From: DDoyle9570@aol.com
Date: Sun Apr 04 2004 - 16:28:19 PDT
In a message dated 4/4/2004 5:44:42 PM Central Standard Time, the_real_jumpmaster@yahoo.com writes:
When I disassembled the brake system, I found that
what used to be the wheel cylinder seals had become
sludgy, goopy (is that a word?) black crud. It was a
mess
Glad to hear no one was hurt. From the description you wrote above, the problem was not incompatibility between DOT3 and DOT5, but rather between the elastomers in the wheel seals and something.
FWIW, the official army procedure for converting from DOT3 to DOT 5 is to open the bleeders and pressure feed DOT5 in until no more DOT3 comes out. They did test the flush with alcohol method but found that they could not expel all the alcohol from the system, leading to concern that the low boiling point alcohol would remain in the system. This lead to concerns that the alcohol would vaporize, and the vapor being compressible would cause brake failure. Expeilling the alcohol with compressed air was tried (in fact, this method was used on the initial 8 test vehicles, as well as installing new wheel and master cylinders and brake lines), but the atomized alcohol presented a fire hazard, and alcohol remained trapped in dead ends in the system.
The issue of conversion to silicone brake fluid was first addressed in MERDC report 2132 in Feb 1975, it was revisited in Feb 1982 with report 2348 and once again by BRDEC (successor to MERDC) in May 1992.
Interestingly, the DOT standards applicable to brake fluid (#116) specifically address some of the problems you experienced, as stated below:
S5.1.5 Brake fluid stability.
S5.1.5.1 High-temperature stability. When brake fluid is tested
according to S6.5.3 the ERBP shall not change by more than 3 [deg]C.
(5.4 [deg]F.) plus 0.05[deg] for each degree that the ERBP of the fluid
exceeds 225 [deg]C. (437 [deg]F.).
S5.1.5.2 Chemical stability. When brake fluid, except DOT 5 SBBF, is
tested according to S6.5.4, the change in temperature of the refluxing
fluid mixture shall not exceed 3.0 [deg]C (5.4 [deg]F.) plus 0.05[deg]
for each degree that the ERBP of the fluid exceeds 225 [deg]C (437
[deg]F.).
S5.1.6 Corrosion. When brake fluid is tested according to S6.6--
(a) The metal test strips shall not show weight changes exceeding
the limits stated in Table I.
Table I
------------------------------------------------------------------------
Maximum
permissible
weight
Test strip material change, mg./
sq. cm. of
surface
------------------------------------------------------------------------
Steel, tinned iron, cast iron.............................. 0.2
Aluminum................................................... .1
Brass, copper.............................................. .4
------------------------------------------------------------------------
(b) Excluding the area of contact (13 [plusmn]1 mm. (\1/2\
[plusmn]\1/32\ inch) measured from the bolt hole end of the test strip),
the metal test strips shall not show pitting or etching to an extent
discernible without magnification;
(c) The water-wet brake fluid at the end of the test shall show no
jelling at 23 [plusmn]5 [deg]C (73.4 [plusmn]9 [deg]F.);
(d) No crystalline deposit shall form and adhere to either the glass
jar walls or the surface of the metal strips;
(e) At the end of the test, sedimentation of the water-wet brake
fluid shall not exceed 0.10 percent by volume;
(f) The pH value of water-wet brake fluid, except DOT 5 SBBF, at the
end of the test shall not be less than 7.0 nor more than 11.5;
(g) The cups at the end of the test shall show no disintegration, as
evidenced by blisters or sloughing;
(h) The hardness of the cup shall not decrease by more than 15
International Rubber Hardness Degrees (IRHD); and
(i) The base diameter of the cups shall not increase by more than
1.4 mm. (0.055 inch).
S5.1.7 Fluidity and appearance at low temperature. When brake fluid
is tested according to S6.7, at the storage temperature and for the
storage times given in Table II--
(a) The fluid shall show no sludging, sedimentation,
crystallization, or stratification;
(b) Upon inversion of the sample bottle, the time required for the
air bubble to travel to the top of the fluid shall not exceed the bubble
flow times shown in Table II; and
(c) On warming to room temperature, the fluid shall resume the
appearance and fluidity that it had before chilling.
In summary, something was not up to spec in the brake system. Either one of the fluids was out of spec, or more likely one of the rubber components of the brake system.
Regards,
David Doyle
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