brake fluid

[Matthew Ziegler]

I was checking the levels in my M37. I noticed the Gm mastercylinder I added a while back says use only dot#3 fluid. I've been using the purple military stuff since I owned the truck, will it have an adverse effect on the master or the seals etc on my disc converted fronts? thanks in advance, Matt

[Gordon Maney]

What markings are on the container for the purple stuff ?

[74w300uteline]

Dont mix em

Ive been told not to mix brake fluids on my m880. The purple stuff That it came with is silicone and ive been warned that mixing it with regular brake fluid will result in cottage cheese . Not sure if its true but i wouldnt chance it.

[Gordon Maney]

Would it have chive?

[Kaiser2boy]

Just wondering if you are asking after the fact. Did you mix fluids and are now wondering if it was a bad idea or are you thinking of doing it?
There are a ton of pros and cons about what kind of fluid. The original brake fluid is hydoscopic and tends to attract moisture but it works and helps lube the brake parts. The sliicon stuff works better in high heat but tends not to lube the parts and is not hydoscopic.
There are different ideas on what happens if you mix them up. They range from "its not a problem to turning the fluid into blue cheese.
Why not just dont mix it and play it safe.
I had a brake problem and replaced the master cylinder and there was a big loss of fluid. The question popped into my mind as to what was in there and do I want to mix things up.
The stuff that was in mine smelled like regular brake fluid -ie- cat pee.
So thats what I replaced it with and it has been a few years and no problems.

[preaction]

brake fluid

I have never herd anyone say that it would be no problem mixing dot of any number and silacon brake fluid. I used dot 5 in a restored car and wish I never herd of it. I will be replaceing it with new dot 3.

[Charles Talbert]

If instructions with a new master cylinder say use DOT3 only. It is because the rubber components within are not compatible with other fluid types. It will most likely result in boot, seal, and check valve failures quickly as a result of chemical reaction if any other type is used.

[preaction]

Hey charles

I have installed a few new master cylenders and have never seen a recomendation or direction as to what fluid to use.

[Matthew Ziegler]

fluid

I had been running purple silicon G>I fluid in the truck since I got it, I changed over to the Helitool disc setup and master cylinder conversion. I noticed a week or so ago the lid for the GM master has use dot3 stamped in it. I think Charles is right, any recommendations on completly cleaning out the system? I'm thinking drain the system then compressed air? Thanks for the advice. Matt

[gmharris]

I think the "Use DOT 3 Only" warning is there to tell people not to use hydraulic fluid, mineral oil or any of the other brake fluids that have been used over the years. It's not a warning against using, for instance, DOT 4.

Silicone is an inert substance and shouldn't deteriorate anything. However, it is subject to pooling of water. If the system is totally dry (like a newly manufactured vehicle) when the silicone is inserted, there shouldn't be a problem. However, if you add it to a system that has had Dot 3 in it, there will be moisture.

Our vehicles don't require the high boiling point of silicone brake fluid. They are better served by using DOT 3. When all else fails, follow the manufacturers recommendations.

The only problem with DOT 3 is that it should be changed every few years.

[preaction]

dot 5

Mat I think besides compressed air you should also use some kind of solvent and or cleaner to clear the lines. I first uesd dot 5 for a restored 67 mercury cougar, so as not to hurt the paint and no need to refresh the fluid due to water absorbtion. I found out after that the dot 5 compreses, where dot 3,4 doesnt and that contributes to a spongy pedel and that was not for me.

[Desoto61]

Mat I think besides compressed air you should also use some kind of solvent and or cleaner to clear the lines. I first uesd dot 5 for a restored 67 mercury cougar, so as not to hurt the paint and no need to refresh the fluid due to water absorbtion. I found out after that the dot 5 compreses, where dot 3,4 doesnt and that contributes to a spongy pedel and that was not for me.

DOT 5 isn't compressible, however it is more prone to trapping air, which is what leads to the spongy pedal. It can be very difficult to bleed a system with DOT 5.

You definitely want to flush the system with something. The problem is that the change in fluid can adversely effect rubber seals and gaskets. Maybe blow some brake cleaner through the system?

[preaction]

Dot 5

Its been awhile, and your right about the air trapping and its very hard to get it all out.