77 C10 HVAC vacuum line replacement through firewall

[Poodlehead]

My vacuum line from the reservoir tank in the right rear corner of the engine compartment through the firewall needs to be replaced.

What is the easiest/best way to get to the opposite end of the vacuum line inside the cab?

Thank you!

 

[75gmck25]

The line through the firewall is GM hard plastic vacuum line, and it’s just pushed through a rubber grommet. If you take the glove compartment door off you can see where it comes through and then runs over to the back of the dash controls. If it is broken you can buy new hard plastic line and/or repair existing plastic line with short pieces of rubber vacuum line. It’s much easier to thread the plastic lines up behind the dash, since it’s a lot thinner than rubber vacuum line.

 

[Poodlehead]

If it is broken you can buy new hard plastic line and/or repair existing plastic line with short pieces of rubber vacuum line.

Great idea!
Mine is broken in the engine compartment so I will just do the repair/replacement there and be done with it, thanks!

I already pulled the glove box and saw the vac lines up there, but was unable to determine where the line went through the firewall. It looks like it's behind the HVAC black box that holds the cores. I'll look again when I put the glove box back in because ideally I'd like to replace the entire line and be done with it during my lifetime.

Thanks again!

 

[Poodlehead]

I have my line 'fixed' for the time being, but it is very brittle.

I took another look behind the globe box and it's not as easy as you'd hope to get at the line at the FW. It appears it's about 3" lower than the top of the black box with the cores.

I hope to pull the HVAC control head tomorrow to see if I might have better luck from that end.

If anyone has any tips, I'd certainly appreciate it!

 

[Poodlehead]

I forgot to add a vac diagram. It looks like the single line goes to the head unit, so hopefully that will help

 

[75gmck25]

They sell packages of GM hard vacuum line at most auto parts stores. There are two sizes (diameters), but I don’t recall which is the best match to original.

Dorman part numbers 47419 3/16” and 47417 1/8”.

 

[Poodlehead]

There are two sizes (diameters), but I don’t recall which is the best match to original.

A friend had some and the 1/16" is the size in my engine compartment.

I've removed some ducts and can feel where it goes through the firewall. My biggest problem now is separating wiring and the vac line at the firewall. I was hoping this wasn't going to turn into a PITA, but that's about par for me...

 

[Poodlehead]

The vac routing diagram I attached earlier was for a C60 model.

Here is the correct one for the C-K10 models.

 

[fnny6770]

Where does this vacuum line connect to in the engine compartment?

 

[Snoots]

Vacuum canister

 

[Poodlehead]

Sorry that I didn't update my results sooner...

Removing the center black plastic duct made a world of difference getting access at the firewall. I got all but about the last 8" at the control block replaced with a nice splice.