Re: swapped the 11 inch discs in and now brakes are worse.
[Re: Andrewh]
#1733322
01/19/15 07:25 PM
01/19/15 07:25 PM
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Joined: Feb 2005
Posts: 28,312 Cincinnati, Ohio
Challenger 1
Too Many Posts
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Too Many Posts
Joined: Feb 2005
Posts: 28,312
Cincinnati, Ohio
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Quote:
well yesterday it was crazy bad. today it is just regular bad.
when I had it inspected last year the guy mentioned that it didn't stop soon enough. I just figured, heavy car, and all. I had noticed when I first start out in the car sometimes, but just attributed it to poor vacuum build up after it had been sitting a while. but I am guessing the booster is going. wish there was an easier test than getting that test kit. it is about half the price of a new booster. if I decide to keep going this route.
I got a rebuilt booster from Rock Auto for my 74 challenger about 4 years ago. I replaced my perfectly working one because it was leaking vacuum inside causing my car to small backfire on decell. And messing with my idle. First noticed it coming down Pikes Peak in first gear, might have been when it let go inside? It was still providing proper brake boost. Just small embarrassing pops out the exhaust. No it was not a exhaust leak.
So the rock auto one sucked from the beginning, only giving me about 3/4 assist but no more vacuum leak or backfires. I checked the rod length and keep driving it. It get's worse the more I drive the car. A year+ later I have just about zero assist from the POS booster.
I took a 35+ year old one off my parts shelf and bolt it. It works like a new one, brakes are back to 100%. Have been now for 3 years.
I never called or complained to rock auto, it was well over a year in use but it was a pos from the first day I got it. I figured getting "fresh" rebuilt would be smarter than a used one when I called Rock auto because my local Car Quest could not get it anymore for me, wrong again. My
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Re: swapped the 11 inch discs in and now brakes are worse.
[Re: Challenger 1]
#1733323
01/20/15 03:04 AM
01/20/15 03:04 AM
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Joined: Jan 2003
Posts: 10,863 Freeport IL USA
poorboy
I Live Here
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I Live Here
Joined: Jan 2003
Posts: 10,863
Freeport IL USA
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Two things you seem to be concerned about. 1) you believe the booster is interfering with travel. 2) you believe there may be a master cylinder issue.
To test #1, unbolt the master cylinder from the booster and step on the pedal to see if the pedal will travel all the way to the floor. If the pedal does not reach the floor, your issue is in the booster/pedal assembly. The vacuum assist of the booster is only an assist, meaning there should still be a mechanical connection and you should be able to overpower a defective booster with pressure on the brake pedal. Without a master bolted to the booster, the pedal should push to the floor fairly easily and smoothly. Get an assistant and measure the amount of travel the rod in the booster travels from pedal completely up, to pedal completely on the floor. If the pedal and booster operate correctly, reattach the master, and move on. 2) Now you have to determine if the master cylinder is the cause of your issue. With the master reattached to the booster. Loosen both brake line connections and see if the pedal will still go all the way to the floor. If it does, the issue probably in not in the master. It is possible the master plunger is not completely returning all the way to the back stop of the master cylinder, upon brake pedal release and it is not refilling with enough fluid to reactivate the brakes. If you tighten the lines you loosened for this test while the pedal is still down, you will not pull any air into the system. Once the lines are tight, you can remove the master from the booster to see if the plunger has returned fully to the back stop. I've seen corrosion build up inside the master that will not allow the plunger to return to the back stop and that can cause an intermittent poor brake function. Sometimes the rod between the booster and the master is too long. That will also cause the plunger to not return all the way to the back stop and cause poor brake conditions. If the rod is too short, it will not allow the master cylinder plunger to push enough fluid out of the master to reach full brake pressure (that could cause the pedal to stop before the pedal reaches the floor.) If you suspect the rod may be too long, you can add a couple washers on each stud between the booster and the master and see of that makes a difference in brake quality. If adding the washers does not make an improvement, remove them. The rod between the booster and the master is adjustable, adjust the length in or out 1/4 turn at a time (a little makes a huge difference). If the pedal reaches the floor with the brake lines on the master loosened, and the master's plunger is returning to the back stop, the master is not the problem, and we move on to the proportioning valve.
For a few years, the proportioning valve actually would block off fluid flow to one side of the valve or the other in the event of a line failure. Unfortunately, it would also do the same thing while bleeding the fluid if the bleeding process wasn't done easily. The process to recenter a shifted proportioning valve is not difficult, but requires a gentle touch. To test the valve, loosen either the fitting for the rear brakes, or the fitting for one of the front brakes, and step on the pedal and watch the fluid flow. Tighten the line, and loosen the other line (one line towards the front, and one line towards the rear) and step on the pedal and watch the fluid flow. If either the front or the rear line has little or no fluid flow, the proportioning valve has shifted towards the side with little on no fluid flow. To recenter the proportioning valve, you have to open the side with the fluid flow, and bleed off the fluid until you hear the pop or snap inside the valve, and immediately close off the line, and release pressure. Gently stepping on the pedal should leave the valve centered, and the brakes should be much better.
You have been messing with these brakes too long. Start at the beginning, and work through the process to this point and lets see what you have. Gene
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Re: swapped the 11 inch discs in and now brakes are worse.
[Re: Andrewh]
#1733327
01/20/15 01:59 PM
01/20/15 01:59 PM
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Joined: Sep 2003
Posts: 1,688 Marlboro, NY, USA
Rick_Ehrenberg
top fuel
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top fuel
Joined: Sep 2003
Posts: 1,688
Marlboro, NY, USA
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I know you said no hydraulic lines were removed, but, to me, the system sure sounds airbound.
Here's and abbreviated procedure, as to how I confirm (or not) in minutes: Plug both master cyl outlet ports. Pedal should be rock hard (or close, with power booster). Not? Bleed master. (Can remain mounted, just slam on some c-shaped tubes).
OK now? Reconnect front fitting (to rear brakes). Still firm? Great. Not, trouble's out back, bleed, excess shoe travel, etc.)
Repeat with rear tube (for front brakes) connected.
The whole process can be done in a few minutes, and, if nothing else, localizes the problem area.
Rick
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Re: swapped the 11 inch discs in and now brakes are worse.
[Re: Andrewh]
#1733329
01/20/15 02:25 PM
01/20/15 02:25 PM
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Joined: Oct 2005
Posts: 9,038 Ontario, Canada
Stanton
Don't question me!
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Don't question me!
Joined: Oct 2005
Posts: 9,038
Ontario, Canada
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Quote:
I took off the master cylinder to see if the rod had backed down but it was still adjusted. pedal has more movement without the master bolted up, so no binding there, nor is it the booster.
It almost sounds like there isn't enough travel left in the master. Is it possible there is too much preload? Fully retracted the master piston should be very close to the mounting surface (bottomed against the c-clip). Mounting it to the booster should not compress the piston.
Likewise, is the booster fully retracted when the pedal is at its uppermost point?
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Re: swapped the 11 inch discs in and now brakes are worse.
[Re: Andrewh]
#1733332
01/20/15 04:21 PM
01/20/15 04:21 PM
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Joined: Jan 2005
Posts: 3,344 Central TX
roe
master
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master
Joined: Jan 2005
Posts: 3,344
Central TX
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Are you sure that the booster is good? Ive had a booster go bad and it was rock hard pedal. Bad master gave me really mushy pedal. Just because booster is new doesnt mean its good. On my moms Oldsmobile Cutlass Supreme went through about 6 bad masters right out the box before I got a good one. Similar deal once with an alternator as well.
1971 Plymouth Satellite 408/904 8 3/4 3.23 SG
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