89 chevy 1 ton vacuum diagram help

[dunecj2a]

I'm havin a hard time findin a vacuum diagram or any help with my older Chevy. I've had this truck for over a year now and want to get the cruise workin. Its an 89 454 TBI 1 ton dually, so it did not recieve any changes like all the other models. I basicaly have to go back to 87 for parts or the 1 ton van since its a 4 door.

The cruise servo is not getting any vacuum. From what I have found online is that the small line going into the servo should have a constant vacuum. The larger line is the dump line from what I understand???...The small line runs back into the firewall and from there I am lost. None of the lines are split or damaged.

Where is the vacuum generated from? I don't see any lines comin off the manifold that lead anywhere close to the cruise lines.

[Rip Wheeler]

I'm havin a hard time findin a vacuum diagram or any help with my older Chevy. I've had this truck for over a year now and want to get the cruise workin. Its an 89 454 TBI 1 ton dually, so it did not recieve any changes like all the other models. I basicaly have to go back to 87 for parts or the 1 ton van since its a 4 door.

The cruise servo is not getting any vacuum. From what I have found online is that the small line going into the servo should have a constant vacuum. The larger line is the dump line from what I understand???...The small line runs back into the firewall and from there I am lost. None of the lines are split or damaged.

Where is the vacuum generated from? I don't see any lines comin off the manifold that lead anywhere close to the cruise lines.

That line going back into the firewall if for your vacuum servo motorsa, ie blend doors and you have a leak. Try pinching that line that goes through the firewall off. If its open, you wont have vacuum if its "T"'d into the cruise circuit.

[dunecj2a]

there is no vacuum at all off the small line that leads back thru the firewall. I am tryin to find out where it goes after the firewall and where it connects?

[Rip Wheeler]

there is no vacuum at all off the small line that leads back thru the firewall. I am tryin to find out where it goes after the firewall and where it connects?

Is it a auto or manual tranny?

[jayh300]

parts manuals on those are not much help.. the diag shows the servo, the tee, the line going to the firewall and the reserve tank..

iirc, the line off tee going to the motor goes to a fitting in the back of the intake, just not sure about that..

it sounds like you are missing a line.. the line going to the servo should first come from the engine, then a vaccuum tee, which is actually a one way valve that breaks all the time.. then a short line off the side of that tee to the servo and the line to the firewall goes to the other side of that tee ( if that makes any sense)

wish i could show you a picture... that would help a ton..

[jayh300]

Edited October 15, 2010 by jhendr3702

[dunecj2a]

Its an automatic. Thanx Guys!!!.the diagram helps alot. At least now I have an idea on where to connect the lines. I didn't have a line from the manifold to the servo at all. Without that line the servo wouldn't get any vacuum to work??.right?...thanx again guys

[jayh300]

Its an automatic. Thanx Guys!!!.the diagram helps alot. At least now I have an idea on where to connect the lines. I didn't have a line from the manifold to the servo at all. Without that line the servo wouldn't get any vacuum to work??.right?...thanx again guys

correct... and in talking to one of my tech buds, he said cruise vaccuum is always constant, so it would have to come off the intake manifold somwhere..

do all your ac/defrost doors work correct ?

[dunecj2a]

I've never even tried the defroster, thanx to livin in AZ. My a/c compressor took a crap last month or I would check. The only line connected to the manifold goes right into the front of the throttle body and the other runs to a metal line that runs down toward the tranny.

[jayh300]

service manual is not much more help.....

on the servo, it shows the large hose to be supply, small is to release valve..

diag only shows kinda the same, with the supply coming off the intake..

[dunecj2a]

I got it goin:thumbsup: I T'd into the vacuum line off of the manifold and ran it into the servo. I also ran another T into the thin line that ran back to the firewall.

I checked my defrosters and they were workin, not sure if they worked before. That line just ran back into a T that went to the servo. I doubt they worked before since there was no vacuum to them.......Thanx again for the help everyone.

[jayh300]

sweet... glad to help..