C-4 clutch problem

[Ed H.]

I was in the process of driving my 1990 L-98 to a car show in L.A. early this morning. I found that when I pressed on the clutch it failed to disengage from the flywheel/transmission. Upon limping home and removing the ECM module I discovered the small clutch master cylinder was dry. I attempted to remove the cap, it would not budge. The shop manual does not state if the cap is removed by prying or twisting off. It is mounted to the fire wall by plastic fittings and I am afraid to put a lot of pressure on the unit. Someone with C-4 clutch systems knowledge would be greatly appreciated. I will address the leak once I can remove the cap. My 3 inch thick shop manual has advised listed for such a problem. Onward and upward.

[Joe L.]

Re: C-4 clutch problem

I was in the process of driving my 1990 L-98 to a car show in L.A. early this morning. I found that when I pressed on the clutch it failed to disengage from the flywheel/transmission. Upon limping home and removing the ECM module I discovered the small clutch master cylinder was dry. I attempted to remove the cap, it would not budge. The shop manual does not state if the cap is removed by prying or twisting off. It is mounted to the fire wall by plastic fittings and I am afraid to put a lot of pressure on the unit. Someone with C-4 clutch systems knowledge would be greatly appreciated. I will address the leak once I can remove the cap. My 3 inch thick shop manual has advised listed for such a problem. Onward and upward.

Ed------

The clutch master cylinder has a twist-off cap. The master cylinder consists of 2 main components---the hydraulic cylinder with associated parts + the plastic reservoir. However, the master cylinder is attached to the firewall by steel studs and nuts, not plastic fasteners. The reservoir is attached to the hydraulic cylinder by, as I vaguely recall, plastic parts including those that are part of the reservoir. By now, the plastic reservoir might be somewhat brittle. So, I would try to use something to hold the body of the reservoir while twisting the cap.

When leaks in the system occur, it can be either the master cylinder or the slave cylinder. However, in my experience, the slave cylinder is the culprit most often. A slow but consistent leak from the slave cylinder may go unnoticed. Plus, the whole system does not have a great capacity for fluid. So, if there is even a small leak, over time the master cylinder can be drained.

Neither the slave cylinder nor the master cylinder for your application are available anymore from GM. However, new parts are available in the aftermarket.

By the way, GM offers a special fluid for hydraulic clutch systems. I use it exclusively. Some folks probably use regular brake fluid. I do not.