Brake pedal drops... - PowerStrokeNation : Ford Powerstroke Diesel Forum
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post #1 of 13 (permalink) Old 06-03-2009, 11:46 PM Thread Starter
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Brake pedal drops...

hey guys


this started a while ago but has been getting worse lately, almost caused me to rear end someone at a stop light(partly because i wasnt paying attention)

here it is: when sitting at a stop, with my foot on the brake....it(the pedal) will slowly start to drop to the floor. as it drops the holding ability of the brakes fades with it, and the truck will begin creeping forward.

if i jab the pedal harder when this happens it will stop(but the pedal will be way low)

now my rear brakes have been pretty bad for a while, so i was thinking it was the wheel cyl's but i have absolutely no fluid loss from the master.

im wondering if there is a problem with the booster or vac pump....

any ideas?

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post #2 of 13 (permalink) Old 06-04-2009, 02:12 AM
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Re: Brake pedal drops...

If you know your rear brakes are bad, I would suggest starting there.....

Dave

'08 F250 6.4/Torqshift Spartan 310EL, Flo-Pro 4", White_monster air intake, RCD 4-link, RS9000's 584/1330
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post #3 of 13 (permalink) Old 06-04-2009, 02:59 AM
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Re: Brake pedal drops...

i had the same issue big red. I replaced the booster and still had the same problem then replaced the little switch and the entire brake system under the reservoir where you add brake fluid. that fixed it a little more then i did hte vaccuum pump and now my brakes are 100%

1996 Ford f-350 7.3l psd Tony Wildman 6 pos chip, 6637 intake, Autometer gauges, 6" silverline aussie stacks
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post #4 of 13 (permalink) Old 06-04-2009, 03:23 AM Thread Starter
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Re: Brake pedal drops...

smokyred... the rears are bad, as in the shoe linnings are worn out. but as i stated, there is absolutely NO fluid loss at the master... and this condition has been present long enough that i would see a drop in the fluid level if the wheel cyl's were leaking(even slightly)

Black, what switch are you talking about?

i was thinking, wouldnt a bad vac pump cause a hard pedal??

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post #5 of 13 (permalink) Old 06-04-2009, 11:11 AM
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Re: Brake pedal drops...

sounds like classic master cyl failure the seals in the master are starting to leak and let fluid past them instead of putting pressure out to the brakes, if you let it go long enough you'll have to pump the pedal just to get enough pressure to stop with. start with the master and go from there.

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post #6 of 13 (permalink) Old 06-04-2009, 11:41 AM
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Re: Brake pedal drops...

Agreed... if it were the vaccum pump or booster the petal would get hard, not soft.

Ford stopped building trucks in 1997
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post #7 of 13 (permalink) Old 06-04-2009, 12:08 PM Thread Starter
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Re: Brake pedal drops...

damn....oh well, hyro-boost time!

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post #8 of 13 (permalink) Old 06-04-2009, 12:11 PM
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Re: Brake pedal drops...

Quote:
Originally Posted by bluedge8 View Post
sounds like classic master cyl failure the seals in the master are starting to leak and let fluid past them instead of putting pressure out to the brakes, if you let it go long enough you'll have to pump the pedal just to get enough pressure to stop with. start with the master and go from there.

1995 F250 SCLB 4X4 Auto - '97 D60/10.5" rear, 4.5" PMF RSK/V's, PMF Trac Bars, Sway Bars, MBRP Exhaust, DP F5, Efuel, RRD Diff Cover, Tymar Intake, Isspro Performaxs/Quad Pod, Recon Cab Lights, 05 Lariat SD Steering Wheel
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post #9 of 13 (permalink) Old 06-04-2009, 01:14 PM
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Re: Brake pedal drops...

the wires under the booster and the fluid reservoir i changed all those pieces as well along withe the booster and vacuum pump.

1996 Ford f-350 7.3l psd Tony Wildman 6 pos chip, 6637 intake, Autometer gauges, 6" silverline aussie stacks
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post #10 of 13 (permalink) Old 06-04-2009, 09:43 PM
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Re: Brake pedal drops...

Ford covered the creeping brake pedal in a TSB, here's the info from Dieselmann's site:

1997 and earlier diesel trucks equiped with vacuum power brakes--Low/creeping pedal:
Many owners have complained of a low or creeping brake pedal on their trucks, often mistaken for a bad master cylinder or Rear ABS valve. If the condition occurs after the vehicle has come to a stop, and no other brake concerns are found, (worn or out-of-adjusted brakes, cocked pads, or hydraulic problems) the condition is normal and the result of the vacuum pump replenishing the vacuum inside the power booster. Ford has developed a Zero-Loss Travel brake booster to correct this condition if the customer finds it unacceptable. This part is only for use on diesel-equiped trucks--P/N F5TZ-2005-CA--and is not a service replacement; it must be ordered by the part number, not vehicle application.

This condition is similar to the low brake pedal concern on all 1995 F-series that required a larger-diameter master cylinder:

Trucks without cruise control:


F6TZ-2140-AB
F-250 Gas 4X2; F-350 DRW, SRW Gas 4X2, SRW 7.3 4X2 168" WB
F6TZ-2140-EB
F-250 4X4, 7.3 4X2; F-350 SRW 4X4, SRW 7.3 4X2 133" WB
Trucks with cruise control:


F6TZ-2140-BA
F-250 Gas 4X2; F-350 DRW, SRW Gas 4X2, SRW 7.3 4X2 168" WB
F6TZ-2140-FB
F-250 4X4, 7.3 4X2; F-350 SRW 4X4, SRW 7.3 4X2 133" WB
These part numbers are from TSB's 96-25-19 and 98-5A-34, and are not normal service-stock replacment parts.

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