dual circuit master cylinder.

[kevin s]

One of the saftey related mods I want to do to my late saloon is a dual circuit master cylinder, I have found a Right hand drive Beetle on looks a very probable candidate, 19mm bore (1mm / 10% less area than the standard one) and already set up for a remote reservoir, the exit ports are on the correct side as well, It looks like all I would need to do is make an abutment bracket and push rod (may even be able to use the minor one). The change in area would give an increase in pedal travel but before we pulled it appart it semed to have very little travel anyway so I don't think this would be a probem has anyone else fitted one of these?

kevin.

[johngrigg]

Kevin
This discussion and pics of a conversion using a mazda 323 M/C may be of interest. It's even the right size 13/16
http://www.morrisdownunder.com/forum/vi ... ght=#38983 Cheers John G

[philthehill]

There should be no problem with fitting the master cylinder you have specified so long as the installation is serviceable and up to the task.
Make sure that when fitting you have the pipe work arranged so that the dual system operates diagonally i.e. R/H front - L/H Rear and L/H front - R/H rear.
Having it in that arrangement will ensure that the brakes even with reduced efficiency and one line has failed the car will pull up in a straight line.
DO NOT install so that the brakes are either front or back as the car will be liable to spin when the brakes are applied
Having the smaller dia master cylinder will result in a slightly higher pressure in the wheel cylinders so make sure that your wheel cylinder seals are ok.
You could also install a distributor valve/light switch and indicator light off a late Ser 3 Landrover which would indicate that a brake circuit has failed.

John
You need to sign in for the link above.
Can you get in i.e. read only without joining/being a member?

[don58van]

...conversion using a mazda 323 M/C...

An Aussie company, Minor Magic, makes a very nice dual-circuit kit using this master cylinder. It has a website, but last time I looked the kit wasn't shown.

BTW -- I have no connection with Minor Magic.

Don

[M25VAN]

Is this the one?
http://www.minormagic.com.au/p/1607/dua ... structions
It seems to also include a remote reservoir kit as well. Priced at about £200.

[philthehill]

Many thanks for the link.
I am surprised that they use the dual system as front and/or rear as it is better to use diagonally as that way there is less chance of the rear of the car overtaking the front. But of course the pipe work is a lot easier just using front or rear.

[rayofleamington]

I'd certainly agree that a remote reservoir adds some safety:
1) easier to check level, therefore checked more often
2) more volume (assuming you have a decent size one) therefore more capable to cope with a small fluid loss.

As for m/c from a donor vehicle with split braking circuit.. I would want to check that you actually get a noticeable improvement for the efforts involved. I had a pipe fracture on a Mk2 Fiesta and despite the split circuit design, it was total brake loss!

I've got no useful info on the relative merits of any particular split circuit m/c, so I'm not really much help here other than offering a warning that some may not do what you want them to do.

[M25VAN]

Many thanks for the link.
I am surprised that they use the dual system as front and/or rear as it is better to use diagonally as that way there is less chance of the rear of the car overtaking the front. But of course the pipe work is a lot easier just using front or rear.

Would there be issues of uneven braking if using diagonal split on a disc/drum setup?

[philthehill]

When a diagonal brake system partly fails the one rear brake and the one front brake diagonally opposed evens up the braking and the car will stop in a straight line.
I am not aware that there would be any imbalance or rotational forces with a split diagonal system but happy to be corrected. Fortunately I have never had the need to test the theory behind it all.
There is quite a bit of info on the web relating to diagonal split braking systems and quite a few differences of opinion regarding the merits of split systems both front/rear & diagonal.
See:-
http://www.ehow.co.uk/about_6545035_spl ... tems_.html
&
http://en.wikipedia.org/wiki/Hydraulic_brake

for tasters

[alexmcguffie]

I'm not sure there's a right answer to this one! As the original purpose of the mod is for safety, then a diagonal split is probably the way to go assuming drums all round. With more efficient discs at the front, if one circuit failed when braking in a corner then the back end might still step out due to the balance shifting forwards while the car tries to rotate around the one working front brake. Shouldn't be a problem if you're taking it steady...

For any sort of motorsport use, a front/rear split is the only way to go giving more flexibility such as different F/R master cylinder bores, adjustable brake balance etc.

[philthehill]

Alex I would agree with you as regards the motorsport requirements but for normal use I would prefer a diagonal split system.
But it is up to the individual on how they like their split (and no bananas required either way with this one )

[kevin s]

Thanks for the replies, I must admit I hadn't thought about how to split the brakes, it seems even the manufacturers can't decide my tr7 is split front /rear not sure about the mx5. I will have to dig out my masters documentation we did a course on calculating brake distribution, from memory it is this which determines wheather you go diagonal or front /rear. Plenty of time to research this though, I wanted to sort out the master cyl installation now while it is a bare shell, it will be whike before it is plumbed in.

The plan is to use drums to start with and see how it goes, they work fine in my landrover, I wanted the dual circuit to limit the possibility of a total brake failure and give a remote reservoir with a level sensor.

Kevin

[bmcecosse]

Another TR 7 !!! Pictures please!! Drums all round will be 'not too bad' with diagonal split, but disc/drum will be next to useless with diagonal. A spin is guaranteed. I too had failure with 'split' brakes (on a Mini which I had just bought...) and it was useless - pedal to the floor....frankly not worth doing in my view. Just keep your brakes in good condition!

[don58van]

I had a fan blade break off (standard factory) when I was driving along, giving the engine a big rev. It made a clean cut through the brake line. Fortunately, I was able to bring the car to a standstill without hitting anything.

That was warning enough for me--these days, I like the security of dual circuits. Minor Magic's kit is easily the best I have seen. It is well-designed and everything is provided down to the last detail. It uses the standard brake linkage.

BTW, the Laser/Mazda 323 MC has been used here (Oz) for ages in Minors--so it is a very well-proven mod.

Don

[simmitc]

if one circuit failed when braking in a corner then the back end might still step out due to the balance shifting forwards while the car tries to rotate around the one working front brake.

Bad driving practice Always brake in a straight line. The correct way is is to brake before the corner and then accelerate gently through it. Better still is to reduce speed prior to the corner by just taking your foot off the accelerator well in advance; but that's probably difficult in today's heavy and fast moving traffic.

[alexmcguffie]

Using conventional driving theory then yes it is bad practice (see Competition Driving by Paul Frere written in the early 60's). If you realised your brakes had failed just before a corner - not an unlikely situation - then what do you do... keep braking instinctively.

Not really necessary with Minors, but many of the top drivers these days 'trail brake' into corners to give the car a better balance for the exit.

[bmcecosse]

That's it - 'Lift and Coast' ! Fuel saving... I always check my brakes with a wee dab before any important braking point - even on the moderns.

[alexmcguffie]

I'm thinking someone watches too much tv on a weekend

[philthehill]

Heel and toe is the way to go.

[don58van]

To me, the debate about whether it is best to have diagonal or front-rear connection is a distraction.

The point is that without dual-circuits, if a brake line fails, the car is likely to only stop when it collides with something.

Dual circuits will give the driver a chance to stop without a collision.

A spin is not the worst thing that can happen. It is quite an efficient way of losing speed quickly--so it may turn out to be an advantage.

Don