8 replies to this topic

[DUF2]

Duffy my ‘65 Elf, has standard single circuit brake system, but is fitted with 8.4” four pot calipers, it also has a remote servo fitted.

I am contemplating converting to a dual circuit system. I perhaps should have done this during restoration!

What is involved in swapping to dual circuit brakes? Obviously I need a dual master cylinder, is there a one available that matches upto the existing pedal box?

what are the implcations of having the servo on the front brakes only? I realise the rear brakes don’t do a lot on a Mini.

As I said, I am only thinking about this at the moment.

[nicklouse]

First off why are you thinking of this?

 

there is nothing incorrect with what you have.

[Spider]

I gather you are contemplating this as a safety measure in case of the failure of one circuit ?

 

I found with the GMC167 and GMC227 Master Cylinders that a failure in one or the other circuit, the pedal will still go all the way to the floor, still leaving you without brakes.

[DUF2]

First off why are you thinking of this?

 

there is nothing incorrect with what you have.

Yes for safety’s sake just in case there is a failure in the hydraulics.

[DUF2]

I gather you are contemplating this as a safety measure in case of the failure of one circuit ?

 

I found with the GMC167 and GMC227 Master Cylinders that a failure in one or the other circuit, the pedal will still go all the way to the floor, still leaving you without brakes.

Yes Spider, as a safety measure.

 

WOW! That is alarming! I thought the whole purpose of dual circuit brakes was in case one circuit failed, you could rely on the second circuit to allow you to stop!  Not very good if that does not happen, I also do not wish to demonstrate that failure.

 

I had it once a few years ago in a Transit Mini Bus, the pedal went to the floor as I slowed down on a motorway slip road, fortunately I had started to brake in plenty time so I could slow down through the gears & stop on the handbrake. One of the brake pipes had snapped.

[nicklouse]

This topic might help you as well.

https://www.theminif...lain-something/

 

There’s another thread I was ready when I posted that on dual circuit brakes. Will see I I can spot it later.

[Ethel]

What you describe can work. The earlier, small pad, pedals have less travel making the pedal hitting the floor a bit more likely. The same is true if you're trying to operate the brakes through an inoperable remote servo.

 

You could pump the pedal, if you have the presence of mind, to get some braking out of a dual circuit (if it has enough fluid). Better to have a well maintained system that doesn't fail.

 

 

I have a cunning plan I've never tried. If you ran just the front brakes off the servo, you could use a solenoid valve to vent the rear of the diaphragm to atmosphere, same as the internal hydraulic valve does. That'd operate the front brakes as long as there was fluid in the servo, even if the master couldn't generate enough pressure to do it hydraulically.

[sonscar]

I was taught with a failed circuit on dual circuit systems to not pump the pedal but to hold it down and stop at a reduced rate.It is designed for one stop,not to continue your journey.Steve..

[Spider]

 

I found with the GMC167 and GMC227 Master Cylinders that a failure in one or the other circuit, the pedal will still go all the way to the floor, still leaving you without brakes.

 

WOW! That is alarming! I thought the whole purpose of dual circuit brakes was in case one circuit failed, you could rely on the second circuit to allow you to stop!  Not very good if that does not happen, I also do not wish to demonstrate that failure.

 

I had it once a few years ago in a Transit Mini Bus, the pedal went to the floor as I slowed down on a motorway slip road, fortunately I had started to brake in plenty time so I could slow down through the gears & stop on the handbrake. One of the brake pipes had snapped.

 

 

 

Yes, the idea / concept of a Tandem System is built in redundancy, so a hydraulic failure in one circuit is supposed to leave you with the other operational, just with a lower pedal and obviously, reduced braking ability.

I have found however, with both of these, when bleeding the system, which is from a hydraulic point of view, the same as a hydraulic failure, that after getting one circuit bled, when doing the next, the pedal still goes all the way to the floor with zero resistance / pressure. This has been with the correct pedals and fittings.

One day, when I get some time to burn (hahahahaha,,,, that made me laugh !), I'll look more in to this and why this occurs when it shouldn't.

The late servo boosted tandem systems I have yet tried this with, but I wouldn't be surprised if it was the same.