Ok, here's a problem I'm having with my power drum brakes on a stock 300cu in 66 Skylark. The booster doesn't seem to be working (I replaced it), so I contacted the booster rebuilder's help line. They said the booster needed a minimum on 18" of vacuum to work. They said most cars are putting out 20-22" of vacuum. At idle I'm only getting 14" of vacuum at the booster. I've looked for blocked or damaged hose, or a plugged inlet at the intake manifold. All looks good. The engine idles fine, doesn't burn oil or smoke, has no blow by out the pcv valve or the oil fill cap when running. The rebuilder suggests I put in a seperate vacuum pump, but I've only heard of this on hi-po cars with radical cams. Pardon the pun, but this problem sucks, any ideas???
Sounds to me like the nipple on your intake manifold may be restricted with carbon. Just b/c you have vacuum pressure present doesn't mean there's enough volume. Try removing it again and cleaning it out really well. Also, the hose may be restricting the flow of air. Otherwise, I'd suppose your booster is defective. Incidentally, Mine only has 16- 18" of vacuum at idle in drive (it has a mild cam) and I have had no problems with the power brakes. As far as I know, 18" at idle would be perfectly normal for your car. If you only are getting 14", maybe you're timing is off, but the power brakes should still work. :TU:
Thanks for the input, I'll start pulling things apart this weekend. I forgot about the timeing as that would affect everything if it's way off!
