Silicone DOT 5 Brake/clutch fluid.

[Waldi]

I’m in the DOT 5 family. I understand water that has collected in the bottom of calipers and cylinders cannot be drained/flushed our, but at the same time, corrosion by water collection in the silicone brake fluid is over-estimated (to put it politely). The fact that several on here have had no corrosion related issues over 10 or 20 years is a strong indication.

I will hide now for the other family:)

Waldi

[Z320]

17 hours ago, Andy Moltu said:

The solution to that is to bleed the brakes after a series of heavy braking from speed to get any fluid hot and when you bleed the steam will rise to the top and be bled out of the callipers.

What advice is this?

The moment you get steam to bleed out (if this will ever be the case)

you hopefully will not die by a car accident because of a brake failure.

Please everybody: don’t do that.

[r-fox]

Hi Roger,

oh yeah , of course you're totally right.

Two solutions to overcome  (austrian trolls told me)

firstly , srewing off the caliper and fixing it in a position so that the bleeding screw is lowest point.

Secondly, plain and simple turn arround the whole car in order to achieve same position as described above .

I really like your knowledge and thoughts all the time and your hat too.

Wolfgang
 

[Tim D.]

4 hours ago, Waldi said:

I’m in the DOT 5 family. I understand water that has collected in the bottom of calipers and cylinders cannot be drained/flushed our, but at the same time, corrosion by water collection in the silicone brake fluid is over-estimated (to put it politely). The fact that several on here have had no corrosion related issues over 10 or 20 years is a strong indication.

I will hide now for the other family:)

Waldi

I think Waldi has a very good point hear. Do any of us actually have evidence of the volume of water that accumulates in Dot over, say, a year? I know in my old cars the hydraulic clutch and brake systems running Dot 4 can look pretty nasty after 5 or so years even with periodic fluid changes. Almost like the seals a falling apart. When I take them apart the slaves are almos5 always corroded, hence I always replace. My 2 cars running Dot 5 have been running for more than a decade and fluid is clear and when I last took the brakes apart to replace the flexi hoses everything "looked" good. Now obviously I didn't take the calipers apart and perhaps annoyingly I didn't empty them to see how much water was in there. However I have yet to have a caliper or brake slave fail due to rust with dot5. May be I should empty a caliper this winter layup so for the good of the debate?

What do you think?

Tim

[Waldi]

Hi Tim,

If you want to check for water collection in the wheel cylinders, if you press the piston fully in the cylinder most fluid will be flushed out. I’ not planning to do that, unless I’m there for other work. 
I vented my system recently (after a PDWA seal leakage), and the fluid that came out was “as new” and had no water in it. It was in there since 2018.

Waldi

[pinky]

I use silicone,  I use it  because of paint damage  caused by the other dots,

My own personally experience, with dot 4 is that for no reason, the car is garaged parked, with no leaks, starts to leak for no apparent reason 

I believe dot 4 is a very good lubricant,  never had a problem with silicone never had a soft peddle, never had a leak 

Pink 

 

[paul bond]

Hi, watched this thread with interest

I have used silicone fluid in competition car clutch systems with success but have had less success in brake systems on road cars.

Probably OK but only if the system is completely drained and flushed before using silicone.

Attached photo of TR5 Caliper piston showing rust stains at the level between the old dot 4 and the new silicone, because the system was not emptied before the silicone was introduced. Rust is from water; water is what we are trying to avoid.

[stillp]

8 hours ago, Waldi said:

I’m in the DOT 5 family. I understand water that has collected in the bottom of calipers and cylinders cannot be drained/flushed our, but at the same time, corrosion by water collection in the silicone brake fluid is over-estimated (to put it politely). The fact that several on here have had no corrosion related issues over 10 or 20 years is a strong indication.

I will hide now for the other family:)

Waldi

+1. DOT 5 since 1989.

Pete

[Waldi]

7 hours ago, paul bond said:

Hi, watched this thread with interest

I have used silicone fluid in competition car clutch systems with success but have had less success in brake systems on road cars.

Probably OK but only if the system is completely drained and flushed before using silicone.

Attached photo of TR5 Caliper piston showing rust stains at the level between the old dot 4 and the new silicone, because the system was not emptied before the silicone was introduced. Rust is from water; water is what we are trying to avoid.

Hi Paul,

that is my personal experience too.
Some 20-25 years ago I replaced the dot 4 by dot 5 in my car after a supplier had told me flushing was sufficient. Not true! I found 2 separate phases in the system when I drained it, the dot 4 being black from corrosion products. Apparently the mixture (which was say 99% dot5) was much more corrosive than either of the single products would be. In my case it blocked the tiny vent hole in the master cylinder, so pressure was building up. That was on an XK140. I had to rebuild the entire system.

Waldi

[Tim D.]

8 hours ago, paul bond said:

Hi, watched this thread with interest

I have used silicone fluid in competition car clutch systems with success but have had less success in brake systems on road cars.

Probably OK but only if the system is completely drained and flushed before using silicone.

Attached photo of TR5 Caliper piston showing rust stains at the level between the old dot 4 and the new silicone, because the system was not emptied before the silicone was introduced. Rust is from water; water is what we are trying to avoid.

That's a great demonstration.  All my dot 5 installations were in newly rebuilt brake and /or clutch systems.  I happen to be working at the department of polymer chemistry in stellenbosch this week. One of the profs is an expert in silicone oils. Might have a chat with him. 

[Z320]

By the theory water diffuces in any liquid as long there is a difference of concentration,

also when there is no absorption of water from the liquid.

I hope for somebody who has DOT5 in his brakes for +20 years!

Please drain your brake system and specially the calipers as well as possible and catch ALL liquid as good as possible.

Give it some time to separate DOT5 from water - if there is any water there it will be on the ground.

And examine the pistons and ground of the calipers from rust, please.

I hope somebody is kid enough to do this for all of us, thank you.

Ciao, Marco

  

[Misfit]

Thank you, I have found this topic interesting, I have had silicone Dot 5 in my TR7 since 2000 followed brake fade on the Stelvio pass. I have changed pads and shoes but not my fluid. In view of the comments here I will be replacing the fluid. 

[RogerH]

38 minutes ago, Misfit said:

Thank you, I have found this topic interesting, I have had silicone Dot 5 in my TR7 since 2000 followed brake fade on the Stelvio pass. I have changed pads and shoes but not my fluid. In view of the comments here I will be replacing the fluid. 

Hi Derek,

as mentioned above when you drain the fluid try and save as much as possible and then leave to stand for 24Hr (sealed)

to see the water content.

 

Roger

[stuart]

What I find interesting is that people are using this as a road going fluid as it was developed for the US armed forces for "Long term storage" of vehicles. Not for use on the road.

Stuart.

[RogerH]

Hi Stuart,

I know you are right but sadly there are 'experts' put there that haven't a clue but proclaim the new truth.

As they say - if you say it loud enough for long enough it will become the truth. Amen

Roger

[Z320]

Derek,

you had brake fading „currently“ although you use DOT5 since 22 years?

You are our man!

If there is water in the DOT5 sadly it is down on the ground of the calipers and you  only get it out by bolting the calipers off from the axle and turn them upside down.

And you have to be free in your mind to find water and not being convinced not to find water.

The issue is: we all tends NOT to realize what will disappoint us (cognitive dissonance reduction) or what we have been convicted for a long time.

Ciao, Marco 

 

Edited September 13, 2022 by Z320

[stillp]

1 hour ago, Z320 said:

 

The issue is: we all tends NOT to realize what will disappoint us (cognitive dissonance reduction) or what we have been convicted for a long time.

 

 

Yes, that's true for both sides in this debate!

Pete

[Z320]

Yes I know

[Spit_2.5PI]

2 hours ago, stuart said:

What I find interesting is that people are using this as a road going fluid as it was developed for the US armed forces for "Long term storage" of vehicles. Not for use on the road.

Stuart.

Stuart, I think military vehicles need to stop, just like road-going ones. I had naively assumed that DOT5 was for vehicles whose use included periods of long term storage. After all, DOT stands for (USA) Dept Of Transportation, right? Are you saying that it was a requirement - or an expectation perhaps - that the brake fluid would be changed for conventional before such a vehicle was returned to active duty? In view of the dangers of mixing types of brake fluid, this would seem an onerous overhead involving flushing and changing the seals throughout.

Cheers, Richard

[Charlie D]

1 hour ago, Z320 said:

...And you have to be free in your mind to find water and not being convinced not to find water.

The issue is: we all tends NOT to realize what will disappoint us...

2 hours ago, RogerH said:

...if you say it loud enough for long enough it will become the truth...

It’s all getting a bit: “Zen and the art of classic car maintenance” now.

[RogerH]

6 minutes ago, Spit_2.5PI said:

Stuart, I think military vehicles need to stop, just like road-going ones. I had naively assumed that DOT5 was for vehicles whose use included periods of long term storage. After all, DOT stands for (USA) Dept Of Transportation, right? Are you saying that it was a requirement - or an expectation perhaps - that the brake fluid would be changed for conventional before such a vehicle was returned to active duty? In view of the dangers of mixing types of brake fluid, this would seem an onerous overhead involving flushing and changing the seals throughout.

Cheers, Richard

Hi Richard,

 silicone brake fluid was developed for long term military vehicle storage. And then when required burst into life for a decent battle or war.

No changing back to DOT 3 etc.

However although some of its characteristics are better than DOT 3 it was never going to be equal or replace DOT3. 

you can take advantage of a big lorry brake system and it will still work  - slow lorries tend not to boil.

Eventually some bright spark rear the spec and reason and popped it into his car.

Roger

 

[Spit_2.5PI]

3 minutes ago, RogerH said:

 silicone brake fluid was developed for long term military vehicle storage. And then when required burst into life for a decent battle or war.

Hi Roger. Yes, you can't beat a good war, eh! It sounds as though the mistake was giving silicone a DOT number/approval. Perhaps it needed that so the military could drive on the road to get to their war.

Richard

[RogerH]

They don't like it up them.

No harm in having a DOT number.

It is interesting the world wide car manufacturers have always stayed clear of SBF.

Probably cost, then technical (ABS) etc.

 

Roger

[stillp]

25 minutes ago, RogerH said:

 

you can take advantage of a big lorry brake system and it will still work  - slow lorries tend not to boil.

 

TRy going down a long descent in a loaded wagon Roger! They (if hydraulic) boil quite well.

Pete

[stuart]

41 minutes ago, Spit_2.5PI said:

Stuart, I think military vehicles need to stop, just like road-going ones. I had naively assumed that DOT5 was for vehicles whose use included periods of long term storage. After all, DOT stands for (USA) Dept Of Transportation, right? Are you saying that it was a requirement - or an expectation perhaps - that the brake fluid would be changed for conventional before such a vehicle was returned to active duty? In view of the dangers of mixing types of brake fluid, this would seem an onerous overhead involving flushing and changing the seals throughout.

Cheers, Richard

FWIW the US military are going back to standard Glycol based fluid now as theyve discovered that under long term use the silicons lower lubricity is wearing systems more quickly.

Stuart.