Need help badly, Ambulance is driving us nuts
 

2003 ford E350 7.3l Power stroke.
The brake pedal drops approximately 1" with very little pressure then it is hard as a rock. a few blocks down the road the pedal will drop clear to the floor. When it does either of these the brakes are not slowing the truck down hardly at all. This continues intermittently throughout a drive cycle. The brakes will actually work normal maybe a handful of times with a 4-5 mile drive. I have gotten the B1676 code only and no dash lights illuminated. I have changed the power steering pump, hydroboost, master cylinder, and swapped the abs module from a good working truck, flushed the system twice also. I'm at a loss and not really sure what to check next. I've never ran across this particular issue before so and and all opinions, suggestions, beers are very welcomed.
Thanks
Tim

That's a weird one. I'd start looking at the slave cylinders. Can you get it to malfunction in the driveway, maybe up on jack stands? I'm thinking if you can, you could block off one caliper at a time to test for the problem.

Can't offer a real beer but gosh could you use one about now huh? Here's as close as I can get: :-drink

The B1676 DTC relates to battery voltage according to Actron but not sure how that would affect braking.

This sounds very much like a master cylinder issue, at least with the usual vacuum booster only type of brake system. By new master cylinder do you mean brand new reman'd or one swapped out of the known working truck?

Are there any proportioning valves or any other pressure device in the system that could be releasing pressure back into the fluid reservoir and not directed to the calipers?

And I'm further guessing you're not seeing any evidence of fluid leaks anywhere?

Check for a collapsed rubber line that's keeping you from getting all the air out of the system.

Thanks for all the responses. I found the issue with the code, which ended up being a bare wire several inches away from the alternator.
The braking issue is not with any part of the master cylinder hydraulic system. I say this because just sitting still in the shop, the brake pedal is hard/stiff to push down. If you hold pressure on the pedal and just barely turn the steering wheel the stiffness goes away and the pedal goes down like normal. If I keep turning the steering back and forth while sitting still or driving, the brake pedal seems to work perfectly normal. If I hold the steering wheel straight while driving, I get one normal brake, then its back to hard pedal again.
Like I mentioned before literally everything has been changed except the steering box, and today I changed the hydraboost unit and the master cylinder again, but this time off of another truck.
I may be leaning towards some whiskey here pretty soon and skip the beer :)

Your problem is going to be from the steering gear. When the steering is straight and you hold the brakes and rotate the wheel, does the brake pedal rise or drop? The steering gear is worn causing a pressure loss and the hydroboost doesn't have enough pressure to operate. This was a very common issue years ago on our fleet 450 Van's when I was working at Penske. A way to verify is to use line lock pliers and clamp the pressure hose to the steering gear 50% this will leave enough pressure and your brakes should work normally.

Thanks ford390. That makes perfect sense. I was just researching about the steering boxes this morning considering changing it sense it was the only thing not changed. I seen that they have a check valvle in them so thats what I will be doing today.
Thanks a million
Tim

Out of curiosity did you verify the new pump had the same pressure regulator valve? There is multiple orifice sizes, the valve is screwed into the pump and is where the high pressure hose connects to.

Well, um no I did not. Never thought about doing that. I never have before, but also never ran into this problem either. lol. New steering box now and still the same thing.
Is there a way to check the orifice size or is it noticeably different?
Thanks
Tim

Ok so here is what I have. After changing the steering box and bleeding the system (I bled it for 30 minutes just to be sure lol), Truck up on jack stands turning the wheel back and forth, the brakes work as they should, a low gentle pedal about 1-1/2 or so, and feels good. If I stop turning the wheel the brakes will work twice, then they are hard as a rock. At this point of being hard, I can barely twitch the steering wheel and you can feel the pedal and steering wheel jerk a tad bit and the brake pedal goes down. Its like turning the steering wheel is allowing enough pressure into the hydroboost for it to work properly. I also noticed this test failed with all 3 of the hydroboost I have had on it. If you shut the truck off and pump the pedal 2-3 times to clear the pressure out of the accumulator, then hold pressure on the pedal while restarting the truck, the pedal does "not" drop as it should, so the accumulator is not getting fluid/recharged when the truck is started. After starting the truck doing this test, If I barely turn the wheel 1/4", the pedal will drop as it should.
ford390gashog Im hoping for some magical dust from ya buddy. Or anyone else for that matter. :)
Thanks
Tim

I know this is probably silly, but is it possible that the brake pedal itself is hitting the steering column or something under the dash, as if some bracket is slightly bent, and moves out of the way just enough when you barely turn the wheel? Probably impossible, but I'm just trying to think of anything at this point.

Tim, are any of the return hoses soft? Do you have flow from the hydroboost return at all times or only under braking? The pressure valve is screwed into the power steering pump but that doesn't sound like your issue. By chance was the hydroboost a cardone reman? What color is the accumulator? Is it gold, blue or silver?

warrene350 thanks for thinking but thats not the issue.
ford390gashog, The main pressure line is brand new. The other line that has rubber is fairly new and feels to be firm. When I flushed the system before and after changing the hydroboost, there was fluid coming out of the return when I would lift off of the brake pedal. It will spit a handful of fluid everytime I released it. I found if I turned the wheel right to the lock position and tapped the pedal the fluid would flow consistently out of the return. Is it supposed to come out of the return when you push the brake pedal also? The new hydroboost is a proshop brand. I dont know to much about that brand, its the same local parts place we have done business with for over 25 years. The accumulator is black. Its a remanufactured so the whole thing has been painted black. The second one I tried was off another truck and it was the original off that truck. It was the same year make model etc, as the truck Im currently working on.
Im gonna go a head and change the other steel/rubber line just to try and see if it does anything.
Thanks
Tim

Sure sounds like a collapsed brake line to me. My 2000 E-150 did something similar and my right front rubber brake line was messed up inside. It felt OK, but after I took it off and put it on the bench with pressure, I could feel a restriction when I simulated a brake release. The new hose solved it.

I chopped the line up trying to find the problem but never did.

Replied once before on this. Try changing out your rubber brake line hoses and see if it makes a difference. Every time you change the steering you say your braking changes. The front rubber lines flex with the front hubs being turned. If one or more are bad inside they will pinch shut inside and turning the hub can open the line.
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