Drum Brake Pressure Switch

[Chaparralman1974]

Good morning everyone!

Does anybody know where I can get the pressure switch for a drum brake distribution block? The one in my 67 K20 is rusted and trashed. I contacted Inline Tube and they don't sell the switch seperately from the block itself. I ordered one for a disc brake setup, but it is too big.


Here is what I am talking about? Does anyone know where I can order just the swtich?

[RichardJ]

Have you checked to see which switch you have?
There are two that I am aware of for that distribution block.

One switch is in the lower part of the photo. It is self contained with a spring loaded nipple at the bottom. When the nipple is pushed IN, the ground connection for the terminal post is made through the body of the switch.

The other switch is a long steel pin, insulated from the switch body by that nylon sleeve. When the brass piston is pushed to either side, it makes electrical contact with the steel pin. The ground path is actually through the springs, because the two "O" rings isolate the piston.
This last switch can be easily cleaned up. The other switch could probably be saved be spaying cleaner past the nipple and continually operating it till it frees up.

[Chaparralman1974]

Originally Posted by RichardJ

Have you checked to see which switch you have?
There are two that I am aware of for that distribution block.

One switch is in the lower part of the photo. It is self contained with a spring loaded nipple at the bottom. When the nipple is pushed IN, the ground connection for the terminal post is made through the body of the switch.

The other switch is a long steel pin, insulated from the switch body by that nylon sleeve. When the brass piston is pushed to either side, it makes electrical contact with the steel pin. The ground path is actually through the springs, because the two "O" rings isolate the piston.
This last switch can be easily cleaned up. The other switch could probably be saved be spaying cleaner past the nipple and continually operating it till it frees up.

Hi Richard, that block looks a little different than mine....I just have the switch that screws into the bottom for the warning light. I don't believe that I have the other components....I will have to double check.


Clay

[BanjoDude]

Originally Posted by RichardJ

Have you checked to see which switch you have?
There are two that I am aware of for that distribution block.

One switch is in the lower part of the photo. It is self contained with a spring loaded nipple at the bottom. When the nipple is pushed IN, the ground connection for the terminal post is made through the body of the switch.

The other switch is a long steel pin, insulated from the switch body by that nylon sleeve. When the brass piston is pushed to either side, it makes electrical contact with the steel pin. The ground path is actually through the springs, because the two "O" rings isolate the piston.
This last switch can be easily cleaned up. The other switch could probably be saved be spaying cleaner past the nipple and continually operating it till it frees up.

I’ve been wondering how these come apart. Do you just force the whole assembly out one side, or are there clips of some sort that hold the brass caps in place? I’ve been afraid to force anything.

[loudchevy]

If this works, it's yours. I just pulled it off of my old drum/drum MC. I still have the block too if you want that

[Chaparralman1974]

Originally Posted by loudchevy

If this works, it's yours. I just pulled it off of my old drum/drum MC. I still have the block too if you want that

Hey Scott! That is it!! Yeah man I will grab it from you! Thanks man!


Clay

[loudchevy]

Originally Posted by Chaparralman1974

Hey Scott! That is it!! Yeah man I will grab it from you! Thanks man!
Clay

[RichardJ]

The brass piston shown has square shoulders and makes contact with the steel pin. The switch at the bottom of the photo would be mated to a piston that has tapered shoulders. The taper pushed the nipple on that switch, back into the body of the self contained switch.
I've not seen the one Loudchevy has pictured. It appears to be just a slight variation of the one I have shown with the long thin steel pin. The protrusion with the slot appears to be electrically insulated.

If yours needs cleaned internally, it isn't that difficult to disassemble. If you are careful, the sheet metal screw will do little damage to the brass inserts and can be reused. There is nothing in there, but two springs and the piston.
In this picture, there is a residual pressure valve below the seat, but you won't have that. They're showing seat removal for a MC, which may or may not have a residual valve.
Push the piston out with drift pin and clean with solvent and flush with brake fluid.

[Chaparralman1974]

Originally Posted by RichardJ

The brass piston shown has square shoulders and makes contact with the steel pin. The switch at the bottom of the photo would be mated to a piston that has tapered shoulders. The taper pushed the nipple on that switch, back into the body of the self contained switch.
I've not seen the one Loudchevy has pictured. It appears to be just a slight variation of the one I have shown with the long thin steel pin. The protrusion with the slot appears to be electrically insulated.

If yours needs cleaned internally, it isn't that difficult to disassemble. If you are careful, the sheet metal screw will do little damage to the brass inserts and can be reused. There is nothing in there, but two springs and the piston.
In this picture, there is a residual pressure valve below the seat, but you won't have that. They're showing seat removal for a MC, which may or may not have a residual valve.
Push the piston out with drift pin and clean with solvent and flush with brake fluid.

Hey Richard, thanks for the information....I didn't realize that there was a plunger inside. I didn't event realize that you could pull out the little brass inserts. I went ahead and did that, and the inside of mine is a complete mess....it is rusted solid. I think that I am just going to order a new block from inline tube.

The one from inline tube specifies that it is for 1/2 ton trucks. I can't see there being a difference, but I could be wrong. Do you know if the distribution blocks differ between 1/2 ton and 3/4 ton trucks? They look identical.


Clay

[Jason Banks]

Originally Posted by Chaparralman1974

The one from inline tube specifies that it is for 1/2 ton trucks. I can't see there being a difference, but I could be wrong. Do you know if the distribution blocks differ between 1/2 ton and 3/4 ton trucks? They look identical.
Clay

I bought the PR111 for my 1967 K20 and it works fine. Need to dig into the GM parts manual and see if there are different part numbers for 3/4 ton....

[70STOVEBOLT]

I have one from my ‘70 you can have if you pay the shipping. It was working when removed and it’s still connected to my Yeungling master cylinder, which is full of fluid.

[Chaparralman1974]

Originally Posted by 70STOVEBOLT

I have one from my ‘70 you can have if you pay the shipping. It was working when removed and it’s still connected to my Yeungling master cylinder, which is full of fluid.

Thank you for the offer....I went ahead and ordered a new one.


Clay

[70STOVEBOLT]

Originally Posted by Chaparralman1974

Thank you for the offer....I went ahead and ordered a new one.


Clay

Ok.

[Jason Banks]

Not sure what makes it Unique, but the 1967 valve is different than the 1970 anyway...

[Jason Banks]

Looks like all models use the same PN 3904303 for 1967 and then 68-70 use 3923719