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Old 12-03-2003, 07:52 AM
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Please help with my soft brake peddal

Hello Friends,
Over the past couple of months my brake pedal on my 1980 CJ-7 has become soft. sometimes it's "normal" (stiff and responsive), but half the time it's soft and almost non-existent. When this happens I have to pump the pedal to return pressure. I'm not a brake expert so I guess I'm asking what's wrong, and what I should replace. This car does have power brakes. Thanks for your help.
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Old 12-03-2003, 08:17 AM
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It sound's like the Master Cylinder or the Power Brake unit. Push the brake pedal down with light pressure and see if the pedal keeps creeping all the way to the floor. If it does the Master Cylinder is having a problem. If the pedal doesn't creep to the floor my guess is the Power Booster. I am assuming that you have a factory system and haven't changed proportion or other valves.

Bob
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Old 12-03-2003, 03:35 PM
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Yes, it definitely does that! often at a stop light the pedal will slowly sink to the floor. I have to "pump" it to regain pressure.
I just bought this jeep so I assume it's the original equip. Should I change out the master cylinder?
Iv'e seen replacement master cylinders w/ brake boosters for sale from newer model jeeps. They say it will fit on my CJ.
Should I consider this? Is it worth the extra cost + energy to install? Thanks for your help!
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Old 12-05-2003, 12:38 PM
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Youmight check the level of fluid in the M/C. If it has not gone down then the M/C is probably leaking internally. If the level is down, check wheel cyl,hoses,etc for leaks. Good luck
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Old 12-05-2003, 12:41 PM
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Ditto on the Master Cylinder. Don't let it go too long without getting it fixed. All it takes is ONE failure.

Kevin
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Old 12-05-2003, 11:45 PM
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Water in the fluid will also cause a spongy pedal, when was the last time you had the system flushed? Water does not compress like brake fluid and it will cause your brakes to do weird things. Under heavy breaking it can turn to steam and the pedal will go to the floor!

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Mark
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Old 12-06-2003, 10:55 AM
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The fluid level is good. When you say "leaking internally" what does that mean? Thanks for your help.
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Old 12-06-2003, 10:12 PM
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Best way is picture a piston with a bad ring, the pressure is simply going around the piston instead of allowing it to build pressure in the system. More than likely a seal in the master cylinder itself is gone. This will allow the brake fluid to flow around the piston instead of forcing it down the brake line

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Mark
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Old 12-07-2003, 08:42 AM
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Great explanation! Thanks for your help.
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Old 12-07-2003, 10:17 AM
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Sounds like the master cylinder needs changed. For future reference, if the power booster where bad the pedal would be hard, almost impossible to push down. Pull the vacuum hose off the booster and see what I mean. Water can get into the brake fluid by leaving the master cylinder cap loose or off while the car is out of service. Old brake fluid should be changed but I don't know the recommended intervals. I Bleed off the old brake fluid when brake lines get changed because of a leak or wheel cylinders are changed when they go bad. Be careful it can be a messy job.


Todd


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Old 12-07-2003, 01:14 PM
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Sounds like a bad master cylinder to me, too. Don't buy a rebuilt, get a new one, then you may have to bench bleed it before you put it in. I have bled MC's inside and outside the car though, just don't forget to bleed that along with your four wheels.
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Old 12-07-2003, 05:25 PM
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yes, the rubber piece in the top of the m/c seams to be pushed out and warped. Thanks!
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Old 12-25-2010, 08:14 AM
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i have the same problem with my 84 k10 blazer and the mc cover rubber peice seams to be expanded and out of shape bad any explanations?
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Old 12-25-2010, 08:37 AM
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Quote:
Originally Posted by Wildwestshow
i have the same problem with my 84 k10 blazer and the mc cover rubber peice seams to be expanded and out of shape bad any explanations?
This thread is 7 years old. You may want to start a new one.
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Old 12-27-2010, 06:39 PM
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Quote:
Originally Posted by Wildwestshow
i have the same problem with my 84 k10 blazer and the mc cover rubber peice seams to be expanded and out of shape bad any explanations?
Have you refilled the master and pushed the rubber diaphram back into place? These are made to open and look distorted as the fluid level drops.
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