In the Clutch

The clutch comes out, and the Camaro launches hard. The tach hits 6,000 rpm and you stab the clutch pedal, yank on the shifter, and slam the trans into Second gear. Again the motor climbs to 6,000 rpm and you press on the clutch and bang the shifter into what should be Third, but you miss the gear. The motor revs, your foot comes off the gas and you search for Third. On the next pass, the same thing happens. You discover that the only way the trans will shift into Third is if you granny-shift the trans. First to Second is OK, but Second to Third just won’t go.

If this sounds familiar with your fourth-generation Camaro or Corvette, you’re not alone. The LS1 Camaros and Corvettes are plenty quick and have great power. The T56 trans shifts great most of the time, but often it just won’t let you bang Third gear. Several clutch companies claim to offer the solution, but in a recent discussion with Steve Cole of The Turbo Shop, he let us in on a cool little secret that he says will solve these clutch problems and make that T56 shift like a dream.

Ironically, the solution is not with the clutch, but with the hydraulic actuating system. Steve has been building and fine-tuning a high-rpm 302ci LS1 Camaro for Chevrolet that debuted at the SEMA show last year. The Camaro suffered the same fate as the description above and managed to kill a clutch in a matter of minutes. This led Steve to investigate the problem.

The hydraulic clutch actuating system in ’98-and-later Camaros is very simple. It starts with a plastic, injection-molded master cylinder that uses a standard piston and seal assembly to apply pressure when the piston is stroked by the clutch pedal. A –4 steel-braided, Teflon-lined hose connects the master cylinder to a hydraulic slave cylinder that bolts to the front of the transmission and actuates the push-off diaphragm clutch. Steve decided to create a complete bench-mounted system to see if he could locate the problem.

Through experimentation, Steve discovered that it took 5 ½ strokes of the master to move the slave piston through its complete travel. After many hours of experimenting, he discovered a delay in both the actuation of the slave cylinder and the time it took for the fluid to return to the master cylinder. Eventually, this pointed to a restriction in the hydraulic line between the master cylinder and the slave. After a little more detective work, Steve discovered a restrictor in the steel-braided line just downstream of the master cylinder line fitting. By using a pin micrometer, he discovered that the –4 line (which should have an inside diameter of around ¼ inch) included a restrictor that reduced the inside diameter (id) of the line to 0.064-inch or roughly ¼ the id of the hose.

Steve surmised that the restrictor not only delayed release of the clutch, but, more importantly, slowed engagement of the clutch as well. This means that after releasing the clutch pedal when the car is launched, the hydraulic fluid is still trying to return to the master cylinder when the clutch pedal is hit again for the One-Two shift. This again delays the return of fluid to the master. When it comes time for the Third-gear shift, the fluid is still stacked up in the line, preventing the clutch from releasing properly. This is what causes those missed shifts. Slowing the shift down allows the hydraulic system time to recover and perform its normal function.

Once Steve discovered the restrictor in the line, he used a 1/8-inch drill bit and carefully drilled out the restrictor to 1/8-inch, cleaned and flushed the line to remove the chips, reassembled the line to the system, and then bled the system to remove any air. With the system back on the car, a quick test blast down the street instantly eliminated the Third-gear shift problem. Since then, the Camaro has run numerous 12-second quarter-mile runs with no hint of a problem.

So why did Chevy engineers design the hydraulic system like this? Steve thinks that the restrictor has little noticeable effect on clutch disengagement. However, when engaging the clutch, the restrictor softens the “hit,” which reduces the abuse on the drivetrain. On quick, fast shifts, this unfortunately adds slippage and also builds heat very quickly in the clutch and flywheel. For everyday driving, the restrictor may be acceptable, but for performance driving and dragstrip use, this could mean the kiss of death.

This quick fix also applies to older supercars if they employ the stock Chevrolet hydraulic clutch actuating system. Steve’s only experience has been with the ’98-and-newer hydraulic clutch systems, but it’s possible that the older hydraulic systems may also use a restrictor. The only way to determine if the line has a restrictor in it is to slide a 1/8-inch drill bit down the length of the inlet side of the braided steel hose. If the bit hits a restriction, then you know you’ll need to modify the hose. Unfortunately, typical AN –4 lines will not work on this system since the GM line uses special GM hybrid fittings that are not compatible with AN lines.

The best news about this whole deal is that other than investing a couple of hours to remove the line and drill the restrictor, this modification costs nothing. We’re not guaranteeing that this modification will earn you the title of Mr. Six-speed, but it can’t hurt. It certainly doesn’t cost anything to try it.