We run silicone brake fluid in our LBCs (Little British Cars) and this is widely accepted among that crowd. This week I am putting new front wheel cylinders in the 47 Dodge P.U. truck cause we don't run it enough and they pitted.

So why not use the silicone fluid in a 914? Yes, there is a slight compression you can feel in the pedal, but in my TR6 you can hardly feel it. I now have enough toys so that routine maintenance is a pretty big chore. Keeping up with batteries and tires is bad enough. Yes, I know that you should bleed out the old fluid, but frankly I doubt that would have helped me with the truck. The problem was the lack of movement of the seals over the cylinder. My time flies!

So - what do you think?

Thanks,
Warren

I don't use DOT5 because it's incompatible with other fluids, so it takes a full brake system rebuild to switch. And then you have to make sure that you always have a can with you since DOT5 can be hard to find in the middle of nowhere.

And.... why? There's a ton of restrictions and no practical benefits.

You could add speed bleeders to make change time faster.

Russo will put silicone in the race cars for storage but then flush it and replace with race fluid to put the cars on the track. We just use dot4 on everything. Eric Shea reccomends flushing with new every year. Dot4 is cheap.

So what I am hearing from several is it is inconvenient to use silicone, so instead I should bleed the system every year. Not trying to throw stones, but that is what it sounds like. In all cases, I have started with clean new lines master and wheel cylinders, so I had the choice at the time.

Any real performance (normal driving) or safety issues?

DOT 4 is fine for any applications, even racing. And in my experience DOT 5 creates a funky pedal, and that was after running multiple cans through the system. And it costs more.

There's just no value in DOT 5. I run ATE Blue (while I still have some) and Amber/Gold in everything, street and race.

The value that the British crowd sees is reduced damage due to humidity in the fluid, a process that starts the moment you open the bottle. I agree that it isn't suitable for racing. With six toy cars I found I couldn't do big restoration and conversion and keep track of bleeding the brakes on time. Also, I am old with a bad back. Unfortunately that 47 Dodge truck is in truth hard to drive, so it sort of languished. That thing is so hard to steer and stop I wouldn't consider experimenting with silicone. On the other hand my TR6 with silicone stops quite a bit better than my 914 with DOT 4 - but then the TR has a vacuum booster.

I am not trying to talk anyone into this, but I am a scientist, so I want the reasons people have, including subjective ones, and in Wisconsin we are required to Sift and Winnow the ideas. Sometimes.

Thanks to all who responded.

Starts the moment you open the bottle and takes 30-40 years to really do damage to the system? Okay, maybe that's overstated, but even at 10 years the moisture in the brake system isn't a significant issue on a properly maintained brake system.

Use whatever you want (obviously), there's nothing wrong with DOT5 if you like it. But as far as "Why don't P-car people use DOT5?" You've seen why. For most of us, the DOT4 satisfies our needs better than DOT5.

Mine has DOT5 in it. Previous owner wanted the convenience of not having to flush/bleed system every year. For how the car was being used, it was likely the better solution.

That said, it can be difficult to bleed, is not compatible with Dot4 or Dot3 and for those who track their cars, DOT5 is usually not recommended or allowed.

Since DOT5 doesn't absorb moisture like DOT3/4, it won't hold moisture in suspension either. If moisture does get in the system, the water (being heavier) will slowly pool at the lowest point, and can cause rust or corrosion there. I was taught that if I used DOT5 in my off road ATVs that I needed to completely disassemble and flush if I ever got one really wet, say when fording a river or deep creek.

I worked at a British shop and we had NLA m/cyls and wheel cylinders re-bushed with brass sleeves. The DOT 5 didn't seem to lubricate as well with the brass and we saw a lot of sticking wheel cylinders until we went back to DOT 3 or 4. I've been reluctant to try it ever since.

It was also my understanding that silicone does not absorb moisture, but really holds onto air, and that's why bleeding can be a challenge.

Warren, I've had similar thoughts to reduce maintenance on the fleet but ultimately resolved to use DOT 4 and just monitor the moisture in the fluid with a simple tester. They are available through amazon for about $10. This has given me peace of mind that I'm not neglecting the brake system on little used cars without needing to change the fluid every year. .

I saw Ed on Wheeler Dealers use this one time and it got me motivated to investigate. So far so good. The tester confirmed my gut feeel on which cars had marginal fluid and which should still be fresh.

Brake fluid tester

I saw that tester on the JEGS site. I probably will try it, since when I had the opportunity to change to DOT5 with the P-cars I didn't take it.

I can say that during a period of five years with the cap tightly on the master, and the truck staying always indoors, the brake system absorbed enough water to put deep rust pits in a wheel cylinder. Rust lined the bottom of the wheel cylinder like mud in a culvert. I used only freshly opened fluid and new components - master, wheel cylinders, hoses, etc. The system was flushed and clear to start. But the truck was exposed to summer humidity (which I have never learned to like). Had I both bled the system and driven it this would not have happened.

I now have a better understanding of how some of you folks feel about it. Sounds like it is to some degree a personal or cultural thing. Some of us fantasize or participate in days at the track. Others want to ford streams. Which is fitting given one Porsche design

Click to view attachment

Panzer VIII Maus. The vehicle's weight made it unable to utilize most bridges, instead it was intended to ford to a depth of 2 metres (6 ft 7 in) or submerge up to a depth of 8 metres (26 ft 3 in) and use a snorkel to cross rivers.

I better put the top up.

Early on when DOT5 was introduced, I heard stories about mold growing in/on/under it. That, and the point about water not being absorbed but simply sitting in a layer, convinced me not to try it. I'm still not using it, probably because of inertia...

--DD

Well I was a microbiologist for more than 20 years studying yeast, and knowing what those critters can do I am not surprised. But the same can be said for camera lenses in some parts of the world. As for puddling I suspect that does less damage because there are no ions or probably oxygen. But that is a guess.

This is all in aid of getting the truck going to move a Lotus 907 motor. Not too German tho.

DOT5, the 'solution' to deferred maintenance.

Just do your maintenance...

Problem solved!