Replaces the worn line pressure boost valve and sleeve in Ford AODE, 4R70W, 4R75W and 4R75E valve bodies to restore full line pressure and firm shifts.
When a Ford with a 4R70W or AODE engages forward fine but hesitates before it goes into reverse, slips backing up a driveway, or loses reverse altogether once it is hot, worn reverse boost hardware in the valve body is one of the first places a rebuilder looks. The Sonnax 76948-02K is a replacement boost valve and sleeve for the pressure regulator circuit in the AODE, 4R70W, 4R75W, 4R70E and 4R75E. Both pieces are hardcoat anodized aluminum, sold as a matched pair, for F-150, Expedition, Crown Victoria, Grand Marquis, Mustang and Town Car owners chasing a reverse problem.
The main pressure regulator valve sets line pressure, and the boost valve and sleeve sit at the end of that bore and push back against it. In this family the factory boost assembly is there mainly to raise line pressure in reverse: when the manual valve is in R, reverse oil is routed to the boost valve, which adds force to the regulator and gives the reverse clutch and low-reverse band the extra pressure they need. Over time the aluminum boost sleeve wears where the valve strokes, oil leaks past, and the extra reverse pressure never fully builds. The reverse clutch and band then apply on too little pressure, slip, and burn.
Sonnax lists these for the 76948-02K:
Forward-gear complaints such as soft shifts in every gear, an erratic buzz or general low line rise point more toward the main pressure regulator valve, the EPC solenoid or the pump, which are covered by separate parts.
Put a pressure gauge on the line tap and compare pressure in Drive and in Reverse at idle and at stall. A healthy unit shows a clear jump in reverse; little or no rise with forward pressure normal points at the boost circuit. Wet air testing the circuit with the valve body off, or a vacuum test of the bore, confirms sleeve wear. Our 4R70W Crown Victoria shift problems guide covers pressure testing on this unit, and the Expedition common problems guide shows how reverse complaints overlap with other known failures.
Sonnax lists the 76948-02K for 1991-later AODE and 4R70W-family valve bodies, which covers the AODE, 4R70W, 4R75W, 4R70E and 4R75E. If you are replacing the main pressure regulator valve with an oversized Sonnax kit, use the boost valve and sleeve supplied in that kit instead of this one, because Sonnax pairs those parts. This kit is the boost valve and sleeve only; it does not include the pressure regulator valve or spring. If you are not sure which valve body you have, send us the year and VIN. More parts for this unit are on our 4R70W parts page.
Because the pump has to come apart for this job, many owners fold it into a rebuild with the 4R70W master rebuild kit for 1998-2003, or replace the pump outright with the 4R75W pump for 1992-2003 when the bore itself is worn.
| Part number | 76948-02K |
| Fits | Ford AODE, 4R70W, 4R75W, 4R75E, 4T70E |
| Material | Hardcoat anodized aluminum |
| Kit contents | Boost valve and sleeve |
| Ports | 2 |
| Brand | Sonnax |
Doing this repair right usually means replacing these at the same time. Same transmission, ships together.
It restores the extra line pressure the 4R70W family builds in reverse. Sonnax lists low reverse boost, delayed reverse, reverse slip, no reverse and burnt reverse clutch as the symptoms it helps cure.
No. This kit is the boost valve and sleeve only. If the main pressure regulator valve is also worn, it needs its own replacement part.
Sonnax lists it for 1991-later AODE and 4R70W-family units, which includes the 4R70W, 4R75W, 4R70E and 4R75E. Send us your year and VIN if you are unsure.
No. The pressure regulator and boost valve bore is in the pump, which comes out only with the transmission removed. It is normally done during a rebuild or pump service.
Probably not by itself. The boost valve mainly affects reverse pressure. Soft shifts in all gears point to the main pressure regulator valve, the EPC solenoid or pump wear.
