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MG MGA - Silicon Brake Fluid

I've acquired an early MGA 1500. It was garaged several year ago and now I am preparing it to run again.

I notice the master cylinder is quite low and needs refilling. The owner "thinks" it has DOT5 silicon brake fluid.

How can I confirm it's silicon? I hesitate to top it off with DOT5 without knowing for sure.

Thanks
bobsie

Remove one or two cc. of brake fluid from your system and put it into the smallest bottle you have ( a scent bottle maybe) then add the same quantity of water. Give the bottle a good shake and leave for ten minutes. If it's silicone then you will see the silicone fluid floating on top of the water. If not then the fluid will completely mix with the water and will not separate..................Mike
m.j. moore

Search the archive for this exact phrase, "How to tell the difference between DOT 4 & 5?". The easiest test is to put a few drops of your brake fluid on a painted surface, a non-automotive surface would probably be best. Not a powder coated or POR15 surface. DOT5 will not raise the paint but DOT3 & 4 will. There is a very remote chance that DPO used DOT5.1 which is not compatible with DOT5. DOT5.1 will likely lift paint.

Since you don't know the exact history of the brake work you may want to pull one of the brake cylinders. If there are bits of black goo in the fluid it is likely that the system was not adequately cleaned when it was switched over to DOT5. Return to garage, do not pass GO, do not collect $200, start over. Troll the archives for all kinds of good advice regarding brake system rebuilds and fluids.

brakes are perhaps the most important safety component on our cars so if there is any question about the compatibility of fluids or anything else it would be wise to do a complete teardown, cleaning and rebuild.

Safety Fast,
John
jbackman

Take some fluid out of the master cylinder and pour it over your paintwork. If it strips the paint off it is dot 3 or dot 4.
Only joking of course.
I use Mike's method. If it mixes in water it is dot 3 pr dot 4

Graham M V

Thanks everyone.

I'll try Mike's water test first. That should reveal any tell tale black goo too. Though it will delay my return to the road, I'm seriously considering the complete break rebuild. That way I'll know for sure what I've got.

Bob
bob sieling

Sometimes , as far as I know, DOT5 has a light purple-ish colour to it. Water test sounds good too. Once you determine the type of Fluid, make sure you make a good label, and attach it to the M/C cap or somewhere close. Nice reminder when the memory fades.
C.R. Tyrell

"Sometimes , as far as I know, DOT5 has a light purple-ish colour to it"

Many years ago, there was also a DOT 5 that was a yellowish color. Also, the purple fades over the years. I remember checking the fluid in the master cylinder of our TD - it had been quite some time since I had checked it. I crawled into the foot well of the TD and removed the MC cover and shone a flashlight into the MC. I was horrified to be looking directly at the bottom of the inside of the MC. It was only when I stuck my finger into the MC that I realized that it was completely full of crystal clear DOT 5 fluid - not a speck of dirt in it at all. Cheers - Dave
David DuBois

This thread was discussed between 25/11/2012 and 26/11/2012

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This thread is from the archive. The Live MG MGA BBS is active now.