Silicon brake fluid

[Richmac]

Hi I need some more advice please. I need to bleed my brakes after fitting a new rear cylinder. I have a bundle of old receipts that state the brake fluid is silicon but the latest one is 2002. I have no idea whats happen in the last 18 years but have to assume its still silicon. However the brake fluid looks like regular brake fluid in colour. When I search silicon brake fluid it suggests all silicon fluid is DOT 5 and dyed purple. My question then is how can I be sure its silicon brake fluid in the system if its not dyed? Is all silicon brake fluid DOT 5 and dyed the same colour and does the colour last? Looking at the DOT 4 in my garage says synthetic What will happen if I get it wrong and mix this with silicon. I would be grateful for any words of wisdom before I bleed with silicon fluid please

 

Regards Richard 

[RogerH]

Hi Rich,

silicon brake fluid will not mix with water.

Decant some of the master cylinder fluid into a glass jar. Then add an equal amount of water..

Mix gently and see what happens.

If it separates then you have silicon (DOT5). 

If it appears to mix than you have  DOT3/4/5.1)

The colour is not a good way of telling the difference.

 

Roger

[Richmac]

Thanks Rodger I have done as you suggested and mixed some with water along with some new DOT 4 and water in a separate jar to compare. I also put some of each on a painted surface to see if it reacts the same with the paint. My first impression is the brake fluid mixes with the water but are you saying the water and fluid will separate over night and in the DOT 4 the water will remain suspended?

[Tim D.]

Yes

[Andy Moltu]

The purple colour fades with time.

[Richmac]

Ok so this morning I can see the water is floating on the top but not as much as I would expect as I mixed 50=50. My feeling is its been contaminated with normal DOT 4 so I am thinking I will bleed the lot out with DOT 4 until I am convinced there is no more silicon fluid left. Is this a good idea please? Should I be worried about any pitfalls?

Regards Richard 

[RogerH]

Hi Richard,

you are entering an interesting area. 

Automec, the brake pipe kit suppliers, suggest you can drain a DOT4 system and then top up with DOT5.

Nobody has proved that mixing one with the other will affect the seals

So, can you refill in the other direction - why not.

DOT4 is the better fluid - BUT!!! DOT5 does not hold water. So very hot braking should be more stable.

 

If you flush the system with DOT4 (Ethylene Glycol) you should get a big majority of the 'possible' DOT5, any water and old DOT4 out of it.

It will work but monitor the pedal action - as you are in uncharted territory.

Change the fluid every 2 years

 

Roger

[harlequin]

When I changed to DOT5 many years ago I flushed the system with methalated spirits, since then I have replaced the master cylinder and rear wheel cylinders but this was due to wear not deterioration of the seals and this was at least 5 years after I started to use DOT5

George 

[Richmac]

Thanks Rodger I'm not bothered about fancy pants DOT 5. If it was in there and looked fine I would stick with it but I think its contaminated and the fact that you can't buy it at your local store puts me of as well. Do you think I should have more water separated if I mixed 50/50? Do you think I will do any damage if i'm wrong? My thinking if I'm right and its been contaminated by DOT 4 then the damage has been done a long time ago?

Regards Richard

[Richmac]

Working on the assumption that if they put DOT 5 in the brake system then they would also put it in the clutch I took a sample. Nice and clean with a bluish tinge. Compared to whats in the brake system (see above) I'm even more certain its contaminated. It's coming out!! What could possibly go wrong? Shall I flush with DOT 4 or 5 ? What do you guys think please as I want to do it tomorrow and will go with the majority

[Waldi]

Hi Richard,

Probably not the answer you like to hear but if I were in doubt about it I would just replace all rubber components and hoses, so can be confident it will work as intended. Maybe very conservative, but that’s what I would do. 
Not very expensive if you do it yourself too.

Cheers,
Waldi

[Richmac]

Thanks Waldi.  I think that would be sensible. Do you mean rebuild the the master cylinder, brake cylinders and calipers or just the flexible hoses?

Regards Richard

[Waldi]

Hi Richard, I would do the entire system. Also flush the metal pipes with brake cleaner until clear fluid comes out, that blow dry with compressed air. And check these pipes for external corrosion.

The servo can be left, it that’s still ok, as it should not affect the new brake fluid, whatever type you use.

Cheers,
Waldi

[ntc]

32 minutes ago, Richmac said:

Thanks Waldi.  I think that would be sensible. Do you mean rebuild the the master cylinder, brake cylinders and calipers or just the flexible hoses?

Regards Richard

Waldi is correct all seals need replacement and piping flushed clean 

[Andy Moltu]

If you don’t clear out the old fluid/blend you will end up with a mix of Dot 4 and 5 that retains the problems of both and the benefits of neither. In an emergency you can top one up with the other. 

(Dot 5 - long life, high boiling point and paint safe but harder to bleed the air out and any water will separate out and if that’s in the caliper boil at 100c and seals more prone to wear)

(Dot 4 easier to bleed and smaller amounts of water won’t separate out and kinder on the seals, but damaging to paint, hygroscopic so absorbs water with progressive drop in boiling point)

[boxofbits]

33 minutes ago, Waldi said:

Hi Richard, I would do the entire system. Also flush the metal pipes with brake cleaner until clear fluid comes out, that blow dry with compressed air. And check these pipes for external corrosion.

The servo can be left, it that’s still ok, as it should not affect the new brake fluid, whatever type you use.

Cheers,
Waldi

I’m sure Waldi would be aware of this, but make sure you drain your compressor tank prior to doing this and then blow through the airline for a while before the brake lines.

I used an air sander yesterday for the first time in a few weeks and the air was saturated with water due to the recent climate.

Kevin

[Waldi]

Good point Kevin, drain the compressor  tank regularly, although this does not fully solve it. Pressure dew point is different from atmospheric dew point. I’m always surprised how much water I collect at my little cyclone separator on my grit-blasting cabinet. 

Waldi

[SpitFireSIX]

On 8/27/2020 at 8:41 PM, Waldi said:

Good point Kevin, drain the compressor  tank regularly, although this does not fully solve it. Pressure dew point is different from atmospheric dew point. I’m always surprised how much water I collect at my little cyclone separator on my grit-blasting cabinet. 

Waldi

A cyclone separator will not lower the dew point unfortunately.

[Mike C]

12 hours ago, SpitFireSIX said:

A cyclone separator will not lower the dew point unfortunately.

But if the separator gets all the saturated water out and is properly drained , the dew point will drop when the air is subsequently expanded. In a previous life I used to install float traps under the receivers to do this. Of course if you're really worried about water there's always refrigerated or desiccant air driers.

[Waldi]

Indeed the cyclone separator will not lower the pressure dew point, but once it expands it will be drier. 
Waldi

[SpitFireSIX]

1 hour ago, Mike C said:

But if the separator gets all the saturated water out and is properly drained , the dew point will drop when the air is subsequently expanded. In a previous life I used to install float traps under the receivers to do this. Of course if you're really worried about water there's always refrigerated or desiccant air driers.

I have engineered a non-heater auto regenerating desiccant dryer from two gas bottles, 6 valves, two flow control valves, two old car mufflers, assorted pressure gauges, a couple of timers, loads of 1" pig iron pipe fittings and several buckets of aluminium oxide desiccant. Lowered the dew point more than any refrigerated air dryer you could buy. Modelled it off a large Pall air dryer. Oil contamination from a kak compressor killed it in the end.

[Mike C]

1 hour ago, SpitFireSIX said:

I have engineered a non-heater auto regenerating desiccant dryer from two gas bottles, 6 valves, two flow control valves, two old car mufflers, assorted pressure gauges, a couple of timers, loads of 1" pig iron pipe fittings and several buckets of aluminium oxide desiccant. Lowered the dew point more than any refrigerated air dryer you could buy. Modelled it off a large Pall air dryer. Oil contamination from a kak compressor killed it in the end.

I've used a lot of Pall stuff in Australia and PNG over the years, it's good gear. It's amazing what you can do when you set your mind to it with scrap and a bit of thinking.Your dryer could have well outperformed a refrigerated dryer. From memory the dew point limit on a refrigerated dryer is set by water freezing in the compressed air line. I always used oil free compressors when I needed to use a drier- recips with carbon or later teflon rings or screw compressors.

For most of us though, provided the compressor is fitted with a good aftercooler, trapping and draining the water condensed in the receiver is good enough.