tviscomi

As like many I am having an issue with the vacuum lines on my 1978 C3. I've isolated one of the issues to a leak I hear under my dash, thus I plan on replacing those lines. My question is...are there any tricks/tips for removing/replacing the lines through the firewall grommet?

lakerider57

I pulled the grommet out which had much smaller lines than what I was replacing so I drilled the holes bigger and fed the new lines in and replaced the grommet. Took about 30 minutes for all of it.

Richard

Mooser

FWIW, most you can usually jamb in using some silicone spray, I normally use some 303 protectant (like Armour all) to help it slip easier. Sometimes cutting the end of the hose at a steep angle helps and then trim it back off straight after
For those hoses that are in a more awkward spot or don't want to go, I use a length of expandable sleeve (normally used to cover wires or hoses etc) and place it over the end of the hose (maybe half a foot or better, wipe the hose with cleaner to remove any slickness) and then feed the empty end through the grommet, since it collapses down to nothing it fits easily. Spray a little 303 (armour-all type stuff) in the grommet itself and then pull the sleeving through from the other side. It works like one of those finger trap things and grips the hose tight and gives it a tapered end to slide into/through the grommet.
M

Rotonda

I believe you should do some more diagnosis before tearing into your dash, and possibly causing yourself additional problems. There are two uses for vacuum under your dash - 1) the headlights and 2) the HVAC system. The headlights vacuum is on the drivers side, near the switch and in the vacuum switch under the column. The HVAC vacuum is in the console (the HVAC control head) and on the passenger's side (various vacuum motors to move doors in the unit.

Where is the sound coming from? This will help narrow your search. Does your HVAC work properly? Do your headlights raise & lower properly? Does the vacuum by-pass under the column raise & lower your headlights? Have you done any work in or around your dash recently?

In my experience, most vacuum problems occur at the ends of the hoses (where they split or lose their elasticity) or from leaky seals in various vacuum motors. The first can be resolved by removing several inches of hose and splicing in fresh hose. The second is a remove and replace. FWIW, I HATE vacuum accessories in a car. I have NONE left in my 77 - everything is either electric or hydraulic, and the only vacuum used is on my TPI MAP sensor. Good luck!!

tviscomi

Disconnected AC a while back...the sound of the leak just started very recently. Always had slight issues with slowness, but bearable. Since my 1st post I ran a long vacuum line from the check valve directly to the switch and all seems to work. I don't hear the leak as of yet.

Kevin68

I just did this last weekend. I whittled the end of the hose down to a smaller diameter about an inch from the end so it went through the grommet easily, then grabbed the tip from the inside and pulled it through. Cut off the whittled end; the kits from the vendors have plenty of length to sacrifice an inch. I tried lubing the first one (brake fluid) and tried to jam it through, but couldn't get any further than about 1/8th of an inch from being able to grab it.

nearflack

I just replace the tree lines from under the hood that pass through the firewall this weekend. The replacement line is much larger than the original. Fortunately I was able to pull enough through the grommet and slip the new over the old smaller line. The replacement hoses come with a small spring clamp that I used. The old lines would not pull out so i used a 1/8" bit to clear out the holes. The one with the green line goes to the A/C heater door plenum through another grommet. Unfortunately the original small line had a hole in it in the windshield wiper well so I had to drill a larger hole to accommodate the new larger line. Worked fine but Im learning way more than I wanted about the vacuum system on my 1980. Waiting on the fresh air door now and not look forward to replacing it in the fender well. Good luck