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My truck is a 1992 Dodge Dakota. The front brake line burst! The rear brakes should have worked to stop the truck. They didn't. The pedal went to the floor. Brake fluid from both reservoirs not just the front shoots out the broken front line when the pedal is depressed. My mechanic says the part called the proportioning or combination valve could be the problem, but is no longer available. Any help greatly appreciated!
First, you need to fix the broken brake line before looking deeper.
The brakes will go to the floor with a completely open line such as yours
The fluid from the back line is creating return pressure shooting out the front. Following the least point of resistance.
I'm quite certain you'll be fine after fixing the ruptured line. Remember when bleeding, start from the furthest away from the master cylinder.
First, thanks for the reply. The line has been replaced and the truck does have brakes now. But when the line broke, it had absolutely none. I was under the impression that if a front line broke, the rear brakes would still work. Is that only in case of a minor problem, perhaps a tiny leak? The emergency or parking brakes worked, but are not very effective. My concern is that a truck that old (32 years) could have the same thing happen to the other front brake line.
Yes they did, Bob. From reading about it on the internet, It's possible a malfunction of the combination or proportioning valve could have caused the pedal to go to the floor when one front brake line broke. And pumping the pedal did no good. I appreciate your reply.
The proportion valve is just that. A larger proportion upwards of 80% of the stopping power goes towards the front brakes. It's not an absolute system where the front reservoir serves the back and rear the front.
Hummmm.... I would have figured the Proportion valve would took over after the first couple of pumps of the pedal? But you say that's not the case here?
I'm not sure if 1992 had the ABS system? But if it does have it, i'm thinking possibly it may have activated and slowed the ability of stopping?
I also see the point of Kuvasz, In the rear brake % aspect....
Possibly if the brake were not at the correct adjustment, they would only be able to work at a even lesser %.... Point being, If the rear brake control only about 20% and they are way out of adjustment, this would leave a much less amount of braking ability for them...
Hey Bob, I believe the rear drum brakes on this model are said to be self adjusting. You are correct in that they don't do much, because if they did, when I applied the parking brake as hard as i could with my left foot, there certainly was no screeching halt!
Hey Bob, I believe the rear drum brakes on this model are said to be self adjusting. You are correct in that they don't do much, because if they did, when I applied the parking brake as hard as i could with my left foot, there certainly was no screeching halt!
Well, Hope you and everyone is ok? and Hope you get the trucks issue sorted out..... Cheers...
On any car, if you cut a brake line it's going to lose the brake pedal.There will be some fluid still going to the front or rear depending on what was cut. It's not a total safeguard but it's something.
I ran almost a full can of brake fluid through it trying to get some pedal by crushing the broken end of the metal line. The pedal never showed any resistance (I had the engine running) and the fluid levels in the reservoirs were going down equally. I'd say the dual master cylinder safety feature is either useless, or this one malfunctioned. The truck does have anti lock brakes so that could be the problem, or part of it. When I picked up the truck at the repair shop, the ABS warning light was on. It went out after I pressed the pedal a couple of times with the engine running.
That line you crushed has air in it for sure. You would need to get that air out of that line but it's not possible or even why would you bleed a crushed line? .
The air came out, and a lot of brake fluid behind it. The only difference in the crushed line and the uncrushed line was the size of the squirt. A friend who used to do car repair suggested trying it to get enough brakes to drive the 3 miles to a shop, not a brake shop, but he said they could put on a new line. I had the truck hauled there instead. If you read my first post, you see that I wrote that the mechanic who worked on it said the combination valve could be the problem, but was no longer available. That sounds a bit dangerous to me, so I plan to take it to a brake specialty shop next week.
A Haynes Repair Manual came with the truck when I bought it. On page 1 of the chapter on brakes, they say, "The hydraulic system has separate circuits for the front and rear brakes. If one circuit fails, the other circuit will remain functional, and a warning indicator will light up on the dashboard when a substantial amount of brake fluid is lost, showing that a failure has occurred."
My truck didn't do any of that. The pedal just kept going to the floor.
By the way, I didn't see your answer to my question. You said it's not an absolute system where the front reservoir serves the back and rear the front. So, once again if fluids from the front and rear reservoirs are able to comingle, what is the reason for 2 small reservoirs instead of one big one?
I think you're expecting to have a solid hard pedal with a major leak. Like I said before the system or lines aren't exclusive. There are distribution and proportioning valves in the system which are not completely isolated. Yes, the 2 reservoirs are separate that feed the system. In your case you had a major blowout. The master pumped fluid into your lines that eventually back fed through your distribution box and proportioning valve causing both reservoirs to empty. I'm quite certain if you fix your ruptured line you'll be good to go. If the system was meant to be independent both lines from the distribution box and proportioning valves wouldn't exist. You'd have separate lines from the master to your wheels. I attached a video that should help.
Thanks, but what I am looking for is a better outcome if the left front ruptures like the right front did. Just replacing the broken one is hardly the answer to that. Why would I expect the "failsafe" system to stop the truck if it does? The old Dodge, according to the Haynes Manual, has a rather complicated ABS for the rear drum brakes, consisting of the hydraulic valve, the control module, speed sensors, etc. and at 32 years old could be unreliable and difficult to troubleshoot. The question now comes up that if the front lines are completely replaced from the master cylinder to the wheel cylinders and the rear brakes spring a leak, will the front brakes work? I sure hope so but I wouldn't bet the farm.
I think this comment you made pretty well cuts to the heart of the matter.
"On any car, if you cut a brake line it's going to lose the brake pedal.There will be some fluid still going to the front or rear depending on what was cut. It's not a total safeguard but it's something".
I was under the impression that it WAS a total safeguard and would stop the vehicle, not as well as all 4 but better than nothing which was what went down with my truck.
Automobile brakes aren't 100% failsafe for sure. I've had master cylinders suddenly go to the floor losing all braking. It's good to have a good working emergency brake, hence the word "Emergency". Good luck!!.
Driving an elderly truck is a little like being a paratrooper. They hand you a parachute and say if it doesn't work bring it back and we will give you another one.
Let me add something here.... You are correct in your assumption that the Front is seperate from the back... The proportion valve should have activated but didn't. At this point i'm going to guess that is has some trash in it and is stuck.
As for the lower of both sides of the brake fluid reservoir, If I am not mistaken, that has a plastic reservoir? if that is the case, most of those have a slot in the middle divider? and will swap fluid until it gets down to the cut off point of that slot and will leave just enough fluid to do its job..
I tend to agree. The old truck does not have a lot of miles, still under 130K, but the years take a toll, same as the miles. I saw an article that said people are keeping their old cars and trucks much longer now than 30, 40, 50 years ago because they can't afford the outrageous prices of new vehicles, plus the many other things they have to have. I love that old Dodge, but I might buy a newer truck for my beater.
Your telling me... My Daily Driver is a 1977 Dodge D150 "Warlock" Pick up with a 360 V-8 and a 727 Auto Trans.... It has clocked over 500,000 + miles. (Not all Original installed parts) but never the less) Still my daily driver. And the truck has only been towed home 3 times in its lifetime.
04-18-2024, 10:03 AM
No Brakes!
