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Old 03-10-2003, 11:01 AM
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Arrow Major Brake Problem... HELP ME!

hello everyone... i have a mysterious problem with the brakes on my '86 chevy caprice. i've mentioned every detail i can remember about the problem, so sorry for the long length of this post.

a little background: this car is a daily driver during the winter months while my '70 oldsmobile sleeps in the garage until spring. the car has high miles, but runs great, and brakes have always worked fine. i do normal maintainance on this car, but nothing else - it's a driver only, and a good one til now.

alright, it all started one day when the brake pedal seemed to travel a little farther than usual. quickly the problem worsened until the pedal was pushing almost to the floor without as much braking as i would've liked. i checked the fluid reservoir, and it was near empty! i added fluid, and brakes were normal again. simple enough. now, here's where it gets weird...

couldn't find a leak anywhere. i continued to drive the car for a while, and no trouble for a couple of weeks. then it happened again. this time it was worse, and the red brake light came on. i noticed that if i pumped the brakes hard, i could make the light go out. still, couldn't find a trace of a fluid leak anywhere.

inspected the front calipers and hoses, and all looked well. i installed a new set of pads while i was at it. with the new pads, stopping seemed a little better, but fluid still was leaking somewhere. checked all lines, rear drums, and master cylinder. no dice. interestingly, when the fluid would run too low, and the red light would come on - breaking improved a little - although i could tell that the front discs were doing all the work, and the pedal was near the floor all the time. i drove it like this for a short period until i could work on it some more. i was beginning to suspect the master cylinder was bad, possibly leaking, but i couldn't find fluid coming from anywhere.

bought a new master cylinder, did a bench bleed as instructed. the bleeding method was different than in the past. instead of the little clear hoses, i got two threaded plastic plugs. instructions say just depress the cylinder a few times until the bubbles stop forming. ok, done. one thing - one of the plastic plugs was leaking slightly. i didn't know if this was significant, so i decided to put the MC on the car and see what happened.

mounted the MC on the car and the brakes worked! however, the red light was still on, and no matter how many times i pumped, i couldn't get it to go out. still, the brakes worked fine it seemed, yet i noticed a leak coming from the fitting on the MC - the same one that was leaking during the bench bleed! AAAAAAAAAAH!!!!!!

brakes continued to work great for about a day. then i began to notice i had to pump the pedal more and more to stop. 100 miles later, i had no pressure at all. the pedal goes all the way to the floor, but returns very slowly. after three full pumps to the floor, i have SOME braking power. there is still plenty of fluid in the reservoir. when i turn the engine off, i get pressure again, but it creeps slowly to the floor - like the MC was bad.

i'm fearing there's air in the lines, but not sure. how much air causes ZERO pressure? can air go DOWN the lines from the master cylinder? do small leaks bring air into the system? and that red light still won't go out. does that mean there is a problem with the rear drums?

i have only a basic understanding of brake systems. i don't know where to start looking for problems like this. never had this much trouble with brakes before! my next step is to start bleeding the lines, but before i take that step, i thought maybe some of you might have tips or past experiences that could help out. thanks to everyone in advance...

[ March 10, 2003: Message edited by: 98rocket ]

[ March 10, 2003: Message edited by: 98rocket ]

[ March 10, 2003: Message edited by: 98rocket ]

[ March 10, 2003: Message edited by: 98rocket ]

[ March 10, 2003: Message edited by: 98rocket ]

[ March 10, 2003: Message edited by: 98rocket ]

[ March 10, 2003: Message edited by: 98rocket ]

[ March 10, 2003: Message edited by: 98rocket ]</p>

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Old 03-10-2003, 11:11 AM
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try bleeding the brakes first.
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Old 03-10-2003, 11:20 AM
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this happened to me, i was mysteriously loosing fluid but couldnt SEE any leaks, had to fill reservoir once a week then the culprit finally showed it self. apparently one of my rear wheel cylinders was leaking just enough that it didnt drain out of the hub onto the tire to indicate a leak until it finally blew all the way. after replacing that i could only get pressure if i pumped but after letting off for a couple of seconds it would go straight to the floor. so after bleeding, brakes work fine.
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Old 03-10-2003, 11:43 AM
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thanks for the info guys, sounds like i need to bleed those brakes.

galaxie, i too suspected the rear wheel cylinders. took the wheels and drums off and everything looked pretty dry. however, since wheel cylinders are fairly cheap, i'll replace them anyway just to be sure.

thanks again!
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Old 03-16-2003, 10:56 AM
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I have heard of the power brake cylinder [the vaccuum cylinder] leaking and the engine vaccuum could suck out the fluid into the engine. Sorta actc like an uper cylinder lube but I have heard this problem before...
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Old 03-17-2003, 11:29 AM
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wally,

thanks for the tip. i've never heard of that before, but it's good to know.

after further inspection, found a leak in the hose right before the split to right and left rear wheels. must be sucking air in, cause i can't bleed the rears - the bubbles just keep coming out.

we'll see what happens when i put the new hose on. thanks to all for the helpful info.
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Old 03-17-2003, 11:48 AM
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You say you put on a "new" master cylinder. Was it a rebuild? I've had bad luck with them. Pull the master and pinch a piece of shop rag on the end of a cloths hanger.. Fish it down close to the bottom of the booster - if it comes up wet, that's where all your fluid is going.

Some of those old metering valve blocks with the light feature had an override button on them that had to be centered back up manually. The would cut off fluid to the rear brakes if they weren't centered up right. If you're light is on, the valve is shifted one way or another from the pressure differential caused by air in your lines. If your peddle is fadings because of external fluid loss it won't take long to pump the master dry. If fluid is bypassing internally, the light will come on and peddle will fade anyway regardless of fluid loss..

Check the calipers to see if they have been installed on the wrong side of the car. If they are switched left to right, you'll never get all the air out of the system. The bleeder screws need to be ontop or they are switched.

Good Luck.
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Old 03-17-2003, 11:52 AM
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On second thought, just pull the vaccume line and fish the hanger down that hole. It's not nesessary to pull the master to check for fluid in the booster.
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Old 03-17-2003, 05:22 PM
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hello primemover, thanks for responding. i didn't know about the metering block. i'll see if i can find that button to reset the light. i'll check on that booster too.

bleeders are on top, so calipers are on correct sides. you're right, the master cylinder is a rebuild. i'll double check it.

just found a leaky hose in the rear, so i'm going to focus on that for now.

thanks again for the info.
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