14 replies to this topic

[spaulwill]

does anyone have a diagram of a single circuit brake system? my original system was a dual with servo, i have now added a cooper s mk1 servo and so need to change systems, i think i have all correct parts prv etc and single circuit line just a little unsure how it all goes together.

[Tupers]

There's one on the Somerford website. Clicky

[tiger99]

Depending on the age of your car it may be illegal, and a MOT failure, to change the dual system to single. Why do you want to make your car less safe?

[spaulwill]

hi thanks for the comments, the car is 1972 someone had put a newer system on previously to use a new style servo but i am led to believe the cooper s servo i have is only to run on a single system, i take you point of being less safe maybe the servo can be run on a dual i will need to take some advice

[Dan]

The system layout installed in Innocentis had a remote servo on one side of a split system. It can be quite unsafe done the wrong way but if the parts used are all well matched then it can work.

[tiger99]

It is possible to get dual circuit remote servos, but they are not usually fitted to Minis and will be expensive, although ideal. But I like Dan's suggestion better, you only need a servo in the front circuit anyway, as the rears need a pressure limiter, or in some cases very small bore wheel cylinders, to get correct balance.

[Dan]

The twin remote servos are massive too!

[tiger99]

Indeed they are. I am not sure where you could put one in a Mini, without it being a nuisance in some way. But here is one that seems to be a bit smaller than some:

http://www.s-v-c.co....l-remote-servo/

[KernowCooper]

The system layout installed in Innocentis had a remote servo on one side of a split system. It can be quite unsafe done the wrong way but if the parts used are all well matched then it can work.

I have that system on my 1980 with the servo on the front brakes as the previous owner put 7.5 discs on and I want more bite for less pressure, works very well

[tiger99]

I am not familiar with the Innocenti, however I would point out one possible problem with having a servo on the front only. At first sight, it is a good idea, because it puts most of the braking force where it is needed on a Mini, and would probably operate very well without a pressure limiter for the rear brakes.

The potential problem comes if the servo or its vacuum supply fails. The vacuum system has nowhere near the integrity of the rest of the braking sysytem, as loss of servo assistance is normally more of a nuisance than a danger, and it depends on the engine, which is not regarded as safety critical. However, in a Mini, if the servo fails, you push harder on the pedal, and the rear wheels will then lock severely, likely causing a spin, with all sorts of unpredictable consequences from just getting a big fright through to a fatal accident.

So, you should not use the presence of the servo alone to set the front-rear balance, but keep a PRV in the rear circuit. The normal type of PRV should be plumbed into the front circuit downstream of the servo, not between master cylinder and servo, to get correct behaviour. You can't use a proportioning valve such as a Willwood, it has to be a limiting type valve like the standard Mini bulkhead-mounted type.

Nothing about Mini brakes is ideal, so if anyone has any better suggestions, I will be interested to hear them.

[JVA10L]

Many moons ago I used the single line system with the 'S' servo operation on the front only on my rally car but with a proportioning valve to the rear instead of the fixed pressure limiter. It worked very well until an internal seal blew on the servo and brake fluid got sucked into the engine causing a huge cloud of smoke. To finish the rally we disconnected the vacuum pipe and blocked off the hole in the manifold. The brakes worked fine that way so I removed the servo and never used it again. I did read somewhere that the 'S' servo only increases brake line pressure by 10%. With modern pad material I would not even consider fitting a servo to a single line system (with 'S' discs) but would strongly recommend an adjustable valve for the rear.

[spaulwill]

thank you all for your comments. what i have is as follows
servo
http://www.minispare...px|Back to shop

PRV
http://www.minispare...ic/21A1774.aspx

so if i understand correctly (as this is new to me) from master cylinder take a t piece with one leg going to the servo for front brakes and the other leg going to the back through the PRV mounted on the rear subframe for the rear brakes

thanks all agin

[KernowCooper]

Here is the setup on the Innocenti, mine is as per that diagram with the exception my PRV is in the standard place on the drivers bulkhead and not the rear subframe as per the diagram

Attached Files

•  mini innc braces.png   146.73K   23 downloads

[JVA10L]

so if i understand correctly (as this is new to me) from master cylinder take a t piece with one leg going to the servo for front brakes and the other leg going to the back through the PRV mounted on the rear subframe for the rear brakes

thanks all agin

Yes this is exactly how to do it. (Note that the Innocenti system is dual line so is quite different). I would still say go for an adjustable proportioning valve (Willwood or similar) because it is difficult to predict what the rear line pressure will be and therefore what size wheel cylinder to use. I know that some 1275GT's with this servo had 0.5" wheel cylinders but the servo worked on the whole system.

[spaulwill]

great thanks everyone