millerbn

I just put a carburated 383 into my 1989 RS. I ran a vacuum hose from the intake manifold to the vacuum booster. The intake has good vacuum, however the vacuum booster is not working. I have good pedal, and everything worked fine before I pulled the 305 TBI. What's the problem?

Green92RS305

i'd use a vacuum gauge and compare the reading to what stock is supposed to be. also do a booster check by pumping the pedal till its hard with the car off and then holding the hard pedal. when the car is started the pedal should drop about and inch, if it doesn't then you prolly have a seal leak in the booster itself.

stage20

iTrader: (3)

sounds like your large camshaft is "stealing vacuum" rather not making enough do to the camshaft specs.
put a filter inline from the help section.
it will help a lil.

when i had a huge nasty cam in mine, i would play with the gas in neutral while hard braking. im good with the feet, so i would keep the RPMS up in the motors high vacuum range.

good luck
whats the cam specs, BTW?
at .050

camaronewbie

Same problem here - just installed a 350, don't have cam specs. Brakes good before, now I have brakes, but it seems that there is only so much brake, then no more - must have plenty of room to stop. Replying to see responses and suggestions.

MurcoRS

If you have less than 12" of vacuum reaching your booster it will not work very well. If that is the case I'd look at converting to hydraboost.
Hydratechbarking

millerbn

My cam was stealing vacuum. I installed a vacuum canister and the brakes work fine now.

IHI

iTrader: (1)

I installed a vacuum canister for my brakes before I even took it out of the shop, brakes were every bit as good as factory brakes on the daily drivers I own.

Am currently investigating manual brakes to get some needed space under the hood, these cars suck to work on enough without that booster crowding the back corner of the engine bay.

camaronewbie

Well, I measured vacuum today, and all I can get, from any location, is 8 inches at idle. For a man, that's pretty damned good. For a car, it sucks. LOL I checked all vacuum ports on carb, as well as the intake port behind carb.

I replaced all vacuum lines, rechecked for leaks - can't find any. Took all vacuum lines off everything, capped all ports except the one being tested, still only 8 inches on any port.

Should the car cut off if the brake booster vacuum line is removed without being plugged? Mine wants to die from this large vacuum loss, but struggles along without actually cutting off. Would this indicate a leak somewhere? I fso, damned if I know where else to search. I've sprayed everything a dozen times with carb cleaner while it's running, with no indications of a leak.

Someone said change timing - I dunno. I thought that if timing is increased, in theory faster motor, but once idle is adjusted back down, you'd be at square one again.

Maybe I need to try the vacuum canister route.

I'll also need more vacuum for the torque converter lockup switch, as it's set for 10 inches vacuum.

Any suggestions greatly appreciated!

IHI

iTrader: (1)

Mine only pulled 5", I had to drill/tap a hole in my 2" spacer to allow a port to get vacuum from for the booster.

If your at 8" your brakes will be fine with the addition of the vacuum can, you really dont need to order it with a guage, but it looks "specail" when you have the guage mounted on it