67 Correct Master Cylinder Replacement

[Kirk M.]

Re: 67 Correct Master Cylinder Replacement

Finally check my brake fluid. It was light yellow and when mixed with water separated out - hence silicone. One thing else I noticed was that the fluid in back chamber (closest to the windshield) of the MC appeared nice and clear and yellow when removed, while the fluid in the front chamber appeared to have something black in it that formed drops when I removed some to look at it. Would that we water in the fluid? Is that normal?

[Joe L.]

Re: 67 Correct Master Cylinder Replacement

Finally check my brake fluid. It was light yellow and when mixed with water separated out - hence silicone. One thing else I noticed was that the fluid in back chamber (closest to the windshield) of the MC appeared nice and clear and yellow when removed, while the fluid in the front chamber appeared to have something black in it that formed drops when I removed some to look at it. Would that we water in the fluid? Is that normal?

Kirk-----


Yes, I'd say that what you have found represents water in the fluid OR some of the old glycol-ester fluid that was left in the system when the silicone was installed. More likely, because of the black color, it is the latter.

Also, the yellow color is typical of silicone fluid after the purple dye changes color. I don't know why they don't use a more color-fast dye in this fluid so that it would remain purple throughout its life for easy identification. I've often wondered if the color change is supposed to "signify something". However, I've never seen anything authoritative which indicated this and the color change actually occurs quite rapidly after the fluid is installed and the system put in service.

[Kirk M.]

Re: 67 Correct Master Cylinder Replacement

Thanks for the quick reply. I guess I'll be testing out the restored MC and silicone fluid after all. Hope I'm not driving along and the brakes give out. Is that what happens when the seals go bad?

[Joe L.]

Re: 67 Correct Master Cylinder Replacement

Thanks for the quick reply. I guess I'll be testing out the restored MC and silicone fluid after all. Hope I'm not driving along and the brakes give out. Is that what happens when the seals go bad?

Kirk-----


It could happen but I feel pretty confident that it won't. At least, it won't because the master cylinder seals failed because of silicone fluid. I first installed silicone fluid in my car about 25 years ago. I rebuilt the master cylinder prior to that conversion. The seals in the master cylinder were obviously made of material available then, which is certainly no better than the material used today (and, likely, that used today is better). My master cylinder never failed.

[Ralph E.]

Per SAE-740128

Unless there is another SAE article, Reading the attached SAE-740128 it appears replacing glycol brake fluid with Silicone should not be as much of an issue as has been stated here. Silicone "will function as an effective brake fluid even when mixed with glycol brake fluids."

Does this mean simply flushing the system is adequate?



HS-014 923

PERFORMANCE CHARACTERISTICS OF SILICONS
BASED BRAKE FLUIDS

Silicone based brake fluids have demonstrated performance
characteristics that are improvements over current brake
fluids. They do not absorb water through elastorneric brake
hoses, and their boiling point and low temperature viscosity do
not change in service. The tendency toward brake system cor-
rosion and the vapor pressure of silicone brake fluids are
minimal. Silicone brake fluids are compatible with brake
system components and will function as an effective brake
fluid even when mixed with glycol brake fluids.

by G. R. Browning

General Electric Co., Schenectady, N. Y.

Rept. No. SAE-740128 ; 1974 ; 6p 7refs

Presented at the Automotive Engineering Congress, Detroit, 25

Feb - 1 Mar 1974.

Availability: SAE

[Terry M.]

[Ralph E.]

Re: 67 Correct Master Cylinder Replacement


Terry,
Thanks for the feedback. Interesting how one can be misled.
Too bad your article was not put in the Restorer.
I would like to convert to DOT5 myself. But reading all the post make me concerned about converting a DOT3 system to DOT5. It would be nice for someone to explain exactly how to do the conversion.

[Terry M.]