Why was dual chamber Master cylinder eliminated

[raaizin]

On the way home from work yestarday, 1 of my rear metal brake lines developed a leak after a mild panic stop. It appears that corrosion ate through the metal. Car is a '96 explorer which has never been offroaded or on the beach ever. It seems a little premature for this to happpen after < 12 years( I purchased it 03/96??
Anyway why was the dual circuit master cylinder eliminated where if such a failure occurred you would lose front or rear breaks only. I was able to stop without hitting anything, but the older mastercylinder were safer in my opinion.

 

[JHZR2]

Don't know much about this stuff, but my guess would be $$$$$$$$

Its on you to do proper PM to ensure that the fluid is dry... and to verify that your lines arent rusted through...

Im sure the OEM would say that if you took the vehicle to the dealer for the full compliment of services, it'd be caught.

JMH

 

[74DartSport]

Uh, that does have a dual master cylinder...

 

[deeter16317]

I thought all modern cars had a dual ciruit MC?

It might have a single reservoir, but I'm pretty sure the MC has to be multiple circuit.

Another thought is that even losing one of the two circuits will greatly reduce braking...

 

[Quest]

Dunno what you mean by dual chamber master cylinder for all single bore master brake cylinder comes to 2 pistons governing 2 chambers already, all in 1 package.

It is known that modern safety requirements call for the ability to perform partial braking if 1/2 of the braking system has failed. In other words, you shall still be able to stop your vehicle safely with 1 front and 1 rear if the other single or pair failed due to leaks or so, abeit longer braking distance.

 

[ms21043]

You got your car stopped using the front braking system didn't you? If you're saying your rear brakes failed and you had no brakes at all then somethings wrong with your car. ALL cars built for use in the U.S. since 1967 have dual piston master cylinders that serve two separate brake hydraulic systems.

 

[XS650]

Originally Posted By: deeter16317
I thought all modern cars had a dual ciruit MC?

It might have a single reservoir, but I'm pretty sure the MC has to be multiple circuit.

Another thought is that even losing one of the two circuits will greatly reduce braking...


Prolly one reservoir with divider part way up so one side retains fluid when the other goes dry.

 

[eljefino]

The pedal will sink to within an inch of the floor when this happens. Also you might have to pump. Never fun.

Amazing how many people think they still have diagnoal brakes; every car I've ever had had front on one MC port and rear on the other.

Had to redo brake lines on a 99 cherokee to pass state inspection; amazing how at only 8 years old the most vital thing your car has underneath, is the first to rust out.

 

[Shannow]

Down here, RWD are front/rear split, while FWD are diagonal split due to the weight distribution.

Haven't seen a parallel cylinder in ages, just the back to back single systems.

 

[raaizin]

I am a little confused. If on brake line fails, it appears that the master cylinder will emmpty itself out and you would have no brakes. According to this post it will not empty totally and you would continue to have brakes.


I was able to stop and pulled over immediately. Would it have been ok to drive it home at a reduced speed??

FWIW, I did flush system every couple of years since new

 

[moribundman]

Originally Posted By: Shannow
Down here, RWD are front/rear split, while FWD are diagonal split due to the weight distribution.


There are five brake circuit systems:

1. Real Dual Circuit Systems (Type HH):
Every brake has two independent brake cyclinders. If one brake circuit fails, full braking power is available.

2. Two-Wheel Brake Circuit System (Type TT):
There is one brake circuit per axle. Not suitable for FWD, since a loss of the front brakes does not meet minimum brake requirements.

3. Diagonal Dual Circuit (Type K):
As the name says. Mostly used for FWD car.

4. Four Plus Two-Wheel System (HT):
One circuit for all brakes. A second circuit for the front brakes. The front wheel brakes have independent dual brake cylinders. The front brakes always work.

5. Three-Wheel System (LL, or Volvo System):
Has two brake circuits: 2x one circuit for both front brakes and one rear brake.The front wheel brakes have independent dual brake cylinders. If one circuit fails, both front brakes and one rear brake will still work.

 

[Gary Allan]

Quote:
2. Two-Wheel Brake Circuit System (Type TT):
There is one brake circuit per axle. Not suitable for FWD, since a loss of the front brakes does not meet minimum brake requirements.


This I never quite got. Every front engined car, regardless of FWD or RWD, has a tremendous weight bias to the front. The exception may be something like some Porsche of the 1978 vintage (the last time I paid attention to it) that put the engine at one end and the transaxle at the other. Otherwise, a Hemi Cuda had a 65/35 split which is surely close enough to all but the most feather weight FWD. Every dual circuit setup required proportioning valves (or metering block) to limit rear lock up due to weight bias.

I just don't see the weight bias "difference". They're all out of balance.

But a little more back sorta on topic...

I've even seen clutch/brake cylinders that share the same reservoir ..and even share the same master cylinder (if you go old enough).

 

[Scott P]

Last June or so, the rear lines rusted through on my 98 Grand Prix. I lost all brakes. I was just lucky the line blew whle in the Wendy's Drive-Thru.

 

[Chris142]

The single master cyl went away around 1966. been dual systems ever since.

 

[swalve]

Can't share the same master cylinder or the brakes would go on when you hit the clutch and vice versa.

 

[Chris142]

Originally Posted By: swalve
Can't share the same master cylinder or the brakes would go on when you hit the clutch and vice versa.
They were 2 seperate systems that were mounted together. Another type uses a reservoir and 2 hoses that fed each unit.

 

[Gary Allan]

Originally Posted By: swalve
Can't share the same master cylinder or the brakes would go on when you hit the clutch and vice versa.


You're too young. I'm too young too, but I ran into one VERY OLD pickup that had the brake and clutch on ONE PEDAL. The clutch was applied with 1/2 application, the brake with full application (some body language was required to get it right). It was abandoned quick enough for the separate pedals and master cylinders.

 

[deeter16317]

Originally Posted By: eljefino
r fun.

Amazing how many people think they still have diagnoal brakes; every car I've ever had had front on one MC port and rear on the other.



Subaru does utilize diagonal braking to ensure a straight stop...it is right in the owner's manual.