383 installed, crappy brakes?

[68 Greenie]

Okay guys just installed my new 383 and now it seems as though its not got enough vacuum for my brakes. They worked great before and booster seems to be fine so looking for some answers. If I need a vacuum pump which do you recommend and I want a quiet one because I don't like hearing those things run. Do you think a canister would be enough. Just looking for suggestions. Thanks.

[s10mk]

Hi bud, before you get to involved, are you sure that you don't have a vacuum leak somewhere? Also, have you put a vacuum gauge on the engine to see how much vacuum your new 383 is making? I would start with a vacuum gauge and go from there.

[AussieinNC]

Check the vacuum level directly from the vacuum port on the manifold...do not use a ported vacuum source on the carb...you should see between 12 and 15 inches of vacuum...if lower, check timing is correct, small differences in timing make huge vacuum differences...
Check the vacuum fitting into the manifold is totally open and the fitting threads have some form of sealant applied...
Then check the vacuum hose is not so soft it sucks shut when the engine is running...
Check valve going into booster is retaining vacuum...start engine, run for a minute or so then shut down...remove valve and the booster should hiss as vacuum is released...
Check booster is not leaking vacuum into cabin area...listen inside cab while engine running for constant hiss sound...
Engine off...pump brakes down to no vacuum...four or five pumps...hold last pump down and start engine...pedal should drop a little...if it rises, the booster is faulty...

Depending on the cam specs in the 383, you may need to go to a hydro boost system...sometimes huge cams just dont make a lot of vacuum at idle...

Enjoy....

[68 Greenie]

I have a 292 cam. Im using the back of the carb. for my vacuum source I will put a port in my manifold and try that next. I will get a gauge and try and see what Im getting. Like the motor just hate not having much brake.

[kwmech]

Cam, I'm sure is the problem. The later model chevy's trucks--as in say-- an '02 had electric vac pumps. And if I recall they were pretty quiet

[68 Greenie]

What pumps would you recommend? I would like to find one that shuts off by itself if I can. I just installed all new power brake system. I have never used a hydroboost system what would I have to do to install that? I just don't want to listen to that vacuum pump running but if I have know other choice I guess I will just have to bite the bullet.

[snipescastle2]

I bought an electric vacuum pump off of an Audi A4 with the Diesel engine. I
made a sheet metal bracket and wired the pump with a relay and had to run an electronic timer to cycle the pump off and on, otherwise it would run constantly.
I found the timer module on eBay for $15.
Makes 20-25" Vacuum all day!
Ben

[rsgt]

Yesterday I was trying to fugure out why my sons car didn't have good brakes, all the brake parts were new. I went to the master power brake website to look for answers. They say " For a power booster to function properly you will need at least 18" of vacuum. " I Checked the vacuum and it was about 14. I set the initial timing up to about 18. and got 18 inches of vacuum and the brakes work a lot better. I am going to have to check the mechanical advance to see what the total is.

[Mollzyie]

Originally Posted by snipescastle2

I bought an electric vacuum pump off of an Audi A4 with the Diesel engine. I
made a sheet metal bracket and wired the pump with a relay and had to run an electronic timer to cycle the pump off and on, otherwise it would run constantly.
I found the timer module on eBay for $15.
Makes 20-25" Vacuum all day!
Ben

Thanks for the follow up ... good idea .. might need to do that in the future 👍🏼