Brake fluid query

Post by **nick_h** » Sun Apr 18, 2004 8:17 pm

I'm planning to change my brake fluid in the coming weeks. Can anyone advise me what is the best fluid to use. I have seen silicone fluid advertised, and it is stated that this is preferable to the original as it does not absorb moisture. I would welcome the views of "the experts" on this. Also is it worth investing in a bleeding kit? I propose to do both cars, neither of which are used on a daily basis. Thanks

Nick

Post by **simmitc** » Sun Apr 18, 2004 9:56 pm

I've got a couple of cars with conventional fluid and two with silicone. For normal braking on standard cars (as opposed to high speed stuff) I can't see any difference in use. The silicone is more expensive but it won't harm paint, is environmentally friendly, and NEVER needs changing, so it is a once in a lifetime cost. If the car is to be kept long term, then well worth it. As it doesn't absorb moisture there is less chance of rest developing in the master cyclinder, and the slaves should last a lot longer without corrosion. Good all round. Recommended. There used to be stories about it being difficult to bleed, but it's no worse than standard stuff - why should it be? Plus. best of all, it's a pretty mauve colour.

Bleeding kits are easy to use. Not necessary, but can save arguments with wife / girl friend: "I said down, not up" "You want me to help you NOW?"

Post by **racer** » Sun Apr 18, 2004 10:05 pm

I stand corrected on this one ,but I was led to believe that using silicone on old (worn)cylinders can cause leakage due to its "creep"properties?

Post by **les** » Sun Apr 18, 2004 10:14 pm

I have put silicone fluid in my system and have been very happy with it, the fact that it doesn't absorb water made me convert. Don't know about it's 'creep qualities. In my opinion an Ezi-bleed kit works well.

Post by **Kevin** » Mon Apr 19, 2004 9:43 am

I stand corrected on this one ,but I was led to believe that using silicone on old (worn)cylinders can cause leakage due to its "creep"properties?

I have heard of this as well, but not having used silicon fluid I have not had 1st hand experience.

Post by **57traveller** » Mon Apr 19, 2004 10:10 am

There was a bit of a debate about silicone fluid on another thread quite recently.
I personally use it in both my Minors successfully - so far

However I think the concensus of opinion was that the braking system eg. seals, has to be in top condition. This is actually advised on the packaging of the fluid. Someone Ray knows had a brake failure after changing to silicone fluid.
There have been reported cases that systems are more difficult to bleed of air but I have not experienced this. The pedal does seem to be abit "softer" with a little more travel, in my case anyway.
It is compatible with DOT4, "conventional" fluid, however if any DOT4 remains in the system the advantages of the silicone are lost.
I would also question the manufacturers NEVER needs changing claim as well.

Post by **rayofleamington** » Mon Apr 19, 2004 11:46 am

Someone Ray knows had a brake failure after changing to silicone fluid.

Yes! However this was on a 40's Riley and the seals were not new. The failure was caused by the seals swelling up. I've also heard of this on a Vittesse.
Since renewing all the seals and going through the whole bleeding process again he has not had any problems.

So the safest way is to renew all the seals, incuding the m/c. Even ignoring the risk of swollen seals it is still a good idea. You shouldn't put fluid into dodgy wheel cylinders so you want to inspect all the bores before the conversion anyway. (otherwise you may get a big puddle of silicone fluid on your drive as it is very searching) Whilst you are inspecting, it's hardly worth rebuilding the cylinders with the old seals.

Post by **Cam** » Mon Apr 19, 2004 12:01 pm

So, if you were replacing ALL the slave cylinders AND the master and all brake lines & hoses, which would be best the best fluid to start using?

Post by **rayofleamington** » Mon Apr 19, 2004 12:25 pm

So, if you were replacing ALL the slave cylinders AND the master and all brake lines & hoses, which would be best the best fluid to start using?

If you're going to do all that - I would use Silicon. No point doing things by half ;-)

Post by **Cam** » Mon Apr 19, 2004 1:41 pm

No point doing things by half

Well, I was thinking Traveller and future............. I don't think I should re-use ANY of the braking system on that baby!

Post by **rayofleamington** » Mon Apr 19, 2004 1:47 pm

Yes, but not much to worry about at the moment - if you braked too hard the wheels would fall off

Post by **57traveller** » Mon Apr 19, 2004 3:58 pm

The Eezibleed kit has been discussed at length elsewhere as well and it's a useful piece of equipment. Also saves all that pedal down/up hassle and the arguments that are probable.

There was a programme on the telly recently where that ex vet (Mark Evans) was building a motor tricyle (three wheeled bike

) and was using (comparitively expensive) vacuum pump brake bleeding gear. He didn't have much success because the vacuum was drawing in air from somewhere in the new system. He smeared joints with grease to stop the air getting in

and managed to get a bit of braking which was said to be o.k. until after testing the trike when the problem could be sorted out.

I would have thought on a new system or when air was being drawn in a method where positive pressure was used to force fluid through would have been better at indicating where the leaks may be.

Post by **rayofleamington** » Mon Apr 19, 2004 4:03 pm

Pressure fill on a new system?
Nah - they use vaccum to fill new cars as it can remove 99.95% of the air.
They also use high pressure to push the fluid in, but that's just to speed the filling process up, because when it's two thirds full, the 0.3 bar remaining vaccum doesn't pull fluid in quickly enough. The only time the bleed nipples get opened on a new car is if it is faulty!
However - those who have experience of hydraulics know you should never use a vaccum pump on a used (wet) braking system! Even if this blokes trike wasn't leaking, by the time he got some brake fluid in the pump it wasn't likely to draw a good enough vaccum anyway

.

Post by **Cam** » Mon Apr 19, 2004 4:05 pm

that ex vet (Mark Evans)

He's good, he is. I have watched a few of his programmes (e-type, kit car, helicopter, 'plane) and thought his approach was pretty good.

Post by **57traveller** » Mon Apr 19, 2004 4:21 pm

"new system" and the vacuum method didn't work because of the leaks but the pump was creating a good vacuum and drawing the fluid through. He should have used positive pressure from the other end to locate the leaks once he was aware of them, that has to be the easiest way to locate them. I wouldn't have used the vacuum method in the first place. Private workshop or home garage is a different scenario to a car production line.

Post by **les** » Mon Apr 19, 2004 9:29 pm

However - those who have experience of hydraulics know you should never use a vaccum pump on a used (wet) braking system!

That's not me Ray, is there a short explanation?

Post by **rayofleamington** » Tue Apr 20, 2004 12:31 am

When you pull brake fluid to a vaccum on a wet system, brake fluid gets into the pump - it can't really be avoided. Vacuum pumps are notoriously short lived when you get brake fluid in them.
Don't expect the warranty to be valid either. I would be surprised if a manufacturer recommends their pump to be used on a wet braking system.

Even if you think the (expensive) pump is worth risking, the other reason not to vacuum a partially full system is that the vaccum fill itself is just unreliable as the brake fluid becomes volatile at low pressure and you don't acheive such a good vacuum as you would normally do. Also on modern cars (eg. with ABS) the braking system is complex with valves etc.. and there is higher probablility of trapped air due to the fluid in valves and connections.

Post by **57traveller** » Tue Apr 20, 2004 10:19 am

I'd personally rather push the fluid through anyway, £15 for an Eezibleed compared to £42 - the cheapest vacuum pump I've seen.
Sorry Ray but I'm still a bit puzzled (or thick

) re this wet/ dry thing.

Surely when the fluid is drawn into the system said system is then wet. How can
you know that all the air has been removed until it flows from the bleed nipple? The fluid doesn't enter the pump anyway, it flows into a container separate to the pump.

On an old Peugeot car I used to own the hydraulic clutch HAD to be bled by drawing fluid, by a vacuum, through the "wet" system to the bleed nipple. The air couldn't be removed by "conventional" means as I found out after changing the slave cylinder

and had to drive clutchless and cap in hand to a main dealer for them to do it.

Apologies for prolonging this but I am confused.

Post by **lowedb** » Tue Apr 20, 2004 1:13 pm

Vac filling a new brake system is normal, as Ray says.

You connect to the filler cap on the master cylinder and suck all the air out (or 99.xx% as Ray said). You then stop the vacuum, and connect the system to the brake fluid supply. The vacuum then draws the brake fluid in, to replace the vacuum. The same is used for filling coolant systems.

Regarding Silicon fluid. A friend at the last place I worked had worked in Brakes before he moved to our section. We had quite a discussion about this. He told me that they had done some trials, and although the silicon fluid doesn't absorb water, it doesn't make any difference to the little bit that gets past the seals each time you use the brakes. What happens then is the water collects in one place instead of dispersing in the fluid. For this reason you need to change the fluid anyway, so lose the supposed benefits of silicon fluid. His opinion was that you were better using DOT standard fluid and changing it regurlarly. I have no experience so can't comment, and have to point out that I've had duff information from work colleauges before!

Post by **57traveller** » Tue Apr 20, 2004 1:43 pm

Yes, but most of us live in the real world where this fancy equipment is not available. There are vacuum units that attach to the bleed nipple and draw the fluid through the system which is not the same as that method you describe. This is what Mark Evans was using and his pedal would not "firm up" because air was being drawn in somewhere. Which prompted me to suggest he would have been better pushing the fluid through from the other i.e. master cylinder end and pressurising the system, above atmospheric to try and locate the leak(s).
There are other "home mechanic" vacuum devices that operate at the master cylinder end but I don't know how they are used, there must be a supply of fluid somewhere for it to be drawn into the system to the reservoir. Which again makes it a "wet" system. With each system there is a reservoir separate to the pump and as a consequence the pump does not become contaminated.