Soft brake pedal
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Soft brake pedal
I've a 91 F350 super cab, 7.3 diesel. I rreplaced both front brake calipers and master cylender. Brake pedal goes almost all the way to the floor easily with almost no brakes. Now what? Very frustrating. I replaced the calipers cause the bleeders snapped off. Spungy pedal so I replaced the master cylender. I read the thread a couple down, and I believe my rear brakes shoes are adjusted properly. I don't see any leaks anywhere. Any input or advice would be greatly appreciated. Thanks.....Matt
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Will they pump up?
Rare, but hoses can buldge without leaking. Have you checked all three?
Can you verify good pressure (loosen a fitting some and watch it when someone pushes the pedal) on the down side of the master cylinder - to be sure it been bench bleed enough or maybe bad from the box?
Calipers aren't upside down (swapped right to left) are they?
Rare, but hoses can buldge without leaking. Have you checked all three?
Can you verify good pressure (loosen a fitting some and watch it when someone pushes the pedal) on the down side of the master cylinder - to be sure it been bench bleed enough or maybe bad from the box?
Calipers aren't upside down (swapped right to left) are they?
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They pump up ok when bleeding with the truck not running. With the truck running they're soft. I'm sure the master is good since it was doing this before I replaced it. The front rubber lines are good and not bulging. I read in my Haynes manual about the power booster push rod mybe needing to be adjusted. Thanks.....Matt
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I do not have anti-lock brakes. According to my Haynes manual, I have a soft brake pedal with a slight groaning noise from the booster while applying the brakes while the engine is running, is due to the power booster pushrod being adjusted too short. Tomorrow I will check this, adjust if not within specs, and report back. Thanks for the input so far.....Matt
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From: Millersville, MD
I believe you DO have REAR anti-lock brakes...I just sold my old '92 F250 and it had REAR anti-locks only. I also had a VERY hard time getting my brakes right. I finally bought a good brake bleeder tool and they tightened right up...go get one of the bleeders that reverrse bleed....sucks the new fluid from the bleeder valve instead of pumping down from the master cylinder.
Last edited by BPofMD; Jan 31, 2006 at 09:21 PM. Reason: Addition of info
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Ah hah, I do have rear anti-lock brakes. Is there a way to test the rear ABS valve? I saw it yesterday, drivers side in the frame rail under the front seat. Also, my brake warning light is not on if that matters. Thanks.....Matt
Last edited by mtsnieg; Feb 1, 2006 at 09:22 AM.
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No. It doesn't. But read this:
http://www.asashop.org/autoinc/dec99/techtips.htm
Lazy K may be right, and if so, that link might help you. Personally I don't think that's the problem, and maybe BPofMD is right. Reason I don't think it is the RABS is that you say the pedal goes to the floor easily. RABS is normally a brake fade thing, and should not have anything to do with the truck running or not.
Please clarify the problem alittle for us. Does the pedal fade, or can you pump them up and they stay solid? Try this with truck not running, and again with it running.
I think you're going to have to isolate the system....systematically (with out trying to be a smart @ss). This will most likely be a pain, as you have to unhook and plug various lines.
First find out it the system will hold pressure (IE: no fade at all).
http://www.asashop.org/autoinc/dec99/techtips.htm
Lazy K may be right, and if so, that link might help you. Personally I don't think that's the problem, and maybe BPofMD is right. Reason I don't think it is the RABS is that you say the pedal goes to the floor easily. RABS is normally a brake fade thing, and should not have anything to do with the truck running or not.
Please clarify the problem alittle for us. Does the pedal fade, or can you pump them up and they stay solid? Try this with truck not running, and again with it running.
I think you're going to have to isolate the system....systematically (with out trying to be a smart @ss). This will most likely be a pain, as you have to unhook and plug various lines.
First find out it the system will hold pressure (IE: no fade at all).
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With the truck not running, it feels like I can pump up the brakes a bit. Not a huge difference, but noticable. If someone is pumping the pedal and I'm underneath the truck looking at the caliper I can see the caliper pistons moving.
With the truck running if I depress the brake pedal, it softly goes to the floor, as if there is air in the system. (I cannot believe there is any air, I've bled through almost for big cans of fluid.) If I hold the pedal on the floor and put 'er in reverse and slowly let out the clutch, the brakes hold. Then I release the brake pedal and try it again, no brakes, they wont hold.
Same when driving. Hit the brakes and the pedal goes softly to the floor, but just enough brakes to stop the truck. Let go of the pedal. Hit the brakes again and the pedal slowly goes to the fooor but no brakes. If I try pumping them they don't work. Like a one time shot, then have to wait a couple minutes to use again.
With the truck running if I depress the brake pedal, it softly goes to the floor, as if there is air in the system. (I cannot believe there is any air, I've bled through almost for big cans of fluid.) If I hold the pedal on the floor and put 'er in reverse and slowly let out the clutch, the brakes hold. Then I release the brake pedal and try it again, no brakes, they wont hold.
Same when driving. Hit the brakes and the pedal goes softly to the floor, but just enough brakes to stop the truck. Let go of the pedal. Hit the brakes again and the pedal slowly goes to the fooor but no brakes. If I try pumping them they don't work. Like a one time shot, then have to wait a couple minutes to use again.
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I read the asashop arrticle from the link you provided. I will try this evening. If it's not the master (after performing the tests in the article), and if I bypass the RABSV according to the article, if the brakes appear to be fine it would be the valve then, right? If so, could I leave the valve bypassed and run without the RABSV? Thanks, again.....Matt
Last edited by mtsnieg; Feb 1, 2006 at 12:44 PM.
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