'76 K25 brake issue

[76JimmyBlue]

I am having a weird issue with the brakes in the '76. The brakes feel like they should be stiffer, but have not had a problem ever being able to stop the truck. However, occasionally when coming to a stop slowly and dragging the brakes I've had the pedal suddenly go to the floor. It happened one time recently where I was sitting at a stop light and felt the brake pedal suddenly lose pressure. One pump and it was back. Could it be air trapped in the system? The only other idea would be the master cylinder is going bad, it has occasionally wept fluid from between the m/c and the booster. Again this isn't a consistent issue of losing pressure on the pedal. Any help would be greatly appreciated.

[jdaniel]

sounds like the master is going bad! Block off the 2 ports and press the pedal, if you get movement the master is bad.

[76JimmyBlue]

I thinks so too. It was leaking again the other day. I want to try and rebuild the master, when I go looking for a rebuild kit what info would I need? She's a 3/4 ton, 4x4 camper special and according to the option list has the heavy duty braking system.

[SCOTI]

Originally Posted by 76JimmyBlue

I thinks so too. It was leaking again the other day. I want to try and rebuild the master, when I go looking for a rebuild kit what info would I need? She's a 3/4 ton, 4x4 camper special and according to the option list has the heavy duty braking system.

That should be all you need to get started on searching for a kit. Manual/power versions might be diff as well (bore size).

[76JimmyBlue]

I went to NAPA and they can't get the kit and they say the manufacturer doesn't make it anymore. Don't know which manufacturer it was. Any other places to look?

[Dead Parrot]

Probably not enough demand for a DIY kit as most folks just buy a rebuilt MC.

[c30]

You won't find a rebuild kit but here is what I did.
I want my truck to look as original as possible. When replacing the master cylinder, it seems all I could find was a big ole squared off looking thing that did not look at all like the original. Had a single bolt on cap instead of the two wire bales.
Knowing that the bore of my original was 1", I think, I ordered a master for the correct application with the same size bore. I disassembled both, honed out the original to clean it. Then reassembled the old master with the new innerds and it's been doing fine.

[SCOTI]

Originally Posted by c30

You won't find a rebuild kit but here is what I did.
I want my truck to look as original as possible. When replacing the master cylinder, it seems all I could find was a big ole squared off looking thing that did not look at all like the original. Had a single bolt on cap instead of the two wire bales.
Knowing that the bore of my original was 1", I think, I ordered a master for the correct application with the same size bore. I disassembled both, honed out the original to clean it. Then reassembled the old master with the new innerds and it's been doing fine.

Creative 'end around' solution. Kudos for thinking outside the lines.