Wednesday, October 19, 2011

Repairing 1990 Miata Clutch Hydraulics Master / Slave DIY

Date of manufacture is 08 / 1989

The 4th photo shows the connection between the hard line ( that runs from the master ) and the flexible hose that goes to the slave cylinder.

[  A good article about slave cylinders ==>   ]

I started looking at the clutch hydraulic system because the clutch pedal started by getting soft and then after a few days ... went to the floor with no activation of the clutch.  The clutch was always engaged.  I drove about 20 miles ....  I put the shifter in first gear ;  then I started the engine ... shifted gears without the clutch ...... turned off engine when I had to stop for a light.  I only had to stop 3 times because traffic was very sparse and I was able to time the lights.

One great thing about this is that the slave cylinder is not buried inside the transmission.  Other cars bury the slave cylinder in hateful , hard to reach places.   Starting at the master, I disconnected the hard line and had an associate pump the clutch.  I had my thumb over the fluid outlet from the master.  I could feel pressure and could not hold the fluid from coming out.  I reconnected the hard line and went to where the hard line connects to a flexible hose.  I disconnected the hard line at this connection and put my thumb over the opening.  Pumping the clutch caused nothing to happen at first.  I think this meant there was air in the hard line.  Then there was pressure.  I reconnected the hard line.  I went down to the front wheel and removed the front wheel.  I loosened the air bleed at the slave which I could reach just behind the front disc brake.  I pumped the clutch a few times and re-tightened the air bleed.

Now I have discovered there is a steady leak  ( a drip every 5 seconds ) from the slave.  At first I thought it was leaking from the piston assembly.  I removed the slave from the Miata.  The slave is held on by two bolts.  One is kind of hard to reach and requires a open end wrench and some contortions.  Perhaps is would be easier on a lift.  Maybe a flex coax drive would help. ....... Anyway , I got the slave out and took it apart.  I was surprised to find corrosion and a blob of gunk/dirt/  inside the piston barrel.  Perhaps the DOT3 fluid was absorbing water and that lead to corrosion.  I cleaned everything up and reassembled the slave and reinstalled the slave.  I was surprised to see the same steady drip ... it was coming from the air bleed nipple.  I tightened the nipple as much I thought safe...... The nipple still leaked.  ( I am leaving out  a lot of false moves and cursing from this story )  I created a rubber seal from some rubber I had laying around.  It was a cylinder about 5 mm in diameter and about 5 mm high.  This seemed to seal the leak.  It also made it more difficult to bleed the air from the clutch line.  Now the clutch is stiff and seems to work.  We shall see how long the clutch works.

2011m10d25    Clutch still leaks  ( takes about 24 hours )

You may contact me to ask questions at y e s    at    n o p e 9  dot com

99guspuppet      99miata   99clutchhydraulics

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