Silicone v. Petrol brake fluid: Uh oh...

pcf_mark

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Aug 22, 2008
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I think I may have silicone and petroleum based brake fluid mixed in the same car. Now what do I do? The brakes seem to bleed fine but I only did the front. I am not 100% sure either - how can I tell? It looks like the old brake fluid took some paint off in the engine compartment and the master cylinder is rusting in the same way as every other old car.
 
Coming out of the can, the DOT 5 I use has typically had a blue tinge to it when in the m/cyl....others were yellowish....

DOT 3 smells like fresh fish outta the wrapper, 5 has no smell at all, to me....


:beer:
 
I think I may have silicone and petroleum based brake fluid mixed in the same car. Now what do I do? The brakes seem to bleed fine but I only did the front. I am not 100% sure either - how can I tell?

I don't think the silicon and brake fluid will mix. Brake fluid will dissolve water, I don't think silicon will. If you dump a lot of your barke fluid in a tall glass, the silicon and brake fluid should form two layers. Whatever you have, it's mostly brake fluid if it's removed some paint already and you've got rust in the MC. Rust in the MC means your brake fluid is contaminated with water.
 
If you do have it mixed or even think you do, the only thing to do is flush it and start over. Drain the lines, blow them with compressed air and flush with alcohol, then blow again. Might have to take the calipers apart to get them clean. Fill and bleed
 
Ive seen some guys use silicone to flush the petrol out and ive seen others use petrol to flush out the silicone with no "known" side effects. Silicone is easier on paint but its spongy especially if you don't boil it and it can cause internal rusting of the lines. I prefer old fashion petrol fluid bled out every couple years it keeps moisture from damaging the brake system by absorbing it.
 
Ive seen some guys use silicone to flush the petrol out and ive seen others use petrol to flush out the silicone with no "known" side effects. Silicone is easier on paint but its spongy especially if you don't boil it and it can cause internal rusting of the lines. I prefer old fashion petrol fluid bled out every couple years it keeps moisture from damaging the brake system by absorbing it.

i don't get this part of your post can you talk more about it. thanks
 
I believe silicone brake fluid is slightly compressible but standard synthetic dot 3/4 isn`t..at least it isn`t until it gets "wet".
 
Its actually 2 parts. Silicone fluid has air in it and if you put it in a pan and bring the temp up to around 250 the air comes out and the pedal is more solid.
Most brake systems suffer from moisture and petrol fluid absorbs the moisture.
Silicone doesn't absorb moisture so any moisture that gets in pools, wherever the pool collects the line rusts on the inside (unless you have stainless).
 
Its actually 2 parts. Silicone fluid has air in it and if you put it in a pan and bring the temp up to around 250 the air comes out and the pedal is more solid.
Most brake systems suffer from moisture and petrol fluid absorbs the moisture.
Silicone doesn't absorb moisture so any moisture that gets in pools, wherever the pool collects the line rusts on the inside (unless you have stainless).

fair enough i guess i was thinking that the fluid would be flushed and there for not have water in it... as far as the air in the fluid i know it does "foam" easy but air in the fluid that i did not know. i also konw that if you get air in teh system it is a PITA to get out.
 
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