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Unread 02-22-2014, 07:50 AM   #1
zbtc8
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1978 CJ5 
 
Join Date: Feb 2014
Location: Bristol, TN
Posts: 3
Cj5 Brake Problems

Hi everyone, I would love some help with my brakes. I have a '78 CJ5 and whenever I slowly depress the brake pedal it will sometimes travel almost completely to the floor until the brakes are activated. When it is depressed at a "normal" speed, however, the brakes feel and act normal. I've bled the brakes and don't think there is any air in them. Could this be a master cylinder problem? This issue can occur anytime I slowly depress them, whether it is during start up, after driving around for a while, or when it is hot or cold out. Also, I don't have a brake booster and I have discs up front with drums in the back.

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Unread 02-22-2014, 09:13 AM   #2
John Strenk
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1976 CJ5 
 
Join Date: Feb 2005
Location: Shalersville Ohio
Posts: 13,185
1. Is the fluid level OK?
2. Any sign of fluid leaks?
3, Have you checked the adjustment of the brakes in the rear?
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Unread 02-22-2014, 12:42 PM   #3
zbtc8
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1978 CJ5 
 
Join Date: Feb 2014
Location: Bristol, TN
Posts: 3
The fluid level is fine and surprisingly no leaks. The brakes in the back have been adjusted as well.
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Unread 02-22-2014, 08:31 PM   #4
jeepdaddy2000
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1971 CJ5 
 
Join Date: Jan 2002
Location: Secret Squirrel hideout, afghanistan
Posts: 6,259
Probably an internal master cylinder leak. The cups have probably shrunk. When you push slowly down, the fluid is passing between the bore and the lip of the cup. When you blast down on the pedal, the pressure rises quickly, forcing the cups up against the inside of the bore, sealing the cylinder.
I would think about replacing it.
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Unread 02-22-2014, 08:47 PM   #5
jammer1
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Join Date: Jan 2009
Location: cleveland, ohio
Posts: 135
X2 Jeepdaddy2000. I had a jeep that did that and the rubber cups would let the fluid leak past. If I hit the brake hard, the pedal would be almost normal. If you hit the brake hard and stop, leave you're foot on the brake with pressure. If the rubber cups or the bore is scored, the petal will slowly go to the floor (as the fluid leaks past the cups).
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Unread 02-22-2014, 11:47 PM   #6
zbtc8
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1978 CJ5 
 
Join Date: Feb 2014
Location: Bristol, TN
Posts: 3
Looks like I'll be replacing the master cylinder and hoping that fixes it. Thanks and I'll keep you posted if it does!
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