Info needed: M38A1 vent tube

[rob love]

Originally Posted by Les Kovacs

Hi Rob....thanks a million....sound fairly easy but messy.....I am assuming that brake fluid will puke out and empty all four lines. Also, are these master cylinders poorly built? As I mentioned in my paragraph the one I am replacing is not rusty (but pukes fluid out of the plunger side) at all and dude said that he replaced it during the rebuild in 2011 so there should be only about 2000 kms on the unit.

PS....I bought a replacement cylinder for about $70.00 CDN delivered from either Eriks Military or Walcks Jeeps.

Regards,

les

They won't empty, since the lines are kind of at their high spot at the master cylinder. But you will end up with some minor loss, so you will have to bleed the lines. There are only two lines at the master cylinder...they each split up at the diffs to make 4 lines. You will most likely get away with just bleeding one front and one rear wheel, but quite frankly fresh fluid to all 4 wheels is a good thing.

As Wayne says, it is the sitting that kills these things. As well, if the boot is not on properly, it can fill with water depending on when you drive it, and that water will sit there rusting at the front of the cylinder. But also, brake fluid itself (Dot3 and Dot 4 at least) are hydroscopic, so will absorb moisture from the air. So if there is no vent line, water or moisture in the air will get into the master, be absorbed by the fluid, and can start rusting the cylinders. Ideally, you flush the fluid every few years, although nobody does. As well, a cylinder installed in 2011 is very near it's end of service life anyway......I usually count on 7 years of service for this older stuff.

That said, my own master cylinder on my Jeep is probably 10 years or older and still working just fine. But it is driven all the time in the summer months, and held in deep freeze storage the remainder of the year.