Quote:
Originally Posted by JLMounce
I have a feeling something else isn’t right. 12” of vacuum at idle should be plenty to run power brakes. Heck I run power brakes without issue with about 10” of vacuum. I’ve got to get down to about 9” before I start feeling an issue.
One thing to note about the vacuum reservoirs is that you are absolutely pulling more vacuum than 12” during low load driving operation. Probably over 15” of vacuum, if not more. That’s what you would actually have in reserve. That’s also the vacuum level your booster is going to be seeing as you decelerate and break.
That’s what specifically leads me to believe you have something else going on.
Are you running an actual vacuum hose to your booster and not fuel hose? Vacuum hose is specifically designed not to collapse. While fuel hose is not. If that hose collapses, there goes your vacuum assist.
As mentioned already I’d also be looking at line size, verifying the combination valve is setup for disc/disc operation. Disc brakes need more fluid volume than drums. I’ve seen a lot of people try to reuse the original drum/drum combination valves and that’ll be a recipe for poor braking performance.
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Yes, running Gates vacuum hose, also combo valve is disc/disc. Line kit for 4 wheel disc conversion from Inline Tube. I would have to check the line size but the line sizes and flare fittings matched the the disc/disc proportioning valve. BTW, the front brakes suck with no lockup also.
Here is what it looks like. Pretty but works only marginally better than the junk I took off (drum/drum master, original drum booster) extended drum brake lines and used GM calipers the prior owner had done).
