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MG MG Y Type - Silicone brake Fluid

Hi Folks...

Whats the latest view on silicone brake fluid in our cars....
I've heard polar opposites so far....
brilliant because it wont allow moisture into the system....
avoid at all costs as it rots all the rubbers...
Whats the truth?

Rob King

Rob

I am no tribologist but my understanding is you cannot mix the two so you will have to completely drain and flush the system if you are switching over from DOT3 or DOT 4 which are indeed hydroscopic (they such in moisture) to DOT 5 Silicon. I understand that you also will have to replace all the seals in both the master cylinder and the wheel cylinders as these will retain traces of the old fluid and will react and (possibly) degrade them.

Yes DOT 3 and DOT 4 are hydroscopic but provided you have the fluid changed every 2, 3 or 4 years I do not believe this is a real major problem.

DOT 5 has a lower boiling point, but so long as your brakes are not binding I personally do not believe this advantage is really worth the hassle of changing all the seals for, and really does not lend much to reducing braking distance.

Although I was in my MG ZA today, and I know this isn’t an MG Y but it is on DOT 3 fluid (and all drum brakes, as is my Y) and the traffic lights/signals to my front changed suddenly, I had to jump on the brakes sharply, but the car came to a dead stop from 35mph (speed limit) to 0 in about 25 feet – well within the recommended stopping distance I believe. The brake fluid in that car hasn’t been changed in 7 years … and there is no problem with the brake system. Maybe the driver should have been paying slightly more attention to the road though - :-)!!

Any one else got any comments/observations?

Paul
Paul Barrow

Silicone brake fluid has its advantages but as Paul correctly indicated you have to replace ALL the rubber seals in the entire system and flush out the brake pipes, master cylinder etc.- this was the accepted view last time I heard the topic discussed some years ago. I have stuck to the ordinary brake fluid and the disadvantages are that the wheel cylinders corrode (aluminium) and eventually sieze up. The advantages are that 'normal' brake fluid is a known quantity in terms of automotive use. One thing I have found is that if you adjust the brakes so that the shoes are very close to the drum you get only a small amount of movement in the wheel cylinder which I believe aids in them sticking. I adjust my shoes 2 clicks back to allow just that bit more travel when braking and this seems to have, if not eliminated the problem, then helped it. Lack of use of the car is the main culprit as is not changing the brake fluid every 12 months if the car is not driven regularly.
D MULLEN

I had cause last week to look into brake fluids because of problems with my other classic - a 1934 Lanchester. I found a really useful website, which I cannot remember, but I did copy some useful data on the various fluids and made it into a pdf document for future reference. I have sent a copy to Paul for possible inclusion on this website.

My opinion on the current recommendation to change brake fluid every 2 years is, perhaps, cynical, but I believe that it has more to do with generating work for garages than anything else. Modern cars require little routine maintenance, reducing the workload on garages. I was recently charged about £40 + VAT for the second routine replacement of brake fluid in my Mini Cooper at 4 years.

Although it is irrefutable that brake fluid is hydroscopic, the opportunity for it to absorb moisture surely must be limited. Unless there is a leak in the system, the only source of moisture is the air space above the fluid in the reservoir, which is finite, even allowing for the small air changes that take place when the brakes are operated.

Mike

M Long

Thanks for your contribution gents....Paul and Dave..... I am starting from scratch...a totally new braking system with new rubbers and copper piping. On this basis it seems most of your concerns will be addressed.
Am I correct in thinking that Silicone fluid will not have the same paint stripping qualities as that of Dot 3 or 4?
Dave....on the point of (aluminium) cylinder corrosion....I have recently unpacked many new items bought from the Octagon and Moss some years ago.
These items, which are all new, were in as good a condition as when I stored them away with the exception of a pair of YA front cylinders which are cast aluminium.
The steel pistons within the cylinders were stuck fast and required a great deal of encouragement to come out.
The pistons outer egdes were red with rust and the bore of the cylinder was white with oxydation. I see that all currently supplied YA front cylinders are cast bronze...a better choice I feel!
Rob King

Hi Rob

The comments above are spot on with what you will need to do. I can only add that with regard to my experiences with an MGA I that bought last year. This was indeed fitted with a complete new braking system, pipes, discs on the front and cylinders on the rear and used DOT 5.Silicone does not have the paint stripping qualities of DOT 3 and DOT 4 and is a cleaner product to deal with.

Brake cylinders which are bronze are fine. You could get your aluminium front cylinder re-sleeved in stainless steel. Past Parts in Bury St Edmunds offer an excellent service and its worthwhile haveing a look on their website. I used them for the YT and also a TA that I used to own.

All the best

Jerry
J P BIRKBECK

I concur with Jerry's recommendation of Past Parts for refurbishing your brake wheel cylinders although they are not yet on our list of recommended suppliers at http://www.mgcars.org.uk/imgytr/links.shtml#Brake%20%20/%20Friction%20Systems I do intend adding them presently. I will also add the article from Mike Long too referenced above.

One interesting comment that Mike mentioned in his email to me was "The interesting bit to me is
the reference to DOT5 being developed for the US Army, which is seeking
permission to stop using it. Enough said?"

Paul
Paul Barrow

Food for Thought!

As I work in the engineering department for a luxury car manufacturer, several years ago I asked the brakes section about silicon brake fluid and why was it not used in new cars, they then asked the brake supplier in Germany and the answer was:-

If water gets into the brake fluid then a good quality dot 4 brake fluid will absorb this water this will slightly reduce the maximum and minimum temperature that the brake fluid will boil or freeze at.
Where silicon fluid does not absorb water but then become a problem as the water will remain as globules in the pipes and this water can freeze at 0C and boils at 100C which can cause various issues such as blocking the pipe with ice or if your on a hill descent using the brakes a lot, boil and the vapour will reduce the braking efficiency.
Stephen Randle

I am certain I will not be offering the decision breaking point here, but lets not forget the wonderful paint removing qualities of DOT 3 & DOT 4 fluids.

For some of us the elimination of the possibility of "another" spill related paint removal incident from our car is sufficient to override the issues surrounding fluid conversion to DOT 5.

Just my $.02 worth

Phil
Hawkflyer

Granted Phil, but considering the MG Y's location of the master cyliner, there isnt much to worry about spilling on and removing paint from too!

Paul

PS Dot 3 or Dot 4 for my 2cents.
Paul Barrow

I've been catching up on discussions as my computer spat the dummy a week ago. I did a scan of a couple of articles a while back from "Skinned Knuckles" magazine on silicone brake fluid for a friend. They are still on my hard drive, but would probably break copyright laws etc to post it on line though. Can email to anyone if interested, but they are large files [4mb+ for two, and just under 2mb for the third.]
My Y has got silicone fluid in it, along with stainless steel lined cylinders etc. This was all done by the previous owner, so I am unaware as to what sort of seals etc are installed. Haven't been any problems with it anyway.
Cheers
John
J B Turner

Paul,

Spillage at the Master is only part of the problem. If/when the slaves begin to leak, fluid spills out inside the brake drums. Presumably we are all catching this before it gets serious because when the fluid gets in the linings the car becomes significantly more difficult to stop.

However, if not caught, this fluid will eventually get to the drum and be flung out inside the fender wells. I have been fortunate not to have this happen to me because I stay ahead of any such issues. I have however seen these results on other cars. It is not pretty and neither is the repair.

There is of course always the spillage that can occur when bleeding the system too. But my point is that none of these areas are anywhere near the master, and so that is not the only area of concern.

At the cost of good paint jobs these days, this is something to think about.

Regards
Phil
Hawkflyer

Dont disagree with that Phil.

Hopefully none of us are that bad at periodic maintenance whether DIY or getting a mechanic to do it for us!

Safety fast

Paul
Paul Barrow

Bit late to this one, but after 15 years with a silicone-fluid system I'm a complete fan. I started with a new system, having had all the original cylinders stainless lined, and copper-nickel brake lines.

Silicone fluid gives you a (very) slightly spongier feeling at the pedal, but the car's brakes perform well and there is zero deterioration of the cylinder surfaces even after this period and 20,000 miles. I have found absolutely no evidence that silicone fluid rots rubber - it's completely inert.

Tim Griggs

This thread was discussed between 29/04/2012 and 23/05/2012

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