Ford C4 and C6 Transmission Trouble Shooting Guide

It’s good to have a source to guide you when you’re struggling with troublesome transmission function. You can be methodical and cover all the bases during a rebuild and still things can go wrong. This is where a step-by-step approach to the problem can help get you steered in the right direction. As with just about any type of troubleshooting, begin with the simplest item first and work the problem from there. Don’t panic, but assume the worst.

The first thing to do is find out whether the transmission works. With the engine running, does the transmission engage when you put it in drive or reverse? If not, immediately shut off the engine and check the transmission fluid level.

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Is there fluid on the dipstick? If not, add fluid in small amounts until the dipstick shows at least “half.” Then, start the engine. You want a half-stick reading because fluid expands as it warms.

Operating temperature is 150 to 170 degrees F. If (with a fluid reading on the dipstick) your transmission doesn’t engage, control pressure likely isn’t reaching servos and clutches. This means there’s either no control pressure or pressure isn’t making it to the clutches and servos. The absence of control pressure to components happens for several reasons: pump not making pressure, torque converter cavitated, stuck pressure relief valves, manual shift valve not working, valve body malfunction, failed servo piston, or failed clutch piston seals to name a few possibilities.

If there is fluid on the dipstick, check the manual shift valve, which is where control pressure begins.

Transmissions that are overfull tend to foam or aerate causing air bubbles to be drawn into the torque converter and pump, which causes a great disruption in control pressure. With the engine running, listen closely for abnormal noise such as torque converter improperly seated, which can cause squealing, no control pressure, and an inoperative transmission. An improperly seated torque converter can’t turn the pump or the input shaft rendering a transmission inoperative. At the same time, it damages the pump, sending metal particles into the system doing further damage. When transmissions don’t engage, most of the time it is an improperly seated torque converter, a pump issue, or a manual shift valve problem.

The following are common symptoms and their likely causes.

 Transmission Doesn’t Engage in Drive or Reverse

1. No control pressure.
2. Low fluid level.
3. Torque converter and/or front pump cavitated (no fluid or air in fluid).
4. Torque converter improperly installed, doesn’t turn pump (listen for noise).
5. Manual shift linkage between car and transmission improperly adjusted.
6. Manual shift valve inside transmission pan not connected or stuck.
7. Pressure relief valve (or valves) unseated or missing.
8. Forward clutch pressure leak or improperly assembled (air check clutches by removing the valve body).
9. Blocked filter.

No 1-2 Upshift

1. Governor valves malfunction.
2. Governor improper installation on the output shaft (is the drive ball in place?)
3. Shift valve jammed.
4. Intermediate servo malfunction.
5. Broken or improperly assembled roller clutch.

 Early or Late 1-2 or 2-3 Upshift

1. Vacuum modulator or rod malfunction.
2. Valve body malfunction.
3. Governor malfunction.
4. Loose tubes on governor distributor.

No Upshift at Wide-Open Throttle

1. Vacuum modulator or rod malfunction
2. Governor or fluid passage malfunction.

No Reverse

1. Low fluid level.
2. Manual shift valve out of adjustment.
3. Manual shift linkage improper installation and/or adjustment.
4. Vacuum modulator malfunction or failure.
5. Valve body assembly error.
6. Blocked filter.

Slippage in All Gears and Start Out

1. Low fluid level.
2. High fluid level (foaming).
3. Blocked filter.
4. Faulty vacuum modulator.
5. Insufficient pump pressure (sticking relief valve, gear/cavity damage).
6. Faulty torque converter.
7. Insufficient clutch engagement (pressure, clutch clearances).
8. Insufficient band engagement (improper adjustment, pressure).

Vehicle Slips or Ratchets in Park

1. Improper shifter adjustment.
2. Parking pawl damaged or improperly installed.

Delayed Upshift or No Upshift When Cold

1. Hard or damaged clutch piston seals.
2. Insufficient pump pressure (sticking relief valve).

No 1-2 Upshift

1. Governor issue, stuck valve.
2. 1-2 shift valve issue.
3. Intermediate band servo not applying.
4. One-way clutch defective or improperly assembled.

Slips at 2-3 Upshift

1. Improper direct clutch clearances.
2. Damaged direct clutch piston seal.
3. Leaking iron-sealing rings.

No Engine Braking in Second Gear

1. Valve body issue.
2. Damaged intermediate band or improper adjustment.
3. Intermediate band servo piston seals.

No Engine Braking in First Gear

1. Valve body issue.

Written by George Reid and Republished with Permission of CarTech Inc