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Old 07-24-2010, 06:47 AM
 
Location: Earth
4,212 posts, read 10,873,445 times
Reputation: 1986
Default Why do they say you have to bleed all 4 brakes if you only opened up 1 side?

Say for example, you have a dual reservoir master cylinder like 99% of all cars on the road have. A front brake caliper has to be replaced. So you "open" the front brake system. Ok. Obviously you will need to bleed at least the front side.

Yet it says when you bleed the system you must also bleed the rears too. Why? Did you actually let air in the rear system too?
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Old 07-24-2010, 07:00 AM
 
Location: Hills of TN
61 posts, read 99,490 times
Reputation: 45
Never Have. The brake line on my RR rusted through and had to be replaced. Luckily I was able to use a torch and heat the bleeder to get it to open.
Daughter did the pedal, I did the bleeder and we have good brakes. Might wana do them all if you lost all the fluid up top, causing air to get into all the lines. As long as you still have fluid above the ports I think you might cause more trouble than it is worth messing with the others. Two sayings come to mind here.:

" If it aint broke, don't fix it."

"K.I.S.S."
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Old 07-24-2010, 07:02 AM
 
Location: Michigan--good on the rocks
2,544 posts, read 1,953,772 times
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I would say it's because of liability. "They" (whoever that is in this case. Is it in your shop manual?) are telling you to do the entire system because they don't want responsibility if you do one part and somehow another part of the system was inadvertently affected. Honestly, if I replaced one caliper, I would most likely bleed only that part of the system, depending of course on things like how long I had the system open or how much of that part of the system I replaced.
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Old 07-24-2010, 07:16 AM
 
Location: Incognito
6,987 posts, read 12,199,844 times
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Not to be greedy but 4 is better than 2.
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Old 07-24-2010, 09:13 AM
 
19,121 posts, read 10,074,360 times
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You don't.... You can just bleed the fts. What I would do is antiseize the ft bleeders, then allow graviety to feed the farthest away, close it. open the closer to the master and allow graviety to feed that one.

Then go bleed the farthest away for real till no air. Then go back to the closer and bleed that for real.

Test. Do not allow the pumpie to work overly fast and cause foam of air and BF to be a problem.

Some people flail away wrongly and create a froth of air in the what should be solid columb of BF.

I tend to work the air out backwards too, tapping on the lines at the master to cause air to let go of fitting edges, and reurn up thru the master. I use a screw driver handle for the hammer. You just vibrate the lines.

However in this case it might be a real good idea to remove the rear bleeder, perhaps after the ft is bleed out and antisize their threads and FLUSH the entire system.
BF is hydroscopic and will draw moisture from thin air. The black is partly rubber seal material in suspention in old fluid, and partly water born contaminates.

Many times a total flush each 2 years works wonders, and even sticking calipers can come back to serve a usefull life for nothing more than new BF.
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Old 07-24-2010, 10:21 AM
 
Location: U.S.A.
2,438 posts, read 3,289,043 times
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You don't have to do it but considering a brake fluid flush is something that should be done annually it is just good measure.
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Old 07-24-2010, 12:13 PM
 
12,897 posts, read 5,674,557 times
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when you open the system on one side only, especially on fords and other cars that dont have self centering brake warning switches, when you bleed the corner you worked on, the system sees it as a leak, and will trigger the brake warning light. thus you have to at least crack the system on the other half of the master cylinder to rebalance the pressures front to rear to put the light out. you can avoid this by taking out the brake light warning switch, and use a bolt to hold the plunger in its position, then you dont have to open the other side to rebalance the system.
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Old 07-24-2010, 01:12 PM
 
Location: Sarasota FL
3,732 posts, read 2,857,986 times
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Almost all vehicles are dual brake systems, but they are not 'the front', 'the rear' , they are one front, one rear [diagonal]
Brake fluid is hydroscopic meaning it attracts moisture. Older vehicles, high mileage vehicles should have the system flushed in areas of moisture, lots of rain, high humidity periodically. If the vehicle is really old, also replace the 4 rubber hoses that go from frame to caliper/drum. They clog from rubber swelling and rust. If the brake puck is sticking, it's usually because of rust.
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Old 07-24-2010, 03:32 PM
 
12,897 posts, read 5,674,557 times
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Quote:
Originally Posted by d4g4m View Post
Almost all vehicles are dual brake systems, but they are not 'the front', 'the rear' , they are one front, one rear [diagonal]
absolutely NOT true. all american cars, with the exception of a few, are one side of the master cylinder controls the front, and one controls the rear. there are some foreign cars that have their brake system split like you suggest, but not as many as you think. even race cars are split front and rear.
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Old 07-24-2010, 03:42 PM
 
Location: Johns Creek, GA
6,321 posts, read 18,881,290 times
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Quote:
Originally Posted by d4g4m View Post
Almost all vehicles are dual brake systems, but they are not 'the front', 'the rear' , they are one front, one rear [diagonal]
.

Wha?
Let's see here:
One res (piston 1) front brakes
The other res (piston 2) rear brakes
And depending on the actual brake type setup, there could be a
proportioning valve- but it stays F/R.
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