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silicon brake fluid
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Ray White



Joined: 02 Dec 2014
Posts: 3292
Location: Derby

PostPosted: Sat Jan 18, 2020 11:53 pm    Post subject: silicon brake fluid Reply with quote

Forgive me if this has been raised before but a search gave an incomplete answer.

My MG TC would traditionally have had DOT 3 Glycol brake fluid although some owners use DOT4. A few use DOT 5 silicon.

There seems to be an ongoing debate about the use of DOT 5 silicon and it's propensity to search and leak out. Is that a serious problem?

(There is also 5+ ??)

From what I can gather glycol based fluid should be changed every two years because is is hydroscopic whereas silicon is not so needs changing less frequently. It is more expensive but that is not an issue here.

The question I am struggling with is... which should I use in the MG rebuild??.

The point I would stress is that every part of the braking system (excepting the back plates) is being replaced with brand new - and of a superior quality.

I also intend to have a remote and more convenient master cylinder reservoir rather than access under the floor so keeping a check on the level should be easier.

I would appreciate some suggestions as I keep going round in circles with indecision.

Thank you.
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Keith D



Joined: 16 Oct 2008
Posts: 962
Location: Upper Swan, Western Australia

PostPosted: Sun Jan 19, 2020 2:32 am    Post subject: Reply with quote

Ray,

I am probably the most enthusiastic supporter of using silicone fluid on this forum.

As I have posted on a previous thread, I renewed all the brake parts on my Austin A40. I used silicone brake fluiid - DOT 5. I did this back sometime around 1990. The fluid is still in the car and the brakes still work perfectly. After about thirty years I have had no problems whatsoever.

Please remember that you must NEVER mix DOT 5 with anything else. DOT 5.1 must NEVER be used with DOT 5.1.

I've been told all sorts of horror stories about the fluid boiling, corroding parts etc. NONE of which have occurred.

Keith
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1932 Austin Seven RN long wheelbase box sedan
1950 Austin A40 tourer
1999 BMW Z3

You are either part of the problem or part of the solution
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Ray White



Joined: 02 Dec 2014
Posts: 3292
Location: Derby

PostPosted: Sun Jan 19, 2020 10:53 am    Post subject: Reply with quote

Thanks Keith. I guess you mean DOT 5 should not be mixed with DOT 5.1?

As I am more likely than not to put off changing the brake fluid at the two year interval I think silicone would be favourite.

Incidentally, I have only just now discovered that silicon and silicone are two completely different things.
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D4B



Joined: 28 Dec 2010
Posts: 2091
Location: Hampshire UK

PostPosted: Sun Jan 19, 2020 12:11 pm    Post subject: Reply with quote

My friends who run 1950s and 1960s Peugeots in France have stopped using Silicone due to swollen seals and leaks, here are some messages poorly translated for you to read.....


J'ai un client dont la voiture est au silicone, il a des fuites sur les étriers régulièrement malgré la rénovation de ces derniers.

I have a client whose car is silicone, it has leaks on the calipers regularly despite the renovation of the latter.

Pareil dans mon entourage , des inconditionnels du silicone et des déçus par des fuites ,des coupelles ramollies et gonflées par ce même silicone ..

Pour ma part: Dot 3 Bendix moins de 10€ le litre ..en grande surface
purge compléte tous les deux ans car pas mal d humidité dans mon secteur .et ça roule , je procède ainsi sur mes 403 depuis bien des années aucun souci ..
Moyen de controle dans le bocal : couleur champagne quand il est neuf lorsque il rougit vers une couleur ambrée il est bon a changer ..

Same in my entourage, unconditional silicone and disappointed by leaks, softened cups and swollen by the same silicone ..

Dot 3 Bendix less than 10 € per liter .. in supermarkets
purge completed every two years because a lot of humidity in my sector. and it rolls, I do so on my 403 for many years no problem ..
Means of control in the jar: champagne color when it is new when it blushes towards an amber color it is good to change.

Hope this helps
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Keith D



Joined: 16 Oct 2008
Posts: 962
Location: Upper Swan, Western Australia

PostPosted: Sun Jan 19, 2020 12:16 pm    Post subject: Reply with quote

Sorry Ray.

That should read that DOT 5 should never be mixed with DOT 5.1

With my A40, only the two front brakes are hydraulic. The rear are mechanical, so if my hydraulic brakes should fail. I still have the rear brakes to stop me. (Obviously far less efficiently that the front ones) This does mean that I will not experience complete brake failure. I must admit that I have very rarely changed the fluid in all this time.

Silicone brake fluid repels any water. Glycol fluid on the other hand, can absorb up to 10% water and it is this moisture that causes the pitting inside the master and wheel cylinders that ends up tearing the rubber pistons and causing brake failure. The big advantage of using silicone fluid is when the car stands for long periods the brakes still function perfectly.

Keith
_________________
1926 Chrysler 60 tourer
1932 Austin Seven RN long wheelbase box sedan
1950 Austin A40 tourer
1999 BMW Z3

You are either part of the problem or part of the solution
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Ray White



Joined: 02 Dec 2014
Posts: 3292
Location: Derby

PostPosted: Sun Jan 19, 2020 1:01 pm    Post subject: Reply with quote

I think problems are more likely to occur when you switch from Glycol to Silicone without replacing everything - including brake lines. I need to hear from other users like me who have replaced everything that comes into contact with the fluid.

I would imagine that new cars are all equipped with silicone -and have probably been for years now.
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ukdave2002



Joined: 23 Nov 2007
Posts: 3491
Location: South Cheshire

PostPosted: Sun Jan 19, 2020 3:14 pm    Post subject: Reply with quote

Silicon brake fluid and ABS systems don't work well together, consequently modern vehicles use Glycol fluid (Silicon is too spongy).

Harley Davidson used Silicon for a short period but went back to Glycol .

Dave
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Ray White



Joined: 02 Dec 2014
Posts: 3292
Location: Derby

PostPosted: Sun Jan 19, 2020 4:29 pm    Post subject: Reply with quote

ukdave2002 wrote:
Silicon brake fluid and ABS systems don't work well together, consequently modern vehicles use Glycol fluid (Silicon is too spongy).

Harley Davidson used Silicon for a short period but went back to Glycol .

Dave


spongy? Why would anyone make a spongy brake fluid?
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norustplease



Joined: 11 Apr 2011
Posts: 610
Location: Lancashire

PostPosted: Sun Jan 19, 2020 6:05 pm    Post subject: Reply with quote

Silicone brake fluid is slightly more compressible than DOT 4 type fluids and so the pedal may be slightly softer in feel. It has also been known to attack the rubbers in very old systems that have not been renovated with modern seals. However, this is said to be rare since most systems in 50 plus year old cars have been overhauled with modern composition seals and you have completely replaced your system with new, so should be no problem.
You may, incidentally get issues with microbubbles, which generally have to be left to settle out and then rebled after a few days. This is the cause of an extremely soft pedal.
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Ray White



Joined: 02 Dec 2014
Posts: 3292
Location: Derby

PostPosted: Sun Jan 19, 2020 7:04 pm    Post subject: Reply with quote

norustplease wrote:
Silicone brake fluid is slightly more compressible than DOT 4 type fluids and so the pedal may be slightly softer in feel. It has also been known to attack the rubbers in very old systems that have not been renovated with modern seals. However, this is said to be rare since most systems in 50 plus year old cars have been overhauled with modern composition seals and you have completely replaced your system with new, so should be no problem.
You may, incidentally get issues with microbubbles, which generally have to be left to settle out and then rebled after a few days. This is the cause of an extremely soft pedal
.


Thanks for that. I remember having trouble bleeding the brakes in my Austin Cambridge. I gave up and left it overnight. In the morning the pedal was firm.

I was told at the time it was micro bubbles of air in the fluid.
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norustplease



Joined: 11 Apr 2011
Posts: 610
Location: Lancashire

PostPosted: Sun Jan 19, 2020 9:47 pm    Post subject: Reply with quote

I had the same problem with the LHM in my 2CV. The air bubbles initially cling to the walls of the pipework apparently.
The only downside of Silicone is that it has a lower boiling point than Glycol and is not therefore recommended for racing applications. Fine, however, for day to day use in an ordinary road vehicle. Not recommended for ABS either, although many use it without issue.
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1986 Renault 4
1990 Citroen 2CV
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MVPeters



Joined: 28 Aug 2008
Posts: 679
Location: Northern MA, USA

PostPosted: Sun Jan 19, 2020 10:28 pm    Post subject: Reply with quote

Ray
For your own safety use the fluid the seals were designed for = DOT 3 or 4. Never mind all the rumours about bubbles & silicone - please use what you know will be safe.
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Ray White



Joined: 02 Dec 2014
Posts: 3292
Location: Derby

PostPosted: Sun Jan 19, 2020 11:55 pm    Post subject: Reply with quote

MVPeters wrote:
Ray
For your own safety use the fluid the seals were designed for = DOT 3 or 4. Never mind all the rumours about bubbles & silicone - please use what you know will be safe.


Good advise. My late father would have said exactly the same thing. DOT 4 is probably better for spirited driving and having gone to the trouble and huge expense of fitting 'Alfin' type drums (cast iron with a aluminium fins) to avoid brake fade, the last thing I want to do is compromise on safety.

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lowdrag



Joined: 10 Apr 2009
Posts: 1288
Location: Le Mans

PostPosted: Mon Jan 20, 2020 5:14 am    Post subject: Reply with quote

I must admit that I have used glycol based fluid for over 30 years now and am loath to change. Water is nor ever has been a problem. And I'm afraid that like others, the two-year advice is and never has been respected. The cars get some spirited driving each year, although less than before sadly, and the brakes seem fine with no pulling left or right. If I changed now I'd need to replace all rubbers in the system.
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