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
|