1980 truck w/Holley 1945, I am baffled...

I am working on a slight bog off idle and stumbling at idle at times. The vacuum is around 15 in. at 5400 ft. elevation.

No brakes, sitting in my driveway in gear the idle is perfect. My driveway is slanted so my truck doesn't move forward. Once I hit the brakes I get what I would call a miss or stumble. Let off the brakes idle goes back to normal. Go to Park and the stumble is back, no brakes. Apply brakes, the stumble gets worse.

Sounds like you have power assist brakes?
If so, replace the plastic valve that plugs into the booster, it's leaking vacuum.
They are cheap and are hanging on the Doorman display at your local autoparts.

_________________
Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

Dorman p/n 80192... I was just looking at one here at my work for mine, Im having the same issue when I hit the brakes...

_________________
"if it aint broke, fix it till it is"
78 Plymouth Volare Super Six wagon
89 Volkswagen Golf GTI 16v
92 Chevrolet K1500 5.7
98 Ford Escort ZX2 zetech

Awesome guys thanks. I'll post back after I get the part installed.

FYI, Dorman PN 80192 is discontinued. You can still find them on the net. My how times change

After an exhaustive search around town by phone I went out and looked at this check valve. 80192 seems to be the wrong PN for my truck as I don't need the triple prongs since mine is single pronged. I ended up finding Raybestos CV89000 on Rockauto which crosses to Dorman 80190. The local Autozone has the Dorman one and I am going to go pick it up in a bit.
http://www.summitracing.com/parts/rnb-8 ... /year/1980

And I thought this would be a cakewalk.

ps
And after inspection I doubt the check valve itself is bad. Probably the 34 year old grommet or hose. Anyway for five bucks I'm going to replace it.

Yes, that is the one and they come with the grommet. I have them on two of my cars and always keep spares. The Dorman rack at our local auto parts still has them!

Both the 69 Chrysler 300 and 72 Imperial use them.

_________________
Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

Crazy, I literally just bought one from my work. Must have been the last one out there lol. My original doesn't have 3 either so I'm a little confused on why it was listed. I noticed the reman brake boosters we list for my car have the 3 port on it?

_________________
"if it aint broke, fix it till it is"
78 Plymouth Volare Super Six wagon
89 Volkswagen Golf GTI 16v
92 Chevrolet K1500 5.7
98 Ford Escort ZX2 zetech

Geez, came back with an 80189. The valve looks exact, but both the grommets are wrong. I'm going to use the old grommet for now.

Maybe a little grease on the grommet will help it seal better. I always use a little clear synthetic grease.

_________________
Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

No slant love for me today.

Replaced the valve, still doing it. With the vacuum advance disconnected and the hole plugged at the carb of course, doesn't seem to do it. In fact it seems to run a little better. Could be in my head.

I can't wait until this thing is emissions exempt.

try pinching of the booster hose to see if leak is in the booster diaphram. also if you are have having idle quality change when disconnecting vaccum hose, your seeing to much advance timing at idle speed. make sure the carb connection doesn`t have vac adv at idle just mech adv.

It does have advance at idle. I think that's how it should be but not totally sure. I set the timing to +12 degrees according to the sticker under the hood. When I connect the vacuum it jumps up.

With a 1945 there should be no change in the advance plugged in or unplugged if your on the correct ported fitting for the distributor. My 74 Swinger came with a 1945 Holley.

_________________
Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

I am on the right port. It used to go to the OSAC, but I connected it directly to the distributor. Maybe that is the problem. Is the OSAC necessary?

Yes.
No it's not, I bypassed mine. If you see any vacuum there at idle then the throttle plates are open to far. You may have to readjust the mixture screw so you can close them down to where there is little to no vacuum showing. I always screw the vacuum advance canister adjuster out so it will not engage anyway.

I was able to get that at 750 rpm per the manual. At 800 rpm it starts to pull some vacuum. So it is a critical setting.

_________________
Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG