8 replies to this topic

[Syma]

As my restoration gets closer to getting on the road I have been thinking about my brakes. My setup is currently as follows. 

4 wheel dual cylinder drums

Dual master cylinder. Front line runs to a T connector, one port runs to the front brakes the other has a bleed valve. Rear line runs to a inertia valve located on the rear subframe (Canadian Mini) that splits to the left and right rear drums. It's unlike most minis that have the proportional valve in the engine bay. http://www.minispare...|Back to search

 

What I am thinking of doing is adding in a remote servo. I'm new to all this but I think I need to change my master cylinder to a single line, run that to the servo, and then the servo to the T connector. I would then remove the bleed valve and connect the line that runs to my rear brakes.

 

Does that make sense? Am I on crack? What are peoples thoughts?

 

I would love to convert to disc brakes up front but the cost of the restoration has been higher then expected so that is not an option at the moment.

 

Thanks in advanse

 

[tiger99]

This is an intriguing problem. Firstly, please do not downgrade to single line brakes. It may be illegal to do so or may cause insurance problems and in any case is less safe.

You have at least two other options, firstly fitting the servo only in the front circuit, where it will do more good, or secondly, fit a dual line remote servo. These are a bit bulky so I don't know where you would want to put it. Actually a third option exists which is to fit two servos and while techically corrrect it is even more bulky.

As you have an inertia valve, not a pressure limiter, if you do fit a single line servo at the front you can fit larger wheel cylinders at the rear to get better initial braking balance, the valve still coming in at the same level of deceleration.

But you really, really do not need a servo with the twin leading shoe front brakes, unless you or one of the other drivers is not very strong. However there is plenty of room for personal preference. Maybe aiming for the same level of pedal force as the local cars is a consideration? In that case you may want power steering too, and the electric system from a Vauxhall Astra is said to work well.

I would sugggest carefully checking up on your local laws. The setup you have now was specially devised to satisfy them. Things may be different now, and I have no idea about how the authorities handle modifications.

Please do keep us informed of what you do. It is always interesting to see a new situation like this one and its solution.

Others will be along soon to tell you to fit disks.....

[whistler]

You can fit a servo under the wing as long as the air filter is extended through the inner wing into the engine compartment. The other alternative is under the passenger side dash.

[Syma]

This is an intriguing problem. Firstly, please do not downgrade to single line brakes. It may be illegal to do so or may cause insurance problems and in any case is less safe.

You have at least two other options, firstly fitting the servo only in the front circuit, where it will do more good, or secondly, fit a dual line remote servo. These are a bit bulky so I don't know where you would want to put it. Actually a third option exists which is to fit two servos and while techically corrrect it is even more bulky.

As you have an inertia valve, not a pressure limiter, if you do fit a single line servo at the front you can fit larger wheel cylinders at the rear to get better initial braking balance, the valve still coming in at the same level of deceleration.

But you really, really do not need a servo with the twin leading shoe front brakes, unless you or one of the other drivers is not very strong. However there is plenty of room for personal preference. Maybe aiming for the same level of pedal force as the local cars is a consideration? In that case you may want power steering too, and the electric system from a Vauxhall Astra is said to work well.

I would sugggest carefully checking up on your local laws. The setup you have now was specially devised to satisfy them. Things may be different now, and I have no idea about how the authorities handle modifications.

Please do keep us informed of what you do. It is always interesting to see a new situation like this one and its solution.

Others will be along soon to tell you to fit disks.....

If I can legally get away with swapping my dual master to a single and then adding a remote servo is there any other down side? I am trying to make the braking softer so when my wife drives the mini she is more comfortable. I plan on finishing the car and seeing how it is before making any changes so I will not be jumping into this right away. I will be buying the drum to disc conversion from mini spares when funds permit. I wish in Canada used parts were more common but even used cost the same if not more then ordering from the UK for some things. 

Thanks

[GraemeC]

Normally the main down side is that any failure of the hydraulic system in a single line set up means you will lose all brakes, whereas in a dual circuit system you'd only lose the affected circuit (so half the brakes)

[tiger99]

Your reason makes perfect sense. If you are prepared to put the servo under the wing, a dual one one may be possible.

If you can find out what is legally permissible, we can probably suggest other things. If you could check the bore size of your rear cylinders it may help. If you are allowed to get rid of the inertia valve, a change of rear cylinders, a standard master cylinder, and single servo on the front would be viable.

But there are various other combinations. You will definitely want the servo for disks so it would be good to get the rear setup to allow for that in future. At one time 0.5" cylinders were used, with no pressure limiter, which suggests that 0.7" rears and a 2:1 servo on the front only would be correct.

Rover took the easy way out in the end with the direct acting servo, so a dual line master cylinder could be used, but the loss of underbonnet space is considerable.

If you look at the Somerford Mini web site you will find lots of information on what parts were used over the years.

[jagman.2003]

I have the servo under the dash. It takes a bit of plumbing in but keeps the engine bay clear.

[Ethel]

Convert to discs - somebody had to say it 

 

Actually discs, certainly for 10 inch wheels, are likely to require more pushing than drums, which have a built in servoing action. Though discs don't fade as much and will pull up squarer.

 

Swapping rear wheel cylinders would give better anchors at the back, but I'd be more worried about running out of pedal travel, chances are they're already more than adequate if you have to brake hard and transfer weight to the front tyres.

 

An alternative may be to swap the master for the yellow banded GMC227 (if one isn't already fitted). It has a larger bore at the bottom meaning the upper outlet produces proportionally more pressure for the front circuit of a front/rear split dual setup. It was also used with 8.4" discs without a servo, 7.5's may ideally need pushing a little harder to give their best - though brakepads will have improved from what they were designed for in the 60's.

 

Confirm if you have the small, square, pedals or the later 6 sided variety. The later ones give a bit more mechanical advantage, so less call for a servo.

[Syma]

I love this forum. Thank you everyone, you have given me so much information and things to think about. Its good to see different ideas and see what other people have done. I think for now I will see how my brakes are once I have finished the car. Then i will add a servo to the front followed by disc brakes down the road when funds permit. When I get the car back from paint I will check what rear cylinders I have on my car.

Thanks