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  #1  
Old February 23rd, 2006, 09:35 AM
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Question Clogged brake lines?

I think my brake line is clogged... here is why...
I noticed that my brakes felt extremely weak a while ago (only after driving someone elses truck).
I tested them out on some gravel.
Speed up and slam on them to see if they lock.
Fronts lock (reluctantly--with a lot of force)
Rears don't lock up.
The rears do put some pressure on the wheels when off the ground.
So I take it to an expert
Well it turns out my calipers are seized and it is a $1000 job.
Next expert...
Because the first one said the wrong thing...
I let the second one replace my pads and asked him to flush the system (which I think he did not do).
So I get the truck back and it still brakes like CRAP (but about 10% better than before).
Still rears wont lock and the truck really doens't stop.
So I thought...
Maybe the first guy was right...
Maybe the rear calipers are partially siezed
Next I find some remanufactured calipers for $54 each (with pads).
I put them on the rear. bled them. and ... SAME THING.
They kinda stop...

I think there is rubber or dirt or something clogging the rear.
You know that little rubber washer that used to be on the master cylinder cap?
Not there... deteriorated. Maybe a piece of that is lodged in the brake line, bathing in brake fluid?
How would I go about fixing this?
Can I drain the entire system and blow compressed air throught the lines?
What should I do?
Thanks,
Heath
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  #2  
Old February 23rd, 2006, 09:47 AM
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Ian McCormack
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I would wedge the brake pedal down overnight and bleed the brake lines to ensure there are no air locks, and see if there is any improvement in the brakes. If there is not then I would suspect a brake master cylinder problem
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Old February 23rd, 2006, 09:56 AM
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Quote:
Originally Posted by ne4x4
I would wedge the brake pedal down overnight and bleed the brake lines to ensure there are no air locks, and see if there is any improvement in the brakes. If there is not then I would suspect a brake master cylinder problem
I've bled the crap out of the brakes...
Front work, rear don't.

I have good reason to believe that pieces of that rubber seal on the master cylider have gotten into the master cylinder and beyond.

Wedge the pedal overnight? I will try it, but I don't think there is any air in the lines.
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Old February 23rd, 2006, 10:09 AM
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Hmm, I wonder there is a break propotioning valve that regulates the pressure from front to rear. If there is something wrong with this then maybe the frontbreaks get all the power andthe rears don't. Changing the break fluid every few years isn't a bad idea either. Is there possibly a kink in the break line someplace?
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Old February 23rd, 2006, 10:17 AM
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It could be a kink I suppose.
I haven't done anything that could have struck a hard line...
But maybe a piece of gravel from my driveway coming off the mud tires at 50mph could have whacked the line?
I will check for visible dings in the line.
Is there a valve on a 1995 D90 ST?
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Old February 23rd, 2006, 10:21 AM
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Yes, there is a valve! I think it is mounted on the firewall.
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Old February 23rd, 2006, 10:24 AM
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This is going to be a bitch no doubt.
Has anyone ever completley drained a brake system and refilled?
I might as well put some extended stainless lines on now...
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Old February 23rd, 2006, 10:46 AM
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I've drained a brake system when I replaced all calipers, flex lines and almost all of the piping. Bled it through extensively with a 1 man bleeder and have a nice firm pedal ever since. If you are able to bleed the rear then you must be getting pressure there, I think the proportioning valve sounds like a good possibility.
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  #9  
Old February 23rd, 2006, 12:00 PM
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there is a brake proportining valve, it can get airlocked and will cause that problem. On UK spec vehicles it is mounted on the chassis just in front of the firewall. Wedging brake pedal down overnight then bleeding rear brake lines the following morning normally clears any airlock in proprtioning vavle
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Old February 23rd, 2006, 12:39 PM
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You might also want to bring it to a shop that can pressure-bleed the system. Instead of drawing the fluid out through the calipers with a vacuum pump or by working the master cylinder, it's pushed into the calipers under slight pressure and the old fluid is removed from the master cylinder. This backflushes the system, and also doesn't have as much of a possibility to draw air into the system. But you have to specifically ask if a shop does that, since it's not the most common way of doing things. In fact, a lot of mechanics don't even know about it.

Now, have you also considered the possibility of the booster not functioning properly? Check the vacuum lines leading to it and make sure they are all attached and in good condition. Here is another way to check it as well. Sit in the truck with the engine off and push down hard on the brakes about a half dozen times to get a feel for them with the engine off. They should feel rock-hard right from the first push. If they get more solid as you push on them by a significant amount, they may need to be bled out again. If they are consistantly solid then you want to wait about 30 seconds and, with the truck in neutral of course, start the engine while you're pushing hard on the brake pedal.... when it starts, the pedal should go down a bit. Then pump it a few more times, it should feel a lot softer than with the engine off.

-Hans
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Old February 23rd, 2006, 03:29 PM
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Brake lines do not clog unless something truly extrordinary has happened to your truck.

The rubber brake hoses do swell up and they act "clogged" If that happens change them all. It's a good idea to change 10-year-old lines anyway.

Also, we always bleed under air pressure to get consistent results.
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Old February 24th, 2006, 08:39 AM
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A piece of rubber from that little grommet seal type of thing that used to go under the master cap was in there one time and I pulled it out with a pair of needle nose pliers. I was pretty sure that I got the whole piece out, but I may have broken a piece of of the piece. After I had the truck detailed a long time ago, that piece of rubber turnned into flakes. They must have used some chemical that broke down the rubber.
This is a long time ago, so the memory has faded. But I can't remember my brakes ever working properly.

I'm going to replace the rubber lines with stainless. When they are off, I am going to flush the system and blow compressed air through it. I will also inspect carefully to make sure there are no kinks in the hard lines. Is there anything else I should replace? The master cylinder seems to work fine.
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