lumina split brake system question

[snick]

Hi looking for some information on 98 lumina brakes. I recently had a rear leak in a brake line and completely lost all brakes -luckily I was able to slow it done with the parking brake. The question I have is this - my understanding is that cars have split brake systems so either the front or rear will continue to work in cases like this. To not have a working split system sure seems like a problem with an ageing car in the northeast where roads are salted. Does this car truely have a split system ? Should the car have continued to have front braking when the rear line burst?


Just trying to understand how this system works on this car. Thanks!!

[rkvons]

Originally Posted by snick

Hi looking for some information on 98 lumina brakes. I recently had a rear leak in a brake line and completely lost all brakes -luckily I was able to slow it done with the parking brake. The question I have is this - my understanding is that cars have split brake systems so either the front or rear will continue to work in cases like this. To not have a working split system sure seems like a problem with an ageing car in the northeast where roads are salted. Does this car truely have a split system ? Should the car have continued to have front braking when the rear line burst?


Just trying to understand how this system works on this car. Thanks!!

Not 100% sure, but my '98 Grand Prix and '98 Malibu brakes will continue to work if just the rear brakes are lost. You really have to step hard on the brake and will get what seems like partial braking though.

[McLin]

The Lumina has a split break system. The front left wheel and the rear right wheel are on circle and the fron right wheel and the rear left wheel the other. But if the brake line broken, I think the pressure is gone. You can totally push the peal to the floor, because all the fluid is coming out on the leaking one.

[jeffcoslacker]

It's known as split diagonal, common on FWD cars. Works as McLin described.

Since front/rear bias on FWD cars is close to 90/10, you'd have almost no brakes at all if you lost the front in a front/rear split system. The split diagonal assures you'll always have one front and one rear available, which gives you sufficient stopping power in a loss of one side of the system...but whenever you experience a sudden catastrophic loss of fluid pressure you're gonna lose the pedal and be without brakes, regardless of the design.

The only way I could think of to prevent this would be the use of hydraulic "fuses" that close and isolate the leaking part of the system when too much fluid tries to move through too quickly without pressure...that's how aircraft systems work now...but you aren't gonna see the car companies put this kind of fail safe in...not for what they'd consider to be out of warranty fatigue/corrosion related failure, something that's really not their responsibility.

They don't claim or expect these cars to last long enough to rot out the brake lines...

[Schurkey]

With any dual-circuit hydraulic brake system, losing one circuit due to fluid leakage will result in VERY LOW pedal, and piss-poor braking--but you should NOT have lost braking altogether.

Either you still had some braking ability, but you didn't push the pedal far enough, hard enough, or something else is still wrong.

[jeffcoslacker]

Originally Posted by Schurkey

With any dual-circuit hydraulic brake system, losing one circuit due to fluid leakage will result in VERY LOW pedal, and piss-poor braking--but you should NOT have lost braking altogether.

Either you still had some braking ability, but you didn't push the pedal far enough, hard enough, or something else is still wrong.

I've blown many wheel cylinders and lines suddenly in a variety of vehicles...that little bit of drag you get right on the floor once the proportioning valve locks out the leaking side doesn't really qualify as braking for me....and usually it takes several strokes of the pedal before it moves the spool far enough to lock out...so it is essentially without any brakes until that happens. Most people don't know to rapidly pump and get this process going when the pedal falls to the floor...they just know nothing's happening...

[jeffcoslacker]

PS and often I've found a 10 or 15 year old PV on a car that's never had the brake fluid changed, the valve and seats are so crapped up with corrosion it can't close properly, or sticks closed and won't reset after the problem is fixed...