Vacuum fitting for brake booster

I’m nearly done (hopefully) with my manual to power disc conversion !!
Last step is to connect the booster to the intake manifold.
What fitting to use ?? The kit only came with a hose. I’m hoping to find a generic one from NAPA or any part store. Any suggestion ?
I’m assuming the bolt is there for that reason ? It seems the thread is 5/8 x 18 but then I really can’t figure out SAE. Hose that came with the kit is 3/8 ID. Can anyone confirm? Can I find a generic fitting for this?

Mine is connected where the bolt is on your picture, I assume that is the stock location. Others can correct me if i’m wrong :slight_smile:

Any idea of where I could find that fitting locally
Been looking at NAPA online, grainger etc but haven’t seen anything yet.
Is 5/8 x 18 the same as 5/8 npt?

A reverse flare tube screws in here:

Looks like this connected:

oh so there’s a hard line that goes in there. I thought i’d just connect the hose directly to a fitting screwed in to the square-ish block.
Out of curiosity, what are the 2 other vacuum lines coming out of it ? top one is the headlight actuator, what is the bottom one ? mine is plugged. Is it tilt away steering ?

Top one is HVAC, bottom one is headlights. The C4 transmission gets vacuum from the smaller fitting on the brake booster.

That’s not a bolt in that block, it’s a plug. And the threads are NPT.

The block has reverse flare in it. The plug might be NPT, if so it it’s not made for the job it is doing.

The end that screws into the intake is pipe thread.

I have worked on a couple of autos where the fittings utilize threads you wouldn’t expect. For instance new metric vehicles where GM has used SAE fine threads on brake line fittings. I think they were grandfathered. When I tried to source the parts locally it was tough-everybody (parts suppliers and even GM dealers suppliers used generic fittings not OEM PN replace which just didn’t work for a clean install). When I got into jams I went to the Brakequip. I searched a lot of companies for autos and heavy equip and Brakequip was the answer for autos. I believe they one of the major wholesalers and supply lines/fittings for OEM suppliers and parts houses. They used to have a large catalog-it used to be on-line at I think I have a copy on disk. If you get the part number you can usually get it ordered through someone.

With the flare, I suspect it’s straight thread, not NPT.

OK boss ! Noted ! :slight_smile: Non-native speaker, so not always easy to use the right words when it comes to specific domains.

Thanks all. So I have ordered a 3/8 NPT fitting from amazon. Should be easy to return if it doesn’t fit. I learned in the process that the 3/8 NPT doesnt mean the size is 3/8" …
If that doesnt work I think i’ll try with a flared piece of tube. Should be easy to find at NAPA or equivalent.

I’m hoping that’s all i need to take the car for the first test drive (before the snow forecast next week :frowning: ) !! so excited !

I think this is the part you’re looking for?

Winner winner chicken dinner. 3/8" reverse flare line assembly.

Go to the local parts store and grab a piece of 3/8 brake line with the fitting (inverted flare). Cut and bend to whatever works for you.
Make sure it’s inverted flare and NOT a bubble flare.

from my NAPA pro site: $9.50
Bendable: Yes
Brake Line Diameter: 3/8 in.
Brake Line Length: 60 in.
Brand: AGS
Contents: Brake Line Assembly
Fitting Size: 3/8 in.
Fittings Included: Yes
Hex Size: .62 in.
Manufacturer: American Grease Stick Company
Manufacturer Part Number: PA-660BK
Material Type: Double-Wall Copperized Steel w/ PVF Coating
Thread Size: (5/8" - 18)
Tubing End Type: Inverted Flare
UNSPSC: 25171716
VMRS Code: 013-007-000

sweet exactly what i was looking for. Inverted flare is same as double flare right ?

Correct, just a double flare is stronger. It’s folded once before it’s flared.

Worked like a charm!! And the best part is that I didn’t have to waste money in shipping!! :joy:

That brass block has a male pipe thread nipple on the bottom. The large hole under the plug is for a standard inverted flare fitting. You can buy these inverted flare fittings at most hardware stores with a hose nipple rather than a hard line. The other 2 hose nipples can go to wherever you need full manifold vacuum.