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Changing to Silicone (DOT5) brake fluid)


StevieB
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I know this is a much discussed topic, but I have seen arguments one way, and just as many the other way. I thought I would just ask anyway;

 

I have at long last got round to start changing the front calipers on my GT6 (one of the pistons on one caliper has seized, so am using this opportunity to change both calipers, and fit Mintex Pads). I have all the parts so am about to start stripping down. I will be changing Calipers only, as far as the brake fluid is concerned. Now, I am pretty certain that the system is currently using DOT4 brake fluid at the moment. Now I know ideally you should strip it all out, and change all the seals before changing to Silicone (DOT5) but as I said earlier i have heard arguments both ways.

 

What is the real thinking about just putting DOT5 in when I am ready to refill the system? 

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I always believed you had to change all the rubber seals.

So masters, wheel cylinders, and I assume clutch system too.

 

And having tried silicone, I went the other way and went back to mineral. On the basis if I got a leak and needed fluid, there is no chance of getting hold of silicone easily. And changing the fluid every few years is no big effort either.

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Thanks Clive.

 

I was starting to err towards putting DOT 4 back in. Mostly because there will be no problems, and I don't need to rip the whole system apart. You also make a good point, DOT 4 is readily available, so in an emergency no problemo :-)

 

I think, unless someone can sway me the other way I shall be refilling with DOT 4, and bleeding the brakes tomorrow. (Once I have got the last pad in -there is always one stubborn one isn;t there!)

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And therein lies the definitive answer. As you might have gathered from above I had formed an opinion in my own mind after Clive's response, based on practicality alone. The article you linked too is excellent, it could not be clearer. I shall be sticking with DOT 4, and re-commissioning the brakes tomorrow. :-) I am looking forward to some serious braking improvements, new calipers (not seized), Mintex pads, and fresh brake fluid - god knows how old the stuff I have just taken out was, but it looks rank).

 

Thanks again Pete. Your contribution to this forum is invaluable and hugely appreciated by newbies / numpties like me.

 

Steve

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I put silicone in my Herald,  and later on in my GT6.  Although some components were replaced in the process (mainly the pipes), not everything was. It has been 10 years with the Herald and about 6 with the GT6.  No issues whatsoever.  On the availability question,   l just keep a couple of bottles to hand,  and  one in the car when touring.

 

Alternatively, I have a TR4A, which has Dot4,  and leaked all over the place causing very bad paint damage in the engine compartment and the footwell.  It will be changed to Silicone when I get round to it.

 

Dave

==== 

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I used silicon in the brakes once and it was enough!  The pedal was longer and soggier, so I have NEVER used it since in the brakes, although it is perfectly good in the clutch, but why complicate the issue with two fluids?

 

Every garage I have ever spoken to has advised against silicon in the brakes and my experience is part of their reasoning.  All seals and rubber hoses should also be changed when the change is made and the system should be flushed out before changing the type of fluid. 

 

In my book it's not worth the hassle, or safety risk - one day you might have to rely on good brakes and the best fluid might just make that difference!

 

Regards

Mike

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when in truck manufacturing some military specs used a silicon type  use to avoid moisture content whilst in long periods of storeage

 

we did water content tests on trucks in storage and it was common for the reservoir to be upto 40% moisture in 6 months just from the breathing in the cap due to temperature changes 

 

 if brakes  fade  ( have no grip) its due due to overheated friction material, thin worn down , or lubricated .

 

if the pedal goes spongy or lost completely then its  down to water in the brake cylinders 

 

if the pedal id lower  when running but pumps up when stationary its excess bearing end float.

 

 

pete

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I too have used Silicone DOT 5 in my car for 6 years without problems, and it stops very well. I made the choice because classic cars, by their nature, tend to spend long periods not being used, and conventional DOT 4 is hydroscopic, and that way lies rusted caliper pistons and all the rest of it. I also did not fancy a fluid leak wrecking my painstakingly-applied paint. I do agree that changing from one to the other without rebuilding the system is probably not a good idea. I started with a completely dry refurnished brake and clutch system before I put the silicone fluid in.

 

Regards

 

Steve

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Finally, finally, finally got the GT6 MOT'd today,and she sailed through. No advisories or any comments at all. 

 

Thanks to everyone who helped with my various brake related questions. The new pads (Mintex) work a treat, and are noticeably a lot better than the old ones. Pedal was a little soft, so I bled them again, now it feels a lot better. Not rock hard, but way better than on my wife's Panda!

 

I decided to stick with DOT4, as I would not be touching the rear brakes, and the clutch is still on DOT4. All done now, and a happy chappy.

 

Thanks again

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  • 5 months later...

It's based on the weight of the car vs. stopping ability, so if you exceed a certain figure based on the weight for your car then you can go over 100%. From memory I think the fronts on mine were 103%......I have the print out from the MoT station, even the tester commented on the result.

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  • 8 months later...

Hi

 

I`m new around here, having just bought a kit of parts that will one day emerge as a 13/60 convertible!, as part of my "retirement" project. My experience of Silicone fluid goes back to 1987, when I rebuilt the brakes on a 2L Mk1 Vittesse. The rebuild included new copper/nickel pipework and ALL the seals, which was the advice I was given. It ran as daily for my wife on short commutes for 3 more year until we sold it. without any issues.

 

I suspect that said Herald will get the same treatment in the braking dept; Allied to the conversion to MX5 seats, and some updating of the electrical system, New guts for the Radiator and Heater too I suspect. BUT first I have to finish the decorating!!!.

 

Pete

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Buckeye Triumphs have a very good piece on the varies DOTs and the misconceptions, some of which expressed here. 

 

Summarising Mr Buckeye. DOT 5 is much more expensive and less available. The others are cheaper but should be replaced regularly because of water absorption, every two years as I recall. There is no problem emptying the other DOTs and pouring in DOT5. Mixing the two together, the other DOTs absorb some of the DOT 5 colour but not the DOT5 itself. As to spongey brakes, DOT5 does NOT lubricate the rubbers like the others do, so any weaknesses in your rubbers will be exposed. So best to change all the rubbers before you upgrade.

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