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Topic: Leaking engine vacuum on 1980 Thunderbird with vacuum headlamps (Read 5173 times) previous topic - next topic

Leaking engine vacuum on 1980 Thunderbird with vacuum headlamps

Reply #15 –
I'm pretty sure the booster is alright. I bought this booster used this summer out of an 87-93 Mustang 5.0... replacing my leaking 1980 booster.
I also upgraded my master cylinder to an new aluminum cylinder w/1” bore from a Lincoln Towncar.

When I installed the Mustang booster, I went through all the recommended ways of testing it that I was aware of, (holding pedal down and shutting the engine off and stuff like that) and it all seemed just right.
Maybe I need to go back over testing procedures again.

Leaking engine vacuum on 1980 Thunderbird with vacuum headlamps

Reply #16 –
Do these headlight covers have springs pulling them open and vacuum pulling them shut?
"lol.. because not too many people care for that style of car"
[size=-2]Click on paw print \/[/size]

Leaking engine vacuum on 1980 Thunderbird with vacuum headlamps

Reply #17 –
Quote from: Cougars 2 go;441384
Do these headlight covers have springs pulling them open and vacuum pulling them shut?

Uhhh.... I'm not quite sure. I seem to recall seeing springs attached to the doors and I know they work off vacuum but as far as how they open and close, I'm unsure. 

I just went out to the car and warned it up to 180 degrees, then used a special tool I have to crimp each of the vacuum lines, one at a time.

1. I crimped the port coming off the front drivers side on my Edelbrock carburetor, right past the vacuum gauge connection (this hose line feeds my vac operated headlamps). I have a mechanical advance MSD distributor, so I don't use the carb port that would be hooked up for vac advance. The unused port is capped off. The vacuum remained about 11 inches when in drive.

2. I next squeezed off the vac line that comes off the rear of my Edelbrock RPM Airgap manifold. This runs to my vacuum can for the headlights and splits off to my C4 transmission's modulator. The vacuum remained about 11 inches when in drive.

3. I crimped the main vac line going into the brake booster. It comes from the back of the carb...still no change.

4. I finally sprayed nearly 1/2 can of starter spray around my carbs base, all around the plastic spacer that I'm using between the cab and manifold and around all the intake runners and the engine didn't surge one bit.
Just to see...I sprayed a little into the air cleaner and heard an immediate difference, so I'm very certain I don't have any leaks.

Leaking engine vacuum on 1980 Thunderbird with vacuum headlamps

Reply #18 –
Usually you check the engine vacuum with the engine idling hot in park, not drive. My idle RPM is about 580rpm in drive, 120rpm lower than the idle in park (700rpm). That results in a reading 1-2 inches lower than the reading in park (16.5-17 in park, 15.5-16 in drive).
88 Thunderbird LX: 306, Edelbrock Performer heads, Comp 266HR cam, Edelbrock Performer RPM intake, bunch of other stuff.

Leaking engine vacuum on 1980 Thunderbird with vacuum headlamps

Reply #19 –
I always thought it was done in drive, so perhaps I should have kept it in park.

However, in park and heated up, with an idle of just under 900rpm, my vacuum gauge is reading about 13.5" .... and between 11" and 11.5" in drive at about 675rpm.

Leaking engine vacuum on 1980 Thunderbird with vacuum headlamps

Reply #20 –
That still seems about 1.5 inches low, at least.
88 Thunderbird LX: 306, Edelbrock Performer heads, Comp 266HR cam, Edelbrock Performer RPM intake, bunch of other stuff.

Leaking engine vacuum on 1980 Thunderbird with vacuum headlamps

Reply #21 –
Maybe I need to pull the valve covers and go over setting valve lash. I read if they are set too tight, that will result in low engine vacuum, however I did recheck them this past summer (when I replaced leaking valve covers) and despite some slight adjustments, they all seemed set properly.

I'm using Comp Cams magnum steel roller tip rockers and locks...maybe I should just go through them once again for piece of mind.

Leaking engine vacuum on 1980 Thunderbird with vacuum headlamps

Reply #22 –
As long as your rockers are adjusted at around 1/2 turn past zero lash (if using stud mounts) you should be good on that front.
88 Thunderbird LX: 306, Edelbrock Performer heads, Comp 266HR cam, Edelbrock Performer RPM intake, bunch of other stuff.

Leaking engine vacuum on 1980 Thunderbird with vacuum headlamps

Reply #23 –
I haven't given up on this situation, only its currently about 18 degrees outside and snowing at the moment. I think this will be a spring weather project....If I only had room in my garage.

Leaking engine vacuum on 1980 Thunderbird with vacuum headlamps

Reply #24 –
It's -1* here right now. 18* is plenty warm to do work ;).
88 Thunderbird LX: 306, Edelbrock Performer heads, Comp 266HR cam, Edelbrock Performer RPM intake, bunch of other stuff.