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


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


Sonnax drop-in boost valve kit restores hydraulic integrity to the bore.


Boost Valve Kit
Part No. 56947-05K

Factory Style, Low Ratio

You need this if... View Instructions Find a Distributor

Some typical problems in vehicles with a Ford A4LD transmission are 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 boost valve kit 56947-05K replaces worn parts and matches the OE-style, low-ratio valve.

56947-02K 56947-05K
Ratio High Low
Ø A .388" .323"
Ø B .571" .571"
Ø C .634" .606"
Engine 4.0L 2.3, 2.8, 2.9, 3.0L
  • Low ratio, OE-style valve
  • Hardcoat anodized aluminum valve combats premature wear
  • Sleeve manufactured from highly wear-resistant aluminum
  • Drop-in Zip Valve parts install quickly and easily
Learn More About Zip Valve™ Drop-In Repairs
  • Sleeve
  • Valve
  • A4LD Boost Valve Kit 56947-05K
  • A4LD Boost Valve Kit 56947-05K

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 pres-sure. 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:
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.

A4LD Boost Valve Kit Vacuum Test Locations