Replaced Carb no brakes?????

[JRANGER]

I replaced my carb and now my brakes dont work...Hooked everyhing up like the last carb, brake booster is connected to the brake vacuum and t in a pcv valve....Not sure why but thats how it was on the other carb and when they didnt work i put it back that way...


ANy ideas? There is fluid in the brake booster....but they worked before and now they dont...I cant stop the truck unless i mash them all the way down and it doesnt really stop all the way

[clinebarger]

With the engine running....Physically check for vacuum at the booster check valve.

[tucsonjwt]

x2 on obvious vacuum issue. Odd story, when I replaced my booster check valve the brakes worked fine for about 5 miles, then the extra proper pressure blew the vacuum booster If you need a new booster, I recommend an OEM Delco rebuild - from online discount OEM GM vendors - about $120 as I recall, about twice that for a new Delco booster. This is one place where I think OEM makes sense.

[Square_78]

I fixed a bunch of vacuum leaks on my Edelbrock carb and my drum brakes suddenly worked better than before!!

[bilfman]

Honestly doesnt sound carb related, I think that it may just be a fluke that it occured after the carb change. It is the "to the floor" that make me suspect another issue, vacuum is an assist so you dont have to power mash the pedal. I would check your hoses and lines for a leak and if that does not yield any fruit try bleeding them.

I assume that you have unhooked the booster vac line when running and put your finger on it to see if there is vacuum there?? If not, disconnect it from the booster and run the engine, check with your finger to see if there is any vacuum.

[JRANGER]

ahh WTF the power/brake connection has not suction...But the pcv valve connection on front does....Am i missing something here? On my old carb it was all connected to the PCV valve connection as their wasnt a brake booster connection

[clinebarger]

Clogged vacuum line, Bad check valve??

[JRANGER]

NO i checked i direct at the vacuum valve..... and this Street Avenger is brand new..

[clinebarger]

?????

[JRANGER]

yeah i dont know lol....

[68Timber]

The little 90 degree plastic elbow inbetween the booster and large vacuum line is pretty easy to crack. The get old and brittle, you may have cracked it. Ask me how I know.

[JRANGER]

There is no vacuum at the valve on the carb...... The PCV has vacuum though....Just not the brake booster valve

[68Timber]

I missed that. The master cylinder may have pushed though.

*edit* I just read closer about the vacuum problem. I don't know, I've obviously already thrown out the two things that have happened to me that resulted in a similar sounding brake failure. But that's a new one to me.

[INSIDIOUS '86]

The one way valve isn't backwards is it?
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[bilfman]

The port may be plugged by the carb gasket. But in your case I would just pull vacuum off the intake, there are several ports on it. Some may be used , some plugged. Just tap into one with the proper fitting and leave the carb out of it if it is giving you grief.

[bilfman]

I just re-read your post, just tap into the pcv line and dont use the other. Easier then the intake solution.

Also just to test if that is the brake issue, and you dont have a 'T' fitting, hook up the booster to the front vac and see if the brakes work.

[hatzie]

Originally Posted by bilfman

The port may be plugged by the carb gasket. But in your case I would just pull vacuum off the intake, there are several ports on it. Some may be used , some plugged. Just tap into one with the proper fitting and leave the carb out of it if it is giving you grief.

I've seen gaskets block that rear port. I'd cap it if you don't use it. I had a few G20 vans with the brakes tapped off a port behind the carb into the manifold.

The fleet's all diesel now so it's been a while.

[JMac11]

Make sure the port is not plugged on th NEW Carb. Installed a new Holly once, no vacuum. There was a port plug inside the vacuum port on rear of "universal carb" not all vehicle have power brakes and they did not send them out with a rubber plug on them, back in the day.....

[JRANGER]

Im not sure whats up with the port but its not being used now....Im wondering if maybe the diagram for my carb was wrong...As it didnt show another vacuum line on the back of the carb even on it... Eitherway i removed the plug from the back and hooked the brakes up to it and its all working now

Thanks guys

[byeoficr]

you may not have enough vacuum to run both you might want to run the booster off of a manifold port an see what happens. incidentally do you hear vacuum noise inside the cab when you step on the brake? if so you need a new booster

[JRANGER]

everything seems to be A-OK right now...