My Truck would stop but not like I felt it should. Pedal was soft and the front brakes would smell got. I needed an upgrade. Changed rear axle complete with fresh brakes. I pulled it from my 460 truck and it had a good pedal and stopped good. I did a chevy conversion on the front with slotted rotors and all. Well same deal. Soft pedal and hot fronts. I'll replace the mc and valve later this week. Landed myself in the va hospital for another dirt bike crash today. Anyway what's your thought since I can't wrench today. If I don't like your answers I'll start a new thread

 

It sounds like you have air in the system someplace, could even be in the RABS valve.

Master cylinders from 1996/1997 F350's have a larger bore size and offer better performance over previous years.

 

That's good to know about the bigger bore. I do think maybe it's air also but I've bleed it but who knows maybe one more time

 

What do you mean by chevy conversion on the front?

 

I used a kit from lugnut4x4. It uses 3/4 ton chevy rotors and calipers.

 

Why did you do the Chebbie front brake conversion? Did that KP front axle have drum brakes originally?

There is an order to bleed the system; RR, LR, RABS, RF, LF.

Keep in mind, just because a part is new, doesn't mean it's not defective. Especially master cylinders.

 

If the fronts are overheating it is indicating that the brake bias is incorrect (proportioning valve) (possible caliper(s) drag) or the rear brakes are not adjusted correctly or are non-operational/frozen.

Correct pedal height comes as a result of properly adjusted rear brakes, especially drum (considering sound hydraulics).

 

Ok...... But why?

 

The king pin 60 I bought came from a mud race buggy. It had no brakes at all on it and it was cheaper to buy the lugnut kit than to piece together the factory stuff. Plus people were saying that it was a better setup. I blew my shoulder out this weekend and haven't had a chance to dig in to it yet to see what's going on with it. I can tell you this. I can't spin though the rear brakes. Even at 20lbs of boost it holds till I release then it blows the tires off so they do work .

 

Okay, what we know; rear axle was swapped, brakes were good after swap. Chebbie conversion done to front, brakes get hot and mushy pedal.

So, Chebbie calipers are single piston and Ford calipers are dual piston. I'm pretty sure the Chebbie setup is smaller, i.e. smaller diameter rotors and lower swept surface for the pads. The factory Ford setup will not work as hard as the Chebbie setup to get the same amount of braking effort because it's more robust.

Mostly that Chebbie conversion is meant to run 15" wheels on an 8-lug axle.

Does the RABS still exist or was it removed for racing?

The statement about the rear brakes holding under 20 lbs of boost says the rears are working correctly. At this point, since the symptoms seem to point to the front brakes, I would proceed as follows;

Check front rotors for runout. Warped rotors will push the pads back, causing a soft pedal. Check flex hoses for swelling when the brakes are applied.

Do some due diligence and see what size MC piston bore the Chebbie calipers were originally paired to, then compare with Ford MC sizing to come close when replacing the MC.

Make sure rear brakes are adjusted properly so there is ever-so-little drag on the drums when spun by hand.

Install new MC and pressure bleed the system. Harbor Freight sells a pressure bleeder for cheap. After that, I don't know what to tell you. Sometimes mix and match doesn't match. Just the nature of the beast.

 

That's all a good point about the single to dual caliper conversion. I didn't do any testing or measuring but the amount of fluid displacement was said to be the same. 2 small pistons to one large. I feel better today so I'm going out to figure it out.
Edited for my bad spelling
The front brakes were getting hot before the swap. So basically it's doing the same with all new or different stuff. Only original pieces are the mc and rabs. All flex lines are braided stainless. I'll get a new master cylinder on my way though town. I'll post back later on what I find

 

Turns out I had a new ford 1.125 master cylinder on the shelf. It came with a parts truck I got awhile back. That fixed it