vac. guage readings?

[BRONCADONK]

so finaly i'm getting healthy vac readings. a steady 20 inhg @ 850-900 rpm idle in park. my question is should my vac drop to 14 in drive? also when i hit the brakes it drops a few points, more so in drive. i'm sure the brake booster is bad, maybe check valve too. but could the booster be leaking when the brakes are not applied? i know when idling in park i can disconect a small manifold vac port and very little changes if any, but in drive the same port disconect will almost **** the engine. i guess what i'm getting at is what should my vac guage read in drive, and how important is a vac resivoir? i have all vac sources capped, only the vac advance, modulator, and booster are hooked up. i did this to eliminate all possible vac leaks. saturday is the big day, i'm hoping to pass smog after a year of fighting this beast. any thelp is greatly apreciated.

 

[Seabronc]

Well, I don't have any leaks and it runs near 20 in park and when running on the road at cruise it hangs in at about 15. If you have everything disconnected with the exception of advance, modulator and boost, I have some doubts about passing the smog test though it is possible.

The vacuum reservoir is for the environment controls if you have A/C. If you don't have a reservoir, then the vents will drop out when you have a low vacuum condition. Default for no vacuum to the A/C controls is, Defrost. Some vacuum designs have small in line vacuum reservoirs about 2 1/2 inches long by 1 inch in diameter for other vacuum operated items which keeps vacuum up for short periods when it suddenly drops like during acceleration.

Good luck on the smog test. Also, it helps if you add your truck vitals to your signature. Answers may depend on that information.

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[BRONCADONK]

thanks seabronc, that's exactly what i was hoping. before i was lucky to get 15 wile in park, and around 10 in drive. my stock manifold would not seal. i think it sat too low on the heads. the clearance betwee the front and rear of the block to manifold was so tight i could not use the stock rubber seals. the new edelbrock intake sits quite a bit higher, so high that the bead of rtv wasn't thick enough. so once again i'll be pulling the intake. i'll wait till after i smog it though. i only capped the vac lines to tune the motor, i'll hook everything back up before i smog it. the smog shops aroud here are very militant, and will fail me for any little thing. most of them wont even touch my bronco. yea the peoples republic of california is a great place to live. i'll fix my profile as soon as i figure out how. thanks again this forum has been a huge help!

 

[cantbecaught4]

thanks seabronc, that's exactly what i was hoping. before i was lucky to get 15 wile in park, and around 10 in drive. my stock manifold would not seal. i think it sat too low on the heads. the clearance betwee the front and rear of the block to manifold was so tight i could not use the stock rubber seals. the new edelbrock intake sits quite a bit higher, so high that the bead of rtv wasn't thick enough. so once again i'll be pulling the intake. i'll wait till after i smog it though. i only capped the vac lines to tune the motor, i'll hook everything back up before i smog it. the smog shops aroud here are very militant, and will fail me for any little thing. most of them wont even touch my bronco. yea the peoples republic of california is a great place to live. i'll fix my profile as soon as i figure out how. thanks again this forum has been a huge help!

Just wondering how the smog test went. There isnt smog tests here, it that something you have to get done once or is it a yearly thing??