67-69 Corvair Brake System Differential Pressure Indicator Switch Rebuild.

[Lane66Monza]

While searching the Internet, I found this procedure for the Corvair Brake System Differential Pressure Indicator Switch and its Parts Kit in a couple different places. I have put them together and cleaned them up for easier reading. This switch block may be on earlier Vairs, if installed by owners. I have put it on both my 66 Vairs with a red light by my park brake handle light switch.

I have credited the original author of the procedure at the beginning of the procedure.

Corvair Brake Systems Pressure Indicator Switch.jpg (36.19 KiB) Viewed 241 times

switch block.jpg (48.87 KiB) Viewed 320 times

Corvair Brake System Pressure Indicator Switch Assembly Rebuild.pdf

(843.8 KiB) Downloaded 12 times

[toms73novass]

Nicely done Al.

[MtnVairMike]

Al is one of the best on how to articles.

[Lane66Monza]

I redid the Clarks Disc Brake Kit Installation procedure for Clark's. I also posted it on ccf.

Anyone want it posted for reference on the forum? I don't know if Clarks is using my revised procedure.

[Frank DuVal]

FYI it is just a switch block, that will close the switch to light the dashboard warning light when a differential of pressure is detected between front and rear brake plumbing, no pressure differential valving inside as found on some other cars. Yes, I know, everyone calls it a differential pressure valve, I am not picking on Al who provided a GREAT write up. Think of my comment as Spell Check of the technical variety!

Great picture! Shows exactly how the switch works.

[Lane66Monza]

Part name in procedure is what original writer called it. No offense taken, Frank. I expected that comment to be posted once I posted the document.

What does Chevrolet call it in parts book or shop manual. Official manuals of our cars is Bible for parts nomenclature. I will fix title and procedure to proper name of component

[Lane66Monza]

Here is what I found at the bottom of GROUP 4.000 TRANSMISSION - BRAKES. Switch is not illustrated in the section.

'
So I will change the procedure to what Chevrolet calls the item. Just remember, you have to remember what other people call the part to get the parts you need to fix it.

Now the hilarious part of the document. Author interchanges his given part name and true part name in the parts documents he made. It is a valve in the repair procedure.

========================================================
1967 - 1973 GM Brass Brake Pressure Differential Valve Rebuild Kit

Muscle Car Research is proud to offer a rebuild kit for the brass pressure differential switch used

1967 - 1975 GM Brake Pressure Differential Valve Tube Seat Kit
SKU: gm-pd-valve-tube-seats-1 Price $10.00
The pressure differential valve and switch used on
=========================================================

Good luck, but don't get confused as the breakdown photo shows what the assembly really is. It is a switch.

I will get switch repair and parts document cleaned up for the Vair family members that will use it.

[Lane66Monza]

Frank:

Procedure now has correct name for the component. I have changed it throughout the procedure and also in my first posting and this discussion's title.

I am glad I went back into the procedure. It was not complete. It had no disassembly info. I found the "Autopsy" report on a "valve" the Author did on one and added its teardown info to our document. So now the document has beginning to the end repair instructions for this switch assembly.

[Frank DuVal]

Just remember, you have to remember what other people call the part to get the parts you need to fix it.

RIGHT! That's why I just wanted to add it was a switch, for information purposes, knowing most people call it a valve. We have so many colorful names for parts , is that a drag link, a center link, a center tie rod ... top shroud, fan shroud, turkey roaster.... pitman arm bushing, center link (here we go again...) bushing (which it really is!). And add in my and others misspellings of parts it is amazing we even get proper answers to searches and questions.

I've been known to use different names for the same part in the same sentence.

I meant to use this emoji for your post's switch photo:
It really shows what is going on inside.

[Lane66Monza]

Thanks for the help Frank. I found the switch guts photo online. I liked it because it explains without words what is happening inside the switch housing (or as you call it switch block)

[Richard]

No one wants to call it a distribution block? Distribution block / pressure differential switch / valve. Whatever .

Part of the problem may be that some of the pressure differential valves actually use a separate switch. In the photo, the item circled in green is an actual switch. The electrical ground path for the switch is through the threads on the body of the switch itself. This type of switch is generally used on pressure differential switches that are part of a combination valve.
The little nipple or plunger on the end of the switch operates the internal switch contacts. The brass piston inside the pressure differential valve must have tapered shoulders in order to push the nipple back inside the switch.
Laying on the distribution block is a steel pin with a nylon sleeve and a steel hex nut. When unequal hydraulic pressure pushes the piston left or right, it makes contact with a steal pin. Current flows from the pin, to the piston and through sprngs to the brass seat, to ground. The pin and the brass piston are the actual switch contacts. The brass piston for this type switch has square shoulders. The other type of switch requires a brass piston with tapered shoulders in order to push the plunger into the switch.

I posted this picture years ago with the orange and yellow wires, showing the path of the fluid through the pressure differential valve. I was trying to explain and show the path through this valve had nothing to do with the flow through this valve into a metering valve on one end of a combination valve and the path through to the proportioning valve which would be on the other end. A combination valve has three separate valves with three functions that are completely independent from each other housed inside the same device. A difficult concept for many.

That brass seat removal tool that "Muscle car Research" shows is ridiculous. Turn a sheet metal screw into the brass seat and pry it out with a screwdriver. You shouldn't need more than half a turn on the screw and it will allow you to easily pry it out with little damage to the seat . The image below is actually prying a brass seat out of an MC in order to remove a residual pressure valve. Same seat, same proceedure.