The 'E' Type Forum

Anyone got any thoughts on the use of Silicone Brake Fluid DOT5. I see on some forums there are very mixed views. A label on my reconditioned Master cylinder says do not use Silicone fluid but the thought of standard paint remover, I mean brake fluid on my newly painted car makes me cringe.
Any experiences would be appreciated.
Steve.

Steve,

this has been debated to death over the years. I will give my personal experience and view.

You cannot simply pump out the old (non silicone) fluid from your system and replace it with silicone. My understanding is that this can cause the seals to swell.

I have used silicone in all of my cars since 1980 - all rubbers and pipes were replaced as part of the restorations and have never had a problem. I will be using silicone on my current car.

I have heard of people who have had problems in the past but have never met anyone who has only used silicone on a new system that has had a problem. (Plenty of anecdotal evidence though!).

Have to disagree with Angus, never use silicone. It has little merit in a road car and providing you change the DOT3/4 fluid every two years there will be no problem with water contamination. Obviously it is a personal choice and if you are starting from fresh, as Angus is, then it is OK to use it but I have never yet seen a convincing argument as it why it is better. If you suffer fluid loss on a journey or holiday DOT3/4 is available everywhere, silicone is not.

I'm with David. Silicone fluids can contain suspended air that can make bleeding a real pain. Some folks have gotten around this by evacuating the fluid prior to putting it in the system, but most of us lack the required bell jar and vacuum pump. Castrol GTLMA is available almost everywhere and I feel that the system benefits more from regular fluid changes than anything else. The only advantage I can see with the silicone stuff is that it won't damage paint.

Moeregaard wrote:I'm with David. Silicone fluids can contain suspended air that can make bleeding a real pain. Some folks have gotten around this by evacuating the fluid prior to putting it in the system, but most of us lack the required bell jar and vacuum pump. Castrol GTLMA is available almost everywhere and I feel that the system benefits more from regular fluid changes than anything else. The only advantage I can see with the silicone stuff is that it won't damage paint.

Now see what you have started..... Firstly, I have never needed to top up fluid when away from home but carry half a litre with me at all times. I don't think silicone is any better or any worse as a fluid but having seen the damage it does to paintwork (I had a clutch master let go over night and also a repro clutch reservoir bottle dumped its contents into the engine bay and dripped down the drivers sill - luckily I had silicone in the system as the damage to the car doesn't bear thinking about).

Bleeding is not a problem when you realise that you can't keep topping up with the fluid you have pumped out - it has to be left to stand for quite a while for the air to be expelled.

1954Etype wrote: I don't think silicone is any better or any worse as a fluid but having seen the damage it does to paintwork (I had a clutch master let go over night and also a repro clutch reservoir bottle dumped its contents into the engine bay and dripped down the drivers sill - luckily I had silicone in the system as the damage to the car doesn't bear thinking about).

Ahh, yes, but ..... if you ever need to repaint the car that splashed silicone will be a nightmare for the paint shop - you can never get rid of the stuff. So Moe is right it does not damage paint, it just makes repainting very difficult. The question is Angus, did your master cylinder and clutch reservoir fail because of the silicone? Spooky.

In Steve's case I think the answer has to be to carefully consider using it in a totally new system (pipes, calipers, reservoirs the lot) but it is really not worth the effort if you are thinking of 'upgrading' an existing system.

Sorry for stirring a hornets nest. my system is all new and so it seems views are split 50/50 dot 4 or dot 5. Thanks for your comments, I think I will sleep on it.
Steve.

Heuer wrote:

1954Etype wrote: I don't think silicone is any better or any worse as a fluid but having seen the damage it does to paintwork (I had a clutch master let go over night and also a repro clutch reservoir bottle dumped its contents into the engine bay and dripped down the drivers sill - luckily I had silicone in the system as the damage to the car doesn't bear thinking about).

Ahh, yes, but ..... if you ever need to repaint the car that splashed silicone will be a nightmare for the paint shop - you can never get rid of the stuff. So Moe is right it does not damage paint, it just makes repainting very difficult. The question is Angus, did your master cylinder and clutch reservoir fail because of the silicone? Spooky.

In Steve's case I think the answer has to be to carefully consider using it in a totally new system (pipes, calipers, reservoirs the lot) but it is really not worth the effort if you are thinking of 'upgrading' an existing system.

David, difficult to say that it was the silicone that caused the failure of the slave (doubtful). The reservoir failed because it suffered a mechanical fracture where the hose connects underneath (rubbish repro part). Agreed, it is not worth the effort unless you are replacing the entire braking system. (Phew, glad we got that sorted out!).

One thing you may want to do with the reservoirs is insert a short length of steel or brass tubing into the plastic nipple. This allows the hose clamp to tighten without squashing the plastic and also strengthens the whole assembly. You can get suitable tubing from model shops. The original Jaguar items had a filter in the nipple which served the same purpose but no one seems to sell them. Most people chuck away the old reservoirs without investigating further and retrieving the filter assembly.

May this thread now rest in peace. :D

It is not unknown for brake fluid to enter the engine because of faulty brake seals.
What is the affect on the engine of burning silicone in the cylinders?

Just my 2 pence worth: I used silicone fluid solely because I was worried about paint damage - a good decision as it turned out! The brake system was new and hadn't seen any DOT3/4 and after 2 years no problems. There are a lot of stories but I haven't experienced the 'soft pedal syndrome' nor the air lock problem. Many people have told me of these issues, non of them were first-hand but they all knew of someone who had suffered.

If using DOT3/4 I would have to have a bonnet respray - my stupidity I'm afraid but now I just have a very shinny bonnet :) Second time was a faulty repro clutch reservoir bottle - it is a b****r to get off the drive though. If the brake system was working well and stable I wouldn't change the type of fluid but in a new system I would only use silicone.

One thing to consider; every time the fluid is changed and the system is bled the master cylinder piston moves further along the bore than normal, if this area is suffering corrosion etc. then the seals will suffer. Perhaps this is why silicone gets such a bad press.

Dave

Just my 2 pence worth: I used silicone fluid solely because I was worried about paint damage - a good decision as it turned out! The brake system was new and hadn't seen any DOT3/4 and after 2 years no problems. There are a lot of stories but I haven't experienced the 'soft pedal syndrome' nor the air lock problem. Many people have told me of these issues, non of them were first-hand but they all knew of someone who had suffered.

If using DOT3/4 I would have to have a bonnet respray - my stupidity I'm afraid but now I just have a very shinny bonnet :) Second time was a faulty repro clutch reservoir bottle - it is a b****r to get off the drive though. If the brake system was working well and stable I wouldn't change the type of fluid but in a new system I would only use silicone.

One thing to consider; every time the fluid is changed and the system is bled the master cylinder piston moves further along the bore than normal, if this area is suffering corrosion etc. then the seals will suffer. Perhaps this is why silicone gets such a bad press.

Dave

The principal advantage of silicon fluid is the one which has not been mentioned : unlike ester fluids, it is not hygroscopic, and thus one does not get the rusting of the master and wheel cylinders which is an inevitable concomitant of using traditional fluids

I have to agree with Angus and Dave here I have used silicone since I restored my car 4 years ago and never had a problem with it never had to top it up or replace any seal.
I agree to a certain extent with Christopher it doesn't absorb moisture but you will get rusting taking place in the brake cylinders as it will sit there so you need to flush the system every two or three years. I did mine last year and there was water present in the jar as I flushed it through.

Dave

Hi Steve,

You've just pushed one of several hot buttons with e-type guys (don't ask about tyres!!).

I've used both. I drive long, far and hard in big mountains. Both types of brake fluid are good.

Silicon (DOT 5) has the distinct advantage of not damaging paint. If you have a really nice paint job this is the smartest choice.

I now use DOT 5.1 which is ethylen-glycol based like the DOT 3 and 4 brake fluids. These enhanced DOT 4 fluids have an even higher wet boiling point than the DOT 5 fluids do. But like DOT 3 and 4 it will destroy paint.

There is never a reason to use DOT 3 fluids (unless you like playing football with one leg tied behind your back).

DOT 4 is pretty good and cheap. If you don't drive hard and have lousy paint this is a good choice.

DOT 5 and 5.1 (often referred to not as DOT 5.1 but as exceeding DOT 4) are both great.

If you have great paint get silicon (DOT 5). Yes you can live without it. But why? The cost is zero compared to any paint damage. The performance of these fluids is significantly better than DOT 4 fluids. Silicon fluids don't absorb very much water (people are wrong when they say none). However water can pool in this type of fluid leading to rusting of brake lines, etc.

If you like to drive hard get the newest DOT 5.1 fluid. Most companies make great fluids of this sort. They typically absorb less water than DOT 4 fluids and have much higher boiling points when wet than any other type of fluid (including the silicons).

Miscellany:
No matter what you pick: all of them need to be changed every year or two!!!! That is the solution for pooling, contamination and water absorption. It is way better to buy cheap DOT 4 fluid and change it every year or two than to buy something more expensive and let it sit for a long time.

Seal compatibility with all of the above is fine with modern rubbers. If your seals degrade with the change it means that they were severely degraded before the change and needed to be replaced. Or it means that they were a cheap aftermarket seal that was about to fail anyway. There are lots of stories about how the change (in either direction) caused trouble with seals or hoses. There are way more where there was never a problem with the change. If you've got good rubber the change will not matter.

Cheers,

Larry

One other note:

DOT 3, 4 and 5.1 can all be mixed...although the resulting properties are degraded. This should only be done in an emergency.

DOT 5 should not be mixed with the others.

Larry

Thanks Larry.
you have summed it up perfectly. The result, I am going to use Silicone fluid. And thank you everyone for your contributions.

Steve.