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Interesting brake issue
#1
Well, as this old car gets driven more, new problems keep showing up. This is one that I have not yet experienced myself, but a friend of mine has twice now. I got my truck back running, so I put the car off to the side so I could work on it when I had the chance, but a friend's car had some issues, so I loaned him the Mustang while I worked on his car for him. Being I haven't been able to spend much time with it, I have not experienced this, but I'll tell you what I was told. He said that the brake pedal gets very hard and extremely sensitive after driving for awhile and everything is hot. When the car is cold, the brakes work as expected. But as you drive and parts begin to heat up, the pedal gets harder and eventually the lightest touch will almost lock the wheels. Now, I don't claim to be an expert in anything, but usually braking power usually goes down as stuff gets hotter (brake fade and whatnot). I know he's not trying to race the car, he won't even try to race my truck when I tell him have at it, so it's nothing he's doing. If it did it all the time, I would've replaced hoses and gone from there, but since it only does it hot, I'm not too sure where to start out. To my knowledge, it still has the original calipers, wheel cylinders, master cylinder, and brake booster. It does have new hard lines as they're nice and shiny and the old ones were in the trunk, and I would assume the rubber hoses have been replaced. The one time that I did actually check for this was when I was just told it was acting weird and I took it down the street and back with no trouble. Then today, he drove it to work with no problem, but he had to go out of the way for some stuff after and he said it started doing it after about 10 miles or so. Let it cool down and it's back to normal. I'm gonna try to get in and drive it some distance tomorrow, but I don't really know where to look as far as what would be doing this. Any ideas? Thanks for the help.
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#2
Hello,
Maybe you have some seized brake, and this can cause the warm?
It's only my thought after reading you.
I m probably thousand miles from your issue, but let try to figure out.
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#3
manu64;241582 Wrote:Hello,
Maybe you have some seized brake, and this can cause the warm?
It's only my thought after reading you.
I m probably thousand miles from your issue, but let try to figure out.

That is what my friend had suggested, but I don't think that would be it. I know it needs new rotors, but that wouldn't cause this I don't think. When I put the new brake pads on it, the calipers compressed very easily and were very smooth going in. It also doesn't act like a stuck caliper. It doesn't pull to one side while driving, it holds a straight line when you let go of the wheel and brake, and they're not dragging. The few times I've had brake issues over the years that were heat related, it was either the brake fluid was boiling due to air, or brake fade because of how hot they were; both of which caused a very soft pedal with almost no brake pressure.
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#4
Is it both front and rear? If it's just one or the other that may help in determining the problem.

It may be gunk in the proportioning valve or pressure residual circuit.



“If you can't explain it simply, you don't understand it well enough.”
--Albert Einstein
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#5
Can be also the brakes hoses, the master cylinder which keep the pressure on...
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#6
how old is the brake fluid? if you have lots of water in it it would expand as it heated.


possible dragging rear drums heating up and causing problems. possible dragging front calipers.

i had an issue with brake pull when driving for a while and i touched the brakes the car wanted to go left harder and harder. i rebuilt the entire brake system after that issue started. the calipers were very rusted and i think the piston was dragging when the fluid got hot. at the time i had flushed the brake system a couple of times and after a few days the fluid would go from clear to black. i knew the brake lines were bad and since i was going in i opted to replace everything with new stuff.
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#7
72HCODE;241637 Wrote:how old is the brake fluid? if you have lots of water in it it would expand as it heated.


possible dragging rear drums heating up and causing problems. possible dragging front calipers.

i had an issue with brake pull when driving for a while and i touched the brakes the car wanted to go left harder and harder. i rebuilt the entire brake system after that issue started. the calipers were very rusted and i think the piston was dragging when the fluid got hot. at the time i had flushed the brake system a couple of times and after a few days the fluid would go from clear to black. i knew the brake lines were bad and since i was going in i opted to replace everything with new stuff.

I never thought about that. The car had sat for somewhere around 15-20 years before I got it going and all I did was check the fluid level. So the fluid is somewhere around 15-20 years old if not more. It is very dark, I just never thought anything of it since the brakes worked. I'll flush out the system and see what happens. Thanks.
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#8
oh boy; brake fluid sucks in water from the air. just sitting for all those years that fluid is no good. totally flush out the brakes, get a big bottle of dot 3 or dot 4 and use the whole bottle. just flush it all out until everything is super clean and looks clear. then fill as normal and bleed.

check the fluid color over the next few weeks after the flush in the master if it gets dark brown or black again then you have a lot of internal rust in the brake lines and you might think about replacing them, brake lines rot from the inside out due to the water that gets in the fluid. that rust in the system wears out the rubber o-rings and seals and then you get weeping leaks in wheel cylinders.

now if the system is really that old and neglected then REALLY take a hard look at the soft lines, 2 at the front and the rear line over the rear axle. bend the hoses, if you see cracks in any one of those hoses outer skin then replace all 3 hoses they are cheap compared to a brake system failure and crashing the car.
the soft lines can also collapse internally when they get old that can also cause the brakes to become sensitive because the fluid can not drain back when the pressure releases or you could have a brake failure as the hose pinches off internally and sends pressure to all the other wheel brakes that makes the system lose balance and you could have 2 different wheels lock up while the other 2 do nothing.

if you do end up going for a brake line replacement, do not go with stainless steel lines they are nothing but trouble, stick with mild steel lines that are galvanized. do not switch to Dot 5 stick with either dot 3 or dot 4
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#9
72HCODE;241637 Wrote:how old is the brake fluid? if you have lots of water in it it would expand as it heated.


possible dragging rear drums heating up and causing problems. possible dragging front calipers.

i had an issue with brake pull when driving for a while and i touched the brakes the car wanted to go left harder and harder. i rebuilt the entire brake system after that issue started. the calipers were very rusted and i think the piston was dragging when the fluid got hot. at the time i had flushed the brake system a couple of times and after a few days the fluid would go from clear to black. i knew the brake lines were bad and since i was going in i opted to replace everything with new stuff.

+1

You asked a good question about how old was the brake fluid, brake fluid needs to be flushed, the best to keep the quality is every 2 years.
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#10
72HCODE;241645 Wrote:oh boy; brake fluid sucks in water from the air. just sitting for all those years that fluid is no good. totally flush out the brakes, get a big bottle of dot 3 or dot 4 and use the whole bottle. just flush it all out until everything is super clean and looks clear. then fill as normal and bleed.

check the fluid color over the next few weeks after the flush in the master if it gets dark brown or black again then you have a lot of internal rust in the brake lines and you might think about replacing them, brake lines rot from the inside out due to the water that gets in the fluid. that rust in the system wears out the rubber o-rings and seals and then you get weeping leaks in wheel cylinders.

now if the system is really that old and neglected then REALLY take a hard look at the soft lines, 2 at the front and the rear line over the rear axle. bend the hoses, if you see cracks in any one of those hoses outer skin then replace all 3 hoses they are cheap compared to a brake system failure and crashing the car.
the soft lines can also collapse internally when they get old that can also cause the brakes to become sensitive because the fluid can not drain back when the pressure releases or you could have a brake failure as the hose pinches off internally and sends pressure to all the other wheel brakes that makes the system lose balance and you could have 2 different wheels lock up while the other 2 do nothing.

if you do end up going for a brake line replacement, do not go with stainless steel lines they are nothing but trouble, stick with mild steel lines that are galvanized. do not switch to Dot 5 stick with either dot 3 or dot 4

Okay. Thank you for the information.
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