What all runs on vacuum?

[Selahdoor]

92 NA.

Can anyone tell me what are all the things that are supposed to run on vacuum on this thing?

I think I have a vacuum leak, and I want to eliminate as much as possible from that system.

 

[1mouse3]

Just HVAC system and brake booster if you dont have hydro.

 

[franklin2]

And the cruise if you have that. A common area for a leak is right off the vacuum pump. The line runs from the pump very near and sometimes lays on the pass side inner fender. These engines shake a lot and over time that hose can get a small hole rubbed in it by the inner fender.

 

[subway]

Some might say the driver

Like mentioned the HVAC, brake booster but I am not sure about the cruise. my 94 does not have any vacuum lines to the cruise. just a electrical plug and cable to the throttle, 92 might be different.

anyway, I have had issues with the thin little vacuum lines pulling out of the rubber adapter at the end where they plug into the HVAC box. You got to watch the vacuum motor that switches the blend door on top of the box also.

You might want to check vacuum directly off the pump to make sure the pump itself is doing what it should.

 

[Big Bart]

Add to the list -
Brake light vacuum sensor
VRV and modulator if your tranny is an auto
Possible bad plug on or broken vacuum splitter
Any hoses in between
Check for a loose alt or vacuum pump belt

Why do you feel there is a leak?

Have you tested vacuum at idle?

I am sure you know, but unlike a gasser, a vacuum leak on these motors does not effect the engines air fuel mixture or performance.

 

[Selahdoor]

When I am stopped, if I press the brake pedal hard at all, it slowly leaks down.

I have checked the brake system. No leaks. No air in the system. (Replaced the long hard line on the rear axle recently, and bled the system again.)

So I am wondering if it is just because of a tiny leak in the vacuum system.

I will have to find my vacuum gauge. I'll test directly from the vacuum pump. If that is good, I may run a line directly from the pump to the brake booster and bypass everything else. Just to test.

I just didn't want to do that if I would be disconnecting anything vital.

I do have the auto trans, so I may have to do a tee, and keep that connected with new line, as well.

I built a new vacuum canister for this. And I know for a fact that that is working good.

Probably just going to look for the gauge, buy a bunch of new hose, and then get at it.

Still working on the front bearings right now, though. I was supposed to have a ride today to get the new spindle nuts, but it looks like at least tomorrow, now.

Nose of the truck is up in the air, so I won't be getting to this until that is done.

 

[CharlesG]

I do have the auto trans, so I may have to do a tee, and keep that connected with new line, as well.

Your E4OD doesn't need vacuum. The C6 trans uses vacuum to control shifting.

 

[chillman88]

When I am stopped, if I press the brake pedal hard at all, it slowly leaks down

That sounds like a leaky booster to me.

 

[Selahdoor]

That was my first thought, too. But it's a new booster. Less than 3k miles on it. Ergo, maybe just a vacuum leak. Got to check out the easy stuff first. Booster might even have a warranty on it if it comes down to that.

 

[chillman88]

That was my first thought, too. But it's a new booster. Less than 3k miles on it. Ergo, maybe just a vacuum leak. Got to check out the easy stuff first. Booster might even have a warranty on it if it comes down to that.

I hope it's simple, but with the quality (or lack thereof) of new or rebuilt parts lately....

 

[TNBrett]

When I am stopped, if I press the brake pedal hard at all, it slowly leaks down.

I have checked the brake system. No leaks. No air in the system. (Replaced the long hard line on the rear axle recently, and bled the system again.)

So I am wondering if it is just because of a tiny leak in the vacuum system.

Are you saying the pedal goes to the floor? That sounds like you need a new master cylinder.

 

[Selahdoor]

That is also new. Less than 3k miles on it.

 

[snicklas]

A vacuum leak normally makes the brake pedal very stiff and hard to push (like when the engine is off).

When was the last time you adjusted the rear brakes? A slowly sinking pedal that still has normal assist is the rears out of adjustment, and the wheel cylinders slowly filling...

How close to the floor does the e-brake pedal get before it starts to firm up and set the parking brakes?

 

[Selahdoor]

Thank you!

That is interesting.

I'll be moving on to the rear brakes, after this. But the fact is, at least the passenger rear brakes were dragging. Badly enough to actually brake the truck any time I let off the go pedal. And make it take more go pedal than it should, just to get it moving.

I replaced the long hardline in the rear when it burst. Now it takes off like a bat out of... whatever place bats fly out of. And when going down the highway, if I let off the go pedal, she just coasts. Doesn't slow down immediately as if the brakes were on.

I figure a flake of rust inside that hard line was letting the pressure through to the brakes, but wasn't letting the fluid back through FROM the brakes.

But that would be kind of the opposite to what you describe.

Except... It could be out of adjustment on the driver's side rear!! I'll find out when I dig into the rear brakes.


Also, if misadjustment were the case, wouldn't pumping the brake pretty hard many times, eventually take up all that slack, and give you a pedal that doesn't just continue to slump?

I've tried that several times, and it just continues to slowly slump, no matter what.


There is nothing dangerous about this. The brakes work normally. And you don't have to push very hard to keep it still at a stoplight. So it normally doesn't bleed down at stoplights. Only when I push harder...

 

[Oledirtypearl86]

@Selahdoor. Pumping the brakes a bunch wont adjust the rear brakes gotta pull the plug and use a flat blade screwdriver to adjust off the star wheel also a inconsistent pedal could be a leaking brake master cylinder bleeding by in my experience that is usually the problem. Also new reman parts are usually a gamble at best