Jim Smart
August 1, 2009
The intermediate servo on the right hand side is removed first. Because this C4 is for a six cylinder, it has the "Z" servo, the smallest for a C4. Servo size is a matter of piston/bore size and displacement. High-performance applications call for the largest "C" servo, which yields a firmer intermediate band lock-up. The "C" servo is available as a reproduction. TCI Automotive also has a large intermediate servo kit (No. 523005) available for C4 transmissions.

If you're running an '82-up 5.0L engine, you will need a 50-ounce offset balance flex plate or face severe engine vibration.

157-tooth flex plates have a 10.5-inch torque converter bolt pattern while 164-tooth have 11-7/16-inch.

How To Adjust Bands
Intermediate Band Adjustment: Left side of case, tighten to 10 ft. lbs., then back out 1½ turns counterclockwise. The 10 ft. lbs. snugs the band around the drum before backing out 1½ turns. Tighten locknut.

Low-Reverse Band Adjustment: Right side of case, tighten to 10 ft. lbs., then back off three turns counterclockwise.

Torque Converter-How Does It Work?
TRC has the rare distinction of being a transmission shop that rebuilds its own torque converters. Ron Hazelton's son, Troy, specializes in torque converter design and function. Troy walked us through the rebuilding of Gary's factory original torque converter, which needed little more than a good clean up and inspection. It was in perfect mechanical condition.

On the left side, neutral safety switch and kick-down linkage are removed next. We suggest a new neutral safety switch and kick-down cable/linkage from National Parts Depot. The neutral safety switch tends to be a weak link with time and age, causing a no-start condition.

A torque converter does three things: it transfers power from the engine to the transmission's input shaft, multiplies torque to give the engine mechanical advantage, and turns the transmission's front pump to make hydraulic pressure for proper function.

Torque converters consist of five major components - front shell (impeller), stator (hub), turbine (drives the transmission input shaft), rear shell (drives the front pump), and sprag (one-way clutch). The front shell, which contains the impeller, is what gets fluid moving through the converter. The stator is the torque converter's traffic cop. It vectors fluid from the impeller to the turbine, which is splined to the input shaft. The sprag is a one-way clutch located inside the stator, splining it to the transmission's front hub. The sprag's job is to keep the stator locked in position when the torque converter stalls.

Stall speed is when engine rpms are high enough to move the vehicle. As vehicle speed picks up, the stator whirls around with the rest of the torque converter. The stator's primary job is to get us started when the accelerator is pressed. In short, torque multiplication.

This is the low/reverse servo, which controls the low/reverse band and clutch drum. The cover is stamped steel, unlike the intermediate band servo cover on the other side, which is cast aluminum.

Torque converter stall speed should be chosen based on where your engine makes the most power. For stock applications, stall speed should be somewhere around 1,400-1,800 rpm. Weekend racers want to see a higher stall speed around 2,400 rpm, which helps the drag racer get rolling because that's where an engine starts making power. Serious racers want an even higher stall speed around 3,500 rpm. So what does that feel like? When you step on the gas with a high-stall converter, the engine will rev, but not begin to move the vehicle until rpm reaches 3,000-3,500 rpm, which would never be good for the street. Street engines need immediate transmission response right off idle, which calls for a lower stall speed. Street torque converters with low stall speed don't need to be as rugged as racing converters either. Racing converters with higher stall speed need to be rugged, with furnace-brazed fins and heavy-duty components.