Split braking systems

[I.Mupferit]

With split braking systems, ie separate lines to front and rear of the vehicle, if the rear brake line is punctured and leaks the fluid out thus leaving braking to the front only, why would the brake fluid eventually run out at the front as well?

 

I was under the impression that the reservoir to the master cylinder is split thus effectively giving 2 separate braking systems in 1 IYSWIM. Is this not the case?

 

Any ideas please?

 

Brent

 

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[Rob Walker]

Brent,

 

There is a small dam seperating the two circuits at the bottom of the fluid reservoir above the MC. This prevents total loss of fluid if either circuit leaks its fluid.

 

Rob

[Sheds Moderator]

The MCs I have seen have a divider down at the bottom of the reservoir, just below the Min mark. This means, in line with your thoughts, that if one circiit leaks, the other will retain enough fluid to continue working.

[Sheds Moderator]

Blimey, make a note of the date, Rob Walker and I agree on the subject of brakes! 😬

[I.Mupferit]

Hmmm, I seem to be in the situation where as I described in the first post, I lost all fluid to the rear due to a puncture in the brake pipe but then the front has also lost all fluid resulting in no pressure at the pedal whatsoever. There is definitely no leak in the front brake line so I am rather at a loss to explain why there is absolutely no fluid in the reservoir.

 

As you have both said, I believed there would always be some braking from 1 pair of brakes due to a divider in the reservoir but, alas, that doesn't seem to be the case.

 

Brent

 

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[Peter Carmichael]

The reservoir design may mean that the fluid level gets very low. In a typical m/c, the paired action of the two circuits is backed up with a mechanical coupling within the m/c. In normal operation, the pressure is equalised between the two circuits with the primary operating the secondary via a hydraulic coupling (equalised pressure). If the primary circuit loses fluid, the primary will have to move further for the mechanical linkage to operate the secondary. If the scondary loses fluid, the primary will have to move further until the secondary bottoms out before it will pressurise.

 

Are you sure the pedal didn't just get very long in travel?

[I.Mupferit]

Oddly enough the pedal travel initially was no longer than usual and although I did think the brakes didn't seem quite as good as normal I stupidly (with the benefit of hindsight) put this down to the fact I hadn't driven it for 2 months and had become used to the heavily servoed brakes of my new tin top.

 

I came off a motorway, braking down to a sensible speed and all seemed ok, I then came off the brakes at around 20 mph and back on them again shortly after to stop at the roundabout. It was at this point the pedal went straight to the floor leaving me totally without brakes.

 

On checking the m/c later, it is completely dry although it was full the previous weekend when I checked everything over.

 

The fluid level warning light in the test switch is completely useless in an open top car, especially when the sun is shining so although it does come on, it is impossible to see in such circumstances. I am considering fitting a buzzer as an audible backup for the warning light to give warning in future.

 

I still don't fully understand why the m/c is dry when the front circuit is still intact though.

 

Brent

 

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[Unclefester]

Brent, it's because you were generating so much G force on acceleration, all the front section fluid went over the 'weir' into the (leaking) rear section.

 

The same thing happened to me with a Grinnall Scorpion. I had a leak in the FRONT section of the MC, (rear brake) and after several km and a few braking sessions, I suddenly had no brakes at all.

 

Turned out on the Grinnall the MC is angled DOWN to clear the very low nose, and on the Ford for which it's designed the Girling MC is always nose UP, in which position this can't happen as the angle of the weir doesn't allow the fluid in the rear compartment to flow over it into a leaking front compartment circuit.

 

Check the angle of the MC with original specs......is it nose up or at an angle other than designed for?

 

The final solution is to have two remote reservoirs plumbed into the MC, as on 'bikes.

 

Lucy in the Sky with Diamonds..ooooh hooo hooo!!...

😬 😬Abbey Road Time-Machine *eek*

 

 

Edited by - Unclefester on 18 Jul 2007 11:58:18

[I.Mupferit]

I don't know about hard acceleration on this occasion. Mrs C was with me and she complains bitterly when her head gets snapped back if I accelerate fiercely 😬

 

All very strange but once it is repaired a loud audible low fluid warning is definitely on the upgrade list. I know of one other 7er who has had a similar problem with his brakes and although I haven't asked, I assume his light came on as well but wasn't seen. It is the switch on the far left of the dash in the standard set up and really isn't at all obvious to the driver in daylight although, admittedly, it was never something I ever looked at whilst driving. 😔

 

Brent

 

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