Dad needs help

So my Dad has a 86 f250 4x4.   My dad and I are just stumped we cant figure this out.  The truck has a new brake booster replaced like 3 years ago,  new front calipers and new brake pads and rotors,  just replaced the master cylinder,  the drums shoes are fairly new because we dont drive the truck often drums were turned also the rotors were turned.  For the life of me it has the slowest reacting brakes it like you Emergency stop and it acts so slow I'm not saying I want it to brake like a new car but it has to better then what its doing.  We bled the rear and we bled the fronts when we replace the rotors I'm not sure what else could it be or what I'm doing wrong.  

How Is the multifunction valve (aka proportioning valve/brake switch)?

You know you have to hold the pin/button while bleeding a dry system, right??

No I didnt.  I've always just done it the way dad showed me press the brake 3 times crack the bleeder and do it until the brake pedal is firm but the pedal is only firm when the truck is off as soon as it running it feels spongy.

I don't know if that procedure is written up somewhere here on the forum, and unfortunately my '87 truck is the first year of the RABS system and updated master cylinder so I can't take a picture for you.

I know Gary likes pressure bleeding the brakes on his trucks.
Let me see if I can find some documentation

You might check under Documentation/Driveline/Brakes/Overall/General Brakes Service.     https://www.garysgaragemahal.com/brakes1.html

I'm going to look for a thread that directly addresses making sure the pressure differential valve is bled.

Might look at some of these

https://forum.garysgaragemahal.com/Proportion-Valve-Blues-tp2789.html

https://forum.garysgaragemahal.com/86-F350-1-ton-Brake-bleed-procedure-tp65878.html

https://forum.garysgaragemahal.com/Brake-pedal-low-what-now-tp43116.html

https://forum.garysgaragemahal.com/Spongy-brakes-that-react-slow-then-are-good-tp42404.html

You are very helpful, Jim!

I don't know that any of those threads ever gave solid resolution to the issue.  🤔.
And like I said, I have the later Master cylinder and a RABS module under the driver's seat.

You got any ideas David?

Jim the General Brake Service document does have the bleeding instructions.  They start on Page 12 with bleeding the master cylinder, which I'd recommend doing first to ensure it doesn't push air into the system, and then proceeds on to tell how to bleed at each wheel.

Thank you guys for all your help.  I told dad tomorrow I would take a look see if I could figure this out.  Again guys I'm grateful and I appreciate you guys!!!

Fordboy300 wrote

drums were turned also the rotors were turned...

Are there shops out there still turning drums and rotors? I can't even imagine asking a shop around here...none of them would even know what I was talking about lol.

Heh yeah its a local parts store not a chain parts store.  The only one in town that I know of that cuts rotors and drums they do flywheels too