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I have a ’98 Chevy S10 that has always had great brakes. It has ABS and there were no lights on in the dash so I assume the ABS system isn’t dead (the light comes on for a few seconds when you start the engine like it should).
Well, I was backing down the driveway one day, it stopped fine while I dropped off the garbage. Then when I jumped back in to pull forward the pedal just flew to the floor, no pressure at all, pumping didn’t help. I got it back up to the house and looked around and I found a metal line on the rear axle was leaking where it rusted through, no other leaks anywhere. The dash light came on saying “Brake!” but not the ABS light.
Can anyone explain to me why I lost all brakes from this? Shouldn’t the ABS module sense the problem and “cut off” the rear brake circuit so I still have front brakes? The pressure differential switch turned the “Brake!” light on, so I know that’s working, but I thought a major feature of any modern braking system was the dual-circuit design that should stop this exact scenario, with or without ABS this shouldn’t happen should it?
Is it possible my master cylinder is bad as well? I purchased all new brake parts for the rear drums and new pre-bent stainless lines and a rubber hose. But I would like to know why my system isn’t giving me front brakes before I install the parts in case it needs other work first.
Note that I’m not sure if the ABS module should do this job or if there’s still a combination valve somewhere or what, but I thought something should be preserving my front circuit. Thanks for any advice.
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from my knowledge, brakes are a hydraulic system, if there is a leak anywhere, the whole system looses pressure.
ABS= Anti-lock Brake System… which prevents your wheels from locking up when you slam on the brakes, nothing else.
Brake! would mean you have a loss of brake fluid, sort of like a check engine light but for the brake system., inspect the brake system.
the master cylinder consists of a cylinder that is pressed when you hit the brake, creating a pressure that is split into the front and the back brake lines. if one looses pressure, then all the fluid would rush to the opening, leaving the rest of the brake system compromised.
When you bleed the brakes, and your pressing the brake pedal, and someone opens the valve on the caliper/drum, then the pedal goes to the floor, which it would react the same way with a leak.
the ABS system would be after this( in the brake line system), which then would distribute more/less braking power as needed to prevent the loss of traction
if you got air into the ABS system, be sure to get all of it out, it was tricky last time i had to do it.
Good luck!
Phsycomike is spot on.
I will add to this information on the brake fluid. It is hygroscopic, which means it attracts moisture. Over time, this causes the hard lines to rot from the inside out. New break fluid is clear like water. If you look in the resivior and it isn’t clear or at least mostly clear, then the fluid is contaminated and needs to be flushed out. Doing this can also give you a much firmer brake pedal. This is often overlooked, but is generally required every 2-3 years.
I’ve known people to spend over $1000 on break work, then get frustrated because the brake pedal still hit the floor. I fush the old fluid out and they act like I just put in better parts, but can hardly believe that all I did was flush out the old fluid.
No offense guys but you’re incorrect about it being normal to lose all brakes if there’s a leak on only one circuit. I was asking what the part was called because I know it exists it’s called the Isolation Valve and it’s often part of a Combination Valve. It’s a basic safety feature on every dual-circuit brake system since the 1940’s.
“The isolation valve is controlled by the front and rear incoming brake pressure. The valve has incoming brake pressure acting on each side of a piston. If the pressure on one side of the piston is more than the other side, the piston will start moving toward the lower pressure. At a predetermined point of piston movement, the brake light warning switch is triggered. If the pressure difference continues, the piston will move far enough to completely stop fluid flow to the side with the lower pressure.”
This is what I was looking for, found this while searching around last night. My light came on (not because of low fluid but because of a pressure differential) but fluid flow wasn’t being stopped. I simply wasn’t sure if this valve is still in use on modern cars OR if the ABS module takes over this responsibility, but I know it has to be one or the other.
I knew this thing existed because I had the exact same situation on my ’83 Monte Carlo, the rear line blew and the isolation valve kicked in and plugged up the rear circuit so I could still have front brakes. I drove it like that for a year!
I also found this:
“Some of the toughest vehicle components to diagnosis are ABS/ESC Hydraulic Control Units (HCU). Even in a “passive state” the HCU has to keep designated solenoids open or closed to allow the ABS system to be bypassed. One of the most common failures for HCUs can be dump/isolation valves that are stuck open. This problem can be the most elusive to diagnose. Solenoid valves can remain open due to contaminated brake fluid, rust and sediment.”
Guessing my ABS module is gummed up, might not even work at all. 🙁
The thing you just mentioned only works when there is fluid on both sides of the valve mentioned, otherwise is does little.
As for your old Monte Carlo, the shape of the brake fluid resivior tells a story. There are two sections with a partition in the middle. The partition has a slight relief cut in the middle, but it doesn’t go down very far. If you drove like that for an entire year then you must be used to some horrible brakes.
By the direction and tone your using, are you tying to just get by on front brakes only? That would be horribly ignorant as well as I intensely disrespectful of the the lives in other cars you would take when you slide into them.
The ABS light comes on when one of the ABS sensors stops signaling most of the time, or if the ABS module has a complete failure. I had an s10 blazer that seemed fine. On the hyway, nothing odd. Exit the hyway with slight brake pressure then the brake and ABS light came on, pedal went to the floor and I nearly saw dead relatives. I unplugged the electrical connections on the ABS module, then I had normal brakes at all four corners.
Nodak 81,
You noted that your S10 always had great brakes and no trouble lights. This typically implies that both front and rear were working fine and did not have any appreciable air in the circuits. It also implies your ABS valves were not clogged and allow normal braking where the fluid just passes through.
I don’t know exactly what is in your brake circuit, but my guess is you still have the hydraulic proportioner with the built in warning switch that will light the RED brake light indication a foundation (i.e. normal) hydraulic brake failure. The YELLOW ABS light will turn on if there is an electrical or sensor failure of the ABS system, but the full function of the foundation brakes are maintained. Newer systems have eliminated that external valve and everything is controlled in the ABS/ESC unit.
So assuming no other leaks to the front, the warning switch was working properly and no air in the front then there are two possibilities I can think of…
1) You thought the pedal went to the floor when it was just a very long stroke since you lost one half of your system. This is a common sensation for some drivers in this situation especially if the seat is far back. Also pickups and SUV have relatively large rear brakes compared to passenger cars due to the payload requirements, so that would also imply more travel loss in event of a circuit failure.
2) There could have been a false ABS signal that commands a pressure release mode which would then have allowed the fluid to be routed to the internal storage accumulators in the ABS modulator instead of to the front brakes. This kind of false signal has happened, especially on early ABS units, but it is usually triggered by going over a bump or driving on rough surface where the wheel speed sensors get fooled.
3) There was some other internal leak in the proportioner valve/pressure warning switch that only showed up in failed system mode.
Good luck on solving this one. Keep us posted what you find out.
[quote=”peshewa” post=152612]The thing you just mentioned only works when there is fluid on both sides of the valve mentioned, otherwise is does little.
By the direction and tone your using, are you tying to just get by on front brakes only? That would be horribly ignorant as well as I intensely disrespectful of the the lives in other cars you would take when you slide into them.
[/quote]It only needs fluid on one side to move the piston to the other side with no pressure. I don’t really get where you’re coming from about my tone. I was trying to give you an example of how I know for a fact that it’s not normal to lose all brakes. I’m trying to find out what is wrong so I can FIX IT. If I just replace the line and leave everything else as is, THAT would be horribly ignorant. An important safety feature of my brakes is not working, I need to find out what and why…
@Mechmann Thanks for the input, to be honest I don’t have half a clue as to the internal working of an ABS system. The sensor that sets off the Brake! light is working but apparently that’s all it does, it controls the light nothing else. It looks like the ABS module isn’t sensing that there’s a problem and/or it’s just not working or something. I tried banging it all over with a rubber mallet in case a solenoid was stuck but nothing changed. Very possible it’s failed with a valve partially open or closed that shouldn’t be, who knows! lol
I checked several times and the truck will roll freely with the pedal mashed to the floor, no front brakes at all.
I think the easiest and cheapest thing might be to eliminate the ABS altogether and just install an older valving system. Seems like lots of S10/Blazer owners have done this due to the costs involved in fixing the module.
In the mean time I’ll probably replace the rear line and keep driving it but only as a yard truck, I already cancelled the registration and insurance back in October when this happened. No way I’m going to risk having another line blow and lose all brakes again, I lucked out big time that it happened when I wasn’t even moving, can’t imagine happening on the road.Well, the mystery deepens. Looks like I may have been barking up the wrong tree altogether! I finally got my garage cleaned out and moved my truck in there and gave the pedal a good pump, then I looked underneath just to verify where it’s leaking and I’m getting 3 leaks! (it was parked on gravel up until now, made it hard to see the leaks I guess).
One is at the rear axle, one is from the frame rail mid-way (I assume the long brake line is leaking here), and I have a leak near the pass. side front wheel!! So I guess I have fluid blasting out both circuits, so at least that hopefully means my MC and ABS module might be okay.
There’s something really weird here, no way would 3 lines rust out and break-through at the same time. I will take an up-close look at where the leaks are in the next few days. Could be that the flex hoses croaked in the front and at the axle but even so that’s a bizarre coincidence to all happen at once.
That is bizzar, but not unheard of. From my experience, I learned to replace flexible lines in pairs because if one goes out, the other side is close behind.
You can pick up a roll of steel brake line for about $25ish. Most vehicles use 3/16 size line, but there are many sizes available. I had a Silverado that had 1/4 size, but that was the exception.
You can look up some vids on making double.flares. there are some expensive tools that work well, but you can do it with more basic ones as long as you have the proper size anvil for your brake line.
I’ve seen people do patch work on metal lines, but I prefer to use one line from the master cylinder to each destination with no unions for a solid hydraulic circuit.
There is one line on the frame from the.master cylinder to a block on the rear axle, then there are two lines from that block to each wheel cylinder. If the lines are rusty, the bleeder screws on the cylinders are likely to snap off easily so getting new wheel cylinders is cheap insurance on saving time and frustration. The size of fittings are not always the same at each connection, best to remove the old ones and take them to a parts store to size up what you need when you get that far.Brakes are a hydraulic system. If you loose hydraulic fluid, the system fails. With an ABS system, the ABS module handles the proportioning. Since the problem was in the rear, you likely lost enough fluid to take out the system.
Sometimes it doesn’t pay to overcomplicate things. If the problem was repaired when you repaired the line and bled the system, then you fixed the problem. The rule of K.I.S.S., Keep It Simple Stupid.
More info here.
[quote=”EricTheCarGuy” post=152705] If the problem was repaired when you repaired the line and bled the system, then you fixed the problem. The rule of K.I.S.S., Keep It Simple Stupid. [/quote]
Slow down there, you’re getting ahead of me, I haven’t fixed anything yet! 😛
[quote=”peshewa” post=152688]That is bizzar, but not unheard of. From my experience, I learned to replace flexible lines in pairs because if one goes out, the other side is close behind.
You can pick up a roll of steel brake line for about $25ish. Most vehicles use 3/16 size line, but there are many sizes available. I had a Silverado that had 1/4 size, but that was the exception.
You can look up some vids on making double.flares. there are some expensive tools that work well, but you can do it with more basic ones as long as you have the proper size anvil for your brake line.
I’ve seen people do patch work on metal lines, but I prefer to use one line from the master cylinder to each destination with no unions for a solid hydraulic circuit.
There is one line on the frame from the.master cylinder to a block on the rear axle, then there are two lines from that block to each wheel cylinder. If the lines are rusty, the bleeder screws on the cylinders are likely to snap off easily so getting new wheel cylinders is cheap insurance on saving time and frustration. The size of fittings are not always the same at each connection, best to remove the old ones and take them to a parts store to size up what you need when you get that far.[/quote]Yeah, I might be looking at having to bend my own lines, the place I got the rear lines from doesn’t appear to have any of the others. I finally had a look and the front line looks like it’s rusted out right behind the flare nut that attaches to the flex hose. Looks like the one on the rear axle is the same, right behind the flare nut on the left side metal line.
The 3rd leak is inside a boxed section of frame, but I’m betting there’s a joint in there where two sections of pipe meet and I bet it’s leaking right behind a flare nut…
Really weird situation but like I said, I’d rather be replacing lines than ABS modules and master cylinders!! Think I’ll replace all the front brake components since they’re so cheap and they’re looking old, that way I’ll have 100% new brakes front and rear.
Thanks for the advice guys, might be a while before I attack this job, but I think I might make a YT video documenting it since I’ll literally be replacing every brake component downstream of the ABS module. Might be helpful to somebody.
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