Brake woes

The_Josh_Bear

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No problem. Just remember we expect it to be worse than before, that would mean the pv is atleast somewhat working. If its no different than before or barely different, something is wrong with the pv.

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Will do!

I will look and see if I have that little brass fitting. If you go back and check your shoes, it should be dusty and dry back there. If it's black and greasy looking, and the shoes have a shine to them, I would suspect they are contaminated.
Yep I've pulled them 3 times during this whole thing and each time they are dry and dusty.
They also squeal/screech a little since they are working so hard!
 

The_Josh_Bear

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Well boys and girls, I gutted the PV and took a spin. No change. Time for a new PV!

Although it also might be a perfect time to install an adjustable PV. Something like this:
https://www.summitracing.com/parts/...GW9Dgh7Fu0VwJMau_NnfT4efurrGS8K8aAqrLEALw_wcB
Thoughts?

I guess for my application it doesn't make a ton of sense, since I tow but only up to about 4,500lbs plus a 9.5ft cabover camper. Trailer has brakes.
 

79jasper

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Its It's interesting to see the update in information. Previously everyone called that a residual valve.

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The_Josh_Bear

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So today the mailman brought me a shiny new Motorcraft PV. I installed it and took a spin, but no change in brakes. The rears still lock up on dry pavement under medium braking. ARRRR.
-cuss-cuss-cuss

Ideas? Could I have gotten the most grippy shoes NAPA has ever put out and for some reason they are too much?

Also, while driving around with the previous PV gutted, it sprung a leak and I began loosing pedal and brake power and it wasn't long before the pedal was nearly on the floor. Thankfully I was near my home and it was no biggie to jump out and inspect, then drive home.
My question is, why won't the pedal still have plenty of resistance with the fronts still fine and hooked up? They are on separate hydraulic systems, right? This is a pretty big safety issue for me and I can't believe two separated hydraulic systems both fail to work if one has a leak.
 

The_Josh_Bear

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I tried googling it for the fourth time and it's a tough string of words to search but I sort of found an answer on the separate hydraulic systems thing. Here's what I found:

"Dual master cylinders are configured to operate two separate braking systems. The brake booster push rod engages the primary piston first(this is the rear brake). The secondary piston is normally engaged by hydraulic pressure generated by the primary piston. In a conventional arrangement, the front and rear axles operate as two separate systems." Found at this website: https://www.tomorrowstechnician.com/undercover-taking-a-brake-to-examine-master-cylinders/

So if the primary piston looses all hydraulic pressure, it fails to activate the secondary piston much and hence the total loss of brakes when the rears are leaking and the sensation everyone hates when the RABS valve dumps pressure and the pedal falls to the floor. Finally! Man you'd think they would design them a little better than that...
 

hacked89

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It cant be many things. Unfortunate it wasnt an easy swap of the pv.

1. Contamination like Franklin said - you mentioned they are new
2. Improper adjustment - you verified the adjustment
3. Worn/parts issue in the drums- this all new
4. PV sending excessive pressure - new pv

I've never seen shoes be too grabby from a parts store but theres always a chance.

The only other thing that I dont trust in your setup is the modified RABS with the spring removed if something happened to the valve and its holding pressure to the rear.
On my truck I did the f450 delete of the rabs.



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The_Josh_Bear

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It cant be many things. Unfortunate it wasnt an easy swap of the pv.

1. Contamination like Franklin said - you mentioned they are new
2. Improper adjustment - you verified the adjustment
3. Worn/parts issue in the drums- this all new
4. PV sending excessive pressure - new pv

I've never seen shoes be too grabby from a parts store but theres always a chance.

The only other thing that I dont trust in your setup is the modified RABS with the spring removed if something happened to the valve and its holding pressure to the rear.
On my truck I did the f450 delete of the rabs.



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Thanks man, well said. Looks like since the PV gutting and then swap didn't change anything I was never even getting to the PV threshold and it wasn't activating in the first place, so definitely something else amiss, like you said perhaps the shoes or the RABS. I also don't trust the RABS. Though it doesn't seem to be the issue since when I back off the shoes there is more pedal travel, they just lock up a bit later but still lock up.

I think I'll swap the shoes first to some cheap Orielly ones and then if not that bypass the RABS. I saw in another thread you list the part sizes for the bypass hardware so I'll have to look that up and order those bits or hope my NAPA has them in the back, they are pretty big with a machine shop.
 

hacked89

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Thanks man, well said. Looks like since the PV gutting and then swap didn't change anything I was never even getting to the PV threshold and it wasn't activating in the first place, so definitely something else amiss, like you said perhaps the shoes or the RABS. I also don't trust the RABS. Though it doesn't seem to be the issue since when I back off the shoes there is more pedal travel, they just lock up a bit later but still lock up.

I think I'll swap the shoes first to some cheap Orielly ones and then if not that bypass the RABS. I saw in another thread you list the part sizes for the bypass hardware so I'll have to look that up and order those bits or hope my NAPA has them in the back, they are pretty big with a machine shop.
Anytime. My recommendation is to get the bypass off an f450 which you can find what it looks like in my build thread. It bolts right to holes already in your frame. There was none in PA so I walked a guy through it over the phone that was in a junkyard in Iowa and he shipped it to me.
You might have better luck in WA, I see better shape trucks there.

If not, like you mentioned I posted how to make your own in another thread.

Goodluck man keep us posted.

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The_Josh_Bear

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Anytime. My recommendation is to get the bypass off an f450 which you can find what it looks like in my build thread. It bolts right to holes already in your frame. There was none in PA so I walked a guy through it over the phone that was in a junkyard in Iowa and he shipped it to me.
You might have better luck in WA, I see better shape trucks there.

If not, like you mentioned I posted how to make your own in another thread.

Goodluck man keep us posted.

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Ok that's smart, I was thinking I'd have to find it myself and my local yard is 45 mins away and not worth the drive or time but having a yard pull one makes total sense.
 

PROFG

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Check RABS Delete thread for parts from Advance Auto and hose from Amazon that fit a 94 F350. Total about $20 and no pipe threads or searching thru truck graveyards. YMMV
 

The_Josh_Bear

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Ok so today I pulled the NAPA shoes and threw in the cheap Orielly shoes. A world of difference. You can tell they haven't bedded in yet so they are really weak now as opposed to grabby. But whatever, I'll see if they get any better in the future. Something about those NAPA shoes. So strange.

But then again the NAPA shoes performed great for a while then started getting funky on me after a few weeks of DD'ing. I'll keep an eye out and see how it goes!

Thanks to all who helped!
Joshua
 

aggiediesel01

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Since this has been so troublesome for you with no clear resolution here's one additional idea for consideration. The F250s were offered with 2" or 3" rear shoes right? Is it possible that either the rear wheel cylinders or the master cylinder is sized for the shoes you don't have? I don't remember if there was a difference in the hydraulics but I do remember always being asked which shoe size I had.
 

The_Josh_Bear

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There is a difference, 2.5" vs 3" but I have the 3" so I doubt if there was a difference in wheel cylinder or MC that it would affect my 3" shoes in the way I was experiencing. I can't rule it out, wheel cylinders are so cheap and they aren't exactly name brand, but the issue started with a different MC and was fine before that, all with the same MC.

I'm starting to think the NAPA pads were just wrong or somehow very slightly contaminated, or both. They also wore funny with the top 1/4 or 1/3 clearly worn, the bottom 1/4 or 1/3 clearly worn and the middle bit untouched. On shoes that were ultra grabby and had plenty of brake dust in the drum. So they weren't the same kind of round that the drum is, dunno if that's common or not.
 

cozinsky

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Last fall I replaced my worn shoes with Napa shoes and wheel cylinders. I cleaned and lubricated everything and replaced all of the hardware. Ever since then the rear brakes have been extremely aggresive and will instantly lock up if I don't lightly ease into the pedal. I've pulled the drums back off and checked everything and readjusted them but it still does it. I'm blaming the lining material on the shoes. They were never this aggresive before I replaced them and everything is assembled correctly. I'll probably try a different brand. Going to try selling it pretty soon and its no good this way.
 

The_Josh_Bear

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Last fall I replaced my worn shoes with Napa shoes and wheel cylinders. I cleaned and lubricated everything and replaced all of the hardware. Ever since then the rear brakes have been extremely aggresive and will instantly lock up if I don't lightly ease into the pedal. I've pulled the drums back off and checked everything and readjusted them but it still does it. I'm blaming the lining material on the shoes. They were never this aggresive before I replaced them and everything is assembled correctly. I'll probably try a different brand. Going to try selling it pretty soon and its no good this way.
SO I'M NOT THE ONLY ONE BUAHAHAHAHAHAHA! Thanks for the confirmation!
 

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