kenmo

Today is a damp day in Nova Scotia...no rain but damp and dreary....While checking my brake levels I left the master cylinder cover off for a few minutes....

My brother brought this to my attention and informed me this was a big no-no... I understand it is for dot4 and below but I didn't think it was an issue for dot5...as it is silicon based and not as assepectable to moisture as the dot4 and below....

Am I correct....????

JohnZ

Although DOT5 silicone fluid isn't as hygroscopic as DOT3/4, you can still get condensed moisture in the brake system; with DOT 3/4, the fluid and moisture are miscible, and the moisture goes into solution with the brake fluid, diluting it, and ultimately leading to corrosion. With DOT5, the moisture and fluid are NOT miscible, and the moisture settles out in low spots, which can lead to corrosion in those locations.

You haven't damaged anything, but it's always a good idea to keep the system closed, even with DOT5.

ffas23

John,
I don't want to Hijack this thread but do you know of a way to tell if a master cylinder has Dot 5 brake fluid in it other then Dot 3 brake fluid? I know they smell differently but that is all I know. How can someone safely find this out before adding more fluid or bleeding the system? I may be in this same situation down the road with my 67' that I purchased a few years ago. I don't drive it much and haven't had to add any fluid as of yet but the last time I drove it I didn't like the way the brake pedal felt and although it didn't go to the floor or feel like it was sinking at a stop sign or light I think I may want to bleed the system in the near future to make sure there isn't any air in it. Problem is I don't know what brake fluid is in the M/C or know for sure if I even have SS sleeved calipers already on the car although if I ever spring a leak in a caliper I will pop a piston out to take a look.

Fred

JohnZ

Take a couple of ounces of fluid out of the reservoir, put it in a glass jar, add an equal amount of water, cap it, and shake it well; set it on the bench and observe as it settles down. If two distinct layers form, it's DOT5. If an ordinary solution with no layering results, it's DOT 3/4.

SWCDuke

As long as you didn't leave it open to falling rain there should be no problem, but it's good practice to leave the cover on unless it's absolutely necessary to have it off regardless of the type of fluid.

Conventional glycol-based brake fluid is miscible with water, DOT 5 silicone fluid is not, so if your're not sure what is installed, take a sample and mix it with an equal quantity of water then let is sit for a few minutes to see if it separates. If not, it's glycol fluid. If it does separate it's something else.

Duke

ffas23

John thanks for the response here. I will do exactly what you said possibly this memorial day weekend because now I am even more curious to what brake fluid is in the 67's m/c. Chances are if it has Dot 5 Silicone brake fluid I can almost bet when this was done the calipers must of been addressed with SS sleeves but I really won't know that until I have a problem with one. Thanks again, this has been something on my mind for quite awhile and after reading this thread I figured why not ask away here on the forum.

Fred