2nd Gen Non-Engine/Transmission Vacuum line deteriorated...heads up

[wlowe]

Was working on my truck the other day and one of the vacuum lines was almost rotted away. The hose is connected to the hose that goes from the pump up to the top of the firewall. Right at the top of the firewall, just before the hose connects to a splitter, the hose has a little round plastic check valve which is connected inline with two rubber pieces of hose about two inches long each. The rest of the hose is made of plastic and still looks good but the rubber pieces were almost disintegrated. Easy fix, most of the parts houses carry vacuum hose, but be aware that each hose is a different diameter. Just a heads up for those who want to check.

 

[BigPapa]

Thanks for the heads up wlowe.

This is a common problem as is the rubber "boot" on the vacuum pump. I imagine you'd also find the plastic lines VERY brittle if you try to flex them at all.

 

[petersonj]

Was working on my truck the other day and one of the vacuum lines was almost rotted away...

I strongly recommend that all vacuum circuits be checked for leaks with a vacuum pump periodically. This check is very important on our trucks because the vacuum pump exhausts its air into the engine crankcase. Vacuum leaks will allow for excessive air flow to enter the engine crankcase and that air flow combined with normal engine blow-by can create excessive crankcase pressure.

The checks include the vacuum controlled front axle lock circuit, some vacuum doors in the HVAC unit, and the vacuum controlled cruise control circuits (disregard trucks that have electronically controlled cruise control). You may have ongoing leaks that go undetected until a component stops operating, but meanwhile a continuous stream of air will be flowing into the vacuum pump and into the engine crankcase, which combined with normal engine blow-by can cause excessive crankcase pressure.

If all of the components in the vacuum circuits are operating properly, the only time air will be moving through the continuously operating vacuum pump is when a vacuum controlled function is actuated - example: a ventilation door is switched from defrost mode to floor mode. The vacuum pump will begin to pump air into the engine crankcase until the ventilation door has shifted to its new position and vacuum has restored to its highest level. At this time, even though the vacuum pump is still operating, the air flow into the engine crankcase will stop and vacuum will remain high.

Each component can be checked individually or as a whole... just note that there should be no vacuum leakage at all on any of these circuits. If a circuit won't maintain a vacuum then you will need to find the location of the leak and make the appropriate repair. Just imagine how much air would be continuously pumped into the engine crankcase if there was large vacuum leak!

This is typically a neglected area of maintenance because it is probably one of the least understood. If the vacuum pump just discharged its air into the surrounding atmosphere, then minor vacuum leaks (or even major ones) would be inconsequential.

- John

 

[wlowe]

Thanks for the heads up wlowe.

This is a common problem as is the rubber "boot" on the vacuum pump. I imagine you'd also find the plastic lines VERY brittle if you try to flex them at all.

You are right about the boot on the vacuum pump, I checked mine today and it was crumbling just like the ones I replaced. There are no dealers in my area so I guess I will try to find a part number and order it online. The boot has a 90 degree bend in it so it may be hard to replace with aftermarket parts.

 

[BigPapa]

I believe it also contains a check valve.

 

[fest3er]

You are right about the boot on the vacuum pump, I checked mine today and it was crumbling just like the ones I replaced. There are no dealers in my area so I guess I will try to find a part number and order it online. The boot has a 90 degree bend in it so it may be hard to replace with aftermarket parts.

IIRC, it's a plain, simple, soft-ish rubber boot with nothing inside. It's something like a 3/8" to 1/8" adapter. I found a suitable replacement at Advance Auto in their display of blister-packed generic vacuum parts.

 

[wlowe]

IIRC, it's a plain, simple, soft-ish rubber boot with nothing inside. It's something like a 3/8" to 1/8" adapter. I found a suitable replacement at Advance Auto in their display of blister-packed generic vacuum parts.

Thanks for the info, I was just sitting here trying to find a part number when you sent your post. Guess I will check the auto parts store next.

Apparently the check valve that BigPapa mentioned is in the part that the boot connects to.

Did you replace the boot that clamps on or just the elbow.