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Old 09-21-2006, 09:59 AM
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High and hard - one time??

Last night my brake pedal kept getting higher and harder until I could feel the brakes dragging. By the time I stopped the pedal had no slack at all, like the brakes were locked up. All the drums were hot, but the backs gave me a blister when I touched them. Once everything cooled down, they were back to normal (about 1 inch of free travel and another 2 inches to full braking). I limped it home slowly and when I felt the drums the fronts were cool and the backs were hot.
This is a stock 41 Pontiac system. No power booster, 4 wheel drum brakes, single reservoir, no residual/proportioning valves. Just the backs locking up I could attribute to faulty relase of the hand brake or deterioration of the flex line to the rears trapping fluid, but it appears to be increased pressure through the entire system. I have lots of miles on the system, so it shouldn't be a setup issue. [the only change from normal - I finally got things right in the handling and last night I pushed it up to 80 for a long stretch, so maybe the exhaust was hotter than normal, but the lines don't appear to be close anywhere] Now that it is back to normal, I don't even know where to start.

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Old 09-21-2006, 10:44 AM
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With both back brakes getting hot, I suggest you change the rubber hose. I have mostly seen the front hoses colaspe during use and you get a pull to the bad side during driving and then it pulls to the opposite side when braking.

Usually hoses are not too expensive. If you plan on keeping the vehicle, you might consider trying braided steel hoses.

Remember brakes are the most important system on a moving vehicle.
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Old 09-21-2006, 02:34 PM
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high and hard

Replacing those lines is on my list, but why would that make the pedal hard?
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Old 09-21-2006, 03:31 PM
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If the hose colasped, no fluid would go past and the pressure builds. Since you now have essentially a solid wall of fluid, the pedal would stay tight. when the pressure bleeds off, the pedal would get soft again. Remember, when you quickly pump the brake pedal it will get stiff.
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Old 09-22-2006, 07:47 AM
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high hard one

Larry, I agree it is probably the rear flex hose. It seems to be the only point in the hydraulic suystem that could create the problem, but I like to understand how things work, and this doesn't make sense to me. Fluid trapped between the hose and the rear cylinders would create part of the problem. But why would that make a pressure buildup throughout the system? The front brakes should still bleed back, and this wasn't just "stiff" like I had pumped them up. The pedal was so hard I could barely move it.
Is it possible to heat brake fluid and get it to expand? Because that is more what it felt like. I'm going to flush the system and check all the routing again, just in case. don
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Old 09-22-2006, 01:55 PM
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high hard pedal

Had a thought ( a rare and pleasant experience). What about a master cylinder malfuncion. If fluid got past the O rings to the back side of the primary cup/piston it would not allow the piston to return, keeping pressure on the wheel cylinders, while also pushing back on the pedal? Not sure why the backs would heat up more, unless they were just adjusted tighter to start with.
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Old 09-22-2006, 04:00 PM
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the M/C could cause this if the compensating port is plugged, it will not allow fluid back in the resivore, or very slowly.
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Old 09-25-2006, 09:45 AM
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hard pedal

Read a lot of posts where suggestions are made, but no results posted. So, just to close this post.
1. Checked the lines. The brake line to the back had come loose from its clamp on the frame and was hanging about an inch off the muffler. Refastened it and took a test drive. Pedal did not firm up as before, so I think heat may have been expanding the fluid. But the rears where still sizzling hot.
2. Rear brakes were dragging, so I backed them off. After pumping them several times they started dragging again. Tore it all down and found they weren't returning properly. The more I backed them off, and the further they had to move to engage, the more they stuck. This car had sat a long time so it was probably a long term crud buildup. Replaced the cylinders.
3. There were wear grooves in the backing plates that may have contributed, so those were ground out.
4. Removed the flex hose and blew through it. seemed clear front to back, but restricted back to front?? Replaced it.
5. The drums had been turned and new shoes put on just before I got it, and I replaced all the springs/holddowns last month, but the shoes looked glazed, so they were replaced and the whole system bled.
A long test drive and everything is OK, though the rears still get warmer than the fronts. Still puzzled about something that I am pursuing in a post under "hydralic pressure". The rear cylinders are 7/8th (Nova rear end) and the fronts are 1 inch. Apparently this makes the rears contact sooner, but the fronts have more stopping power. This leads to warmer rears in normal driving where "slowing" is more prevalent than stopping. I think I need to do a skid pad stop to see if the balance is right, and maybe add a proportioning valve if the backs actually lock up first. If so, that might spread the load on "slowing" a little better.
Hope this helps someone else. Thanks to everyone who contributed.
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Old 02-22-2010, 04:56 PM
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Your problem was the hose...

Like you, I find it irritating that answers aren't posted after questions are asked... nobody learns anything.

What happens when the inside of the hose collapses is that the hose acts as a one-way valve. A flap of the lining might come down to prevent the fluid's return, or a piece floating in there might get stuck.

At a guess, I'd say that when the hose fell down it worsened the situation. It wasn't heat that did it, by the way. The angle of the hose, the point of restriction, was made worse by the hose falling. That's something you can never predict.

I've had this on Peugeots. When I drove my wife's car for a while, front brake pads would last a month. My own identical car they lasted a year or more. The brakes were held on fractionally by the restriction in the hose.
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