were the postings in the brake failure thread on the V8 Bulletin Board that raised
the brake fluid issues?|
Matt Jones launched the thread with a query on brake failure on his RV8
saying "I recently suffered a long brake pedal in my RV8. After checking
the master cyclinder reservoir and finding it empty I bled the whole system and
concluded that due to the almost black nature of the sludge masquerading as brake
fluid that it hadn't been changed for many years! The
pedal feel was dramatically improved but after a weekend of driving where I'd
been keeping a careful eye on the fluid levels it was apparent that fluid was
disappearing again from the master cylinder. I checked the cylinder itself and
found no sign of leaks, there were also no leaks from any of the bleed niples
on the calipers or drums.
this sound familiar to people? I read some notes on seal failure in the Servo,
could it be this and if so does anyone know where to get a new Servo or is it
possible to just replace the failed seal? Any help appreciated as always".
(12.11.08 @ 13.32)
responded saying "I guess you will be getting a lot of 'press' on this one.
Black fluid invariably means perished seals, or damage caused by rusty cylinder
bores & pistons. Did you fluid have a 'tinge' of brown? If there was no trace
of fluid leaks from cylinders or hydraulic lines, including flexi hoses, then
almost certainly your servo is drinking it (see note below) and passing it to
the engine to be burnt off. This would go un-noticed because the volume of fluid
fluid, except the silicone based type, is hydroscopic and will over time absorb
water from the atmosphere. This will present two problems.
rusty cylinder bores and pistons, including the servo.
water 'boiling-off' in the brake fluid at high temperatures, causing temporary
brake failure (when you need it most). The system will then return to normal when
the hydraulics cool down.
is recommended that hydroscopic brake fluid be changed every two years minimum,
regardless of mileage because it's the exposure time that counts. Many MG and
classic car owners have fitted Mr Owen's very excellent 'Brake Fluid Alarm Kit',
see V8 Register Home Page for details. I have fitted one to my car and I consider
it to be a life saver.
conclusion is, new cylinders / seals all round, new servo, inspect/replace hydraulic
lines and flexi's, fresh fluid and the cream on the cake, Mr Owen's alarm kit.
The reward will be, your brakes will never have felt better and the car will be
safe to drive again. Sorry to be the bearer of a costly news, but as we all know,
brakes are at the top of the critical list.
Footnote: the RV8 servo is
in tandem with the brake master cylinder. I am assuming the thirst of a failing
servo is the same as for the remote type as fitted to earlier MGBs. (12.11.08
Al Barnett added a brief comment - "Exchange
servos are available from Clive Wheatley. I had one fitted last year and am entirely
happy with the result. The symptom in my case was a slight hissing noise which
Steve quickly diagnosed as a failing servo; Good Luck". (13.11.08
Matt Jones responded saying "Thanks guys,
I've spoken to Clive Wheatley and will be sending him my Servo on exchange".
(13.11.08 @ 21.06)
Geoff King provided some useful guidance
with "the RV8 (and the late model MGB) has a direct acting servo; a servo
failure alone cannot result in the symptoms you describe. For fluid to leak into
the servo it has to be a master cylinder seal leak. There may also be a servo
problem but your description of the fault doesnt suggest this at all and
the servo simply cannot suck fluid out of the master cylinder.
know what your skill level is but some checks are fairly simple with a few basic
tools. Before you change the servo remove the vacuum hose from the plenum and
check if there is evidence of brake fluid I doubt if there will be. If
the hose is clean remove the pedal box cover to see if there are leaks from the
master cylinder, however, the master cylinder is directly connected to the servo
and fluid could leak without any obvious signs and youll need to remove
the master cylinder and servo assembly and separate them.
Have you removed
the rear brake drums to check for fluid leaks?(14.11.08
A couple of hours later Geoff King added a footnote
- " apologize; my comments concerning the removal of the pedal box cover
to see if there are leaks is misleading - the master cylinder is attached to the
servo on the opposite side to the pedals and leaks may be visible at the joint
face between the servo and the master cylinder".
Robin Gell then
added that he "would recommend refilling the system with SBF, Silicone Brake
Fluid, available from specialists and on eBay. It is expensive at around £20
a litre, but is not hygroscopic and does not damage paint. In fact it puts a nice
shine on things when wiped over! It is DOT 5, has a higher boiling point than
other fluids, and retains this due to the lack of any moisture absorption.
It does not need to be changed at all and therefore is effectively a fit
and forget operation; especially useful on cars which do not see much use, as
this avoids rusting and sticking cylinders etc due to absorbed moisture and lack
of regular use. Rubbers are supposed to last longer too. Filling is easy as systems
don't need to be flushed before filling, other than with the new fluid. It mixes
and works with ordinary brake fluid, although naturally removing as much of this
as possible is to advantage. When bleeding through, the SBF can be seen coming
out from the bleed tube as it is purple and looks like meths. Thus you know it
is all flushed out with new fluid. As disconnection of the master cylinder means
a full fluid change, this is the time to do it. (14.11.08
Mike Howlett then referred fellow members to a
warning note from AP Lockheed reproduced in V8NOTE228
released in June 2001. He concluded by saying "AP Lockheed glycol based fluids
do not contain the adverse properties described above. The recently introduced
Supreme DOT 5.1, which exceeds the performance criteria of DOT5, is suitable for
all conditions likely to be encountered in modern driving conditions".
(14.11.08 @ 18.41)
Linked to that V8NOTE is V8NOTE228A
with contributions from fellow members discussing the DOT4 and DOT5 brake fluid
Dave Wellings then provided a note on his experiences
with an MGBGTV8 over many years by saying "This old chestnut has been around
ever since silicon fluid hit the shelves. I would only consider using it in a
completely rebuilt system, because it can't flush the old fluid properly from
around the seals, so at the very least a full set of new seals and blow through
with compressed air would be recommended. The thing is, I had this decision tomake
in 1991 when my V8 braking system was completely new. I agonised over this choice
for weeks, and listened to all the evidence, plenty of which was anecdotal. Some
well respected concours entrants swore by silicon and had had no problems over
long periods, but with less than average mileage. In the end, the issues highlighted
in Mike's post led me to conclude that mineral fluid - changed regularly would
do the job. And so it turned out.
One other point about servos - the
internals are well protected from temperature/ atmospheric changes. I stripped
my remote servo when it was 18 years old - it worked properly and there was no
trace of corrosion in the bore. I fitted the full repair kit and it lasted another
18 years before sucking the fluid from the master cylinder - fortunately on the
drive at home. (14.11.08 @ 20.31)
Gell returned with another contribution - "It's good to bring these things
into the open, so thanks Mike for posting this. I for one however, am very sceptical
over what AP say here, but at the same time however take it seriously. The issues
for me are:
Compressability. Fluids don't compress. Basic physics?
Even water will work in brakes by itself when cold.
leading to spongyness and slow filling. There shouldn't be any air in the system
if it has been bled properly?
Similarly moisture globules. What moisture?
This should be bled out! There is no difference between the fluids in this respect.
What free unmixed water? Glycol fluid absorbs water leading to lowering of boiling
point. Where would free water come from otherwise? Why would this lead to greater
lowering of boiling point than absorbed water? I don't buy it at the moment. I
don't buy any of it without very much more technical and scientific substantiation
for them as none of them seem logical to me at all.
the viscosity? Don't
think so somehow, but will check.
about this claim too, but again, will check.
I know that I have been
using it for a number of years with none of these problems, and so have many others.
I will send this note to www.automec.co.uk who market SBF and ask for their view
on the subject, and of course, they are bound to stand their corner, as both they
and AP have their own interests to defend. AP have their recommendations and insurance
liabilities to consider and so are not going to support something outside their
box. It is like many other instances of specification of particular consumables.
"Only use xyz sort of stuff" appears regularly all over the place, but
as we well know, there are usually many other choices, just as good, (Comma oils
for example), but which are not "recommended" and so would produce no
come back to the manufacturer.
It will be interesting to
see how Automec defend themselves. Who does one believe? I suspect that the reported
problems here are more to do with incorrect setting up than the stuff itself.
I stick my neck out however, but am loathed to take this at face value! Currently
I have to admit that I take AP's warning seriously, but with scepticism, as SBF
is apparently used as standard by the US Military in all their vehicles, and also
conforms to the highest acknowledged standards, the US Department of Transportation
(DOT)5 standard as well as the Federal Motor Vehicle Safety Standard (FMVSS)116
and US Military Standard MIL B46176. I will see what Automec have to say on the
subject and report again. (14.11.08 @ 20.53)
Smith then added - "I feel that before any suggestion that the advice
issued by the Technical Service Department at AP Lockheed is influenced by "their
own interests", I do think the technical matters over which you are sceptical
should be thoroughly researched first. Surely the technical people at AP Lockheed
are engineers with a special knowledge of auto hydraulics and in particular how
the various available hydraulic fluids perform in both classic car and modern
car braking and clutch systems. Why not telephone the technical department at
AP Lockheed and discuss with them first hand and in detail each of the concerns
you have raised, get clear information as to the technical basis for the concerns
expressed in their warning note (which we reproduced in our V8NOTES series some
time ago when this matter was discussed amongst V8 enthusiasts) and write up a
note or article for the V8 website which would then be a substantial and authoritative
contribution to clarifying the matter? I fear that at present all we have is renewed
confusion." (14.11.08 @ 22.19)
Gell responded saying "Victor, I agree.
I am not leaving it there and have already emailed Automec to ascertain their
view on the points. It is only fair that they have the chance to reply to these
points before taking it farther. It seems as though up to now, they have not had
the opportunity. Then perhaps, Lockheed will be approached for further comment.
will take it from there, but at the end of the day, I suspect there will always
be some polarity between the two. All I am doing is to try to stimulate discussion
on the matter in making suggestions, not accusations, and by questioning what
to me, as an engineer myself, seem on the face of it to be some strange statements.
Sorry if it is thought that this has generated confusion. I will report factually,
anything which I am able to discover. (15.11.08 @ 00.56)
Owen then posted his informative piece featured at the head of this webpage
and sent the V8 Webmaster the image for publication. (15.11.08
Rob Collier then noted Bob's piece was "a
very informative explanation of the pros and cons of DOT4 and DOT5 brake fluids.
We learn sommething new everday and following your explanation I now understand
why DOT5 silicone has not totally replaced DOT4 fluid in all applications."
(15.11.08 @ 12.59)
Smith then added "On re-reading V8NOTE228, which was issued back in June
2001 along with the comments on the brake fluids topic from fellow members in
V8NOTE228A, there are two matters where reliable and authoritative information
is necessary to help clarify some of the issues over the use of silicone brake
fluid in the brake and clutch systems fitted to the MGBGTV8 model and the later
RV8. In V8NOTE228 an experienced motor and aero engineer says "says silicone
fluid attacks rubber seals and causes swelling". The informative posting
from Bob Owen seems to support that comment where he says "silicone fluid
can affect rubber seals" and that he had to "turn down the master cylinder
piston on his MG TC" to overcome that effect where the hydraulic system on
that car was using silicone fluid. Does any member have any authoritative or factual
information on the effects of silicone fluid on the rubber seals fitted as original
equipment and current replacements and in particular the ways the fluid attacks
the rubber seals?" (15.11.08 @ 15.06)
Gell responded saying "Bob's
is a very authoritive and believable explanation. Thank you for the illumination
my mind it does go to
show that many of the cited problems, while having bases in fact, are actually
very small in proportion to the whole picture, and are probably insignificant.
(400 atm. only 1.8% reduction in volume of water against 3.6% for alcohol. 400
atm is collosal pressure, and if it takes this pressure to make alcohol compress
twice as much as water, it puts it into perspective. This is really confirming
what I was thinking. I'm not sure that the analogy with sound travelling through
liquids is a good one though, because these are travelling vibrative pressure
waves rather than volumes of liquid compressing to smaller volumes.
about steel, as an opposite to compression, railway engineers stretch rails by
maybe more than a foot in length (depending on ambient temperature), with hydraulic
pullers(over maybe a quarter of a mile free length) to gain a length equivalent
to a temperature of 27 degrees, and then weld them up. Thus they are in considerable
tension and so compressive forces in hot rails, up to 50+ degrees can be resisted
in the fastening system. I digress, although it does show how significantly the
volume of steel can be changed in this way.
It seems that there is no
ideal answer to the problem of which fluid is best, and indeed, as has been said,
it is often a case of horses for courses.
Indeed I know that the two
don't mix in a homogenious nature, having used it myself, as they are slightly
different in density and form layers when in the same container. What I meant
is that cross contamination, if it happens, say by bleeding new fluid through
a previously glycol filled one, if one wants to do this, is not a problem as the
two can work together, even if this is not exactly ideal. (15.11.08
Collier then posted some useful information on the effects of brake fluid
on rubber seals quoting checkthatcar.com
regarding rubbers seals. "Silicone brake fluids are not hygroscopic,
and tend to retain their dry boiling points for very long periods of time. For
this reason, silicones are favored by owners and restorers of classic and antique
cars, as there is minimal danger that seldom-used and possibly irreplaceable brake
components will be lost to corrosion.
Silicone will cause natural rubber
to swell, even when it's compounded with synthetics. The seals in modern brake
systems are no longer 100% natural rubber, but blends of natural rubber and synthetics
like nitrile. Glycol fluids will also tend to swell blended rubber seals, but
to a much smaller degree then silicone. Swollen seals may leak, or cause caliper
pistons to bind, resulting in brake drag.
Silicone has several other
properties that make it less then desirable for street or track use. When forced
thru small orifices under high pressure, like the solenoid valves in an antilock
brake system, it tends to foam, generating bubbles. Bubbles in brake fluid make
for spongy brakes. Silicone also tends to become slightly compressible at temperatures
near its boiling point, which makes it generally inappropriate for racing.
To get the maximum
benefit from silicone, the entire brake system MUST be flushed of old glycol fluid.
A brake system cannot be completely flushed using the bleeder fittings, as they
are purposely at spots in the system to allow air to be bled, you simply can't
get all the old fluid out by bleeding. The best way to completely flush a brake
system is to dismantle and overhaul it, cleaning everything with alcohol, and
then coating all the parts with the new fluid as they are re-assembled. Going
to this much hassle just doesn't justify changing to silicone, IMHO." (15.11.08
Victor Smith reported
that "from a call to Brovex Nelson at Camelford in Cornwall this afternoon,
I learned from their technical manager that they make a variety of parts for classic
car brake and clutch systems including rubber seals and rubber flexible front
brake hoses. They supply most MG specialists and parts suppliers in the UK and
elsewhere. He confirmed that their rubber compounds work well with either glycol
or silicone hydraulic fluids and their seals do not swell when in contact with
either fluid. In response to the question "do rubber seals, that have been
fitted to classic cars using glycol fluid and then later have been in contact
with silicone fluid following a change from glycol to silicone, swell and increase
in size" he said yes that is a very good question!. But he then
added that Brovex Nelson rubber seals performed reliably as they use their own
rubber compounds and they manufacture their seals. He then mentioned that many
existing seals fitted to classic cars and some replacement seals in the market
are supplied by other manufacturers and he was not able to say how they might
perform in a switch from glycol to silicone fluid.
then enquired how you could identify a Brovex Nelson rubber seal. It was a slight
surprise to learn that their seals do not bear their name or a brand mark, only
the text made in England. However there are three or four small letters
or numbers on the seal which enable them to identify their own seals. So if a
V8 enthusiast is buying replacement seals from a parts supplier, mere inspection
of the seals will not reveal whether you are getting a Brovex Nelson seal or one
from another manufacturer. Your only option is to ask the parts supplier which
manufacturer has supplied them." (17.11.08 @ 16.54)
useful brake fluid articles. More
of the brake fluid debate
Bob Owen is preparing a paper on the glycol-slicone
brake fluid debate with the aim of presenting the facts and the reported observations
and views of experienced motor engineering specialists together with a dispationate
An article providing the information you need to make your own
choice has been prepared by Bob Owen. (23.1.09) More