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Split brake systems.

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Lobo:
Bit naughty as non SOHC - forgive me.

Changed out a rear brake line (old Kombi) recently and upon bleeding the brake thought, “bloody hell, how come the pedal goes effortlessly to the floor during this process… as the system is (supposedly) split”

What am I missing pls? The Master cylinder has divided / isolated reservoirs, with each feeding a separate circuit via a common piston / cylinder mechanism - ie front & rear. It seems to me, should a line rupture occur anywhere, all braking will be lost.

Scratching my head …. and expecting to be embarrassed!

Bryanj:
Even on split system you need to bleed all four

McCabe-Thiele (Ted):
As has been said when bleeding the system the pedal will go the floor that is pretty normal.

On many makes of modern vehicles fitted with ABS even when fully bled with no engine running if you maintain pedal pressure continually the pedal will virtually go down to the floor after a few minutes. In addition if your car has a version of brake assist the movement of the brake pedal with speed causes extra braking force to be applied by the brake booster (servo) this only operates when the engine is running.

I have found that if you have a good pedal with no engine running when you start the engine the pedal will go down even further - this usually confirms that the brake pedal booster(servo) is working as it should. A single pump of the pedal often results in a nice solid pedal again.

I had a front brake hose failure on a Carlton many years ago due to it not having had a recall on the front hoses. A balloon shape like an egg appeared on the hose. I was driving towards a roundabout when this happened - dual circuit was sufficient to bring the car to a stop but it was well scary. Brakes pedal was pretty much on the floor.
It felt as though my brakes were pretty useless I would estimate a 75% loss of braking.

Lobo:
Thanks gents, though still confused. Front discs, rear shoes adjusted, system fully bled & good braking occurs within 1” of pedal movement.
Now, open a brake bleed nipple, and the pedal goes to the floor with little effort (and that slave cylinder obviously ‘bleeds’)

And there’s my confusion… I’d expect appears the ‘other’ circuit of the split system to retain some pedal pressure / stop it going full travel to the floor.

Your last para Ted perhaps addresses it, and suggests the Carlton system was split F/R is opposed to diagonal opposites… given your estimate of 75% loss and no mention of steering upset?

McCabe-Thiele (Ted):
You are correct I ended up with what felt like rear discs only. Iirc I tried but failed to follow the brake lines to determine if it was dagonal or F&R split.

I too would expect the pedal to only go down halfway but that has never been the case. I gave up trying to work out the logic a long time ago.

I have also found that a poor brake pedal often is self fixing either from standing over a weekend or after a brief period of use I perceive some sort of automatic air removal must take place.

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