Wilwood 6 Piston Front Brakes Not Releasing - Seeking Advice

It's our experience that these are very sensitive to any deviation in alignment with the rotor. This would cause them to bind. Pop a front wheel off, push the pistons back in, and measure caliper distance from the rotor top to bottom, front to back, inside and outside.

It sounds like the pushrod is too long not letting the piston retract enough to bleed off. If you loosen the 4 MC bolts while the brakes are dragging that might tell you.

tsolo is most likely correct. Unbolt the master from the booster and see how much of a gap is between the two before the bolts are tightened. Dennis Quella recommends .200"-.210" I believe. If it is more, shorten the pushrod.

Ron

I used this tool to measure and grind the push rod when I installed a willwood master cylinder, I believe I have a GM Booster.

On a side note, I’ve installed a mechanical brake light switch on a flacon that was slightly pushing on the pedal and it would lock up the brakes after a few miles. Not sure what you have or if it’s in front or backside of the pedal.

Dan

I have the rod at its shortest adjustment and there is no preload.  I am doing this in an effort to resolve this issue.  Too much preload can result brake drag once the the brakes heat up from driving.  In this case there is no preload and yet a single push of the pedal makes the front brakes drag while everything is cold and even without running the engine.

I am going to try to connect the front brakes to the output on the master for the rear and see if the problem goes away.  If it does then there is likely a problem with the master.  I am not sure if I can make the line reach.  It is stainless and not very flexible.

Here is some more information.  With both the front and rear brake lines disconnected at the master, the car would not budge when I tried to roll it.  There should not be any pressure at the calipers and the car should roll.  Next I opened and closed the bleeders on the fronts and the car rolled perfectly.  This tells me the issue is likely at the calipers and not at the master.

How old are the flex lines at the calipers?

Everything is new although it sat for several years.  It never had fluid until recently.

I’ve also had the rubber inside of a brake line and act as a check valve holding the pistons out.

on aligning the brakes to the rotors you will find it hard to find shims, I ordered the shims from willwood and shims from bear brakes in Phoenix to get as close as I could. You want as close to centered with the  least deviation top to bottom, on my car there was less than .010 deviation top to bottom on all four brakes so the shims were the same all the way around.

In the case of the master used in the Pantera I am not sure of BUT in the case of the Ford master cylinders often the same master is used with drum brakes and disc brakes.

When you use them with disc brakes there is a small plastic "check valve" that you need to remove.

The check valve keeps the drum shoes from returning to the starting position and is necessary for the auto adjusters to work. You don't use them with the disc brake application and you just pry them out with a screwdriver or similar.

Did you look for that on the master?

I don't think there is a check valve in the DeTomaso replica master cylinder.

I have done some more hunting and it is starting to look like it may be the 01310A - Valve Assembly Pressure Control that is acting as a check valve.  It could also be 01316A Valve Assembly Brake Pressure (the brass block with the brake light switch).

This problem is now fixed and the front brakes are releasing correctly.  I fixed it by the taking the guts out of 01310A - Valve Assembly Pressure Control.  This is the forth or fifth of these valves that I have done such to.  This one was different because it is the only one I have worked on where the piston was not frozen and it actually moved.  The piston in all of the other valves were rusted solidly in place.  Once gutted the valve functions as an ordinary tee for front brake lines.

Nice job Steve.  01310A limits pressure to the fronts?  How does the car drive with it gutted?

I have barely driven the car but the brakes felt great.  I have been driving my 74 Euro Pantera for two years with a gutted 01310A and it stops well.  It has stock brakes.  I recently inspected the rear brake pads and observed a significant amount of wear on them.  This indicates the rear brakes are getting well used.  About 1/3 of the pads are gone in about in 2,000 or 3,000 miles.

I am thinking that most of these valves in Panteras are not functioning because the piston is rusted and stationary in the valve body in the open position and simply acting as a tee.  There is a rebuild kit for the valve but there is usually so much pitting on the piston and valve body that the valve leaks once rebuilt.  When the piston freezes it takes a lot pounding to drive it out.

Wilkinson is emphatic that the valve was never intended to affect front and rear braking performance.  He explains that its intent was to reduce pulsation in the brake pedal when the front rotors warp.

The issue is that you need to do "panic stops" to see if the rears lock up and if they do to adjust the pressure to the rears.

You can't do that on the street. You need a closed course and some time to do it safely on.

Even if you increased front braking you can't just go and increase the rear proportionally even if you knew the number. You have to find the rear lockup point then back off of that with a safety factor.

That kind of braking will cause the rear to steer and that can be lethal.

That entire brake proportioning thing was orchestrated by Ford and they feared braking that was disproportional to other production vehicles as a potentially catastrophic event.

It also involved available traction that the production tires of the time were capable of.

Also, it isn't just the brakes themselves involved. It is also the weight transfer, which is affected by suspension changes such as spring rates and shock response. Ride height also weighs in on this, so it can be complicated. You are going to need to plumb in an adjustable proportioning valve to the rears as a minimal solution.

Some race cars have that driver accessible in the cabin so it can be adjusted by the driver while the car is on the track.

Not everyone financially capable of owning a high performance vehicle was capable of operating it safely. So the unspoken Corporate decision was to reduce the braking capability. Kind of backward thinking if you ask me, but no one is asking me.

That might have involved more development time at additional cost to Ford, so I'd think that was part of the solution for a safe production car as well? Who knows the exact reasoning now? Just educated speculation on anyone's part?

Can I just say what a fantastic resource this forum is. The knowledge shared is outstanding.

I have just got 6997 back together after allot of work , a quick lap around the block and found the front brakes were binding and the center hubs were getting pretty warm. Let it sit for half an hour and it relaxes and no binding.

Everything is standard on my car with respect to brakes and it is all fully refurbished including a freshly rebuilt  01310A, the - Valve Assembly Pressure Control.

So tomorrow out it comes for some TLC !

Thanks Steve.

This proportioning valve was a perfect substitute for the original front splitter and the proportioning valve

bleeding the system was also no problem!

Thanks Lemans- Great information. Did you rerun all new brake lines when you installed it ?

I redid the front brake lines in stainless steel completely, the rear brake line I did splice halfway the sheet metal down the front trunk. The two short brake lines from the master to the proportioning valve come with the proportioning valve. I only had to re-nipple (there is a word never heard before)  the part that goes into the master!

Thanks - great information.

I have a new flaring station coming  so it looks like this might be its first job. The existing flare nuts are showing every month of their 50 years of service !

I knew I’m going to splice at a really difficult place under the car with not much room, so I went with this version…

Hi Lemans- that looks great.

It is the first time I have seen one like that.

Please forgive this post if it seems dumb.

I have been looking into the function of the Wilwood rear brake proportioning valve. There are a series of curves at various settings that can be dialled in with respect to a pressure reduction for the rear brakes to ensure they don't lock up before the front brakes do ( as I understand it .)

Yet the arrangement of the 01310A - Valve Assembly Pressure Control is derating the front brakes at the maximum fixed pressure so as to ensure the back brakes do lock up first before the front brakes ????

What is the objective - rear or front lockup first ? I would have thought rear ?

Can someone please clarify for a country boy  ?

Ideally, they would lock at the same time on a car without ABS.  

In our Panteras, if the rears lock first, the car will swap ends (don’t ask me how I know)…

If the fronts lock, you will lose your steering ability.

Rocky

Thanks Rocky. Thats is clear.