Jay,
I went through some of my SAE journals a while back to look for the real
skinny on brake fluids. DOT 5 is silicon based and is not recommended for open
systems like those found on vintage cars. The DOT 5 is non-hygroscopic so it
will not absorb moisture but since our systems are not sealed moisture gets in
and it collects in the low spots of the system, this will cause piston
corrosion in calipers and scuffing of the piston rubber in slaves. This may be
why your Dad did the clutch but not the brake system. A DOT 5 fluid is also
more compressible than a DOT 4 so the pedal will feel spongier. The only real
advantage to DOT 5 is that it will not ruin paint when (notice I didn't say
"if") the master/slave cylinder fails. Even though it is now a different
formula than of old, good old DOT 4 Castrol GTA/LMA it still glycol-based and
will help keep the rubber piston swollen.
The DOT 5.1 is a glycol-based fluid so it is also hydroscopic, its main claim
to fame is that it is a thinner viscosity than DOT 4 which is needed for some
ABS systems to be able to rapid cycle in cold climates. Not many OEM's use DOT
5, I can only find reference to Harley.
Dry Boiling Point Wet Boiling Point (3% water)
DOT 3 401F 284F
DOT 4 446F 311F
DOT 5 500F 356F
DOT 5.1 518F 375F
The "wet" boiling point is when the fluid has absorbed 3% water by volume, a
feat that can be accomplished on our cars over one typical damp winter storage
period here in the Midwest. Water can diffuse in through the rubber brake
hoses as well. Most of my racer buddies have tried DOT 5 and have gone back to
the racing-spec DOT 3 fluids that actually have higher dry boiling points than
DOT 5, they prefer the harder pedal feel.
I know many Tiger folks that have used DOT 5 without a problem, so it's up to
you. In your climate moisture is not a big problem, I suggest you stay with
the DOT 4 Castrol GTA/LMA for the brake system and flush it every other year.
I made a power bleeder by finding an old master cylinder cap and fitting an
air hose chuck. Fill the reservoir and use about 10 psi to push out all the
old fluid. I can power bleed the brakes in about 1/2 hour.
As for your clutch, you will need to rebuild the slave for sure, so the
easiest way out is to do that and stay with the DOT 5, just don't mix the two
fluids up! Make sure you check inside the firewall for signs of the leaks from
either MC as well.
Bugz
-----Original Message-----
From: tigers-bounces@autox.team.net [mailto:tigers-bounces@autox.team.net]
On Behalf Of Jay Laifman
Sent: Sunday, April 21, 2013 11:19 PM
To: Tiger's Den
Subject: [Tigers] Clutch - DANG IT!!!!!
I just did a search in the archives and found that my dad did put DOT 5 in the
clutch.
Ok, so what do I do? Rebuild the master and clutch?
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