E350 Brake Problem

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May 31, 2011 | 04:51 PM

watsupwitcu

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E350 Brake Problem

I have a very unusual problem. My 1990 E 350 cube van,351 auto on propane runs great untill it has been city driving for about a half hour and gets well warmed up and then it starts to lose power although doesn't buck or stumble, just wont accelerate and get up to speed and then the brakes fail completely. No warning, right to the floor. No spongy pedal, nothing to indicate disaster, right down to the floor. Scared the crap out of me the first time but I got it stopped. I had the master brake cylinder replaced, went for a drive and had the crap scared out of me again. If I allow the truck to sit over night and cool down it is perfect again untill it gets well warmed up and engine power loss and then no brakes again. Somebody is gonna die and my mechanic is scratching his head. BTW the truck has rear ABS. and 300K on the orignal engine. I have owned this truck since 1994 so I know it's history and it has been very good to me and now it's trying to kill me. Any Ideas guys??

Thanks Bill

May 31, 2011 | 06:06 PM

bashby

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From: Charles Town, W bygod Va

The bad rabs valve can cause a sinking pedal. there is a reservoir in it that when the abs needs to it opens a valve to relieve pressure, if that valve is bad or the computer thinks the rear wheels are locking it acts like a fluid leak. It can be bypassed as a test.