Air seeping into slave cylinder?

[96splash!]

96 ranger. Brand new LUK clutch kit, flywheel, master and slave.

Somehow air is getting into the slave cylinder. If I disconnect the master cylinder from the slave the pushrod is solid. Zero play at all. System was bleed as per service manual. Worked fine for a few hundred miles then I lose firmness in the clutch. If I rapidly pump the pedal wait a few moments and repeat 2 or 3 times. Then open the slave and close slave while someone pushes the pedal a time or two pedal firms up for a few hundred miles. I'm stumped. I really don't want to pull the transmission again. Any idea how air can be entering only the slave?

 

[lil_Blue_Ford]

Bad slave?

I know. I knowwwwww… I hate it to. My F-150 was killing slaves once a year for like… 6 years… before I got tired of it and upgraded the transmission, slave, master, and line… then it started blowing the line off the slave. With dad’s help, we cut, bent, and fit a forked clamp that bolts to the bellhousing and clamps the line in the slave. I get about 5 years on a slave cylinder now

 

[96splash!]

It would have to have been bad from the factory. Ulg. I do\nt want to drop this darn transmission again.....

 

[lil_Blue_Ford]

It would have to have been bad from the factory. Ulg. I do\nt want to drop this darn transmission again.....

Yup, unfortunately, parts being bad right out of the box is becoming common. The only other thing I can think of is maybe the line has a bad o-ring or isn’t sealing/seating properly.

Wrestling the ZF5 out of my F-150 to change the slave is a bear. A Ranger transmission is easy in comparison, but still not fun. A garage and a lift would make both a lot easier…

 

[gw33gp]

I had a problem with the last clutch slave I installed. I ran it for about two years and had to bleed it about every two to three weeks due to air getting in it. It was not leaking, and I could not figure out how air got in it. It was a SACHS slave, and it was the first time I use anything other than a LUK. Last year I installed a new LUK, and it has been working properly since then.

I don't think it was the SACHS slave that was the problem. I suspected it was the O-ring in the disconnect. I reasoned that it was the only place that could get air in without leaking. When I pulled the old O-ring out while installing the new slave, I found the old O-ring had damage. I had a new one and used it.

So, before you pull the transmission to replace the slave, try replacing the disconnect O-ring first. It is easy and not very expensive.