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.

[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

[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

[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

[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.

[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.

[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]

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....

[Jason Banks]

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

[Chaparralman1974]

Originally Posted by Jason Banks

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

Thanks for confirming Jason! I ordered the PR111 from inline tube.


I have another question though, while I am thinking of it....


I have always done a bench bleed of new master cylinders, but that has always been using existing lines and components where fluid is still in there. Seeing as how my entire system from master cylinder all the way to wheel cylinders are new and have no fluid in them yet, do I still need to bench bleed the master cylinder? Or do I just fill it all up with fluid and then bleed the entire system? I plan on getting a self bleeding kit to do it all.


Clay

[Jason Banks]

I had hell getting a good bleed on my K20 and also had hell getting a master cylinder that would work.

I would go ahead and bench bleed the master cylinder.

For totally new systems I have historically bench bled the master, used the harbor freight vacuum bleeder(https://www.harborfreight.com/brake-...der-92924.html) to suck fluid through to all wheels, starting at drivers rear, moving to pass rear, pass front and finally driver front.

Then, nothing I have found beats having a helper pump and hold, while I crack bleeders at every wheel....

I even bought the Motive Products power bleeder - https://www.summitracing.com/parts/MVP-0115 - It ends up being a PITA to remove from the master cylinder to add fluid, so I have just defaulted back to pump and hold with a helper.

[Jason Banks]

BTW, what are you using for master cylinder?

[Rust_never_sleeps]

I've had an easier time syringe bleeding the MC than bench bleeding with a screwdriver.
Working alone sucks, so much faster and easier to bleed with a friend. Borrow or rent one if you can
Vacuum bleeding the back drums was a beast with two different methods, but I didn't use the Hobo Freight type
Motive works fine, but it's messy and awkward as mentioned

[Chaparralman1974]

Originally Posted by Jason Banks

BTW, what are you using for master cylinder?

Thanks Jason!

I just ordered a master cylinder from Rock Auto for it. I will go ahead and bench bleed it. I am still waiting for the distribution block to show up and then I can put it all together. I have the lines run and just need to finish snugging up some fittings.


Clay

[Chaparralman1974]

Originally Posted by Rust_never_sleeps

I've had an easier time syringe bleeding the MC than bench bleeding with a screwdriver.
Working alone sucks, so much faster and easier to bleed with a friend. Borrow or rent one if you can
Vacuum bleeding the back drums was a beast with two different methods, but I didn't use the Hobo Freight type
Motive works fine, but it's messy and awkward as mentioned

Syringe bleeding sounds interesting.....I will have to research that one.



Clay

[Jason Banks]

I guess I'll tell you my saga. When I got the truck it had a master cylinder on it that had a GM part number cast into it. So I took it apart and got a rebuild kit for it. Discovered it was a 1 inch bore not a 1 1/8 bore. But proceeded anyway, cerakoted the outside in a cast iron color. Put it back together and it leaked internally. Got another (I think raybestos brand 1 inch bore). Brakes didn't work worth a darn. So... I had a Wilwood 1 1/8 bore and threw it on. Still didn't like the brake feel and it may have been a bleeding problem because there are numerous stories of the wilwood being hard to bleed. Ended up getting this - https://www.amazon.com/dp/B0BJZ4LY1K - basically the cheapest stock looking one I could find and it works amazing. I didn't take it apart to confirm but I believe it has the built in residual valves that a stock one would have had.

[Chaparralman1974]

Originally Posted by Jason Banks

I guess I'll tell you my saga. When I got the truck it had a master cylinder on it that had a GM part number cast into it. So I took it apart and got a rebuild kit for it. Discovered it was a 1 inch bore not a 1 1/8 bore. But proceeded anyway, cerakoted the outside in a cast iron color. Put it back together and it leaked internally. Got another (I think raybestos brand 1 inch bore). Brakes didn't work worth a darn. So... I had a Wilwood 1 1/8 bore and threw it on. Still didn't like the brake feel and it may have been a bleeding problem because there are numerous stories of the wilwood being hard to bleed. Ended up getting this - https://www.amazon.com/dp/B0BJZ4LY1K - basically the cheapest stock looking one I could find and it works amazing. I didn't take it apart to confirm but I believe it has the built in residual valves that a stock one would have had.

I don't remember off the top of my head which one I got from Rock Auto, but I know it was a cheaper one. I am watching some videos right now on YouTube on the pneumatic power bleeders as well.....I have always bled brakes using the buddy method....I have never tried one of the new self bleeding setups, but it looks promising.

I am still in the middle of trying to get the bends in the front lines that go across the front cross member bent correctly. I should have done it before putting the truck back together. Working underneath on my back is a PITA to get the lines to route where they were originally. It isn't a huge deal, but my OCD is kicking in and I want it to look completely factory underneath. LOL!

I am very close to being able to move the truck out of the garage under its own power and that will be a huge milestone.

I did notice an oil leak in the driver side rear wheel the other day though....I am not sure if the oil seal went bad or not, but there is a small amount of gear oil that is dripping out of the drum so I will likely have to take that apart and fix it before driving anything so that the shoes don't get wasted....oh well, it is always something with these trucks. :-)


Clay

[Jason Banks]

Man there is always something. Not sure if I learned it from your build thread, but there are 2 types of seals for the rear. The stock kind and another that rides on a slightly different/fresher surface to seal.

Your so close, has to be a great feeling.

I tried to look up the different seal, but I'm out of time. It might be listed on Torque King...

[Rust_never_sleeps]

Originally Posted by Chaparralman1974

Syringe bleeding sounds interesting.....I will have to research that one.



Clay

It's actually recommended by some MC mfrs
I use "dental irrigators" with the skinny bent tip. They're cheap and versatile