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Hi,

Second post on here. I need some help as to knowing what size the vacuum lines are on my truck. The vast majority of them are dry and very brittle. I know I have to replace most of them. It has a rough idle and poor running overall. When I first got the truck I replaced the cap and rotor, plugs and plug wires, that seemed to help a little bit. The truck is a 81 C10 with a 305 and California Smog so it has vacuum lines galore.

TIA
Joe
 

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Welcome to the club Joe. Vacuum lines, as well as all your evaporative emissions hoses are measured by the inside diameter (some of the evap hoses are thicker walled & will have increased outer diameters over & above the vac lines.) Most of your lines are in the range from 1/8" to 3/8" i.d. except for the brake vacuum booster hose. For determining what diameters your hoses are, use drill bits to measure them.
 

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Thanks for that. I went out and measured things and Found this thing. I have no idea what it goes to. I just figure it needs new hose to attach it into the port.
 

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ha ha, yeah that one definitely needs replaced. I believe that line is for the vacuum modulator valve on your transmission. If it's in that bad a shape then all your other vacuum hoses should be replaced too. That particular line is all metal untill it gets to the modulator valve on your trans (on the passenger side rear corner of trans) & then there is another piece of vacuum hose which is probably needing replacing also.
That hose in your pic was creating a direct leak to the intake manifold & was responsible for a lot of your rough running problems.
 
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