seen in figure 3. An ATSG A6MF1 Tech Guide was used to identify these two solenoids. They are On/Off Shift Solenoid A and B (figure 4).

Figure 3

This manual has complete hydraulics which help determine exactly what had occurred confirming that replacing the bracket would resolve the problem.

Figure 4

Figure 5 is a partial hydraulic showing the OD-L/R Switch Valve. Shift Solenoid A strokes this valve to allow the OD Variable Force Solenoid to supply pressure to the L/R clutch for first gear. In second and third gear Shift Solenoid A in not on the and OD-L/R switch valve closes by spring tension. The OD VLP solenoid does not supply pressure to this switch valve as seen in figure 6. When it’s time to shift into fourth, SSA remains off while the OD VLP supplies pressure to the Switch Valve which passes through the valve and on to apply the OD clutch (figure 7).

Figure 5

With the tab being broken on the retainer bracket, SSA had popped out if its position. Regulated solenoid feed pressure was routed directly into the circuit that strokes the OD-L/R Switch Valve. This didn’t have any negative effect for Reverse and First gear as the L/R brake is applied in P, R and D first gear.

Figure 6

The valve being fully stroked in second and third had no effect as the OD VLP isn’t supplying pressure to the switch valve. But, keeping this valve stroked when a shift into fourth takes place, this causes the L/R brake to apply rather than the OD clutch (figure 8). This means a shift into first gear takes place at a high speed making it feel like a bind up as you kiss the windshield.

Figure 7

The L/R clutches being applied at this speed will certainly cause them to get a little heated, wouldn’t you say? All due to a small tab. Without a doubt, in this case, it’s the little things that matter!

Figure 8

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