[DML] Re: Vacuum brake bleeding kits

["Walter Coe" <Whalt@xxxx>]

When bleeding my brakes, I used the same Mityvac pump only I didn't follow
the directions that well. It didn't occur to me that vacuum bleeding the
brakes is done in the reverse order as pressure bleeding. I followed the
directions for wrapping the bleed screws in teflon tape, but I found that no
matter how much teflon I used, plenty of air still bypassed the bleed
screws. The directions explained how to tell the difference between "small
bubbles" that bypass the bleed screws vs. "large bubbles" that need to be
purged. Since I got plenty of "small bubbles" along with occasional "medium
bubbles" that the directions didn't mention, I dabbed teflon paste outside
the calipers where I thought air was getting in and managed to vacuum some
of the paste into the brake fluid. (Don't try this).

I agree with Dave Stragand that it is a good idea to leave teflon tape on
the bleed screws because brake fluid residue doesn't age well. I've made it
a practice to mop out the remaining brake fluid from the bleed screws before
putting the dust covers on. If you don't remove it, it will turn to gunk
and contribute to problems later on.

As a variation on the theme of vacuum bleeding: If I were trying it again,
I would specially modify a spare set of bleed screws by welding shut the
hole on the side and drilling a new hole straight through the screw. This
would allow the screw to be seated completely so that no air would bypass
the threads. Then when I'm through I would replace these screws with
unmodified ones. No air should re-enter the system with the screws out
because they would gravity bleed.

My biggest waste of time was not keeping an eye on the fluid reservoir. If
you run the thing dry then you have to start all over again by taking the
master cylinder off and bench bleeding it (again!). After that I hooked a
continuity meter to the low fluid switch in the cap so that I could hear
when the fluid got too low. But this safeguard would probably be
unnecessary if you aren't sucking a lot of air around the bleed screws.

The next time I bleed my brakes, I'm going to try the home made pressure
bleeding method only instead of using a bug sprayer I would use dry shop air
regulated to a really low setting. I am apprehensive about pressurizing the
reservoir. It seems like pressure could cause it to leak easily. And
instead of using teflon on the threads, I might buy a bottle of the brush on
stuff that is specifically made for brake bleed screws (not the gooey
plumbers variety).

Walt Tampa, FL