Hey guys, just wanted to give all of you a heads up if your boost gauge has slowly been reading less boost/vacuum than it used to. My Stewart Warner has slowly been creeping towards zero for the past two or three years now. I assumed it was a slight leak at the gauge. For the past couple months, it has read no vacuum and only 4-5 psi of boost, so I figured it was time to replace it. FYI, I also have a Scangauge and it was reading the correct amount of boost/vacuum from the MAP even though there was obviously a leak at the gauge.

Well I pull the gauge and do a quick check and to my amazement, it works fine. I then start checking the line and tee and discover the rubber adapter from NAPA that I used to connect the hard line from the gauge into the tee had split.

This is a picture of the adapter and tee when first installed...

I'm a bit amazed this hasn't caused other problems over the past couple years as it was leaking more and more. What exactly does the boost/vacuum source do for the fuel pressure regulator?

Anyway, I had a new Marshall boost gauge ready to go and since I didn't have a new ferrel or rubber adapter for the hard line into the old Steward Warner, I just put the Marshall in with it's soft line. I have to say, I like the action of the Stewart Warner better. It was much smoother. The Marshall seems to stick at 15 inHg at idle and then jump to zero when the bypass valve starts opening and creep slowly into boost.

 

It's not suprising, for some reason the quality of the rubber of the adapters is nowhere as good as a regular vacuum line, and is far more subject to failure from heat and dirt.

F.Y.I. a good fix for this is to run a regular vacuum line from your T all the way to or through your firewall and then use a straight vacuum coupler with your adapter there, it keeps that lesser quality adapter out of the heat and elements.