JimMueller

When performing a smoke test on the vacuum lines, I have smoke coming out near the bottom of the battery tray. We capped the line by the cowl, but I'd like to replace that vacuum line as it seems to have broken off in the past. Does anyone happen to know the ID/OD of the vacuum line that connects to the vacuum tank? Since I'll be in that area anyway, is there any benefit to attempting to install a larger tank (assuming one exists and would fit)?

Injuneer

The 1998 factory manual shows that line to be encased in a wire loom bundle, with just a short end sticking out of the bundle to attach to the tank. And it appears to show the end of the hose has a preformed "socket" on the end that slips into a hole in the end of the tank, and over a nipple partially internal to that hole. Probably need to get under there and see what part of the hose is damaged, and whether it could be repaired rather than a full replacement.

Free download of 1998 factory service manual, courtesy of GaryDoug - See page 1-112,

http://www.mediafire.com/?40mfgeoe4ctti


As far as a larger tank, have you ever experienced a loss of vacuum at the HVAC controls, that causes the air distribution doors to revert to a default positions? Would only be likely if you have a large cam, producing low vacuum, or if you were on a long uphill pull that caused engine vacuum to be low for an extended period.

JimMueller

I have the electronic version of the '98 service & parts manual, ironically I could only find the vacuum tank listed for the pre-LS1 models even though the service manual shows it. I've been under there once before trying to fix it, I had my hands on the loose end of the hose but that "socket" was neither on the hose nor on the tank. Not knowing what it was supposed to look like, I was trying to pull the hose to connect directly to the tank and the hose busted off. I've ordered a new tank so I can easily test fit. There's some free play in the hose by the cowl, maybe I could push the existing hose a bit towards the tank, and use extensions at each end.

I don't generally fiddle with the HVAC controls while at WOT. Although I have a scanner, I'm not sure how to convert Baro & MAP into a calculated vacuum pressure. I have no idea how long the tank has been disconnected, it could have been years; so I may not remember how it's supposed to behave for comparison. The factory calibration disables the A/C system at 4000RPM, would there be potential side effects to raising that RPM other than minimal lost HP?

Injuneer

BAR minus MAP = vacuum

With a 30”Hg barometer, and 10”Hg MAP at idle, you're pulling 20”Hg vacuum.

The vacuum tank shown in the 1998 FSM diagram looked the same as the one used with the LT1’s.

http://shbox.com/1/vacuum_tank.jpg

http://shbox.com/1/vac_tank.jpg

http://shbox.com/1/vac_check_valve.jpg

To get a replacement hose, take a piece off the other end at the check valve, and match the hose size at a parts store. Use the connector fitting from the check valve end. I suspect the connection at the tank end could be made with a rubber sleeve that fits snuggly over both the hose and the tank nipple. Just have t figure how to route the new hose. Or you could try attaching it to the old hose and using the old hose to pull it through the bundle, if it's loose enough.

JimMueller

Received a new canister. The OD of the nipple is 6mm, ID is 3.3mm.

JimMueller

I stopped by Autozone trying to find an adapter to use between the OEM hose size (4mm OD, 2mm ID) and the tank fitting (6mm OD, 3mm ID) and I wasn't excited with their options. They didn't have any hoses that small either. I'm hoping to locate a single rubber 90* reducer between the tank and the hose but I haven't stumbled across one yet. Maybe I'll have better luck find the right connectors; could I replace the hose with a standard 1/8" OD with a similar ID to stock?

Injuneer

6mm is almost 1/4”. A thinner 1/8” OD (3.2mm) hose with a 3mm ID is a paper-thin wall and it may not be suitable for vacuum, and might collapse.