AW 55-50 / AF23-33: Diagnosis and Valve Body Information

Adapting to the Aisin Warner 55-50SN Valve Body

Some things are less intimidating, if you're not the first one to do it. That statement is relative to both the crossing of a frozen lake and a problematic 55-50SN. Because of a heavy snow cover, it cannot be assumed the ice is sufficient for support. What you cannot see may result in a sink or swim experience. On the 55-50SN valve body, a clean core is not indicative of the function.

This material is a route past the “thin ice” that other travelers have marked. At these flags per say, the test or inspection, frequently points to the valve body, as it accounts for the majority of the transmission’s issues. The 55-50/51SN is installed into a multitude of vehicles and there will be variations to the unit and this data. A similar valve body will bolt to a GM, Volvo, Saturn, Nissan, Saab, Opel or Renault. Failure to test and recognize can create hours of additional effort.

Pressure and Fill:

All the pressure plugs have a 12mm head. Do not mistake the 27mm band anchor (see Figures 1 and 2) for a fill plug or pressure tap. If that anchor is removed, the band will have to be recaptured. Positioning the band requires removal of the servo, at best and possibly the complete transmission.

The turbine sensor hole can be use to improve the fill speed. Low fluid or excessive overfill, can create erratic pressure and poor linear solenoid control, eventually forcing a TCM high pressure strategy.

If the transmission is in the vehicle, “test the ice” per say, at the pressure taps relative to these complaints:

TCC RPM Fluctuation and Overheated Fluid

Check SLT pressure and C-1 clutch. The C-1 clutch is engaged via pressure rise by SLT solenoid and through a series of modulated valves. The SLT pressure should start at 5 psi in Drive and increase with throttle and load to 80 psi maximum. SLT will cut back and spike on various shifts, depending on the TCM program.

Typical C-1 pressure is -0- in Park. As Drive is selected, it quickly steps to 25 psi, then 50 psi within half a second, and remains until accelerated. C-1 psi will then follow load, with a maximum near 200 psi. If C-1 pressure upon selecting Drive is immediately 160 psi and obtains 200 psi during a shift, the unit may be under a TCM code/ failsafe mode. Engagements at this time are abrupt. Some vehicles (Volvo specifically) may use a C-1 disengagement via brake signal creating a neutral at idle. Check for a TCM flash to eliminate this condition.

Compare the B-4, servo apply pressure, to the C-1 clutch. The B-4 tap is at the top of the case, in line with the linkage bolts.
The B-4 circuit has extensive valve body control and includes a tube with o-ring ends that feed the servo. Comparing C-1 to B-4 is an indication of control by the SLS and SLT linear solenoids, a failsafe or leakage condition.

Proper B-4 pressure should follow C-1 and never be less than 10 psi of C-1. (Refer to the C-1 pressure testing.) If C-1 psi is fixed at 160 psi upon engagement, the 1-2 and 3-4 shift may be acceptable, but the 2-3 is generally too harsh. A TCM pressure management code, aerated fluid, or bad speed sensor will eliminate the SLT pressure curve and force B-4 to an immediate 200 psi, which results in the harsh 2-3 shift. If the pressure curve of both C-1 and B-4 are parallel, C-1 initial engagement is near 50 psi, and the 2-3 is harsh, the vehicle may require a flash update, but perform a key cycle and numerous drive cycles first. Some manufacturers (Volvo) have servos and a reflash to improve 2-3, 3-2 driveability.

SLT Air Test:

Before removal of a valve body from the transmission, you can perform a visual wet air test of the SLT circuit.

If you pressurize the SLT port with shop air (80-100 psi), air pressure will push fluid, which you see as a leak. Problematic leaks occur at the steel side cover, SLT accumulator, B-1 and C-1 control valves. A major leak, or combinations, cause delayed engagement or flare up-shift and should be inspected after disassembled.

You can perform a similar air test (Figure 4) with the valve body itself. When doing so, the pump line port and thermal element hole must be closed and the separator plate held as shown to eliminate cross leaks. This might sound confusing in print, but when you do it, the ports will be evident and easy to close with an opposite hand.

Valve Body Inspection:

There are many variations, which complicate coring and matching parts. Figure 5 identifies visual changes. Currently there are 6 different shift solenoids, 4 of which can be installed in incorrect locations or replaced by a normally open vs. normally closed solenoid. The shift solenoids should be checked for proper flow when open and their seal when closed. These are fed line pressure from an orifice in the plate and can be over-pressurized.

Three linear solenoids are calibrated to the valve body. Exchanging SLT, SLS solenoids between cores, without adjusting to the valves, is generally not acceptable. Don’t hesitate to open and inspect the valve body…as it’s comparable to other Aisin Warner designs and not difficult to reassemble. That inspection should include all the removable sleeves, both regulator valves and the solenoid modulator bore. The linear solenoids are fed by this modulator valve which limits the maximum pressure. When that bore is worn, the concern is similar to a bad GM actuator feed circuit.

Excess wear appears as a discoloration, or polished area, in the shape of a moon phase, generally at the ends of the bore or opposite side of fluid entry (see Figure 6).

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SLU-Remains Same Early-Late

• #2 solenoid is N.O. on GM must use Volvo N.C. on #2
• Always resurface castings on all valve body areas
• Seal end plugs for C-1 control, B-4 release, B-1 control

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Linear Lock-up Solenoid ( SLU)

This Solenoid Affects:

• 1-2 up-shift. ie; too firm or bumpy
• 2-1 downshift. ie; harsh, bump
• Light throttle TCC modulation. ie; cycling rpm or cooler flow
• Full TCC lockup. ie; late, bump on coast down release
• TCC release on coast; too early, loss of engine braking
  

Refer to the pressure chart for examples of operation.

SLU Service and Adjustment at the Bench:

• Pre-measure the adjuster, remove the threaded adjuster, then the valve from the solenoid.
• Verify the pintle (shaft passing through coil), is free-floating by performing a shake test.
• Re-assemble and turn the adjuster to the original position.

Driveability and VBT Test Stand Verification:

• The SLU is pulsed during 1-2, 2-1, 2-3, 3-2 shift, also during engagement into Drive or Reverse and TCC apply. Monitoring cooler flow with a SonnaFlow® will indicate if the SLU is adjusted properly. A quick flow reduction of 50% and then a return, indicates the SLU is reacting to TCC valves. For example, 1.0 gpm in Park, then upon Drive engagement, a sharp drop to .06, and a quick return, identifies the correct action.
• If you have harsh up/down shifts and you do not see a cooler flow toggle, the SLU is not adjusted or working properly.
• The correct adjustment on SLU will increase cooler flow. Improper adjustment will reduce cooler flow substantially.

SLU Adjustment in the Vehicle:

• The solenoid can be adjusted if a pass-through hole has been located in the cover during bench rebuild. The SLU access will be at the top, left corner. A 3 mm Allen wrench, will pass approximately 1.60” or 40.9 mm through the cover, when it’s inserted into the adjuster. You should be able to feel the Allen engagement. As you turn the Allen wrench you will feel the retainer click over the index. Always count your rotations, in clockwise (CW) or counter-clockwise (CCW), so you know where you start/stop.

CW/In reduces SLU output resulting in:

• Hard 1-2, 2-1 shifts
• Firmer/later TCC
  

CCW/Out increases SLU output resulting in:

• Softer shifts
• Earlier TCC
  

Road Test:

• If your TCC control, 1-2 and 2-1 are good and cooler flow drops properly as noted above, leave the adjustment as is. If not, adjust accordingly.
• Slight bump on 2-1 down-shift… and/or TCC rpm fluctuates at 30-40 MPH during modulated apply….and/or excess TCC slip at full lockup…and/or SonnaFlow® sensor indicates TCC control valve is continually toggling on-off. If so…turn adjuster screw in/clockwise 1.0 turn.
• Harsh 2-1 downshift….and/or heavy TCC RPM fluctuation at 30-40 mph…and/or late and firm full TCC apply. If so…turn adjuster in/clockwise 1.5 to 2.0 turns.
• TCC will apply not modulate slip RPM at 30-40 mph. Beyond 40 mph, TCC apply is short and harsh…. and/or a harsh TCC release on coast and/or 1-2 shift is too harsh. The adjuster is too far inward, back it out/ counter-clockwise as required 1.5 to 2.5 turns.
• Low cooler flow when in lockup. No TCC flow drop upon engagement or shifting. Adjuster may be too far out/CCW.

Notes:

• The spring between the adjuster and the valve tends to have some memory or coil wrap up. If you over-compensate in one direction, it may require more of an opposite direction to restore.
• During road test, you will need a temporary plug in the access holes.
• If you can feel the adjuster turn out against the retainer, STOP… or you can force the retainer off. If you have adjusted to this point, you are beyond resolving a problem with a solenoid adjustment. Generally 1-2 turns in/ out is all that is needed.

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Line Pressure Solenoid ( SLT)

This Solenoid Affects:

• Reverse engagement. ie; too firm, or delay
• Forward engagement. ie; delay forward
• Upshift/downshift quality. ie: harsh upshifts, coast down clunk
• 2-3 upshift. ie: long flare, or tail bump
• SLT pressure tap. Pressure too low, and slow response
  

Refer to the pressure chart for examples.

Note:

• Increasing SLT , generally will not eliminate a 2-3 flare. Check servo design and travel. Then test B4 pressure tap, It should be parallel to C-1.

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Shift Pressure Control Solenoid (SLS)

This Solenoid Affects:

• Reverse engagement
• Upshift and downshifts
• Does not affect forward engagement
• This solenoid pressure only reacts on the shift pressure control plunger to adjust clutch pressure. It is pulsed to control the feed rate of the clutch, dependent on engine load.
  

Refer to the application chart.

The Service Procedure is the Same as the SLU, and SLT Above.

Driveability and VBT Test Stand Verification:

• The valve body has an SLS access on the back-side, with a 10mm hex nut. It is not accessible in the vehicle. On the VBT the solenoid is operated at 300 Hz. To duplicate the correct on-car operation, this solenoid would have the duty % lowered during each up/down shift. Pressure ranges from –0- to 78 psi.
• Ensure the end plate on the rear control body is flat and the bore of the outer sleeve is not worn. Generally these do not wear in excess.

SLS Adjustments in the Vehicle:

• The access hole will be located on the left side of the cover, lower than the SLU and in the bolt radius of the cover. Turning the SLS screw inward/clockwise, increases the SLS pressure.

High SLS pressure causes (CCW/Out, reduces SLS pressure):

• Harsh reverse
• 1-2 shift harsh
• 2-3 harsh with an end bump
• Loss of TCC apply
• Elevated C-1 clutch pressure
• 3-2 maneuver flare/ bang

Note:

• Some of the 3-2 bang complaints are caused by a noncompatible valve body. Some of these 3-2 flares, can be reduced with SLS adjustments.
  

Low SLS pressure causes (CW/In, increases SLS):

• Soft upshifts
• Low speed 2-3 flare
• Slight RPM flare on 3-4, 4-5 shifts
  

Note:

• SLS does not affect forward engagements.

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• High current causes high pressure
• Solenoid is normally closed (N.C.)
• 300 Hz operating frequency 15%-48% duty 1 AMP, TCC is off
• SLU controls 2nd clutch (B-2) and low reverse (B-3). Manual low for engine, braking
• SLU– Has been know to create 1-2 slip, 2-1 harsh downshift if not adjusted or defective. It also can overheat fluid and affect TCC apply
• SLU generally controls TCC right after 2-3, and will maintain TCC apply coasting or cruise at 25 mph.

Chart Example: ‘03 Volvo V70 XC

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• 300 Hz operating frequency 15%-48% duty
• SLT is normally open solenoid (N.O.)
• Low current causes higher pressure (inverse proportional)

Chart Example: ‘03 Volvo XC 70 Vehicle Data

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• 300 Hz operating frequency @ 15-40% duty
• SLS is normally open solenoid (N.O.)
• Low current causes higher pressure (inverse proportional)
• This solenoid is spiked to increase clutch feed, then modulated between shifts
• Coast down shifts are modulated also with a pressure rise after each shift
• SLS controls: 2nd, 3rd, 4th, B-1 brake, 5th, Reverse, C-2 clutch
  

Chart Example: ‘03 Volvo V70 XC

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Note: If C-1 pressure upon initial engagement is 160 instead of the 50-60 psi, the TCM has commanded a pressure rise. Verify with SLT amperage, then check for codes and electrical issues.

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Separator Plates

Identification:

• Plates must match the top & middle casting.
• A separator plate modification can be performed, if the secondary regulator bore has minimal wear. This modification will increase lube and converter feed oil flow. Enlarging the plate feed holes is not suggested if the valve body casting has excessive wear at the secondary regulator bore, in the area of the spring to spool surface.

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Bob Warnke is vice president of technical development and a member of the TASC Force® (Technical Automotive Specialties Committee), a group of recognized industry technical specialists, transmission rebuilders and Sonnax Industries Inc. technicians.