Topic: 1967 brake pressure warning light / pressure valve

[Hipo giddyup]

 The brake warning light on my 67' coupe had been on for sometime and I have had it disconnected at the brake warning light switch on the distribution block. The brakes work fine of course, but after looking into this issue, it sounds that the pressure differential valve within the distribution block is offset (as if you lost pressure to one corner of the braking system) and needs to be recentered to reset this warning lamp. This typically happens when you perform brake bleeding or repair work like this on the brake system. Does anyone have a description or can explain how to reset/recenter this pressure valve??

Attached is what I found on the internet but might not directly apply to the 67' Mustang application.

[BKnapp]

That appears to be exactly how I have done it. Typically when I have bled my brakes, I start at the rear and end at front drivers side. So, now you have to very slightly open the fitting going to the back brakes and apply slight pedal pressure. Effectively you are creating a very small leak, which will cause the valve to move back to neutral. However, if you open it too much or press too hard, the valve will move past neutral and indicate a problem with the rear system. In this case you would need to repeat the process, using the front system.

I have always wondered if it is necessary to open the "outlet fitting at the distribution block". In a 390, that is not an easy fitting to get to. Assuming you were bleeding the brakes and finished in the front, could you go back to one of the rear bleeder valves and crack that open for the same effect?

Sometimes the valve will be stuck and have heard other people suggesting a hard sharp stomp on the pedal can dislodge it. I will be interested in others input.

[67gtasanjose]

Short BEST answer is rebuilt the block. Kits are available.

The seals break-down and so do the internal springs. This valve was INTENDED to center itself when new or like new.

Now, others might mention how to center the valve, there is a bolt/fitting made to screw into the switch location temporarily while bleeding, it prevents movement while bleeding the system. That would be the "alternative way" IMHO

[Bob Gaines]

Short BEST answer is rebuilt the block. Kits are available.

The seals break-down and so do the internal springs. This valve was INTENDED to center itself when new or like new.

Now, others might mention how to center the valve, there is a bolt/fitting made to screw into the switch location temporarily while bleeding, it prevents movement while bleeding the system. That would be the "alternative way" IMHO

+1. NPD sells the centering pin fitting i believe.

[ruppstang]

+2 NPD has them, I made my own.

[Brian Conway]

BKnapp has got it.  I never open anything on the valve body but you do need to plug the sensor back in.  Essentially a balancing act using the front right brake cylinder bleeder and the right rear brake cylinder bleeder.  One person slowly and firmly pressing on the brake pedal and the other letting air/fluid slowly out of the front or rear cylinder.  The person on the brake pedal lets the other one know when the light goes out and that's the time to close the bleeder.  You'll get the hang of it.  Of course the valve body just may need a rebuild.  Brian 

[Bob Gaines]

BKnapp has got it.  I never open anything on the valve body but you do need to plug the sensor back in.  Essentially a balancing act using the front right brake cylinder bleeder and the right rear brake cylinder bleeder.  One person slowly and firmly pressing on the brake pedal and the other letting air/fluid slowly out of the front or rear cylinder.  The person on the brake pedal lets the other one know when the light goes out and that's the time to close the bleeder.  You'll get the hang of it.  Of course the valve body just may need a rebuild.  Brian

Keep in mind that no brake fluid comes out of the sensor switch opening . The sensor switch is isolated from the fluid on ether side of the depression (for sensor pin) in the piston by rubber o rings .

[Hipo giddyup]

 Thanks for all the responses. I do know that it is dry under the warning switch so the seals apparently are still good in the block. I will try bleeding the rear brake first with gentle  pedal pressure to see if it centers the pin again. If that doesn't work I will try the front brake, then ultimately I might have to rebuild the block. I will hopefully attempt this this weekend and post  my results. 

[Bob Gaines]

I hope you are luckier then I. When ever I have had the problem on a original system it is the result of the piston sticking to far forward or too far backward and is stuck because of corrosion inside. Rebuilding is the only remedy. The only reason for me posting is so that you don't spend too much time going back and forth trying to balance it. When the cars were new or on a completely restored system the bleeding scenario was a typical and more likely solution. After 50 years the more likely solution on a otherwise original unrestored distribution block is to rebuild the block. Hopefully you will break it free and not have to rebuild.

[ruppstang]

I hope you are luckier then I. When ever I have had the problem on a original system it is the result of the piston sticking to far forward or too far backward and is stuck because of corrosion inside. Rebuilding is the only remedy. The only reason for me posting is so that you don't spend too much time going back and forth trying to balance it. When the cars were new or on a completely restored system the bleeding scenario was a typical and more likely solution. After 50 years the more likely solution on a otherwise original unrestored distribution block is to rebuild the block. Hopefully you will break it free and not have to rebuild.

+1 The only time I have been able to reset it was after I rebuilt the block and pushed it off bleeding the system.
Good luck

[Hipo giddyup]

Thanks guys. So then my next question is what would you mean as "rebuilding"? What components of the block are available, the distribution valve seals?? are they still available?? Or are you simply referring to taking the block apart for a good cleaning / removing any corrosion? The car has never sat for many months/years without being moved/used even when I was restoring it. But still, it is 50 years old. What are the chances the warning switch is bad or could there be an elecrtical issue, even though the offset of the valve is easy enough to do.?

[67gtasanjose]

Pretty sure most places carry the kit, like NPD, Virginia Mustangs, West Coast Classic Cougar etc.

Some carry the kit for the distribution valve WITH proportioning valve,  I think they are about $30

NPD carries just the distribution block kit for example: https://www.npdlink.com/store/products/mustang_rebuild_kit_brake_pressure_differential_valve-169774-350.html

PDF file on building BOTH: (I would do both while the system is open) https://d2zl5tj7gmc4tr.cloudfront.net/store/content/download/instructions/2b257-4ak.pdf

[Hipo giddyup]

Thanks for that info and the links. My car is 4 wheel drum so I only have the distribution valve to rebuild. Looks like that is the only and best answer at this time, just rebuild it! I'm ordering the kit today as well as the locking pin to keep the valve in place when you re-bleed the brakes. I'll try and take some pics of what I am dealing with to maybe help others. (But sometimes I get into a groove and next thing you know, I have already completed the job before I remember to get my phone out!  )

[Hipo giddyup]

I also found that the kit number you linked is not correct for my application. Since mine is drum brakes, I will need kit # 2B257-3A.

[mtinkham]

I could not get the spool valve unstuck on the car I was restoring. I soaked it in an array of liquids for three weeks. I tried hot water, brief heating with a propane heater, Ice, 120 lbs of Compressed Air (Caution!!!!I restrained with a vice and clamps to prevent getting punctured by the projectile), tapping, hammering, and even swearing. Nothing moved the valve.

There was no way to attach anything to the valve and the opening was too small for needle-nose pliers. I contemplated drilling out the back end, but decided not too.

The application was a July 67 Coupe, 4 wheel drum, manual brakes.

Reinstalled the valve with my hopes and expectations smashed...left wire disconnected.

A quick continuity test can be performed between the brass case and the terminal.  If the spool valve has shifted off center it completes the circuit to ground causing the light to come on.

This was the only thing that I gave up on during this 7 year restoration. The circuit does not provide any advance safety measure, as it is the loss of brake pressure that causes the light to come on....you will feel the loss of pressure simultaneously.

Completely and Utterly Defeated,
Mark