Hard brake pedal

[Cubey]

Here’s that line that looks like it was plugged but is no longer plugged. Anyone k ow what it’s for?

It’s the middle, left line at the vacuum junction.

It appears the middle, right side of this junction goes into the coffee can at the driver side fender well area

Cruise control perhaps?

 

[rreegg]

Very possible since cruise doesn’t work on this truck. From what I’ve read the vac system is only used for hvac, brakes, and cruise.
The dash blower only really works on the defroster which is another possible symptom of vac leak so things may be starting to add up here

 

[rreegg]

Okay that part is the vacuum manifold as described by Nick Pisca

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[Cubey]

Very possible since cruise doesn’t work on this truck. From what I’ve read the vac system is only used for hvac, brakes, and cruise.
The dash blower only really works on the defroster which is another possible symptom of vac leak so things may be starting to add up here

Yeah that sounds right, hvac, brakes, cruise. C6 would use it but you don't have that.

The vac tubes for HVAC in the dash are somewhat fragile plastic tubes, so it's possible one is broken. Thankfully I've never had to mess with that, so far, so I can't give much insight.

A good way to diagnose leaks is to stick a vac gauge on the junction tee and try removing one accessory at a time and stick your finger over the barb to seal it, and see if the reading is worse with one accessory more than others. I had to do vac diagnose the RV when I got it.

Ended up saving the engine, because the lower radiator hose sprung a leak suddenly (rotten probably original hose from 1985, in 2019!!!) and I caught it before it lost much, and it was just idling so it wasn't very warm.

Anyway, the problem ended up being a bad booster and a weak vacuum pump both. I unhooked the cruise and stuck a vinyl cap over the barb on the distribution block.

 

[yARIC008]

Every time I’ve had similar issues in the past, it has been the vacuum pump going out. My vote is severe leak somewhere or pump failing.

 

[IDIBRONCO]

I put my finger at the end of this line with the engine On and there is no pull/sucking at all so not sure what it's supposed to do.

Here’s that line that looks like it was plugged but is no longer plugged.

Looking at these two statements together should give you something. Since there's no vacuum there while the engine's running, it's still plugged even if it doesn't look like it is. Maybe that went to your "tuna can" that turns on the "brake" light when there's low vacuum? That particular spot on the manifold has the factory plug on my '85 so I'm no help there. The set ups are different. All I can say is to look around. You'll probably be able to find something that's no longer hooked up to vacuum. It can't be too far away from the manifold.

 

[rreegg]

@IDIBRONCO I was actually mistaken when checking for vac at that line. There is suction coming from it but it’s quite faint, since I was comparing it to the bigger line going to the booster.
I’ve since plugged it up but hasn’t really changed the pedal much if at all. So still assuming there’s a vac leak somewhere but maybe narrowed it down not sure

 

[Cubey]

@IDIBRONCO I was actually mistaken when checking for vac at that line. There is suction coming from it but it’s quite faint, since I was comparing it to the bigger line going to the booster.
I’ve since plugged it up but hasn’t really changed the pedal much if at all. So still assuming there’s a vac leak somewhere but maybe narrowed it down not sure

Get one of these to check vacuum. They work well. Works for lift pump pressure checks too. The nylon tee is junk, but that's easy to replace with a brass one.

Fuel Pump and Vacuum Tester

Amazing deals on this Fuel Pump /Vacuum Tester at Harbor Freight. Quality tools & low prices.

www.harborfreight.com

 

[rreegg]

Roger that @Cubey. That’s the one I got and think at this point the only sustainable way to diagnosis thing further is to run the vac gauge into the cab while driving.
The pedal changes feel throughout the day and will be “normal” in the morning and get more firm as it gets warmer. So maybe there is some brake line swelling or something happening idk. But gotta get numbers somehow

 

[Cubey]

Roger that @Cubey. That’s the one I got and think at this point the only sustainable way to diagnosis thing further is to run the vac gauge into the cab while driving.
The pedal changes feel throughout the day and will be “normal” in the morning and get more firm as it gets warmer. So maybe there is some brake line swelling or something happening idk. But gotta get numbers somehow

Zip tie it to the cowl and run the hose through the closed hood by the windshield. i had to use that gauge to check fuel pressure that way, worked well.

 

[tradergem]

I had to replace my vacuum pump a few days ago because my brakes would have power assist in the morning but after driving for a little while I would lose all power assist to the brakes. The brakes were doing this for a while so I first replace the vacuum booster because it was making noise when the brakes were applied, but that didn't cure the problem. Replacing the vacuum pump fixed my brake problems for now.

 

[Old Goat]

Yeah I have the HF one, tried to Zip Tie it to the wiper arm.
Then finally bought a long piece of Vacuum Hose, and ran it
through the Wind Wing into the Cab.

The Plastic vac Manifold on the Fire Wall could, may, does, have
some Vacuum Caps to block off some of the unused ports.
The over time they crack, and could also be a Vac leak. HF Probably
has a box of various sizes.
Summit Racing also has them, but shipping probably same and the
cost of the caps. Lucky it is in Reno, and 60 miles north of us. When
up there I pick up things.
It`s a Candy store of goodies.


Goat

 

[Cubey]

Yeah I have the HF one, tried to Zip Tie it to the wiper arm.
Then finally bought a long piece of Vacuum Hose, and ran it
through the Wind Wing into the Cab.

The Plastic vac Manifold on the Fire Wall could, may, does, have
some Vacuum Caps to block off some of the unused ports.
The over time they crack, and could also be a Vac leak. HF Probably
has a box of various sizes.
Summit Racing also has them, but shipping probably same and the
cost of the caps. Lucky it is in Reno, and 60 miles north of us. When
up there I pick up things.
It`s a Candy store of goodies.


Goat

Auto parts stores have the caps too in the help section:

20 for $6.30

Dorman - Autograde Assorted Vinyl Vacuum Cap 20 Piece

Shop for Dorman - Autograde Assorted Vinyl Vacuum Cap 20 Piece with confidence at AutoZone.com. Parts are just part of what we do. Get yours online today and pick up in store.

www.autozone.com

or 8 for $5

Dorman - Autograde Assorted Black Rubber Vacuum Cap 8 Piece

Shop for Dorman - Autograde Assorted Black Rubber Vacuum Cap 8 Piece with confidence at AutoZone.com. Parts are just part of what we do. Get yours online today and pick up in store.

www.autozone.com

 

[rreegg]

Did exactly what Goat mentioned. Didn’t see anything irregular with he vac numbers while driving, inHg never dropped below about 19-20 and the pedal did firm up a bit.
Letting the truck sit for a bit now to see how vac numbers do with the engine off.

Will do some gravity bleeding to the brakes later on just for kicks, have no firm evidence the vac system is out of line at this point.

cyber trucks are lame and Tesla drivers are frequently bad - ymmv

 

[rreegg]

With the engine off the vac dropped from 22 inHg to ~20 over ~hour. Is it supposed to hold vac?