RBnDFW wrote:

wrote:
On Wed, 22 Jul 2009 08:17:23 -0500, "Pete C."
wrote:

wrote:
On Tue, 21 Jul 2009 22:11:38 -0500, "Pete C."
wrote:

wrote:
On Tue, 21 Jul 2009 17:54:04 -0500, "Pete C."
wrote:

"Steve W." wrote:
Pete C. wrote:
No grinding or anything, just continual clutch no-release problems.
Clutch replaced once, coaxial slave cylinder replaced another time, MCs
replaced like four times. Never had a problem with clutch slip, only
failure to release.

Now that I have a new truck, I'm getting ready to pull the clutch on the
old one myself and see if I can fix it for good. This truck also ate
rear axle seals until I got into it. Axles seals replaced under warranty
several times, when they went again out of warranty I replaced them
myself and haven't had a problem since (195k+ now).
Step down and no release?
Yep, makes it kinds difficult to shift. Bit of a problem when you need
to stop as well.

If you step down a second time does it release
then?
Nope, pump it a half dozen times and you might get it to release enough
to shift with a clunk. Doesn't do it all the time either, can be working
just fine then start acting up.

I have no good way to monitor it for testing, but I suspect the MC
reservoir valve isn't sealing well allowing some of the stroke output to
simply go back to the reservoir.

I expect I could fabricate a better MC setup and add a bit more
displacement as well since I've always felt it bordered on not enough
displacement.
How close is the fluid line to a manifold?
Not particularly close, probably 6" from the manifold, 3" from the pipe
heading down to where it crosses under the clutch bellhousing.

How old is the fluid?
A month or so since I last replaced the MC and flushed a good pint
through and out the coaxial slave cylinder breather.

Sure
sounds like vapour fade due to inferior fluid or overheated lines.
Sounds like it, and some of the cases of it acting up have been after
it's had some time to heat up, but other have been acting up from cold.

I suppose I could find some insulating wrap and wrap the line. Not sure
on inferior fluid, it just uses DOT3 brake fluid. The last couple pints
have just been generic DOT3, is there a particular brand I should look
for?
DON"T use heat wrap - use a properly positioned heat sheild and you
should be using DOT4 fluid, not DOT3.. The best heat sheild is a
stainless steel sheet midway between the heat source and the tube - or
half of a 2" stainless steel tube mounted so it semi-surrounds the
tubeing, about 1" from the tubing.. Three inches from the crossover
without a heat sheild is TOO CLOSE.
Might get by with DOT4 or DOT5 fluid, but you are still pushing it.
I'll see what I can find to fab a shield. What about heat wrap on the
pipe where it crosses under?

If I change to a DOT4 or DOT5 fluid what kind of cleaning would I have
to do and would there be seal material compatibility issues? Brands of
fluid to look for?
DOT4 is a direct compatible replacement. Dot5 requires a flush -
generally alchohol or BrakeKlean.

I'd go with Dot4 for simplicity.
Heat wrap causes premature pipe failure.

there is now a DOT 5.1 that is another breed altogether.
Apparently it's non-silicone and has some compatibility with other types.

www.stoptech.com

DOT 5.1 fluids!

Historically, DOT 5-level performance (specifically boiling points and
viscosity) could only be achieved with silicone-based fluids. However,
modern compounding has created glycol ether-based fluids which now meet
DOT 5 bogeys in these key areas. Consequently, the DOT 5.1 moniker was
created to differentiate between these two very different chemistries
which both meet DOT 5 performance requirements.

In so many words, DOT 5.1 fluids are simply DOT 4-type fluids which meet
DOT 5 performance requirements. Because of this, they typically can be
mixed with DOT 3 or DOT 4 fluids without concern. In some circles, they
are even referred to as ‘DOT 4 Plus’ or ‘Super DOT 4’ fluids because
they are more similar to a conventional DOT 4 fluid by chemistry than
they are to a conventional DOT 5 fluid. In fact, DOT 5.1 is essentially
comprised of Borate Esters.

While it may not be obvious, the big advantage of the DOT 5.1 fluids is
that they contain all of the nifty water-absorbing characteristics of
the DOT 3 and DOT 4 fluids while simultaneously providing for very high
boiling points and relatively stable viscosity over a wide range of
temperatures. The best of all worlds, you could say. The table below
sums it up quite nicely.
PROPERTY DOT 4 DOT 5 DOT 5.1
Dry BP (F)@ 0.0% H2O 446 509 509
Wet BP (F)@ 3.7% H2O 311 356 356
Chemical Composition Glycol Ether / Borate Ester Silicone Based
Glycol Ether / Borate Ester

(As stated earlier, the table data above contains the minimum properties
for a fluid to be called a certain type. For example there are many
racing brake fluids with Dry BP performance at or above 590o F and Wet
BP at or above 390o F.)

So, what is the downside of the DOT 5.1 fluids? Like most things in
life, the good stuff isn’t cheap. DOT 5.1 fluids typically cost three to
four times as much to manufacture as a conventional DOT 4 fluids.
There’s always a catch…

Given the small quantities used, I would expect the cost difference is
pretty negligible.