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MG MGB Technical - Synthetic brake fluid

Hi,

I am about to renew all my brake and clutch pipework. I have changed the seals on the front callipers and have installed new back cylinders. From comments on this BB I have not changed the seals on the master cylinder. The question I have is can I use synthetic brake fluid? Someone suggested to me that there might be a problem with contamination with any old fluid in the system. Does any one know if this is a problem? I'm keen to use silicon fluid since it does not strip paint.

Thanks in advance

Billy
William Beattie

go to chicagoland mg club website, look in tech tips. There are a couple of great articles.
Fred Horstmeyer

I use silicone brake fluid (dot 5) or LMA. Silicone cannot be mixed with any thing else, and some poeple say it has a spongy feel I disagree. Silicone will not eat paint either. LMA is good too but we need to know what DOT rating your "synthetic" brake fluid is to answer your question.
Ross

William-
Silicone Fluid has its problems (which I won't go into because I don't want to start a rehash of the old Silicone-vs-Anything-Else Debate). I use Valvolene SynPower brake fluid. It's a synthetic that will go to F555 before boiling, so it'll do just about anything that Silicone Fluid will do, yet has none of its drawbacks. It's compatible with all petroleum-based brake fluids (such as Castrol LMA), so it won't harm the seals in your system.
Steve S.

William-

Wouldn't mix the two. From all the threads and specs I've read you should only use silicone in a completely rebuilt system.
I use silicone in my GT, brakes and clutch with no problems but all the seals were new and lines were cleaned out.
In my roadster I have LMA in the brakes and silicone in the clutch, the PO did this.
For the hassle involved I'd stick with the LMA and just be careful not to get it on the paint.
I don't think silicone is worth the extra work. After all, your car stopped for many years on DOT 3!

Drive your B,
Sam
Sam

What is LMA???
Mike Howlett

Castrol LMA is a DOT 4 brake fluid, I believe it was the type fluid originally specified by Lockheed in brake/clutch hydraulic systems.
Paul Konkle

William-
I should haved added the following to my last posting: If I was going to go back to using a petroleum-based brake fluid, then I'd use Castrol LMA.
Steve S.

I am keen to know more about Valvolene SynPower - does it eat paint?

My braking system will be have new pipes, new front calliper seals and new back cylinders. I've read in other threads to leave the master cylinder seals alone if it is working ok. So, how do you clean out the master cylinder and callipers enough to allow silicone? Or is it really a case of new callipers and new master cylinder to use silicone.

Thanks for all your comments - they have been as usual very helpful.

Billy
William Beattie

William et al, you MUST read the tech article on the chicagoland mg club web page!!
Fred Horstmeyer

William
I used silicone brake fluid when I completely rebuilt my GT V8 also because it is paint friendly.
But alas I had nothing but problems. Gone back to good old dot 5.

Cheers

Mark
Mark Rawlins

William-
I accidently knocked over and spilled a cup of Valvolene Synpower on the interior of my over-restored engine compartment. Knowing what brake fluid can do to paint, I immediately went into a mild state of panic. Using the only thing I had at the moment, I removed it with dishwashing detergent and rinsed thoroughly with lots of water from a garden hose, praying all the while (No! Please God, no,no,no,no!). I dryed everything with a soft cotton towel and hoped for the best. No damage was done. The container that the brake fluid comes in states "Will damage car finishes.". I suspect that it's slower to damage paint than most fluids. However, choosing a brake fluid on the basis of it's potential to damage paint is false logic. If you have a master cylinder that's leaking fluid onto your paint, then you need to rebuild it. If it fails completely, you're going to have an accident.
Steve S.

Wiliam,

The majority of the problems caused by Silicone relate to three main areas - long or spongy pedal feel, sudden loss of brakes , and brakes ‘hanging on’. SAE publications have ratified these symptoms by identifying certain properties prevalent in silicone brake fluids. These have been named as high ambient viscosity, high air absorption, high compressibility, low lubricity, and immiscibility with water (failure to mix with water). It would seem that there are definite relationships between these properties and symptoms.

If you intend to use your car for fast road use I would be concerned with the second problem and I have experienced the third. If you decide to use silicone fluid and experience these problems the only cure is to purge system and replace all rubbers.

Neither of the major brake specialist companies in England produces silicone-based brake fluid. In fact they are most emphatic in their condemnation of it and I have a copy of their warning about using Silicone fluid.

Paul



Paul

This old chestnut about silicon brake fluid rears its head many times during the year.
I have used it for ten years with NO problems what ever it has never needed changing or the brakes haver never required bleeding. A friend of my has used it in his TD for fifteen years and when he recently rebuilt his rear axle he took the brake cylinders apart for inspection. There was NO trace of rust and the rubbers where like new.

It is immiscibile with water! yes this is true...but how on earth does water ever get in the system?

It is more compressable! Yes this is also true...by 0.4% which would make your brake travel another 1 or 2mm.

High air absorbion! Yes this is also true...but once again how does this air appear in the fluid? if poured slowly into the master cylinder it is not a problem.

If you rebuild your brakes properly including replacing all pipes and seals there will never be a problem.

Howard
Howard

I second all that Howard has said, I have used silicone brake fluid for around seven years and found it to be trouble free.
Several other Coventry MGOC members have tried it again with only one person having any problems at all and I found out from talking to him that he didn't replace all of the brake pipes. Once he had done this properly he has not had any problems either.

Peter
Peter

I can add to the endorsement of the silicon fluid. I used it when I rebuilt my A 14 years ago. I now drive it as my only car (for the last 8 years) and I have never had any problems.

On the other hand if I had used the normal stuff, I would have surely had to replace some wheel cylinders or rubbers by now, you know rust, water absorbtion, etc.... On the other hand all I have had to replace on my system in the last 14 years are worn out shoes, pads and front discs (I didn't replace them at restoration because they were absolutely fine, I just wore them out since!). And who has ever seen a 14 year old system as good as new using "normal" (ie non-silicon) fluid?

So in my experience its a great thing to use as long as you replace everything at the time of restoration. And here I also make the observation that a complete new brake system is NOT that expensive, and it IS cheaper than hurting yourself. It's the one part of a restoration and running maintenance that should NEVER be skimped on.
dominic clancy

I also use the silicon fluid on the brakes and clutch of my MG for about 4.5 years and never had any problems with. I am now dismanting the car to get the bodywork done and removed the master brak cilinder and pipes an so on and found some "normal" brake fluid mixed with silicon.
This was done during a MOT 3 years back. The tester found the level a little low and filled it up with "normal" brake fluid and after filling it up, he saw that the system was filled with silicon fluid.
He then flushed the system but as i saw now not good enough. The "standard" brake fluid was laying as a bed over the silicon fluid in the resevoir. It however never caused any trouble with my brakes.
By the way, i buy my silicon fluid with a Harley Davidson dealer because they fit it from new onto their motorbikes. One would think that with the US legal system with the high claims, they should be 200% sure before putting it in their bikes.
I will fit new pipes and again silicon fluid. My car is a more or less rust free Californian car. The only spot where you find (surface) rust is were normal brake fluid leaked in the past.
Regards
Peter
Peter van de Velde

Every time the silicone/DOT 4 fluid issue is discussed the fact that silicone fluid will not mix with
water is mentioned and I do believe that is true. It is a well known fact that the brake system will
collect some moisture over time and the water will mix with DOT 3/4 fluid. My question is what
happens to water/moisture that gets in a braking system filled with silicone fluid? I don't think
silicone fluid builds a barrier making it impossible for water/moisture to enter the system, it
doesn't mix with the silicone fluid so it must remain somewhere in the brake system. Where?
Just curious. Clifton
Clifton Gordon

Clifton,
Several months ago, I added some water to a small bottle of silicone fluid, and the water sinks to the bottom. A vigorous shaking causes the water to disperse into smaller droplets (still at the bottom of the container) and they start to join together into a single larger drop of water again. This would be a problem if water droplets were inclined to find their way into the hydraulics, but the only way I can see this could happen is if I leave the cap off the reservoir, and drive on a rainy day. On humid days, the moisture in the air is not a droplet and doesn't penetrate the surface of the hydrophobic fluid. In order for humidity to cause water collection in the reservoir, it would have to condense into droplets on the surface to a sufficiently large particle size so that it would sink.
On the other hand, standard brake fluids are hydrophillic, and will absorb moisture from the air. As long as it isn't excessive, this isn't an issue because as many others have pointed out, these fluids mix with water.
For what it's worth, I too have used silicone fluid for the last 5 years and have been very happy with it. My use started with a full rebuild, flush and replacement of all seals, and not a single problem to report.

Gabe
Gabriel Cabral

This thread was discussed between 28/02/2002 and 07/03/2002

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