Silicone or mineral brake fluid for V8s?
Georg Muller has contacted the V8 Webmaster with a
workshop note saying "last weekend I changed my brake
fluid. I'm now using silicone based brake fluid, which might be interesting
for other owners as well. Therefore I wrote the attached note".
Before we publish this note I feel it is worth seeking fellow members'
views because the case for silicone fluid is not universally accepted
and some believe it is not the best choice, particularly for a classic
car. The following contributions are set out in the order received
by the V8 Webmaster. (15.3.05)
from Dave Wellings (15.3.05 @ 0829)
Dave, one of our longstanding members, has commented following
reviewing the draft note that "if a change to silicone fluid
is undertaken, the complete braking system should be stripped and
ALL seals replaced. When I did my rebuild, I was in a position of
having a completely new and dry system. I considered the evidence
very carefully. The anecdotal evidence of problems far outweighed
those who were satisfied with silicone fluid, so I stuck with mineral
fluid. The issues are a softer pedal and a tendency for seals to stick,
making the brakes slow to come off. If it was that good it would be
a standard fit on new cars. The main areas for corrosion when
using mineral fluid are around the wheel cylinders and caliper pistons.
Both easy to deal with, which is why I stayed with mineral fluid.
I have no regrets. My rebuilt servo recently failed after 15 years
by the way, so it lasted 32 years using mineral fluid".
Comment from Gordon Hesketh-Jones (15.3.05
Gordon comments whilst I agree with Georg that silicone
fluid has some benefits, I also totally agree with Dave Wellings that
a change to silicone should only be made at the time of a 100% brake
system rebuild. I went through the 100% brake rebuild process in 1998
but stayed with standard fluid. Frankly
I think that Georg might have some problems in the future as all he
seems to have done is to just to clean the system then put in the
Comments from Steve Bowley (Harvest Gold 0255) (15.3.05
I finished my 1973 GTV8 rebuild last July. I thought long and hard
about silicone fluid and followed various discussions. In the end
I went for DOT 5 silicone for brakes and clutch BUT I must stress
that ALL the brake and clutch components were brand new all the way
down to washers and servo clips. Only trouble I had was bleeding the
brakes. Car was trailered to Brown & Gammons to give it a thorough
going over, especially the brakes, prior to its MOT. So far 1,200
miles and no leaks or long pedals. Using drilled discs and greenstuff
pads with uprated shoes at the rear. It is down to choice but so far
I have not had a downside.
Response from Georg Muller (16.3.05 @
Georg responded "are you aware what a huge market is behind
yearly replacement of brake fluid. In addition all the repairs and
replacement of brake equipment based on failure caused by glycol brake
fluid. There are millions of cars, so there are millions of litres
of glycol brake fluid sold every year, not talking about spare parts.
Do you think vendors like AP Lockheed will give up this attractive
market only because people are getting maintenance free hydraulic
systems based on silicon fluid? This is a billion Dollar market and
the aftermarket sales are much more attractive than dealing with the
car industries. As everybody knows with the car industries there is
nearly no margin left".
Georg notes that only one comment [on points in the warning note from
AP Lockheed reproduced in V8NOTE228 and set out in the box
below] will show already that we are not talking about serious feedback:
loss of brakes
o Air absorption - gasification of absorbed air at relatively
low temperature produces vapour lock effect.
o Immiscibility (failure to mix) with water - whilst
the presence of dissolved water will reduce the boiling point
of glycol based fluids, any free water entrapped in silicone
filled systems will boil and produce vapour lock at much lower
temperatures (100C or thereabouts).
Air absorption: It might be more difficult to bleed silicone fluid
based hydraulic systems. This is beyond all doubt. This takes time
and you need to redo the bleeding a minimum of another time. But once
the system is air free, there will be no issue at all. It's even less
of an issue than with glycol based systems. This is because of boiling
water, which is always available in glycol based systems. This boiling
water will free up air! Result: Fading
Immiscibility with water: Boiling water is "the problem"
with glycol based hydraulic systems we are all afraid of. Once loosing
the total brake system based on fading will stay in your mind forever.
Glycol brake fluid is hydroscopic. Therefore the seals will become
hydroscopic as well. This way water comes into the systems. That is
the reason why we have to change glycol fluid all the time. Conclusion:
o There is no glycol based hydraulic system without water, and
o This causes fading which is a high risk.
Looking to a silicone based hydraulic system we will identify that
it will not have this "type of leaks". It's a real closed
system and so water hasn't any chance to come in.
My conclusion is that we must be very carefully about statements from
market effected industries. I think it's not the best idea to announce
their statements on the register webside without comment. You should
talk to US Army mechanics or Harley Davidson owners. None of them
could state to me serious problems with their silicone based hydraulic
systems. I am not talking about thousands of happy oldtimer owners
singing "Thanks God we got rid of this damn glycol brake fluid".
- MG Car Club
from V8 Webmaster - this note from Georg Muller is not only
critical of the information available on the V8 Website but
also critical that the V8 Register published it without comment.
That is not the case as you can see from V8NOTE228 - the AP
Lockheed warning note was under a comment from Ron Gammons,
a leading MG specialist in the UK and someone who has raced
MGs and other cars for over 40 years, who expressed the view
based on his experience that "silicone fluid attacks
rubber seals and causes swelling. Girling, a leading brake component
manufacturer does not recommend silicone brake fluid".
Reply from the V8 Webmaster (16.3.05 @ 0918)
What is clear is the case for mineral and the case for silicone fluid
is not clear. There are defects and benefits with both fluids and
quite rightly you have to make a judgement, as informed as it is possible
to be, on what will be best for your V8. I am not unaware of the boiling
and fading problem with moisture build up in mineral fluid as I used
to race an MGB in the mid 1970s when I formed and ran the BCV8 Championship.
I found it was necessary to change the fluid regularly to ensure the
brakes would not fade as they got red hot!! I agree that losing braking
efficiency through fade when you are pressing a car to its limits
ona track is not a comfortable feeling at all!
I can also accept your natural concern that manufacturers of equipment
and braking systems using mineral fluid might have a tendency to skew
their advice but so far as a number of members with technical expertise
in the UK are concerned this does not appear to be the case with the
Lockheed cautionary note which we included in V8NOTE228 as long ago
I think the debate of the issues is both healthy and desirable and
your views are very valuable based on your personal experience and
on the evidence you cite of other enthusiast bodies. On a point of
detail, did you in fact remove all mineral fluid so you had a completely
dry system before recharging your system with silicone fluid?
Georg Muller response (16.3.05 @ 1201)
There are basically two ways to proceed.
1. Rebuild and refill: open the brake system and replace all
seals, refill a complete dry and rebuilt system. This needs to be
done, if the seals are more or less gone already. If the seal are
already hardly attacked by glycol fluid they will not recover using
2. Rinse the system and refill: drain off the old brake fluid,
rinse the system with silicon fluid, refill the system with new silicon
fluid, and then the system must be rebleeded after 1 to 2 weeks (the
seals will release glycol fluid and water).
Remark: There may be a third way of doing this - that is getting
the system dry without seal replacement. This will only help if you
keep the system dry for at least 2 weeks. So the seals will release
glycol fluid and water and become dry as well. Otherwise this will
not help and you can go for the second way of doing. I decided to
go for the second and I took about 1 1/2 litre of silicone fluid rinsing
the system. This takes some time and also it will be better to dismount
the calipers and hold them upside down so the old fluid runs out.
The glycol and silicone fluid stay completely separated. You can't
get them mixed. During rinsing, the silicone fluid will blow out the
glycol fluid like bubbles. Once the system is "clean", refill
with new silicone fluid and start bleeding. As the two fluids stay
completely separated - silicone above because it's lighter, I have
been told that you could drain the silicone fluid and reuse it. But
I did not and would as well not recommend this. In two weeks time
I will bleed the system again to get the get contamination out which
was released by the seals.
Allan Doyle (16.3.05 @ 1128)
Allan says that "I work for an automotive supplier and several
of our customers demand that we guarantee silicone-free products.
I'm enclosing two examples".
o Hella (Lights etc)
They even specify the method to be used to determine the silicone
content in indirect materials.
Point 20 on the initial sample checklist is confirmation of silicone
"I've been told that the reason for this requirement is the
"creep" of silicone which can play havoc with electronics.
This may not be a problem with our electronic-free "old bangers"
but I think those two companies know what they are talking about.
I've stayed with normal brake fluid and plan to change it after 5
Response from Georg Muller (16.3.05 @
Hello Allan, I can understand that people for whatever reason stay
with glycol based brake fluid. But five years!!! Are you aware about
the risk you are taking. It's not only the corrosion, it's the risk
that the brake system is going to fail at high speed and on longer
downhill roads. Recommend changing at a maximum of 2 years. Better
would be to replace the fluid every year. In addition - as the brake
system becomes older (seals) then the more often the change should
be made. Take
Posting from Paul Wiley (17.3.05 @ 1305)
I noticed the silicone debate and my understanding of this fluid is
that the large molecules allows air to reside in the fluid. This air
cannot be bleed out and gives the slightly spongy feel. However, if
this is the case what are the effects at high temperature and altitude?
Also Castrol SRF is a silicon ester but still attracts water?
Comprehensive review of brake fluids. More