I replaced the oil filler/breather cap on my SBC yesterday. The spot where the vacuum line comes is was broken so I suspected that it was a vacuum leak. Today when I went to drive it the brakes were extremely hard. They still work just not very well. What do I need to do to fix it. Was the leak I had "theraputic". It ran well and the brakes worked fine before. I think I should have left well enough alone. Thanks, Sam
Fixed suspected vacuum leak now have Hard Brakes
- Thread starter sblesse
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Some pictures would help.
Sounds like a problem with the brake booster or the line from it which should connect to the manifold behind the carb.
This thread has some pictures of my setup, not great, but the best I've got at the moment.
https://forum.ih8mud.com/40-55-series-tech/448066-sbc-swap-manual-steering.html
The vacuum line goes from the drivers side of the booster to the port on the manifold between the distributor and the carb.
Sounds like a problem with the brake booster or the line from it which should connect to the manifold behind the carb.
This thread has some pictures of my setup, not great, but the best I've got at the moment.
https://forum.ih8mud.com/40-55-series-tech/448066-sbc-swap-manual-steering.html
The vacuum line goes from the drivers side of the booster to the port on the manifold between the distributor and the carb.
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The old breather cap appears to have a PCV valve in the top of it. Does the broken part have a piece of metal inside of it that rattles around?
If it was a PCV valve, your idle is likely cr@ppy, and your brakes wouldn't have a a vacuum boost. Having your brake booster line Td with a crank-case breather is also not ideal. It normally runs to another vacuum source to avoid getting oil residue into the somewhat expensive booster. My PCV valve connects to a port at the front of the base of the carb.
If it was a PCV valve, your idle is likely cr@ppy, and your brakes wouldn't have a a vacuum boost. Having your brake booster line Td with a crank-case breather is also not ideal. It normally runs to another vacuum source to avoid getting oil residue into the somewhat expensive booster. My PCV valve connects to a port at the front of the base of the carb.
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I believe it was a PCV Valve. That's why I'm confused about why replacing the PCV valve would change the brake boost. It has always idled fine and after replacing the old broken valve now the brakes are weird and it hasn't changed the idle. Now where would I connect the brake booster to a vacuum line? It is currently "T'd" into the other lines.
The brake booster should go into a (large) source of manifold vacuum with nothing else connected to it. It's actually a law in many states. You need a check valve somewhere too. The big dual-diaphram boosters have it built-in. A mini-truck booster has it external, in-line.
That Mr. Gasket cap looks like it just has a breather... I've not seen one which includes a PCV valve.
Normally if you disconnect that vacuum line the engine will stall. I'm surprised it still idles well.
Normally if you disconnect that vacuum line the engine will stall. I'm surprised it still idles well.
take the tee out of the hose going too the vacumm booster and your pcv , run the teed hose directly to the booster and run the pcv off from the front of the carb (the big vacumm port in the center of the carb in front) good luck