Brake Problem Continued. - Off-Road Forums & Discussion Groups
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post #1 of (permalink) Old 02-28-2005, 01:17 PM Thread Starter
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Brake Problem Continued.

New brake lines 2 years ago, No leaks at all in the lines.
New Master cylinder a month ago
New front calipers 2 days ago
All caliper bleeders at 12 oclock position

Just pressure bleed the brakes. Hooked a hose to each bleeder which went into a jar. Saw fluid come out like it should on all 4 wheels.

Get into the jeep. Pedal goes all the way to the floor.

I am lost. I have tried everything. It doesnt make sense.

Any final ideas before I drive it off a cliff?
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post #2 of (permalink) Old 02-28-2005, 01:23 PM
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Re: Brake Problem Continued.

Do you have power brakes? My daughters mustang had exactly the same problem....and after I had done all of the above + new brake lines.

Ended up being the brake vacuum booster.
post #3 of (permalink) Old 02-28-2005, 01:32 PM
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Re: Brake Problem Continued.

[ QUOTE ]
..Just pressure bleed the brakes. Hooked a hose to each bleeder which went into a jar. Saw fluid come out like it should on all 4 wheels.

Get into the jeep. Pedal goes all the way to the floor...

[/ QUOTE ]

Humm... the cliff seems like a good idea if you've got an understanding insurance man, and the greenies don't see ya!

But you said you pressure bled the brakes... Can you describe how you did that?
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post #4 of (permalink) Old 02-28-2005, 04:15 PM Thread Starter
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Re: Brake Problem Continued.

The only thing that is left is the brake booster. It is an $80 special order but I think I am going to try it. If its not it at least I tried before driving it off the cliff.

Here are a few pics. The last pic will show how I pressure bleed the system. It is just like the ones they sell but I made that setup for 10 bucks.

http://www.umit.maine.edu/~michael.p...8ED6-80000018/

Mike
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post #5 of (permalink) Old 02-28-2005, 06:55 PM Thread Starter
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Re: Brake Problem Continued.

Anyone know anything about any booster upgrades? Possibly chevy or something I could get from a junk yard?
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post #6 of (permalink) Old 02-28-2005, 07:03 PM
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Re: Brake Problem Continued.

Here ya go, happy with it so far. It's explained on more detail towards the last post. It frees up some space for air cleaners too. [img]images/graemlins/grin.gif[/img]

Recent thread S10 booster
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post #7 of (permalink) Old 03-01-2005, 01:28 AM Thread Starter
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Re: Brake Problem Continued.

Seems like everyone has had a similar problem but have all done different things to cure it.

Everyone does a MC upgrade, the e350, mercury or vette.
Seems like most play with the proportion valve.
Then we have the idea of switching my rear caddy calipers to grand wagoneer ones like the front.
And there is the slight chance my vacuum booster is gone.

Could someone please explain to me how a vacuum booster works. Most don't seem to think it is it but I havent ruled it out yet. Could that be why my pedal goes to the floor twice before there is pressue at the brakes? Or do I have a fluid flow problem?

I need some opinions on this one.

Mike
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post #8 of (permalink) Old 03-01-2005, 06:49 AM
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Re: Brake Problem Continued.

I said before that if it takes three pumps to get brakes, you've got air in the lines, but there's another possibility. That is that something is pushing the calipers apart - perhaps a warped rotor. It takes a lot of fluid to move the pads together because the cylinders are so big.

If you pump the pedal until it gets hard, and then let the Jeep sit without moving for ten or fifteen minutes, is the pedal hard with the first application, or do you have to pump it up again?

I keep thinking that it's not a booster problem because if it were, you should get a hard pedal on the first application, every time. It would just take a lot more foot pressure to develop stopping power. There is a solid link from the pedal through the booster to the master cylinder. The booster just adds force to that link.
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post #9 of (permalink) Old 03-01-2005, 10:10 AM Thread Starter
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Re: Brake Problem Continued.

If you pump it up so it gets hard and then wait 5 seconds you have to pump it up again to get it hard. I don't think it is the booster anymore. I think it is a fluid pressure problem and I am 98% sure it is not an air in the line problem. Seems like most everyone has done the MC upgrade anyway. And bypass the PV.
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post #10 of (permalink) Old 03-01-2005, 11:50 AM
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Re: Brake Problem Continued.

[ QUOTE ]
I think it is a fluid pressure problem and I am 98% sure it is not an air in the line problem.

[/ QUOTE ]Iíll take that bet. Hell, Iíd almost be tempted to give you 98 to 1 odds.


[ QUOTE ]
Seems like most everyone has done the MC upgrade anyway. And bypass the PV.

[/ QUOTE ][ QUOTE ]
Seems like everyone has had a similar problem but have all done different things to cure it.

Everyone does a MC upgrade, the e350, mercury or vette.
Seems like most play with the proportion valve.
Then we have the idea of switching my rear caddy calipers to grand wagoneer ones like the front.
And there is the slight chance my vacuum booster is gone.

[/ QUOTE ]Yep, you can get a lot of bad ideas (myths) here. Whether itís a proportioning valve is the problem in the brake system or Saddam has WMDs. One of my personal favorites is somebody who said to use #16 stranded wire to repair a trace on a circuit board fed with #8 wire. Hope the guy didnít do it.


[ QUOTE ]
I said before that if it takes three pumps to get brakes, you've got air in the lines, Ö

[/ QUOTE ]Jim is the guy you should have listened to. He had the answer but probably being unfamiliar with the Cadillac calipers he didnít know exactly what you were doing wrong.

In your picture of the rear caliper with the wrench on it, if thatís the way you bled it, it was wrong. If memory serves, those Cadillac calipers stood straight up and down at the rear of the rotor. You keep talking about 12 Oíclock. The bleeder does not necessarily point to 12 Oíclock, as a matter of fact I believe on that caliper, they pointed straight forward. Remove the bleed screw and put the hole at the bottom, where the bleed screw was, at the very top. Not the hole that the bleed screw came out of but the hole at the BOTTOM that the bleed screw sealed against.

Now, forget your power bleeding system, just gravity bleed the system. Open or remove the bleed screw(s) and just keep the master cylinder reservoir full. You can do them one at a time or all at once. The system will bleed itself.

Go here and click on ď<font color="orange">Spongy or light pedal</font>.Ē for an explanation of gravity bleeding. Donít close the page, well need it later.

Now reinstall the calipers and adjust the parking brake BEFORE trying to apply the brakes. This is explained in the section immediately below the bleeding section for good reason. DO NOT DEVIATE FROM THIS STEP.



[/ QUOTE ]

Now to debunk the myths.

The Corvette (or whatever) master cylinder has equal or nearly equal reservoirs. Disc brakes do not have a mechanical adjustment, they retain fluid behind the puck as the pads wear. This lowers the level in the reservoir. You do not need to upgrade the master cylinder if you can remember to check the level once a year or so. If your master cylinder goes bad, by all means, upgrade to the Ďvette part.

You do not need to upgrade the booster to have brakes but disc brakes do not have the same stopping power as drums, so a booster upgrade could help if you have huge tires and the brakes and you have to use both feet on the brake pedal.

Forget the proportioning valve. You wouldnít even need one with discs at all corners AND if your Jeep had a better weight distribution front to rear. It does give you the brake system fault warning though. One of these days Iím going to find an extra valve and take it apart to see if I can remove everything but the warning switch. <font color="red"> Donít try this without having a spare. I have my doubts that it will ever go back together and work again!</font> (Anybody got an extra laying around?)

You donít need an adjustable proportioning valve. Your brakes will work without one. If you were to remove the OEM valve then you could use an adjustable valve to fine tune the rear brakes to keep them from locking up before the fronts. The rear axle has less weight on it and with the same braking force applied, the rears could lock up first. This is also a function of the puck piston diameter.



[/ QUOTE ]

So, why should you put more faith in what I say rather than somebody else? Because Iíve got those same Caddy calipers on the rear of my í80 Jeep and I didnít have to change another thing. Now the parking brake is another story but I didnít follow the instructions in the link above. In my defense, those instructions were not available to me at the time I did mine.

I knew how a brake system works, some learned at the school of hard knocks (I can tell you that itís not a good idea to put a residual valve in the clutch portion of a MGA master cylinder just because the brake side has one and you donít know what it is).

I did the research as best I could but the internet was not nearly what is today, I didnít know how the OEM proportioning valve worked, so I bought an adjustable proportioning valve that I didnít need.

One more bit of advice. Keep the e-brake mechanism and cables lubricated. Mine failed to release on one of the occasions when I used it just to adjust it up, the rotor got hot and cracked. Once you do the initial adjustment, you need to apply and release your e-brake several times to adjust it up. Do this at least every month or so to keep them adjusted.

Now that Iíve spent over an hour on this post, I remember one of the reasons I quit posting here. Just too much time invested in myth busting.
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