[xk] Brake fluid for replacement master and wheel cylinders

When using replacement brake master cylinders, wheel cylinders and
hoses from vendors like Bill Tracey, should I stick with the Dot 4
brake fluid? I asked the vendor and got a ‘‘use any fluid you like’’
answer that makes me feel a little uneasy.
Thanks for any opinions.
-greg–
GWUISTER , XK 140 MC OTS
RIVERSIDE, CA., United States
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Greg;
There are two schools on this… some of us swear by DOT4 only and swear
‘at’ DOT5 (Silicone) while some folks use DOT5 and report no problems…
I’m sure those who have had success with DOT5 started with a completely
“new” system (M/C, wheel cyls, all new hoses and flex pipes, etc.) while
those who have had problems may not have had a “totally clean” brake system
(Point being: NEVER mix DOT5 with anything!).
I’m a dyed-in-the-wool “Castrol LMA DOT4 ONLY” person… take that for
what it’s worth…
It has come to light, of late, that NOT all brake rebuild kits are DOT5
compatible, and therein lies the problem… “standard” o-rings and cups
don’t seem to tolerate DOT5 at all so one needs to insure the “rubber”
internals are, indeed, compatible with DOT5 BEFORE using said fluid…
getting a "use any fluid you like’’ comment from anyone, much less a vendor,
is hardly a reassuring endorsement…
As Prez Reagan said: “Trust, but verify!” Applies here, as well…
Charles #677556.----- Original Message -----
From: “GWUISTER”

When using replacement brake master cylinders, wheel cylinders and
hoses from vendors like Bill Tracey, should I stick with the Dot 4
brake fluid? I asked the vendor and got a ‘‘use any fluid you like’’
answer that makes me feel a little uneasy.
Thanks for any opinions.
-greg


I am using the free version of SPAMfighter for private users.
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As brother Charles intimated, this subject comes up regularly every year or
so, and I am fond of repeating the story of my experience of around 1992
with DOT5 silicone in my early 120, which shares the same single system as
your 140. After restoring the entire system with all cylinders cleaned,
polished and new rubber, I filled it with DOT 5. On my first outing the
brakes got harder and harder until they locked on and 3 men could not budge
the car an inch. After an hour the brakes released themselves. It was the
silicone that swelled up the seals in the master. Refer to the manual Plate
L16 and item F. It was swelled just enough so it was blocking hole X and the
pressure would not release. This may be a problem specific to this
particular Lockheed single system, and may not apply at all to the late 120
tandem system or the 150 system. But its best to be aware of the potential
problems.
The other problem is silicone has been known to kill brake light switches.
The symptom is having to push harder and harder on the pedal to get the
lights to come on.
Rob Reilly - 679187

There are two schools on this… some of us swear by DOT4 only and swear
‘at’ DOT5 (Silicone) while some folks use DOT5 and report no problems…

In reply to a message from RJ_Reilly sent Mon 28 Jan 2008:

Hi Rob,

Yes, well you surely have many valid points in there.

I had suspected my brake light switch problems being related
to DOT5 silicone fluid, but wasn’t sure if that was the case.

Now I pretty much am.

I have used silicone for 12 years in my E-type, and have had
no other brake problems, than brake light switches dying.
The shortest life for one switch was ca. 3 months (!) and
the longest has been about 3 years. I haven’t taken one
apart, but I have all those switches left, and it seems that
one that had been out of service for many years, worked
again. So does someone know if it’s a mechanical problem
(swelling or blocking the pressure inside the switch) or an
electrical contact problem (the contacts reacting with
silicone and no longer connecting properly?)

However I am otherwise very happy with silicone fluid so
far, and I had planned using the same stuff in my MKV, but
the britts who did the mechanical work put DOT4 inside and
now I don’t know what to do really. All the slaves are new,
but NOS, so they have Girling seals and the master was
rebuilt with a NOS Girling kit. BTW is the early single
XK120 master the same as the MKV single master? I know the
slaves are different, but I thought that could have been
because of a difference in size of the brakes? This would
always be nice to know as it seems so much easier to find
and buy parts for an XK than a MKV or MKVII.

Also I have some fellow Jaguar enthusiasts who used to have
brake problems in their MKVII’s (and also MKII’s and
E-types) due to long stand stills (our winters used to be
long and cold) where a master, booster or some slave would
be stuck, and gentle violence could result in broken seals
or bulged hoses and brakes locking.

I think it is still good to remind that also systems using
silicone should be flushed and bled sometimes. At least in
here you would still get condensation inside the brake pipes
and cylinders due to temperature changes, and although
silicone does not absorb water, it can stay inside the
system and cause corrosion and other trouble (boil and
develop an air bubble etc.)

Sorry, this is sort of the wrong forum for me, but I have
learned many things from here that do not seem to pop up on
the E (XKE) or pushrod (MKV) forums!

Just my 2�c’s worth.

Pekka T.–
The original message included these comments:

your 140. After restoring the entire system with all cylinders cleaned,
polished and new rubber, I filled it with DOT 5. On my first outing the
brakes got harder and harder until they locked on and 3 men could not budge
the car an inch. After an hour the brakes released themselves. It was the
silicone that swelled up the seals in the master. Refer to the manual Plate
L16 and item F. It was swelled just enough so it was blocking hole X and the
pressure would not release. This may be a problem specific to this
particular Lockheed single system, and may not apply at all to the late 120
tandem system or the 150 system. But its best to be aware of the potential
problems.
The other problem is silicone has been known to kill brake light switches.


MK 5 3.5L DHC, E-type 2+2 Ser.1, XJ6C Manual, XJ8 Executive
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In reply to a message from GWUISTER sent Sun 27 Jan 2008:

In my experience, the use of ANY brake fluid other than Castrol LMA
will cause problems in an XK brake system. This is personal
experience not hearsay or ‘‘I heard it on the internet’’.
Use something else as you choose, but be prepared to have problems
with pedal return, sticky cylinders, and swollen seals.

Roger

Once again, that Charles character is correct. :->–
Roger, 1954 120 DHC BRG, S678300
Tamarac, South Fla., United States
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In reply to a message from GWUISTER sent Sun 27 Jan 2008:

Thanks for all the information and insite. I will stick with the
Dot4 when I get it together.
-greg–
GWUISTER , XK 140 MC OTS
RIVERSIDE, CA., United States
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In reply to a message from GWUISTER sent Mon 28 Jan 2008:

I have used silcone for several years without any issue other than
the brake switch. I replaced the switch with a NAPA look-alike
that will hold up to silcone. Before switching over to silcone,
every spring I would have an issue.

I could be one of the lucky ones…not sure. For now, I
going with silcone.–
norm larsen
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