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85 GMC 305 Vacuum LIne Diagram

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New User

Mar 9, 2006, 10:49 PM

Post #1 of 3 (10820 views)
85 GMC 305 Vacuum LIne Diagram Sign In

Unsure Does anyone have or know where I can get a copy a the vacuum line placementy diagram for a 1985 GMC High Sierra Pickup w/305 cid 4bbl, AT, PW/PDL/Tilt/Cruise/Dual Fuel Tanks/Factory Cat Back Dual Exhaust? Crazy Recently had to rebuild QuadraJet Madand old vacuum lines were so brittle they jusy broke all to piecesPirate. I remember where some went, but need to know where the rest go in place and what/where they hook up to. Hopefully will eliminate factory smog pump, etc. Any help greatly appreciated!Blush

Tom Greenleaf
Ultimate Carjunky / Moderator
Tom Greenleaf profile image

Mar 10, 2006, 4:44 AM

Post #2 of 3 (10797 views)
Re: 85 GMC 305 Vacuum LIne Diagram Sign In

There should be a diagram under hood. If you take out the air pump your vehicle may NOT be legal and wouldn't where I live. Think about that. T

Veteran / Moderator
DanD profile image

Mar 10, 2006, 5:49 AM

Post #3 of 3 (10794 views)
Re: 85 GMC 305 Vacuum LIne Diagram Sign In

There are 10 or more different vacuum diagrams that I have; all for an 85 305 pickup.
It all depends on whether it has Federal, California, high altitude emissions and what series this truck is, as in C10, C20 ect.
What I need from you is the series and hopefully the three-letter code that defines this; here are a few examples of the different codes.
Some I need to know the code and what combination of series, trans and gross vehicle weight to come up with the proper diagram.
The sad part is, is this code is usually found on the vacuum diagram that should be under the hood. Yours must be gone or you wouldn’t be asking.
You may get lucky if you find a patient parts guy at a dealership that would be willing to dust off some of their old application books and find what you’re looking for.
All of this will likely be futile anyway, probably the TVS’s (Thermal Vacuum Switch)(s) are no longer functioning due to their age and most are no longer available through the dealer. The after market people may still have them but even when I was dealing with these systems all the time the after market TVS where never quite right, as in doing the proper job.
Good luck with this because I think you maybe in for some trial and error to get this thing sorted out. You may even end up ripping all of it off and connecting just the essentials as in the distributor’s vacuum advance, EGR, transmission’s modulator and heated air intake. How legal that is I don’t know but if you can prove that the parts are no longer available what are you/they going to do? Hook up a bunch of crap so it looks like it’s functioning?
Keep it fun Hoss.

Canadian "EH"

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