Nissan Repair: Bleeding Hydraulic Clutch on 86 2-wheel drive pickup, air compresser, clutch cylinder

Question
Hi Von,  

You anwered several questions from me during the summer, regarding a clutch change on my 1986 Nissan 2-wheel drive, 5-speed, 720 model pickup.  

Everything is now in, but now I'm having trouble bleeding the hydraulic clutch.  My friend and I used a clear plastic hose attached to the zirk with the other end in a jar of brake fluid.  We bled the damper and then the clutch cylinder, holding the clutch down while one person opened the zirk, and only released the clutch when the zirk was tightened up.  We bled until we didn't see any bubbles from either zirk.  There didn't seem to be much of a flow of fluid coming out of either zirk, but the level did go down at the master cylinder.  We topped off the fluid so it didn't go down below the add line.  

However we can't get a firm clutch at all. I replaced the clutch cylinder with a new one, in the hope that would help, but it didn't.  Before the new clutch cylinder I would get a bit of a firm clutch, but with a few presses of the clutch, this would go away.  Now no pressure seems to build at all.    

I've read about pressure bleeding and using a vaccuum bleeder, but haven't tried any of those yet.  I'm willing to purchase these if needed.  I do have an air compresser if that could be used in any way.

Could you give me some instructions and tips on what I'm doing wrong, and how to bleed this clutch so it will work?

Thank you for any instructions and help you can provide,

John  

Answer
John,

Hydraulic clutch systems are difficult to bleed.  You are doing it correctly.  But, it takes many times to get the air out of the system.  Also, a vacuum bleeder or a pressure bleeder will aid in the process.  If you open the line at the bottom, at the fitting, just open it and let the fluid flow.  But, do not let the the fluid get too low in the reservoir.  Once fluid will flow, on its own, close the valve.  Now, bleed the clutch as you described.