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MG MGB Technical - Silicon Brake Fluid Lifespan?

Hi All
Anyone seen any figures regarding the recommended lifespan of silicon brake fluid?
R. Algie

According to the makers, Automec, it NEVER needs changing. I know of one MGB GTV8 that had the silicon fluid in it untouched for at least 17 yeras with no sign of a problem. I have used it in my own GTV8 - but its only been there for three years so far.
Mike Howlett

Hi Mike
Thanks for the reply, mine's now been in for 15 years and seems to be clean so I'll just leave it be.
R. Algie

I've had it in my B for 15 years and I've changed it a few times. It's never turned dark like glycol fluid but in one of the fills -- the first one, maybe -- the purple dye faded out and the fluid became clear like new glycol. That almost caused a problem because I went to top up the master and wasn't paying attention. I had a bottle of LMA tipped over the reservoir and was about to pour when I realised at the last moment what I was about to do. I flushed with fresh DOT 5 just so the dye would be there (I also put a "Silicone Fluid Only" sticker near the reservoir!) I've never had another batch wherein the dye faded like that. Maybe just a bad dye lot?

It's probably prudent to flush out the old with new every once in a while, just because.
Rob Edwards

Interesting about the dye Rob. In my brake cylinder the fluid is still purple, but in the clutch cylinder it is now clear. I wonder why?
Mike Howlett

20+ years in my TD. Not a problem one. 5 years in the B so far.
Bruce Cunha

Hi All
The fluid in my MG very quickly turned clear [probably in less than a year] but the stuff I put in my TR6 about 8 years ago has retained it's colour allbeit slightly faded, maybe the dye is better in the later stuff
R. Algie

Dot 5 in my motorcycle lasted 27 years, and was still fine when I sold the bike.
E.B. Wesson

And are we clear why us silicone? I am not sure myself. Did I read write sometime ago, one needs to flush all the old stuff out, flush with ???? then re-fill with silicone? What about the seals do they all have to be changed, as they were up against glycol? Mike
J.M. Doust

I put silicone fluid in our TD when I finished restoring it in 84. It is still there today and working just fine. In fact drove the TD to our favorite restaurant in the TD to celebrate our 46th anniversary with a bunch of our friends. Cheers - Dave
David DuBois

Yes Mike, you are supposed to give everything a thorough going over and flushing out as DOT4 is not compatible with silicon. I would want to replace all the seals. In my case the car was being rebuilt and every component was new, even the pipework.
Mike Howlett

Don't change to silicone now if you haven't already done so. It's gone out of popular use as ABS systems can't use it (Halfords don't stock it for example) and an improved glycol fluid has been developed that has the performance of silicone at least (although Castrol LMA was always better). The problem is the stupid naming that DOT came up with. Glycol was DOT3 and DOT4, Silicone was DOT5 - all fair enough. But the improved DOT4? That's called DOT5.1! It's why some manufacturers call it Super DOT4 instead. Silicone may not be hygroscopic, but water gets into silicone systems just the same as glycol systems, just stays in lumps instead of distributing through the fluid. That reduces the boiling point just as it does in glycol, and some say it should be changed *at least* as often as mineral if not more. But then some say it doesn't need changing so there you are. The biggest complaint against silicone is that it absorbs air instead of water, which makes for a spongy pedal, and is difficult to bleed. The only unarguable benefit of silicone over glycol is that it doesn't damage paintwork.
PaulH Solihull

This thread was discussed between 27/08/2011 and 29/08/2011

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