11 replies to this topic

[Chris1992]

Hi guys, 

 

Ok so I've been busy with my Mini build, and when the time came to bleed the breaks I decided to go for silicone brake fluid as everything in my engine bay is nicely painted and I don't want to risk ruining it in the case of a leak. However, I have run into an issue. 

 

(I'm aware that silicone brake fluid can make the breaks feel slightly spongy due to more dissolved air (I think) but this isn't a track car so I'm not too worried about this).

 

The problem I have is that my Master cylinder has started leaking, and I now have brake fluid dripping down the brake pedal and onto the carpet. My initial thought was that the seals in my master cylinder had perished, but this cylinder has only seen a year of road use, followed by 2 years of being stored, so I found that surprising. At this point, a friend of mine who restores vintage aircraft told me that apparently brake fluid contains a swelling agent that reacts with the rubber seals and makes them expand to produce a tight seal, whereas silicone brake fluid does not. He also mentioned that I need seals made from a certain type of rubber in order to stop the leak.

 

And so my question is this... Is this true? I don't remember reading about it when I did my research beforehand. If it is true, are there master cylinder seals available in this 'special' type of rubber? I don't really fancy doing a complete fluid swap, so if anyone can help shed some light on the subject then that would be great!

 

Cheers  

[panky]

This is from the Moss technical section, but no mention of special seals.

 

A newly rebuilt and scrupulously clean brake system filled with silicone fluid should outlast a system filled with glycol fluid by several times. There is little advantage in adding silicone fluid to a system which contains even small amounts of contaminants. Merely bleeding the system is not enough, as there will be pockets of old fluid and sludge which will not bleed out. Silicone fluid tends to concentrate any residual glycol fluid, moisture and sludge, into slugs, instead of allowing their dispersal throughout the fluid, as does glycol fluid. This can lead to relatively severe but localized problems, rather than the more general system deterioration experienced with old moisture-laden glycol fluids. This may be a factor in reports of leakage when silicone fluid is used in non-rebuilt systems which had been used with glycol fluid. A "new" system full of silicone fluid will require very little maintenance for years.

[Spider]

I have Silicon Fluid in one of my Cars.

 

There are no different seals and rubbers available to 'suit Silicon' Brake Fluid, the same type of seals are used for Glycol based fluids as is Silicon types.

 

It's always advised though from all suppliers (that I know of) Silicon Fluid that while a system can be retro-filled with Silicon (following Glycol), it's highly recommended that all rubbers in the system be replaced. This is only to gain the maximum benefit from the Silicon Fluid. 

 

I'll also point out, from my own experience, especially once any cylinder has been filled with Glycol based fluids, then at some later point, drained and stored, they never store too well for any period and rust very quickly. This I put down to there being some residual fluid left in the cylinder, which absorbs moisture from the atmosphere. I would suggest to you this is what has happened to your Master Cylinder.

[Chris1992]

I have Silicon Fluid in one of my Cars.

 

There are no different seals and rubbers available to 'suit Silicon' Brake Fluid, the same type of seals are used for Glycol based fluids as is Silicon types.

 

It's always advised though from all suppliers (that I know of) Silicon Fluid that while a system can be retro-filled with Silicon (following Glycol), it's highly recommended that all rubbers in the system be replaced. This is only to gain the maximum benefit from the Silicon Fluid. 

 

I'll also point out, from my own experience, especially once any cylinder has been filled with Glycol based fluids, then at some later point, drained and stored, they never store too well for any period and rust very quickly. This I put down to there being some residual fluid left in the cylinder, which absorbs moisture from the atmosphere. I would suggest to you this is what has happened to your Master Cylinder.

 

Ok thanks for the help!! That certainly clears things up, I was skeptical about what I had been told so just thought I'd ask. So do you think my entire master cylinder is toast due to rust from the inside, or is this a simple case of new seals and a clean? 

[Spider]

 

Ok thanks for the help!! That certainly clears things up, I was skeptical about what I had been told so just thought I'd ask. So do you think my entire master cylinder is toast due to rust from the inside, or is this a simple case of new seals and a clean? 

 

 

It will probably be a new cylinder, but no harm in stripping yours first, just don't get your hopes too high!

[Chris1992]

 

 

Ok thanks for the help!! That certainly clears things up, I was skeptical about what I had been told so just thought I'd ask. So do you think my entire master cylinder is toast due to rust from the inside, or is this a simple case of new seals and a clean? 

 

 

It will probably be a new cylinder, but no harm in stripping yours first, just don't get your hopes too high!

 

 

Ok cheers! Looks like an order from Minispares is on the cards!

[tiger99]

You may find that a chemical reaction has caused small crystals to form on the rubbers, damaging the rubbers, and the cylinder bore may be ok.

 

I have used silicone fluid very successfully on several cars but only in completely overhauled systems with all cylinders fully stripped, cleaned and rebuilt, new Kunifer pipes and Goodridge flexibles, so there was no trace whatsoever of glycol fluid. I will continue to do that. The hydraulic system is safety critical and if one part is worn out or corroded, other parts are likely to be not far behind, so it makes sense to renew it all at once, considering that there may then be 15 years or more of trouble free usage if done properly.

 

It is depressing to see continual incorrect advice in the monthly comics, typically suggesting that silicone grease should be used when overhauling cylinders and calipers. This is a fairly new phenomenon, and proof, yet again, that idiot journalists are incapable of independent thought, but copy from each other. (I first noticed this in the early 1980s, when "weight transfer" and its implications for suspension design were widely and incorrectly disseminated. It happens regularly) You must only use silicone grease, and of the high melting point variety, when the fluid is also silicone. Conversely the red rubber grease usually found in new cylinders must be completely removed and replaced by silicone grease if you do decide to go for silicone fluid.

[pogie]

http://www.minispare...silicone-valley

 

 

This Keith Calver article from 2005  outlines a few issues with silicone brake fluid and it was the last couple of lines that really caught my eye, "And just to underline this, 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. Think on".

 

 

Personally I've never had a problems with regular glycol fluid and will put up with hour or so of work involved in changing it every couple of years.  

[nicklouse]

http://www.minispare...silicone-valley

 

 

This Keith Calver article from 2005  outlines a few issues with silicone brake fluid and it was the last couple of lines that really caught my eye, "And just to underline this, 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. Think on".

 

 

Personally I've never had a problems with regular glycol fluid and will put up with hour or so of work involved in changing it every couple of years.  

there is only one major user of silicon brake fluid.

 

and they have been trying to get rid of it for years but costs are too high to change due to their policy of all brake systems have to use one type of fluid.

[Spider]

While I do have it in one car, it's never gone beyond that for me. I felt the expense of it not worthwhile and by having glycol in there is a forced reason to get my head under the other cars and at the very least, have a look while periodically changing the fluid.

 

I do know Harley Davison fill their bikes from the factory with it. Back in the 80's, after some 20 years of research and testing, the US Army went over to Silicon.

 

I think too, this is another area where there's been a bit of scare-mongering that gone on over the years. Like anything, if it's not done correctly, then you can expect troubles.

[nicklouse]

 
I do know Harley Davison fill their bikes from the factory with it. Back in the 80's, after some 20 years of research and testing, the US Army went over to Silicon.

And are trying to (or have) go back to glycol.

Not sure of why the went to it.

They were finding that they were having issues with the lack of use of the vehicles.so they came up with a plan where the glycol fluid was removed before storage and an alternative fluid was put in to "preserve" the system. This was bled out and the glycol fluid put back in. The DOT5 was meant to save them $20 mil.

Then there was talk of them wanting to bin it in the early/mid 2000. Don't know how it went but I guess some of the issues we know of the bubbles, the water pooling etc etc or just the fluid cost.

If anyone has info on if they did change it would be interesting.

[Spider]

Best as I can determine, Harley are still using and selling DOT 5 (Silicon Brake Fluid). As a service item, it even has a Harley Label on the bottle.

 

http://www.harley-da...a-12-9990277--1

 

 

I did find this article, which I maybe of interest;-

 

http://www.buckeyetr...Fluid/Fluid.htm