brake pedel pressure

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Aug 31, 2002 | 12:24 AM

crewray

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Joined: Aug 2002

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From: nanaimo Canada

brake pedel pressure

I have a cherry 1972 f 250 crew cab sb 4x4 which I swapped in a 7.3 liter diesel ,I've installed a dana 60 open knuckle disk brake front axle,dana 70 rear,the problem I am having with this unit is the brakes I can not get pedel pressure,if I apply the brakes the pedel will just sink to the floor and I will have to pump them up again to keep from rolling and then the pedel sinks again,I know this sound like a master cylinder but I've installed 5 of the things and there not rebuilds also sounds like air but the brakes have been bleed with each m/c change however I've noticed large amounts of air in the system more than you would expect with a simple m/c change, so where could this air be coming from ?,all the lines are new,theres no fluid loss, the two lines that run from the m/c to the proporting valve run within about a inch to two inchs of the exhaust manifold could they be getting to much heat and boiling the fluid? I drive it every day and tow a 9000 pound boat and the trailer brakes dont work,gets scary I need to fix it any ideas?.

Aug 31, 2002 | 05:18 AM

jowilker

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From: Creedmoor, North Carolina

brake pedel pressure

When you bleed the system, what wheel order do you use?

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Sep 2, 2002 | 12:08 PM

crewray

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From: nanaimo Canada

brake pedel pressure

I aways bleed right rear left rear right front left front the old fashon way opening and closing the bleeder while some operates the brake pedel.

Sep 2, 2002 | 07:21 PM

rebocardo

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Joined: Jun 2002

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From: Atlanta GA

brake pedel pressure

If you have done a swap like that, you know more than me... but

Don't Ford diesels have a separate pump for the power brakes? Is it hooked up and working properly.

Did you buy a M/C for a diesel or are you buying one for a truck with four drum brakes?

Did you grab the M/C and brake booster for the diesel or are you reusing the stock booster?

The thing is the pumping up the brakes to get them to hold, to me that says that the M/C + Booster combo is not correct and it could be as simple as the wrong rod.

Here is a little test I thought of. Take a piece of masking tape and lightly wrap it around your brake hose. Go for a ride and test the brakes. Then see if the masking tape split. Your hoses might not be the correct ones and expanding too much under pressure.

Sep 2, 2002 | 11:04 PM

crewray

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From: nanaimo Canada

brake pedel pressure

l like the masking tape trick,the booster is powered by a vaccum pump mounted on the engine its new and works good,m/c and booster are 1977(aplication)1 ton units ment drum/disk front end is a 1977 dana 60 low pinon open knuckle disk,I know it sounds like m/c but I cant be 5 times unlucky but then agian if I didnt have bad luck I would I would have no luck at all,I'll check the rod.

Sep 4, 2002 | 11:09 AM

William

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Joined: Feb 2000

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From: Sun River St. George

brake pedel pressure

Couple of thoughts!! Lots of air may be caused by not bleeding the MC prior to installation? Are the calipers installed with the bleeder screw up? Sinking pedal may be caused by one or both rear shoes not properly adjusted. Are you using the by pass tool on the combination valve? Without the tool bleeding these brakes is a royal PITA! You need to keep both sides of the system open or the combination valve closes off the side you are trying to bleed and later you have to re-center it. With the tool installed your bleeding sequence is correct (farthest from the master cylinder first)
William in Atlanta

Oct 4, 2002 | 06:56 PM

matstangs

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Joined: Sep 2002

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From: farmington,utah

brake pedel pressure

Just agreeing with the last post. Be sure the master cyl. is bench bled properly before install. Also as stated, check to be sure the right calipers are installed. If the bleeder is in the wrong place or even if the calipers are wrong you could have some serious problems. Are there any leaks in the system? All wheel cylinders good? Brake lines? Good luck--Matt