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  • Low line pressure in Reverse
  • Low line pressure in Forward
  • Soft upshifts
  • Poor modulator control
  • Delayed Reverse


Worn boost sleeve allows reverse and/or TV pressure to cross leak or exhaust.


Sonnax replacement boost valve kit restores hydraulic integrity to the bore.


Boost Valve Kit
Part No. 56947-02K

Large Ratio, O-ring style

You need this if... View Instructions

Typical problems in vehicles with a Ford A4LD transmission include low line pressure in forward or reverse, soft upshifts, delayed reverse and poor modulator control. These complaints can often be caused by a worn boost sleeve, which allows reverse and/or TV pressure to cross leak or exhaust. Sonnax high ratio boost valve kit 56947-02K with O-rings replaces worn parts and offers higher line rise than the OE-style, low-ratio valve.

Ø A .388" .323"
Ø B .571" .571"
Ø C .634" .606"
Engine 4.0L 2.3, 2.8, 2.9, 3.0L
  • High-ratio valve with O-rings offers higher line rise than the OE valve
  • Manufactured from highly wear-resistant aluminum
  • Valve is hardcoat anodized to reduce wear
  • Sleeve
  • Valve
  • O-Rings (2)

September 30, 2005

Anatomy of a Transmission: Oil Flow in the Pump-PR-Converter-Cooler Lube Circuits

Gregg Nader

Topics: Diagnostics And Theory Transmission

Read Now
  • 56947 02k combo
  • 56947 02k

You need this if...

Performing these wet air or vacuum tests result in leakage.

Test 1:
With the manual valve in the reverse position and the separator plate still
bolted to the valve body, place a small amount of oil into the "A" orifice. Follow with
low air pressure. There should be no oil or air leakage in the exhaust port at "B," If
there is, the boost valve is worn at the reverse land and should be replaced.

During test of reverse circuit, if excessive oil loss is visible at the reverse engagement control plug, the plug is either installed backward (should be large diameter outward) or the plug or bore is worn. This wear will reduce reverse boost effectiveness.

Test 2:
Place a small amount of oil in the checkball hole "C" or "D," Follow with low air pressure while plugging the opposing hole. There should be no oil or air leakage at orifice "E" location. If leakage occures, the boost valve assembly is worn and should be replaced.

To ensure that the pressure regulator balance circuit is functional, perform a wet air or vacuum test at "F." A worn bore will leak to filter suction hole. Many poor converter charge and engagement concerns are related to bore valve wear here. Worn bores can be repaired by using Sonnax oversized pressure regulator valve kit [56947-06K].

  • 56947 02k test