Clutch slave cylinder failure

[Sailfish]

A few weeks ago I experienced increased difficulty when shifting. Normally, shifting is like butter-----smooth and effortless. However, over a period of a few days shifting became more difficult. I checked the clutch fluid reservoir and, although down just a bit, there was plenty of fluid. Also, there was no sign of leaks or drips at, or under, the slave cylinder. But then, out of the blue, the slave cylinder completely let go. Within a period of about 25 shifts it went from being able to shift to not being able to shift at all. And the clutch reservoir was completely empty. Fortunately, a friend brought spare clutch fluid and I was able to limp home.

I obtained an exact replacement slave cylinder (7/8" bore) at NAPA (p/n 73168) and AutoZone (12413). I wanted one as a spare! NAPA charged $25.67 and AutoZone charged $15.67. Both parts appear identical. I had the new NAPA cylinder installed and all is now working and back to normal. Note: I have a small block motor and I was told these parts are for a small block. I don't know if they will work on a large block.

This is the first time I've had a clutch slave cylinder issue. My car has approximately 22,400 miles and the car serial number is 2144.

[Sawdust]

Sailfish
Make sure the alignment of the rod is perfectly straight going into the slave cylinder. If not you will have premature failure.

[Sailfish]

Thanks Sawdust. We checked the rod alignment during, and after, installation. All was good.

[PaulProe]

As the throwout arm moves back and forth, it forms an arc that the pushrod from the slave cylinder must follow. The movement the rod must make needs to be balanced on both sides as much as possible, or you will get wear.

In an ideal world, the rod from the slave to the arm would be perpendicular when the arm is at 50% of its travel. No way you're going to eyeball that. If your rod is perpendicular at the start, move it to end of stroke and notice how much out of line it is at that point. You need to split the difference or you're loading the piston when it is at full stroke.

The piston is only lubricated by what fluid may be in the grain of the cast iron housing so any side force becomes a real issue.

The arm they are using for the throwout may not be the exact one that Ford designed the slave for back in the 60's and that only adds to the mis-alignment potential.

One way to keep an eye on this is to occasionally lift the rubber boot of the slave cylinder, looking for ANY fluid leakage. As soon as you see some, be prepared for eminent failure.

FYI

Paul