In a message dated 10/5/01 7:45:24 AM Eastern Daylight Time, Emjaxfl@aol.com
writes:
> This is probably an old topic for most of you. I recall that back in the
> '70s, there were problems with the brake parts being Lockheed or Girling
> and
> you needed to use the same brand of brake fluid as your parts. If you
> didn't,
> the rubber seals would rapidly fail. I also recall that Castrol brake fluid
> was compatible with either brand of parts, I'm not certain of this.
>
> Since I need to replace the leaking master cylinder on the B, I'm concerned
> that this problem still exists so I don't ruin the brand new part. Helpful
> comments and feedback from listers would be welcome.
>
- - - - - - - - - - - - - -
Jeez, I can't remember the last time brake fluid came up on the list, so here
goes.
;-)
Original brake fluid in most MGs is DOT4, Castrol GT LMA. Castrol is easy to
find, not expensive and it works well. Actually, any DOT4 brake fluid will
work fine and should be OK to mix with Castrol. Valvoline has a synthetic
DOT4 fluid that is very good, but I would flush and refill if switching to a
synthetic.
DOT3 is used in most American and many foreign cars. Do not use it in an MG,
especially one with an original, in-line brake light switch. If you suspect
that DOT3 may have been added at some time, it would be best to replace every
rubber part in your brake system, but a thorough flushing with DOT4 may
suffice.
DOT5 is silicone brake fluid. Silicone does not eat paint the way other
brake fluids do, so it is preferred by antique resto people who have trailer
queens. It also does not attract water, so any water in the brake lines will
tend to puddle at low spots in the system, and rust out your brake lines.
(DOT5 was not my choice.) Switching to DOT5 requires a complete rebuild of
the brake system and replacing every rubber part, plus a thorough flush with
alcohol and then new brake fluid. (Switching BACK requires the same drill,
but only if you want to be safe.) Silicone causes rubber bits to swell
differently than regular brake fluid, so you can't mix then, no matter what
it says on the bottle.
You may also bump into DOT5.1, but do not be fooled! It is not silicone, but
a new formulation similar to DOT4, and it is OK to use.
In closing, I recommend that you flush your brake system with new fluid
(Castrol GT LMA) since you have to bleed it anyway. It is good practice to
flush your brake system every few years.
Safety Fast!
Allen Hefner
SCCA Philly Region Rally Steward
'77 Midget
'92 Mitsubishi Expo LRV Sport
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