Because we co a lot of restoration work, I thought it would be a good idea
to try silicone fluid. We started using it for the first time about 15
years ago. What we have found is that glycol based fluid does NOT cause
Girling or Lockeed seals to expand, silicone based fluid DO CAUSE SEAL
EXPANSION. This has been confirmed by a press release that I have from
Girling that they put out about ten years ago. In most cases, in street
driven cars this is not a problem because in most hydraulic cylinders the
seal fits into a groove in the piston, The groove is very deep, and the
piston and the seal slide back and forth in the bore of the cylinder in
which they are a close fit. The 10% expansion of the seal, (this is the
figure used by Girling), only makes for a tighter seal. But in some older
Girling master cylinders, the seal fits into a groove in the body of the
cylinder and the piston, which is smooth, slides back and forth through the
seal. In our experience, in these cylinders, the expansion of the seal
causes the seal to lose contact with the piston and the cylinder stops
working. In fact you completely lose ALL pressure and the pedal goes right
to the floor! The type of cylinder where this has occurred is used in all
Morgans up to about 1955. All the sealing setup in most disc brake
calipers is the same as this, we have decided to restrict the use of
silicone fluids to clutch hydraulics and drum brake systems that use the
later design master cylinder and where the cars are driven infrequently and
are really "garage queens."
The other cars we use these fluids on are cars like MG T series and Morris
Minors where the master cylinder is mounted under the floor boards and are
therefore exposed to a lot of moisture as well as having the later design of
cylinder.
WE DO NOT RECOMMEND THE USE OF SILICONE FLUID FOR ANY DISC BRAKE CAR
THAT IS EVER DRIVEN HARD. As the temp of the fluid rises, the fluid becomes
more and more compressible, and it becomes more susceptible to contributing
to a sudden, total, and unpredictable lack of any pedal pressure and
consequent brake failure. It is just not worth the risk.
Regards, Greg Solow
-----Original Message-----
From: Robert Alexander <ralex@unm.edu>
To: Greg Solow <gregmogdoc@surfnetusa.com>
Cc: morgans@autox.team.net <morgans@autox.team.net>
Date: Sunday, February 07, 1999 7:27 AM
Subject: Re: brake (break?) fluid
>Thanks, Greg. I needed to flush the system anyway, so I'll return to
>good old Castrol for this. Have you tried the new silicon fluids?
>They're supposed to be more friendly to rubber, more of a pain to bleed,
>and not so great on the race course but better for street use.
>
>Bob Alexander
>67+4
>
>PS: good picture of you and #45 in the last Format. RA
>
>On Sat, 6 Feb 1999, Greg Solow wrote:
>
>> Date: Sat, 6 Feb 1999 19:21:59 -0800
>> From: Greg Solow <gregmogdoc@surfnetusa.com>
>> To: Robert Alexander <ralex@unm.edu>, morgans@autox.team.net
>> Subject: Re: brake (break?) fluid
>>
>> All Dot brake fluids of the same number are completely compatible with
one
>> another and for sure will not hurt your braking system. At the Engine
>> Room we use Castrol LMA Dot 4 fluid because of its fairly high boiling
point
>> and its' "low moisture activity" which I assume means it has less of a
>> tendency to absorb water. We recommend flushing systems with fresh fluid
>> every year.
>>
Regards,
>> Greg Solow
>> -----Original Message-----
>> From: Robert Alexander <ralex@unm.edu>
>> To: morgans@autox.team.net <morgans@autox.team.net>
>> Date: Saturday, February 06, 1999 4:40 PM
>> Subject: brake (break?) fluid
>>
>>
>> >Hi,
>> > Had a minor road emergency a couple of days ago and had to fill my
>> >brake fluid reservoir with NAPA Dot 4 (recommended by a local LBC type).
>> >Thought I'd better check it out with the cognoscenti. Is this stuff
>> >eating all rubber parts in my brake system, or am I just changing brand
>> >names? Would appreciate your input. I know there was a thead on this
>> >some time ago, but don't have time right now to research it. Thanks for
>> >any help
>> >
>> >Bob Alexander
>> >67 +4
>>
>>
>
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