Club126UK

Fiat 126 Chat => Fiat 126 Mechanical Problem Solving => Topic started by: banjomandolin on December 03, 2006, 11:49:51 PM

Title: Dual circuit brakes.
Post by: banjomandolin on December 03, 2006, 11:49:51 PM

How does the "dual circuit brakes" design offer a  safety benefit ?. Does  it mean that if one circuit fails you still have 50% braking effort: Surely if one single brake pipe fractures you lose all the braking. Opening the bleed nipple at one slave cylinder is the same as a brake pipe fracture. Your brake pedal goes to the floor and all pressure is lost at all four wheels.

Title: Dual circuit brakes.
Post by: hudsonhenry on December 04, 2006, 10:15:55 AM

A dual circuit master cylinder effectivly has two cylinders and pistons rather than one. When one circuit fails there is normally enough fluid in already contained in the other to stop the car, probably only once and the effectivness of the brakes will be much reduced, but they do work.

For clarification read this:

http://www.procarcare.com/icarumba/resourcecenter/encyclopedia/icar_resourcecenter_encyclopedia_brakes1.asp

Nigel

Title: Dual Circuit Brakes.
Post by: banjomandolin on December 04, 2006, 11:43:18 PM

Hi Nigel, Thanks for your help with the info. which I have read but still remain dubious as to my life expectancy in the event of a leakage in one of my brake pipes. The 1st. item under the heading "Trouble Shooting Basic Brake Problems" is :-
       
  "The pedal goes to the floor"
  "Is caused by" -------"Leak somewhere"
  "What to do"  --------"Check / correct brake fluid level" etc.

   Somehow I don't think that the brake system will be doing much braking whilst the pedal is on it's way to the floor although my wife normally does the pedal bashing during the "down/up/down/up brake bleeding ceremonies so perhaps what little pedal resistance there is is enough to activate some effort in the circuit which remains undamaged.

Title: Dual circuit brakes.
Post by: bis13 on December 05, 2006, 07:44:23 AM

i can speak out of experience that when the brakes fail on a 126 they do so wholesale i lost my brakes in a bis turning into clacket lane services and only the handrake saved my bacon . try it its fun!

Title: Dual circuit brakes.
Post by: Matt S on December 08, 2006, 09:10:25 PM

I can confirm that duel circuit brakes are a good thing to have.

Referring back to 2CV's again (sorry)  i had athe front to rear brake pipe burst and i managed to drive the 800 yards or so home slowely with just the front brakes working and a bit of handbrake use.

Duel circuit brakes are very handy, would not want to be in single circuit car with failure.

Title: Dual circuit brakes.
Post by: bis13 on December 09, 2006, 05:08:12 AM

if thats the case how come i had no brakes whatsoever and only averted wiping out a couple of families by mounting a grass verge and using my handbrake when my brake system failed as i left the m25 to enter a service area? i am not trying to rock the boat here but merely trying to highlight that this dual circuit is like a chocolate watch on a hot day. it might work in a 2cv but it dont in a 126 . have your own opinion but mine is if your brakes fail hold on tight to your handbrake !!!!!!!!!

Title: Dual circuit brakes.
Post by: Matt S on December 10, 2006, 05:02:01 PM

Fair enough, can only speak as i've experianced, as can you.  I think it depends on a couple of factors really, how much fluid is lost before you actually have to brake.

I also believe that you are best having the rear circuit fail as it will have the least effect on fluid loss and leave you with the most effective set of brakes.

A similar circumstance on my wifes renault with a badly leaking rear whel cylinder left the car driveable until the fluid level went too far down.

I repeat with a little disclaimer, in my experiance dual circuit brakes will leave you enough to stop safely with in an emergency situation.