I've had the same trouble bleeding my brakes with the mighty vac. So
much so that I no longer use it on the MG. It does work well on my other
cars.
Ron
58 MGA
Bill Eastman wrote:
>
> I spent yesterday doing the annual fall maintanance on the MGA. This
> included changing the transmission fluid since I was worried that the high
> pressure additives in the Amzoil could corrode the synchro rings over the
> winter. For giggles I decided to try Mobil 1 15W50 in the transmission. I
> will report on how it works. Anyone else used this?
>
> I also replaced the brake/clutch fluid. To do this I got out the trusty
> MityVac and vacuumed out the master cylinder. I then filled the mc with
> fresh Castrol LMA and proceeded to use the MityVac to suck fluid out of
> each slave cylinder until they ran clear. I have done this procedure in
> the past on my modern machinery and it has been very successful. The first
> thing that I noticed was that a lot of suction was required to get any
> fluid out. I was also getting an air leak around the bleeders. Using a
> tip from this list, I got out the Teflon pipe tape and sealed the bleeder
> into the cylinder. I also checked to make sure that the bleeder was clear.
> It still took a lot of vaccuum to move the fluid but I wasn't getting as
> much air around the bleeder so I kept going, adding fluid to the mc as
> required. After doing the clutch, the two back, and the left front, I went
> to pum up the brakes to return the front disk to position in case the
> suction pulled the pistons back. The pedal sand to the floor then pumped
> up in a couple more strokes. Air in the system. I had never let the MC
> get low so it must have come from somewhere.
>
> After some quality contemplation time (luckily, the radio station was doing
> a tribute to John Denver so I wasn't too distracted by the music) I figured
> that the high vacuum condition during fluid movement was causing the slave
> cylinders to suck in air when I disconnected the MityVac. So I called the
> SO out into the garage and went on with a standard "pump and piddle" brake
> bleeding session, making sure that she released the brake pedal slowly
> after each fluid release. After this the brakes were fine again. I should
> have done the clutch too but I forgot. Hopefully it will be fine.
>
> Moral of the story? For some reason, the MGA residing in my garage does
> not respond to MityVac bleeding. This process works great on my daily
> driver (Ac*ra Int*gra). I can only think that the mc design of the MG
> requires more pressure to allow new fluid into the system from the
> resevior. On the Ac*ra, fluid starts dribbling as soon as you loosen the
> bleeder. Perhaps this is to help retract the disk brakes? On the MGA, you
> can remove the bleeder, clean it, and replace it without losing a drop. I
> don't know the answer but I would not recommend using MityVac for brake
> bleeding on this car anymore. It is more trouble than it is worth. It
> does a great job of vacuuming the old fluid out of the MC, however.
>
> Regards,
> Bill Eastman
> 61 MGA with clean fluids
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