Anyone know of a fitting that reduces the vacuum to a brake booster? I've heard Gm used them but can't seem to find anything like that. Whoever had my Chevy 11 before me put power brakes on it and the front wheels lock right up as soon as you barely touch the brakes.
If you need power ***ist, you don't want to limit the vacuum. Maybe you're using a manual pedal ratio? Try braking with the booster disabled. Front drums or discs?
I suspect they added the booster to the manual brake cylinder. The manual brake cylinders were usually 1" bore on the manual brakes and 1 1/8" for power brakes on those year gm. Your issue is no going to be with the vacuum
They used to use a different brake pedal to reduce the leverage on power brakes too. If someone put a booster on you need to make other changes (master and pedal).
Don't know the MC bore but it looks like it was a kit. New MC and booster as well as front discs with the original small rear drums. It does have a combination valve with an anodized bracket that fastens to the MC/ Booster as if it came in a package deal. I'll post some pics. Can't tell you what the engine vacuum is right now because it's out of the car. It will be the 406 out of my T coupe and has a hydraulic cam that's not real radical, although it did need a converter. The T never had anything but a vacuum advance on it so I don't think I ever checked it.
Check with the company you purchased the kit from .... I know of 3 guys that had BAD prop valves brand new from the manufacturer .... just a possibility ...
I had a similar issue. When I installed a power booster on a project car I built, the reaction disc (see pic) fell out and I didn't know it. The brakes way over reacted with the slightest input. Took me till I got to my wits end and bought a new booster, that's when I found the rubber reaction disc on my old booster was missing. Gave my old booster a good shake and guess what fell out. Some of the above posts need to be considered also. I'm just throwing it out there because it drove me crazy for a long time. Good luck!
The '60's type GM cars changed pedal ration for power...I researched this out a bit when I went to power discs on old Novas. These and others of the period simply had two holes drilled in the pedal and I simply moved the pushrod clevis from the standard hole to the power hole for that part of the conversion (and, irrelevant here, added a little factory tab that maintained the proper push on the brakelight switch). This was on '68-72 Novas (the '68 being a legit Chevy II) and I don't know if its the same on earlier ones. If it is, I happen to know that the little tab for brakelight can be made from a cat food can... I also swapped the MC for a disc one, don't remember bore specs. I actually used Seville parts there since I was headed for 4 wheel discs.
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