Spitfire Tandem Brake Cylinder on a Spitfire Mk1

[britishcarfreak]

Is there a simple way to get a twin brake line master cylinder onto a spitfire mk1?

I don't want to have to order a new one from a later spitfire.

I was thinking that maybe one from a 2500 saloon might fit. I've got one from an S downstairs.

It would be nice if the power booster could also be fitted somehow.

Anyone done this>>?

 

[piman]

Hello Glen,
I can't answer your question, but I suspect that it is possible. (I have a MK 2 brake M\C - booster on my MK 1 2000, I just had to space out the clutch master cylinder to clear the larger diameter booster body)
However, whenever I rebuild a car I fit copper brake lines and steel braided flexible hoses and don't see any need for a dual circuit brake system.

Alec

 

[britishcarfreak]

I assume that dual brake line offers no more in the way of pedal pressure application to the brakes and that it only offers a level of safety by increasing the likelyhood of still having two brakes in the event of a leaking or broken line.

That said.. I guess there's not a lot of reason to go to dual line. However. The thought of brake bias was my concern. On a single line car how is the split between front and rear pressure acheived?

I'm at the bare chassis stage of my restoration and now is the best time to plum in some new brake lines.

 

[piman]

Hello Glen,

Dual line systems can give variable bias but not using the standard manufacturers dual system. That is a safety feature but to my mind not that effective. There are two types, diagonal, i.e. one front and a diagonal rear or front rear.
I wonder how, as it it such a rare occurence, drivers would cope with the altered balance if they experience a failure.
To get variable bias you need two seperate master cylinders coupled via an adjustable cross bar. If both cylinders are equal in bore, actuating the cross bar in the centre will give 50\50 pressure, the bias being then down to the cylinder diameter at the brakes; pressure on the pads\shoes being line pressure times cylinder area. (Which is how the bias is established with a single line system, relative cylinder size front and rear)
Going back, if the actuating point on the cross bar is moved off centre, pressure increases in the cylinder nearest the actuator and reduced in the other, a basic lever system.

I hope that helps somewhat?

Alec. Very

 

[Eric]

On single line cars, bias is acheived by appropriately sizing front and rear cylinders and/or friction area. Dual line cars are the same, with the added complication of differing amounts of fluid being moved by the master cylinder.

Be aware that discs and drums operated with different amounts of movement, so need different amounts of fluid supplied. In modern cars that come with rear drums or rear discs (depending on the model), different master cylinders are used for each version.

Switching from a single to dual line system will require quite a bit of replumbing, and an appropriate new master. I suspect a GT6 dual circuit master cylinder would be appropriate, but you'd have to look into it.

The GT6 in its last years was supplied with a brake servo that's no longer available. There is a replacement Lockheed booster available (both Rimmers and Victoria British carry it), that operates remotely from the master cylinder, so is more flexible for mounting options. It only operates on the front circuit (as in the original GT6 servo), as discs need servo action much more than drums, which have a mechanical 'self servo' action.

Good luck.