I have Sierra front brakes and, I assume, Cortina rear drums*

* First Question - how do I tell if I do indeed have a Cortina 'back end'? There are no obvious identifying marks on the axle, nor the drums.

What brake fluid do you recommend. A cursory glance through Demon Tweeks has got me all confused.
Silicon or not?
Dot what?
I intend to drain what I have and replace the lot so I am not too worried about it being compatible with existing fluids but, roughly, how much am I likely to need?

I read somewhere that silicon fluid can interfere with the operation of brake light switches as it is not a conductor.
As normal (I assume) the brake light switch is in the 'T' piece at the front, where the line from the cylinder splits into the two seperate brake lines but I cannot see why current would pass anywhere near the fluid.
As I understand it, the hydraulic pressure pushes the bottom (or back) of the switch (which looks like a nut with connections on the front ), which bridges the connection between the two wires. Therefore, the fluid is isolated from the electrical part of the switch...

Does this sound about right?

BTW my brake light is not working at the moment so I have suspicions about the switch but do not wish to take it out yet as I want to drive it before replacing the brake fluid which, I assume, will p*ss out everywhere when I take the switch off?

As always, your musings would be gratefully received.

The higher boiling point DOT5 fluid is 8loody expensive, and is arguably only necessary if you're going racing.
Most sub DOT5 brake fluid is ethylene glycol based, and is thereby hygroscopic, ie it absorbs moisture from the atmosphere. Water in the system reduces the boiling point of the fluid, which results in brake fade.
There is the benefit that silicone fluid doesn't absorb moisture from the atmosphere, although there's not much to prevent water accumulating in the system as a result of condensation.
As the brakes should be bled frequently to ensure the fluid is fresh anyway, I'd just use DOT 3 or 4.
If you do decide to go with silicone, you'll have to flush the old fluid out really well first, as the two types aren't compatible.
If you're using old technology brake components such as Escort and Cortina stuff, you may find their seals won't be suitable for use with DOT 5 fluid. I'd check the relevant chapter in your Heinous manual.
You're correct about the brake switch.

Originally posted by uberf1end
* First Question - how do I tell if I do indeed have a Cortina 'back end'?
Have a look at this picture -> http://forum.locostbuilders.co.uk/upload/dscn1097.jpg If it looks like this then it's a Cortina axle. Note the void bush hangers on top either side of the main diff casing.

As I understand it...<snip> Does this sound about right?
Yep, that's how they work. The fluid doesn't have any electrical contact. I'd go with Rorty and just use DOT 3 or 4 and bleed fairly frequently i.e. once every couple of months of just before taking it out after a period of winter lay up.

HTH

I use Castrol Response from Halfrauds, never had any problems with it and a DAMN sight cheaper than SRF (the racing stuff which is £35+ a litre!). The thing is, you don't really need a super duper ultra high boiling point cos these cars should never get the brakes that hot anyway, cos they are so light.

Chris