The vacuum modulator system on the Hydra-Matic 4T60-E transaxle controls shift feel (may be soft or firm shifts) by sensing the changes in the engine load, which is indicated by the engine vacuum. The modulator does this by controlling the main line pressure boost. The vacuum modulator system may be suspect for firm or slipping shift conditions.

The Hydra-Matic 4T60-E transaxle requires 44-57 kPa (13-17 inch Hg) of engine vacuum at hot engine idle checked at the modulator with the transaxle in Drive for proper operation. An incorrect vacuum supply to the modulator or a malfunctioning modulator may cause some or all of the listed conditions:

The following may cause an incorrect engine vacuum signal at the modulator:

Also, the engine mechanical and the operating conditions related to the following may result in incorrect engine vacuum or poor transaxle performance:

Disconnect the vacuum supply line at the modulator and install a vacuum gage to the line to check for the proper vacuum. Locate the cause and correct as required if there is less than 44-57 kPa (13-17 inch Hg) of vacuum at hot engine idle with the transaxle in Drive. The gage reading must respond quickly (only 1/10th of a second delay) to the throttle movement because the vacuum is supplied through a 0.031 inch orifice in order to stabilize the line pressure when shifting the transaxle between forward and reverse ranges.

Remove the modulator and remove the modulator valve if there is enough engine vacuum available to the modulator. Inspect the valve for nicks. Inspect the valve for scoring. Connect a hand-operated vacuum pump to the modulator. Pump the device until 51-68 kPa (15-20 inch Hg) of vacuum is reached while observing the modulator plunger. The modulator plunger should be drawn in as the vacuum pump is operated. The vacuum should not bleed down for at least 30 seconds after reaching 51-68 kPa (15-20 inch Hg). Perform the next test if the modulator checks okay.

If the following conditions are met then the shift problem is not vacuum related:

Perform the oil pressure check outlined in the Hydra-Matic 4T60-E diagnosis section if the above conditions are met. Refer to the appropriate diagnosis if the pressures are out of specifications.

Perform the following steps to inspect the vacuum diaphragm:

1. Turn the modulator so that the vacuum connector faces down.
2. Replace the modulator if any of the following liquid drains out:

•	If transaxle fluid drains out.

•	If water condensate drains out.

•	If gasoline drains out.

Perform the following steps to inspect the vacuum modulaor for a atmospheric leak:

1. Apply a soap solution to the vacuum connector.
2. Apply a soap solution to the crimped seam.
3. Attach a short piece of hose to the vacuum connector.

Notice: Do NOT use compressed air. Pressures in excess of 41 kPa (6 psi) may damage the modulator.

4. Blow into the hose to check for leaks.

Tool Required

J 36619 Modulator Comparison Gage

Perform the following steps to inspect the load:

1. Install a known good modulator of the same type on one side of the J 36619 Modulator Comparison Gage.
2. Install the modulator to be tested on other side of the J 36619 Modulator Comparison Gage
3. Hold the assembly level.
4. Slowly push the two modulators together.

•	The modulator is not acceptable if the gage line remains blue.

•	The modulator is acceptable if the gage line is white.

Perform the following steps to inspect the sleeve alignment:

1. Roll the modulator on a flat surface.
2. Observe the sleeve for concentricity with the modulator can.
3. Inspect the plunger for freedom of movement.

1. Inspect the engine for the following conditions:

•	Inspect the engine for a tune-up.

•	Inspect for loose vacuum fittings.

•	Inspect for improperly routed hoses.

•	Inspect for improperly routed lines.

•	Inspect the hoses for a vacuum-operated accessory leak.

•	Inspect the vacuum valve, etc., for a vacuum-operated accessory leak.

2. Inspect the vacuum line to modulator for the following conditions:

•	Inspect for leaks.

•	Inspect for loose fitting.

•	Inspect for restricted orifice.

•	Inspect for incorrect size orifice.

•	Inspect for carbon build-up at the modulator vacuum fitting.

•	Inspect for a pinched line.

•	Inspect for grease in the pipe (delayed and/or no upshift-cold).