Silicon (DOT 5) Brake fluid - Pro's & Con's?

[westoz3.0csa]

I had my leaking Brake MC rebuilt 5 or 6 mths ago and also renewed the hoses that go from the reservoir to the MC. I recently discovered that " Yes, I'm pretty sure it (hose) is suitable for Brake Fluid" does not actually mean it is, as evidenced by the brake fluid weeping through the hose and the paint peeling in my engine bay!!

I have now remedied the problem but I am now considering moving to DOT 5 Silicon Brake fluid.
The PRO's being:
1) Isn't corrosive to paintwork
2) Is not Hygroscopic
3) Don't need to change often because of 2)
4) High boiling point
5) Isn't corrosive to paintwork
6) Isn't corrosive to paintwork

However, what. if any are the CON's ???

As ever, thanks for any advice

Carl

 

[deQuincey]

con, if you already have had dot4 in your system, and if you have not pristine cleaned it, dot5 will make a mess inisde those hoses and will eventually stuck inside those hoses, and mechanisms resulting in an impossible to clean problem, ......and you will have no brakes, ......and there will not be chirstmas for you little johnny...:-(

 

[sfdon]

Disadvantages:

It does NOT mix with DOT3 or DOT 4 or DOT 5.1. Most reported problems with DOT 5 are probably due to some degree of mixing with other fluid types. A residue of the former non-compatible fluid is sufficient to cause serious issues. The best way to convert to DOT 5 is to totally rebuild the hydraulic system. Additionally, the same advice applies if switching from Dot 5 to any of the other fluids.

Since DOT 5 does not absorb water, any moisture in the hydraulic system will "puddle" in one place. This can cause localized corrosion in the hydraulics.

Careful bleeding is required to get all of the air out of the system. It is hard to do without introducing bubbles and thus results in soft pedal feel. These small bubbles will form large bubbles over time. It may be necessary to do a series of bleeds.

DOT 5 is less compressible (often creating a slightly softer pedal). It is not recommended for racing
It is hard to pour without introducing bubbles and thus results in soft pedal feel,

It is not recommended by the brake manufacturer, especially for ABS brakes.

It is about twice as expensive as DOT 4 fluid.

So silicone fluid aerates easily. Harley-Davison, one of the sole current OEM users of silicone fluid, warns buyers to let the fluid sit at least an hour before using it. If shaken on the way home, it will aerate enough to look like a freshly poured soft drink. Silicone fluid is also slightly more compressible than glycol fluid, does not change color to tip the user to its moisture content, and worst of all, neither accepts or disperses moisture, making systems using it more corrosion prone, and requiring much more frequent fluid changes. Silicone brake fluid also lacks glycol fluid's naturally occurring lubricity, making it incompatible with the mechanical valving in some anti-lock braking systems.

 

[Honolulu]

Don, please 'Spain to me (still on the road to Damascus) why a slightly less compressible fluid would result in a softer pedal feel...? After all we use stainless braided sheathed brake flex lines so that there is less swelling of said lines, and that's supposed to result in a stiffer pedal...?

 

[sfdon]

Nope- not me!
That splanation is directly from the inter web.
Besides- almost 1:00 am here!
Could be one of those would/wouldn’t things?

 

[sfdon]

Don, please 'Spain to me (still on the road to Damascus) why a slightly less compressible fluid would result in a softer pedal feel...? After all we use stainless braided sheathed brake flex lines so that there is less swelling of said lines, and that's supposed to result in a stiffer pedal...?

Ok- the book says silicon reacts with less movement at the same pressure as dot 4. To achieve the same braking effort as dot 4 you have to push harder on the pedal.
Compressibility

In thermodynamics and fluid mechanics, compressibility (also known as the coefficient of compressibility[1] or isothermal compressibility[2]) is a measure of the relative volume change of a fluid or solid as a response to a pressure (or mean stress) change.

where V is volume and p is pressure.

The minus sign makes the compressibility positive in the (usual) case that an increase in pressure induces a reduction in volume.

 

[sfdon]

Don, please 'Spain to me (still on the road to Damascus) why a slightly less compressible fluid would result in a softer pedal feel...? After all we use stainless braided sheathed brake flex lines so that there is less swelling of said lines, and that's supposed to result in a stiffer pedal...?

So the lines are immaterial to the discussion of the relative compressibility factor of the fluids.

 

[Stevehose]

I think Don meant DOT5 is more compressible, not less?

 

[teahead]

Do it but do the necessary preps for it.

People been using it for years w/no issues.

 

[JFENG]

One of my best car buddies has DOT5 in an old Jaguar. I believe the fluid must be ten years old (maybe more), and this car gets driven a lot in the spring/summer/fall. If silicon brake fluid were a problem i think he would be a key candidate to experience those failures. Perhaps it’s more suitable for cars with drum brakes where long pedal travel is inherent.

Anyway, if I ever have to redo the brakes on any of my old cars, I am going with Silicone fluid.

John

 

[sfdon]

My only experience on Dot 5 was being called to trouble shoot a race car that suddenly had crappy brakes that needed more pressure on the pedal to stop. My first question was what did you do last ?
The answer was “change the fluid”-
There you go........

 

[afeustel]

Post from SPACE...certainly my first...probably somebody has already done it...dunno.
Hi every body. Good times up here on ISS.

My 2 cents: I have been using Silicone Brake Fluid in EVERY classic car I have rebuilt for past 25 years (maybe more). The only car I did not change to DOT 5 was my E30 M3.

I have never had a problem with corrosion and my cars sit for long periods of time. Brakes operate perfectly but I do not race any of them. The very best thing about Silicone brake fluid is that it will not eat paint and destroy your perfect detailing work under the hood. I switched because I got tired of wrecked paint after DOT 3/4 systems started to corrode after sitting idle.

Side note: Our racing Karts all use DOT 5 silicone fluid...so it cant be that bad for performance. Don is right: if you want to switch you need all new rubber lines and components throughout (wipe all new seals with alcohol and then apply a coat of DOT 5 on re-assembly). Also, flush steel lines with alcohol/air before refilling.

Cheers from ISS. I would post a pic if I could but my access to internet is a bit archaic at the moment...hoping for an upgrade from dial-up soon. Check out Astro_Feustel on Twitter and Instagram if you like pics of racetracks from space.

Drew

 

[Markos]

Post from SPACE...certainly my first...probably somebody has already done it...dunno.
Hi every body. Good times up here on ISS.

Drew

This is as close to a NASA endorsement as one can get!

 

[Arde]

What about pneumatic brakes, like trucks use? Will not corrode and with the psttt sound they make your family can open the door before you ring the bell.

 

[sfdon]

We have friends in high places?!!!

See you soon Drew- 72 days?

 

[Stan]

This is as close to a NASA endorsement as one can get!

This is so cool!!! I defy any Facebook denizens to beat that!

 

[Arde]

This is so cool!!! I defy any Facebook denizens to beat that!

Hmmm, no offense intended but satellites are not really know for their ability to brake in short distances...

 

[gwittman]

I had a 1973 FJ55 Landcruiser that required yearly rebuild or replacement of slave cylinders every year. After four years of this, I decided to try Silicone brake fluid. I did it the correct way by replacing all the rubber and flushing all the brake lines with alcohol. I ran that Landcruiser for the next ten years without having to do anything to the brake system. Most of those miles where off-road, including deep water crossings. I could tell the brake pedal had a very light softer feel to it but, but hardly noticeable.

It worked so well that I decided to try it on my race car. It worked well for about two laps and then I had to pump the brake pedal to get them to work and it got worse the longer I drove it. Amazingly the brakes would work again after sitting awhile, but would go bad again on the track. It didn't take much of that to get me to switch back to high temperature brake fluid.

 

[deQuincey]

Post from SPACE...certainly my first...probably somebody has already done it...dunno.
Hi every body. Good times up here on ISS.

My 2 cents: I have been using Silicone Brake Fluid in EVERY classic car I have rebuilt for past 25 years (maybe more). The only car I did not change to DOT 5 was my E30 M3.

I have never had a problem with corrosion and my cars sit for long periods of time. Brakes operate perfectly but I do not race any of them. The very best thing about Silicone brake fluid is that it will not eat paint and destroy your perfect detailing work under the hood. I switched because I got tired of wrecked paint after DOT 3/4 systems started to corrode after sitting idle.

Side note: Our racing Karts all use DOT 5 silicone fluid...so it cant be that bad for performance. Don is right: if you want to switch you need all new rubber lines and components throughout (wipe all new seals with alcohol and then apply a coat of DOT 5 on re-assembly). Also, flush steel lines with alcohol/air before refilling.

Cheers from ISS. I would post a pic if I could but my access to internet is a bit archaic at the moment...hoping for an upgrade from dial-up soon. Check out Astro_Feustel on Twitter and Instagram if you like pics of racetracks from space.

Drew

thank you so much Drew to take the time to send us this
there will probably be a time in which we or our grandchildren will be doing this as a common thing, but somehow you are a pioneer

p.s. on the other hand this demonstrates that no matter if you are in your office in planet earth or in the space, workers cheat their companies using company resources and their time to send mails, post in threads and see funny kitty youtube videos

;-) its a joke, i assume that you will have free time too, kind regards and safe work up there