Re: 1994 F250 diesel brake problem

Posted by JDEM on January 20, 2018 at 06:34:27 from (174.230.0.103):

In Reply to: Re: 1994 F250 diesel brake problem posted by Bob on January 19, 2018 at 20:01:56:

My F250 truck has a plastic vacuum reservoir attached to the big plastic box that holds the air-conditioning evaporator. No metal "soup can" although I have seen them on many other Fords. No leaks. I leaked checked everything. I was sure, at first, I had a vacuum leak in the dashboard from my heater controls. I pulled a lot of stuff apart for nothing to check. I finally just blocked everything except for the vacuum pump, reservoir, and brake booster. If I hold steady on the brake pedal I have 15-18 inches of vacuum all day long if I want. If I pump the brake pedal, over and over,and push hard, vacuum drops near zero for just fractions of a second and then comes back up. It now seems to me when I pump, there is too much volume needed by the booster and once the reservoir runs out, the vacuum pump cannot keep up and the light comes on. I don't know yet, but I assume the excess stroke of the booster and too much pedal travel is the problem.

Did the same with the old master cylinder as with this new one. I bled the master-cylinder on the bench before installing. I ordered another new one and will see what happens. Unlike what some others have experienced here - I have never yet had a bad master-cylinder when new in the box. I have bought many el-cheapos from China and up to now -never had any issues. We'll see.

Same subject, but different vehicle - I have a 2002 Chevy Astro Van I bought as an insurance wreck. Brakes worked fine but the top of the brake master-cylinder was broken off. So I got a new one for $25, bench-bled it - and put it on. No matter how much I pumped - I could not bleed it out. On that - to my surprise - I found out the engine has to be running due to the ABS. I do not know why since I have bled many ABS systems before without the engine running. But hey - what works, works. I started the engine and then was able to bleed the brakes just fine. I almost threw out that new master-cylinder thinking it was bad.

Note - I am on a learning curve a little behind modern auto tech. I never ever buy new. Just older vehicles. So at present - vehicles from the 80s-90s are "current tech" to me, and mid 2000 is "state of the art" since my newest vehicle is a Ford Escape AWD that I have never had to work on yet.

Replies:

• Re: 1994 F250 diesel brake problem Bob 10:36:02 01/20/18 (1)
  • Re: 1994 F250 diesel brake problem JDEM 14:05:20 01/20/18 (0)

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