RABS brake bleeding problem

Lbhsbz said:
First...do you have a spongy pedal that you're equating to air in the system, or are you actually seeing air in the system?

RABS valves were problematic, but easy to test. With the big plug off the back, the piston should NOT move when applying the brakes while just sitting there. If it does, the dump valve is leaking and filling the accumulator which is consuming all your fluid volume, replace the valve. If it's wet inside, the accumulator seal is leaking, and the valve needs to be replaced.

If neither of those 2 conditions exist....

Ford had a bulletin on this years ago, I've not been able to find it in the last 10 years but I did have a copy of it at one point. The F350 used a 1 1/8" bore master cylinder up until 1996. In 1997, they switched to a 1 1/4" bore master cylinder. The bulletin instructed to use the later/larger master cylinder for the earlier trucks to solve a soft/low pedal issue.

Calipers/firewall/everything fatigues over time and tends to flex a bit more than it once did...which is the only reason I can imagine that these things worked just find for the first 15-20 years of their lives and then decided to get ****ty.

If NO other reasons exist that contribute to the low/soft pedal, then do the larger master cylinder. This has solved the problem in every case where I've applied it.
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Okay...I spent the afternoon gravity bleeding everything yesterday. No air and the pedal is still not what I'm used to. I'm going to go with the '97 MC. Here's another thing...is it possible that the cruise control switch could be some of the cause of this? It's not leaking, but who knows what the PO did if anything.

The port on the MC has a bleeder plug in place of, what I presume would be, the switch and the switch is down on the frame rail in the brake lines. From what I've read, Ford moved the switch to the MC in '94. I'm going to get a 1.25" MC that doesn't have the port for the switch. One less thing to deal with.
 
Don. said:
Okay...I spent the afternoon gravity bleeding everything yesterday. No air and the pedal is still not what I'm used to. I'm going to go with the '97 MC. Here's another thing...is it possible that the cruise control switch could be some of the cause of this? It's not leaking, but who knows what the PO did if anything.

The port on the MC has a bleeder plug in place of, what I presume would be, the switch and the switch is down on the frame rail in the brake lines. From what I've read, Ford moved the switch to the MC in '94. I'm going to get a 1.25" MC that doesn't have the port for the switch. One less thing to deal with.
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I'm not sure ford moved the switch...Any master cylinder you see with a 3/8"-24 port is for the switch. Across many ford models will into the 2000s, there was an option for with or without speed control on the master cylinder. If the switch isn't leaking (which they do...remember that big ford recall?) then it can't really cause any issues like you're having.

Go with the later cylinder, should solve it if we've covered the other bases.

Keep in mind, the cruise control switch port has an inverted flare seat (little mountain at the bottom of the hole)...make sure the plug you use has the appropriate mating feature, or just get a switch and screw that in like it's supposed to be. Or just buy the non-speed control master cylinder which is identical except does not have the port for the switch.
 
Drove the wife unit to lunch today after gravity bleeding it all afternoon yesterday. The pedal is still going to the floor. It’ll tighten up a little, but at a light the pedal fades and gets to the floor. It holds, but it’s unsat.
Checked the bleed after lunch and there’s no air out of all four corners and at the accumulator. No leakage anywhere. I’m going to replace the MC. That’s the only variable left. Will report, and hopefully conclude this next weekend.
 
Did it work good before you started ****ing with it? If so I would assume the rear cylinder you added was bad, could have been bad from the parts store.

My other thought was a bad vacuum booster. This can cause you to have a super mushy pedal. Try hooking up a vac pump to it and see if it holds pressure.
 
The brakes were ****tier when I got it…barely worked at all. I replaced a torn check valve grommet on the booster. It holds vacuum just fine. The cylinder was replaced as well as the hub seal and both sets of shoes due to a leak on the one side. I was in there so I did it all instead of having to go back in and **** with something else again. The brakes are the best they’ve ever been since I got it a few months ago, but they’re still ****.

Speaking of ****, I replaced the lower radiator hoses yesterday, as the one at the radiator was about to burst. Whoever the ****sucker at Ford that decided to put the oil cooler in the place it’s in, needs his ass beaten and kicked in the balls afterward.
 
Right_side_up said:
Did it work good before you started ****ing with it? If so I would assume the rear cylinder you added was bad, could have been bad from the parts store.

My other thought was a bad vacuum booster. This can cause you to have a super mushy pedal. Try hooking up a vac pump to it and see if it holds pressure.
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A wheel cylinder is a tube with 2 seals. It's either working or it's leaking...those are really the only 2 options (or rusted solid, but that's not the case if it's new)

A bad booster will cause the opposite of a mushy pedal
 
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Don. said:
The brakes were ****tier when I got it…barely worked at all. I replaced a torn check valve grommet on the booster. It holds vacuum just fine. The cylinder was replaced as well as the hub seal and both sets of shoes due to a leak on the one side. I was in there so I did it all instead of having to go back in and **** with something else again. The brakes are the best they’ve ever been since I got it a few months ago,
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Are you sure you have the shoes adjusted out to the drums properly? If they aren’t just barely dragging you’ll use all your pedal travel making up the slack.
 
JR4X said:
Are you sure you have the shoes adjusted out to the drums properly? If they aren’t just barely dragging you’ll use all your pedal travel making up the slack.
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My first car was a ‘62 Bel Air in the ‘80’s with drums without self-adjusters. I got to do it every 2500 miles with the oil changes. The shoe retainers on this F350 are as ****ed up as the oil cooler, but it didn’t keep me from setting them right.
The culprit revealed itself this afternoon after a test drive followed by replacing the rear fuel pump and filter. There is fluid coming from between the MC and the booster. The new MC is scheduled to deliver this Wednesday.
 
If the pedal is going to the floor while your foot is on the pedal and there is no fluid on the ground, then you have a master cylinder or booster issue.

What is this vehicle? You said 93? is it a diesel?
 
It’s a 93 with a 460. Fluid started coming from between the MC and the booster yesterday. The new MC will be here this week.
 
To conclude this edition of STUPID PREVIOUS OWNER TRICKS, I’ll start by saying the 1.25” MC cured the ****ty brakes. The new MC doesn’t have the CC kill switch provision and bench bled perfectly.
I began the autopsy of the old MC and this is what NOT TO DO when you don’t have the MC mounted switch.
1. Do NOT use JB Weld to seal the cut off line from the donor fitting to plug the port. (Removed prior to pics)
B. Do NOT use a screw to try to seal the cut off brake line installed in said port.
iii. Do NOT get your panties in a bind when you consult with the fine brethren at irate4x4, when in doubt, AND are called a dumb **** for not checking the PO’s ****ty work as advised.:flipoff2:

The brakes now stop this POS and I am able to stop it by not pumping the **** out of the pedal 1/4 mile before needing to stop. Let the insults begin!
 

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The thing came out of Missourah, so I kinda shoulda known, lol!
 
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