722.6 Valve Body Bore Wear: Symptoms, Vacuum Testing, and the Real Fix

722.6 Valve Body Bore Wear: Symptoms, Vacuum Testing, and the Real Fix

722.6 Valve Body Bore Wear: Symptoms, Vacuum Testing, and the Real Fix

A 722.6 that flares on the 2-3 upshift, drops into limp mode on a hot day, or shudders pulling away from a stop is almost never telling you the clutches are gone. In the overwhelming majority of these units the clutches are fine and the aluminum valve body casting is worn. The valves in a 722.6 run at high speed in a soft casting, and once a bore opens up, the pressure that was supposed to hold a clutch simply leaks away.

Shop rebuild kits and parts by transmission

This is the same unit Chrysler calls the NAG1. Sonnax notes the 722.6 went into production for 1996 model year vehicles and shows up in Mercedes, Porsche and Jaguar, while US NAG1 variants include the W5A580, W5A380, W5A330 and W5J400 — and in the W5A series, those last three digits are the maximum input torque in Newton meters. The W5A330 has the widest gear ratio of the group, and the J400 identifies a Jeep application.

The symptoms that point at a worn bore

Per Sonnax, the classic 722.6 drivability complaint is engine RPM flare on the 2-3 or 4-5 upshift, or a neutral flare on the 5-4 or 3-2 downshift. TransGo lists the same pattern for this unit: 2-3 upshift flare, insufficient pressure rise, TCC slip or shudder, soft shifts, and shudder on hard acceleration from a stop — and attributes the 2-3 flare complaints to a slow pressure rise curve caused by wear at the pressure regulator valve bore.

Sonnax lists these specific symptoms against its pressure regulator repair parts:

  • No 2-3 shift
  • 4-3 neutral condition
  • Soft shifts under load or under acceleration
  • Slip codes
  • Delayed engagement
  • No lockup

Separately, the torque converter lockup clutch regulator bore produces TCC apply and release concerns, TCC codes and lube failures, while a worn lubricating pressure control valve bore produces delayed engagement, high stall speed, overheated converter, damaged converter and generally poor performance.

How the 722.6 actually loses pressure

The 722.6 was one of the first five-speeds built around load-sensitive working pressure and overlap clutch control, and Sonnax is direct about the consequence: all of that precise hydraulic control is exactly what makes bore wear so destructive here.

The working pressure regulator valve. Sonnax describes the failure this way: the outer bore of the working pressure regulator valve wears and allows the pMod solenoid signal oil to leak past the boost end of the valve. As the casting wears, working pressure no longer rises with engine load — and that is your flare or loss of gear. Sonnax's technical write-up on this unit goes back to 1998, when high-mileage Mercedes cars repaired under warranty repeatedly showed 2-3 flare and limp mode, and the link was traced to working pressure bore wear. Sonnax attributes the root cause to the lack of hardness in the valve body material itself.

It gets worse than a single wear point. Sonnax notes the PR valve is a long, one-piece design, so when it is leveraged on the larger end it also loads into the bore on the smaller inboard end. You get wear at both ends of the same bore. On the repair side, Sonnax states that excessive valve-to-bore clearance at the modulating pressure area lets modulated solenoid feed pressure exhaust and drops line pressure, while bore wear at the inner spool produces a high line pressure condition instead.

The overlap control sleeves. This is the part most people skip. Sonnax points out that the 1-2/4-5, 2-3 and 3-4 overlap sleeves sit in the same pMod solenoid signal circuit, and that it is common for them to wear on the I.D. and leak at the O.D. as well. Wear at any of those sleeves reduces pressure at the working pressure valve. Sonnax attributes the wear to continuous plunger valve oscillation. TransGo makes the same call, listing worn overlap regulator valve bushings as a cause of flare-up complaints on either upshifts or downshifts. Replace the PR valve, leave the overlap sleeves alone, and the car can come back still flaring.

The lubrication pressure regulator valve. ATSG's Wayne Colonna, writing in Transmission Digest, covers a bore that gets overlooked entirely. The lubrication pressure regulator valve controls converter charge or "in" pressure, which becomes converter "out" pressure to the cooler. When the inboard land wears its bore, unregulated line pressure reaches the converter charge circuit and raises pressure inside the converter. Because the 722.6 converter contains an actual clutch pack with a pressure plate, and the pressure plate end is open to the charge circuit, that elevated pressure partially applies the converter clutch — producing a vibration or judder that stops the moment TCC is commanded on, often with a very abrupt engagement. Colonna also explains the cold stall-into-drive complaint: the lockup solenoid is pulsed at about 40% in Park or Neutral with a slight overlap when Drive is selected, and with elevated converter pressure plus cold oil, that is enough clutch application to stall the engine. Note that ATSG's finding is elevated converter pressure rather than lube starvation, while TransGo describes the same valve's wear as costing both lube pressure and converter apply pressure — either way, this bore has to be inspected.

Diagnosis: vacuum test before you buy anything

Do not guess at which bore is worn. Sonnax publishes a dedicated Mercedes 722.6 / Chrysler NAG 1 vacuum test guide that maps critical wear areas and test locations across both the upper and lower valve body, and the method is straightforward.

  1. Drop the pan and pull the valve body. Note which fluid the unit takes before you start — Sonnax specifies that Sprinter, Crossfire and Mercedes units require a specific fluid due to calibration issues, while the other Chrysler applications use ATF+4.
  2. Clean the valve body thoroughly and separate the halves so both castings can be tested.
  3. Test each valve in its rest position. Sonnax's guide states that OE valves are shown and should be tested in the rest position unless otherwise indicated.
  4. Plug the casting valley with foam or putty at the shift valve test locations, as the guide instructs, so you are reading the bore and not the open casting.
  5. Read the gauge. Sonnax's rule is simple: a low vacuum reading indicates wear. Refer to the individual part instructions included with each kit for the specific in-Hg minimum at that port.
  6. Back up the gauge with your eyes. Sonnax states that both PR valve wear conditions can be found by either a vacuum test or visual inspection, and that the overlap sleeves can be vacuum tested prior to removal or simply cleaned and inspected for wear.

If you have never run this test, our walkthrough on how to vacuum test a valve body to find bore wear covers the tooling and the technique in detail.

The fix: which part, and why

Once a bore tests low, you have two honest paths: recondition the bore and install an oversized valve, or replace the valve body assembly. Sonnax's oversized parts for this unit are:

  • 68942-07K Oversized Pressure Regulator Valve Kit — Sonnax's full-bore repair, using an oversized hardcoat anodized aluminum valve with recalibrated springs. The outer spool is extended for better support, and the spools carry annular grooves to prevent future side-load wear. Sonnax notes it fits bores containing the OE PR valve with a .512" diameter spool only, and requires tool kit F-68942-TL7 plus the VB-FIX fixture.
  • 68942-06 Outer Pressure Regulator Sleeve — restores the modulating pressure bore area only. Sonnax explicitly flags this as an outer-bore repair and points to 68942-07K for the full bore. Sonnax also warns that the required tool kit F-68942-TL6 is no longer in production, so check availability before committing to this route.
  • 68942-02, 68942-03 and 68942-04 Overlap Control Sleeve Kits — the 1-2/4-5, 2-3 and 3-4 sleeves respectively, or 68942-05K for all three. These are drop-in Zip Valve repairs: the sleeve carries an external O-ring for positive sealing in the bore, and Sonnax states the OE spring and anodized valve can be reused. Useful detail from Sonnax for keeping them straight on the bench: one end-face notch is the 1-2/4-5 sleeve, two notches is the 2-3, three notches is the 3-4.
  • 68942-14K Oversized Lubricating Pressure Control Valve Kit — for the converter-charge bore ATSG describes. Hardcoat anodized valve with added length at the outboard spool and a new spring for proper calibration.
  • 68942-10K Oversized TC Lockup Clutch Regulator Valve Kit — Sonnax states this restores normal converter charge and cooler flow and corrects harsh or no TCC apply, TCC slipping and burn-up.

For a unit that is worn in the usual places rather than trashed, a valve body repair kit is the practical answer. TransGo's SK 722.6-A is specified for 1996 and newer Mercedes, Dodge, Chrysler, Sprinter, Jaguar, Porsche and Jeep vehicles with the 722.6, W5A-330, W5A-580 and NAG1, and targets exactly the complaints above.

722.6 shift kit valves, sleeves and calibrated springs for valve body bore wear repair
722.6 Shift Kit — valves, sleeves and calibrated springs for the 722.6 / NAG1 valve body.

Browse the full shift kits collection if you need a different unit, or the valve bodies collection if the casting is beyond salvage.

Replace while you are in there

The pan is already off and the valve body is already on the bench. These go back together with it:

  • Pan gasket and filter
  • Valve body separator plate gaskets
  • The adapter plug and case connector O-rings, a known leak path on this unit
  • All three overlap control sleeves if any one of them tested low, since Sonnax notes they share the same pMod signal circuit
  • Correct fluid for the application, per the Sprinter / Crossfire / Mercedes versus ATF+4 split above

Our 722.6 overhaul gasket and seal kit covers the soft parts for a 1996-up unit, and if the unit already has clutch damage from running low pressure, the 722.6 master rebuild kit carries the frictions and steels as well.

Cost and effort: what you are signing up for

The good news is access. The 722.6 valve body comes out from underneath with the pan down, so the transmission stays in the vehicle. For a shop that is a straightforward lift-and-drain job plus bench time, and it is why a valve body repair is dramatically less involved than an overhaul.

The real dividing line is tooling. Sonnax's oversized valve kits are not drop-in parts: 68942-07K requires tool kit F-68942-TL7 and the VB-FIX fixture, 68942-14K requires F-68942-TL14, and 68942-10K requires F-68942-TL10. Each bore has to be reconditioned before the oversized valve goes in. If you do not own that tooling, your realistic options are a drop-in sleeve where one is offered, a valve body repair kit, or sending the casting to a shop that is set up for it. By contrast, Sonnax's overlap control sleeve kits are drop-in and reuse the OE spring and valve, which is why the sleeves are usually the highest-value hour you will spend on this unit.

Budget the job as one afternoon of labor plus fluid and a gasket set. Against an overhaul or a replacement unit, the math on a bore repair is rarely close.

Frequently Asked Questions

Can bore wear in a 722.6 valve body cause limp mode?

Yes. Sonnax documents that in 1998 many high-mileage Mercedes cars repaired under warranty had 2-3 flare that put the vehicle into limp mode, and the cause was traced to working pressure regulator bore wear. When working pressure stops rising with engine load, the shift never completes correctly and the controller protects itself.

Why does my 722.6 shudder from a stop even though the converter is new?

Check the lubrication pressure regulator bore before condemning another converter. ATSG's Wayne Colonna documents that wear at this valve's inboard land lets unregulated line pressure into the converter charge circuit, raising pressure inside the converter and partially applying the converter clutch against its pressure plate. The result is a vibration that disappears the moment TCC is commanded on.

Do I have to replace the whole 722.6 valve body, or can the bores be repaired?

Most can be repaired. Sonnax offers oversized valve kits that salvage a worn casting, including 68942-07K for the pressure regulator bore, 68942-14K for the lubricating pressure control bore and 68942-10K for the TC lockup clutch regulator bore, along with drop-in overlap control sleeve kits that require no reaming. Replacement is the answer when the casting itself is damaged rather than simply worn.

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