finding my brake issue

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matrass

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Was driving my brother in laws truck the other day and the brakes just went to the floor on me.
I tried to pump them up and they would hold a little pressure but still go to the floor.
Looked at the master cylinder and the fluid was very low as I could hardly see any in there.
I have not seen any fluid on the ground .
Going to fill the master cylinder with brake fluid and have somebody press the bakes while I check for leaks.
How would you troubleshoot this issue to find the problem ?
 
I'd troubleshoot it just the way you're doing it now. Fill the master cylinder, pump the brakes, and look for leaks and a drop in fluid level. If you find neither then you have a bad master cylinder that needs to be replaced. It's a common problem with a common symptom.
 
Are all the pads and shoes totally shot?

As the pads wear, the master cylinder's fluid level drops, to a point where if all the brakes were really worn, it might need a topup. (or new linings)
 
Since there may now be air in the system and you'll have to bleed the brakes at each wheel anyway, it wouldn't hurt to check for leaks at the calipers before buying a new master cylinder. It's possible all the fluid is leaking around one of the pistons or a flexible line has a hole in it, and the master cylinder could be fine. A complete system inspection is in order here unfortunately.
 
The truck I believe is a 1991 ford f 150 pickup with two wheel drive. truck has almost 160,000 miles on it. borrowed it from my bother in law for hauling some versalock, stone and some topsoil. the truck has been sitting for a few weeks and the brakes have always worked well with no signs of being low or fading. not sure how well the truck has been kept up lately. kind of thinking there is air in the system now. was hoping that the master cylinder was the issue but as stated there may be a leak somewhere else. well guess I will fill the master cylinder after work today and pump the brakes and see what happens.the one thing I am glad is that it is a 5 speed and I could make it home with some downshifting. was a scary feeling not having any brakes with a full load in the truck.
 
91 ford check the line running to the rear, between the frame and the gas tank might of rusted through. Look under the truck at the tank and see if it is wet.
 
firefighter

Thanks for the tip. I saw the line running from the master cylinder and it was going along the frame. will fill her up and
see if there are any wet areas where you mentioned. hoping I would not have to check the wheel cylinders , but as somebody else mentioned , once Ilet's wee what happens.
 
firefighter

Thanks for the tip. I saw the line running from the master cylinder and it was going along the frame. will fill her up and
see if there are any wet areas where you mentioned. hoping I will find the leak once I have enough fluid in there.
 
Well just got home from work and filled up the master cylinder. pumped it a few times and heard some fluid squirting out from behind the drivers seat. turns out the brake line rusted through right where firefighter said to look first ( right across from the gas tank in the frame rail. so now that I need to replace it any idea what size it is? looked on advanced auto's website and they have a bunch of different lengths. thinking I should just replace the whole length correct ? suppose I could cut a piece out and take it with me, if I had to .thanks for any info that you can provide.
 
There could be couple of things wrong.
If the fluid was low from normal pad /shoe wear, it may have gotten so low that it sucked air, and simply needs to be bled.
The pads/shoes should be checked - they are therefore quite worn to let this happen.

If you have a leak, it should show a wet area on a line , connection, wheel cyl, caliper, or master cyl.

An internal MC leak can cause these symptoms, but does not cause the fluid to be low.

I suspect low fluid from worn pads, but it could be the other suggestions.
 
mechtech2 ,


I filled the master cylinder when I got home and pumped the brakes. found out that the rear brake line has rusted through near the gas tank.now I need to know how much and what size brake line to buy. was wondering if anybody has a rough idea.
 
Not sure what size it is. You don't have to replace the whole line. At the shop I drop the tank so I can get it back in the proper holders(thats what people pay us for). If it is a beater truck cut the line off in front of the tank where there is no more rust, leave it there and slide another one next to it back to the rear hose. Use a flaring tool to flare the line going to the M/C and put a union in between the two lines (don't forget to put your fitting on before you flare the line). They do have compression unions but I don't advise that. I will not pass that for inspection if I see it, great for emergencies not a long term fix. As for the line Napa has line coated with a pretty thick protective coating. Great for this apploication. They even claim you can bend it by hand without kinking it. I think it is called armor gaurd or something like that. Last but not least don't forget to bleed. Get your wheel cylinder bleeders soaking or you might be replacing them when the bleeders twist off. Have fun
 
Originally Posted By: firefighter
Not sure what size it is. You don't have to replace the whole line. At the shop I drop the tank so I can get it back in the proper holders(thats what people pay us for). If it is a beater truck cut the line off in front of the tank where there is no more rust, leave it there and slide another one next to it back to the rear hose. Use a flaring tool to flare the line going to the M/C and put a union in between the two lines (don't forget to put your fitting on before you flare the line). They do have compression unions but I don't advise that. I will not pass that for inspection if I see it, great for emergencies not a long term fix. As for the line Napa has line coated with a pretty thick protective coating. Great for this apploication. They even claim you can bend it by hand without kinking it. I think it is called armor gaurd or something like that. Last but not least don't forget to bleed. Get your wheel cylinder bleeders soaking or you might be replacing them when the bleeders twist off. Have fun





Thanks for the info. I actually removed the whole line as the rusted out area was only a couple of inches from where the front and rear line were joined through a coupler. the rest of the line was in rough shape so I wanted to replace the whole thing. I took a string and ran it along the entire line and it measure 60 inches. noticed advanced auto and autozone were selling the brake line in 60 inch lengths with the fittings on each end installed already. I will be stopping after work with the old line to make sure I have to correct diameter line. only thing I am wondering is will these lines have the bend in them that the original did or am I going to have to bend it myself. if I need to bend the line what is the best method ( I do not have a bending tool ) thanks for the suggestion on soaking the bleeder valves, makes sense that they will be rusted and want to break off.
 
Buy universal line at the auto parts store.
You have to measure what you need - use a tape measure, and get a bit longer, not shorter, if a decision must be made.
BRING THE ENDS TO MATCH THEM UP!

To take the old lines off, don't try a line wrench. Cut the line flush with the nut and use a 6 point socket. Only takes a few seconds.
This is a great time to soak ALL the bleeders with loose juice/penetrating oil so you can use them later.

Pick up brake fluid if you need it.
 
Last edited:
mechtech2 ,


I did what you said and bought the 60 inch piece with the fittings already on it ( took the old fittings to be sure I got the correct size. I used the poly line from advanced auto ( the green coated stuff ) it was fairly easy to bend but it took me a while to get the back angle just right to screw it in. had the bleeders soaking over night and tapped on them with a hammer but I can not break them loose. I only tires one bleeder and I do not want it to round off. going to get some pb blaster and soak them again. if that does not work , what next ? I thought about a torch but the gas tank is right above me while I would be doing it . any other ideas ? we are almost there , just need to bleed the lines in the back.
 
Also soak the INSIDE of the bleeder - some will get by the internal hole and work the other way..
Can you get a flank drive 6 point socket? [flank drive is the best - it grabs even heavily worn nuts/bolts]
Let them soak some more with your tapping/banging.
Clean the fluid off of the bleeder so it won't act as a lubricant when you actually try to get it off.
As a last resort, vice grips can get them off.

Old rusted bleeders can be tough, and sometimes you have to get a new slave cylinder. They are not too expensive - just be aware that you may have to bite the bullet and get a pair.

And, "just bleed the lines in the back"? C'mon now ... you know better than that!
 
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